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Lack of good-quality planting materials has been identified as the most severe problem militating against increased agricultural productivity in sub-Saharan Africa (SSA) and beyond. However, investment of research efforts and resources in addressing this menace will only be feasible and worthwhile if attendant economic gains are considerable. As a way of investigating the economic viability of yam investment, this research has been initiated to address problems confronting yam productivity in eight countries of SSA and beyond: Nigeria, Ghana, Benin, Togo, Côte d’Ivoire, Papua New Guinea, Jamaica, and Columbia. Research options developed were to be deployed and disseminated. Key technologies include the adaptive yam minisett technique (AYMT), varieties adapted to low soil fertility and drought, nematode-resistant cultivars (NRC), and crop management and postharvest practices (CMPP). This article aims at estimating the potential economic returns, the expected number of beneficiaries, and poverty reduction consequent to the adoption of technology options. Estimates show that the new land area that will be covered by the technologies in the eight countries will range between 770,000 ha and 1,000,000 ha with the highest quota accounted for by AYMT. The net present value will range between US$584 and US$1392 million and was highest for the NRC. The CMPP had the lowest benefit-cost ratio of 7.74. About 1,049,000 people would be moved out of poverty by these technologies by 2037 in the region. These technologies are less responsive to changes in cost than that in adoption rate. Therefore, the realization of the potential economic gains depends on the rate and extent of adoption of these technologies. Giving the knowledge-intensive nature of some of these interventions, capacity building of potential adopters will be critical to increasing the sustainability of the yam sector, thereby enhancing food security and reducing poverty.

During long-term storage of apples, detection of low O2 stress is used to optimise low O2 storage regimes for dynamic controlled atmosphere (DCA) storage. Monitoring respiratory characteristics, specifically the respiratory quotient (RQ), provides a tool to achieve this. The objectives of this study were to evaluate protocols to monitor response of apple consignments to low O2 using a respiration chamber, the SafePod, designed for use in commercial stores and research laboratories, and to compare the RQ response to changes in chlorophyll fluorescence (CF) yield from the fruit skin as used in DCA-CF. Protocols to identify the lowest oxygen limit (LOL), the O2 concentration below which RQ rises, were tested using ‘Braeburn’ (sensitive to low O2) and ‘Gala’ (less sensitive to low O2). A protocol that allows fruit to acclimatise at each O2 concentration takes several weeks and is therefore not practical for commercial use. A rapid profile without fruit acclimatisation can be completed in 2–3 days. Although this underestimates RQ values, and results in an increase in RQ at a higher O2 concentration than observed for acclimatised fruit, the rapid RQ protocol provides a practical method to compare response of apple consignments between cultivars, orchards and seasons. By the rapid protocol, the LOL of ‘Braeburn’ consignments was near 0.6 kPa and of ‘Gala’ consignments was near 0.2 kPa, consistent with detection of alcoholic taints below the LOL in each case. The RQ response using the SafePod was consistent with increase in CF yield using HarvestWatch™. Fruit respiration rates change through the storage season, including a substantial decrease over the first 2 months after harvest. As RQ response is affected by respiration rate, accurate comparison of consignments depends on profiles being measured at the same stage in the storage season. It is more difficult to determine the LOL by RQ profiling later in the season when respiration rates are lower.

The fresh produce industry is constantly growing as a result of increasing consumer demand. Food quality and safety management are still major issues for the supply chain. The use of ozone has been identified as a feasible solution to reduce microorganisms present in food, in this way extending the shelf-life of fresh produce. A number of factors that may affect the efficiency of ozone treatment have been identified, e.g. microbial populations, ozone concentration and time of exposure, type of produce, temperature, relative humidity and packaging material, and they are briefly discussed. Furthermore, practical information derived from studies with ozone conducted by the authors and from their knowledge of the subject directs the reader's attention to the key aspects of ozone use under commercial conditions, i.e. from the practical point of view. Finally, one possible direction for future research with the postharvest use of ozone, i.e. the important role of fruit cuticle in response to this postharvest treatment, is indicated. © 2016 Society of Chemical Industry.

Purpose – The purpose of this paper is to describe the role of the screening liaison nurses for adults with learning disabilities employed by Peninsula Community Health. Design/methodology/approach – This paper reports on the national situation in regard to cancer screening for people with learning disabilities and explores the barriers which limit their participation in these screening programmes. It describes the screening liaison nurse role and presents case examples of the work they do. Findings – The local screening rates for people with learning disabilities have increased since the creation of this role in 2011. Originality/value – Increasing the uptake of cancer screening by people with learning disabilities is clearly in line with existing national priorities. To the author’s knowledge this is a unique role in this country and the authors propose that other areas would benefit from adopting this model of working.

Fresh produce has been recognised as a healthy food, thus there is increasing consumer demand for fresh fruit and vegetables. The shelf-life of fresh produce, however, is relatively short and is limited by microbial contamination or visual, textural and nutritional quality loss. There are many methods to reduce/eliminate microorganisms present in food and ozone treatment is one of them. The use of ozone by the fresh produce industry is a good alternative to chemical treatments, e.g. the use of chlorine. The effectiveness of ozone as an antimicrobial agent has previously been reviewed and has been updated here, with the latest findings. The main focus of this review is on the effects of ozone on the fresh produce quality, defined by maintenance of texture, visual quality, taste and aroma, and nutritional content. Furthermore, ozone has been found to be efficient in reducing pesticide residues from the produce. The treatments that have the ability to reduce microbial contamination of the product without having an adverse effect on its visual, textural and nutritional quality can be recommended and subsequently incorporated into the supply chain. A good understanding of all the benefits and limitations related to the use of ozone is needed, and relevant information has been reviewed in this paper.

Curing of freshly harvested yams (Dioscorea spp.) is a process for wounded yams during harvest to heal. In this work the effectiveness of straw, polypropylene and jute sack on curing of seven key farmers’ yam varieties over a duration of 7, 14 and 21 days was studied. Seven key farmers’ yam varieties identified as Pona, Lariboko, Dente, Mutwumudoo, Serwah belonging to D. rotundata, Matches and Akaba belonging to D. alata were studied under different curing treatments. The percentage weight loss of yam tubers varied among the treatments over curing period. Curing under jute sack showed all yam varieties had weight losses less than 2.0%, within 7 days of curing. Five different varieties had weight loss less than 2.0% except Dente under the straw treatment. Mutwumudoo variety showed the highest water loss (8.4%) for polypropylene sheet and 6.9% for Lariboko in the control treatment. During 7 days curing the control and polypropylene treatment did not support yam curing. After 14 days of curing of tubers, similar tends were observed as in 7 days curing. After 14 days of curing under jute sack, percentage weight loss of the tubers ranges from 2.0% - 3.7%. In the straw treatment, the percentage weight loss ranges between 1.0% - 4.7% in all other varieties except Dente (D. rotundata) (8.2%). Polypropylene sheet treatment showed the highest percentage weight loss in Mutwumudoo variety (18.4%). A similar trend was observed for the yam tubers cured for 21days as percentage weight loss of tubers under jute sacks was 2.5 – 9.8%. Curing temperature and humidity ranged between 27&degC - 40&degC and 87% - 100% rh for yam tubers under the three different treatments of polypropylene, jute and straw. However, the control treatment recorded lower humidity of 60% - 80% rh. Curing material, duration, climatic conditions and yam varieties influenced curing and Serwah variety, which is a D. rotundata is the best bet yam variety to cure under jute sack for 7, 14 and 21 days of curing.

Exogenous ethylene is commonly used as a commercial sprouting inhibitor of potato tubers. The role of ethylene in the control of sprouting of sweetpotato roots, however, is not known. The aim of this study was to investigate the role of ethylene in control of sprouting in sweetpotato roots by observing the effect of an ethylene synthesis inhibitor, aminoethoxyvinylglycine (AVG), and the ethylene antagonist, 1-methylcyclopropene (1-MCP), in the presence and absence of exogenous ethylene on root sprouting and associated sugar accumulation. Continuous exposure to 10 μl L−1 ethylene, 24 h exposure to 625 nl L−1 1-MCP or dipping in 100 μl L−1 AVG all inhibited sprout growth in sweetpotato roots of two varieties over 4 weeks of storage at 25 °C. The observations that both ethylene on its own and 1-MCP, which inhibits ethylene action, inhibit sprout growth indicate that while continuous exposure to exogenous ethylene leads to sprout growth inhibition, ethylene is also required for sprouting. In potato tubers ethylene is required to break dormancy, while continuous exposure inhibits sprout growth. Monosaccharide concentrations in ethylene, 1-MCP or AVG treated roots were lower than in untreated roots, and for ethylene treated roots this was associated with higher respiration rates. This is consistent with the activation of some additional process by ethylene which uses energy through sugar metabolism. 1-MCP and AVG both inhibited this increase in respiration rate and counteracted the decrease in monosaccharide concentrations. 1-MCP presumably counteracts the ethylene stimulation of this process, while the effect of AVG is attributed to its possible inhibitory effects on protein synthesis.

The fresh produce industry is constantly growing as a result of increasing consumer demand. Food quality and safety management are still major issues for the supply chain. The use of ozone has been identified as a feasible solution to reduce microorganisms present in food, in this way extending the shelf-life of fresh produce. A number of factors that may affect the efficiency of ozone treatment have been identified, e.g. microbial populations, ozone concentration and time of exposure, type of produce, temperature, relative humidity and packaging material, and they are briefly discussed. Furthermore, practical information derived from studies with ozone conducted by the authors and from their knowledge of the subject directs the reader's attention to the key aspects of ozone use under commercial conditions, i.e. from the practical point of view. Finally, one possible direction for future research with the postharvest use of ozone, i.e. the important role of fruit cuticle in response to this postharvest treatment, is indicated. © 2016 Society of Chemical Industry.

Two hot pepper hybrids; 'Wonder King' and 'P-6' were grown under high plastic tunnels and fruits were picked at their horticultural maturity stage i.e., full green color with uniform size and shape. The study was conducted to determine the best polyethylene packaging material and low temperature treatment to maximize the shelf life of green hot peppers. Freshly harvested fruits were stored at a range of temperatures; 7, 14 and 21°C in a range of packaging; 7, 15 and 21 µm thick polyethylene bags or unpacked (control) and their post harvest quality was assessed. Minimum weight loss for 'P-6' was observed for fruits stored at 7°C in 7 µm thick polyethylene bags, whereas for 'Wonder King' minimum weight loss was for fruits stored at 7°C in 21 µm thick polyethylene bags. Maximum ascorbic acid in 'P-6' was 53 mg 100 g-1 when stored at 14°C packed in 15 µm thick polyethylene bags whereas in the case of 'Wonder King' maximum ascorbic acid was 107 mg 100 g-1 at 7°C with 7 µm thick polyethylene bags. Total phenolic compounds were 53.62 mg 100 g-1 for 'P-6' when stored at 7°C unpacked while no significant differences were found in 'Wonder King'. No significant carotenoid differences were recorded for 'P-6' whereas maximum total carotenoids (5.93 mg 100 g-1) were found for fruits stored at 7°C with 7 µm thick polyethylene bags. Total sugars, reducing sugars and non reducing sugars in 'P-6' were estimated at 9.16, 2.71 and 2.59% whereas in the case of ‘Wonder King’ these were 6.53, 1.37 and 1.27% at 21°C in open conditions, respectively. Maximum shelf life (20 days) was recorded for 'P-6' at 7°C in 15 µm thick polyethylene bags while in 'Wonder King' maximum shelf life was 10 days at 7°C using 15 µm thick polyethylene bags.

Given the increasing importance of organic produce, a study was carried out to find out how organic production methods affect postharvest and storage quality of ‘Conference’ pears (Pyrus communis). When fruit were taken out of cold storage and artificially infected either with Monilinia fructigena or Penicillium expansum disease development was significantly slower in organic pears than in conventional pears. The effects were more marked for M. fructigena which is the more aggressive pathogen (about 20% inhibition of lesion growth rate), compared with a smaller, but significant effect on P. expansum (5-10% inhibition of lesion growth rate). Organic pears had higher dry matter content (15.6% compared with 14.7%) and were firmer than conventionally-produced fruit, which may affect the rate of pathogen growth. Analysis of total phenols indicated an increase induced by infection by either pathogen, but no significant differences either before or after infection between organically and conventionally-produced pears.

Chlorophyll fluorescence has been tested by many researchers as a non-invasive method to assess physiological damage in chlorophyll containing fruits and vegetables. The characteristic Fv/Fm is most commonly considered. One draw-back of this method is that the fluorescence signal is affected primarily by the state of photosystem II, which is one of the components most sensitive to stresses, including heat, chilling and oxidative stress, so that the Fv/Fm may be more sensitive than the overall tissue. A more reliable strategy may be to look at the ability of the tissues to resynthesise photosystem II after damage, by looking at the rate of Fv/Fm recovery. This strategy shows promising results in predicting chilling injury in peppers and cucumbers, and heat stress in asparagus. Trials are also reported that attempt to predict low temperature injury in apples, but the results are not definitive.

Alternative methods for disinfestation of asparagus against thrips (Thrips tabaci) need to be developed for the Thai export trade, ensuring efficient thrips’ mortality, while maintaining quality and environmental safety. Hot air/water using temperatures of 40-60°C and high CO2 treatments were studied at laboratory level. An appropriate treatment involving hot water at 45°C for 15 min, with or without high CO2 treatment, followed by hydro-cooling with water at ambient temperature (~20°C) was identified. Methods to assess quality, such as objective tests (% mass loss, force measurement, colour measurement) and subjective tests (appearance, decay, off-odour, snap-test for texture) gave no indication of significant quality deterioration. Chlorophyll fluorescence and ion leakage measurements were used to assess physiological stress. The Fv/Fm ratio which indicates the intactness of photosystem II was shown to decrease immediately after all heat treatments tested, but recovered over 24h for non-damaging heat treatments (42.5 and 45°C). A rise in % K+ leakage was observed that increased with treatment temperature but recovered over 24h following treatment at 45°C. High CO2 showed neither significant detrimental effect nor indication of physiological stress, and could kill thrips although not at a sufficiently high rate. Confirmatory trials to demonstrate the efficacy of these treatments in Thailand using naturally infested asparagus were carried out. The mortality rate of thrips was as high as when this method was tested in the UK. Adoption of the selected disinfestation method into existing process lines in Thailand would not be too complicated.

An understanding of the control of sprouting of sweetpotatoes (Ipomoea batatas) is important, both for marketing of sweetpotatoes in the developed world and for the role of the crop for food security in the developing world. Long-term storage of sweetpotatoes requires inhibition of sprouting, while stimulation of sprouting is necessary for the production of planting material. Many studies have been conducted on the control of sprouting/dormancy of potatoes whereas sprouting in sweetpotatoes is less studied. Recently, exposure to ethylene has been introduced as a commercial method for controlling of sprouting in potatoes. Data presented here show that 20 ppm ethylene is effective in controlling sprouting in sweet potato over 4 weeks of storage at 25°C. Gibberellins appear to have a key role in stimulating sprout growth in potato. Trials using gibberellins and gibberellin synthesis inhibitors suggest that gibberellins are likewise involved in the stimulation of sprouting in sweetpotatoes.

It has previously been shown that sweetpotato cultivars differ in the efficiency by which their roots can heal wounds at low humidity, although this does not appear to relate to rate of wound-healing at high humidity. It has also been shown previously that there is a negative relationship between cultivar root dry matter (DM) content and efficiency of root wound-healing at low humidity (assessed by a lignification score; LS). Root DM content tends to be negatively related to root sugar levels. The study presented here was undertaken to examine further the role of carbohydrates in root response and ability to heal wounds in the presence of water stress. Data from 17 cultivars confirmed the negative correlation between LS and DM and the positive correlation between LS and root sugar levels. Measurement of sugar levels at the root surface both at the time of wounding and after complete healing (5 days) for 10 cultivars indicated a stronger relationship of LS with final sugar levels than initial DM content. This was confirmed in further experiments using a system of adjacent tissue cuboids cut from the parenchyma which were able to exhibit lignification almost as efficiently as whole roots. With this system it was also possible to demonstrate a relatively rapid accumulation of sugars within 24 h of healing. The data were examined further by the development of linear regression models of LS. Comparison of the levels of variance accounted for by the models indicates that LS is strongly cultivar dependent, and most of the cultivar effect is related to cultivar differences in sugar levels during wound-healing. Differences in sugar levels between roots/cuboids of each cultivar also have an effect. Further, the similarity of the models for the whole roots and cuboids gives us confidence in the validity of using the cuboids to investigate wound-healing of whole roots.

This paper presents a study on the wound healing processes in sweetpotatoes ( Ipomoea batatas Lam.) when exposed to tropical conditions typical for marketing (RH 50–73%, T 25–30 °C). The physiological processes during healing were revisited. At low humidities (65% ± 10) the depth of the lignified layer i.e. the thickness of the desiccated cell layers was affected by both cultivar and humidity. Some cultivars consistently failed to produce a lignified layer and for others the layer was often not continuous. The continuity of the lignified layer was more important for effectiveness of wound healing than the actual thickness. A method for assessing efficiency of wound healing based on assessing the continuity of lignified layers was developed, and called the lignification score. Wound healing efficiency as measured by the lignification score was found to be a major factor for the shelf-life of sweetpotato cultivars. Lignification of wounds correlated with reduced rate of weight loss and reduced susceptibility to microbial infection. A high dry matter content in cultivars correlated with a low lignification score. This relationship was consistent for five trials, including 34 cultivars.

Five sweet potato cultivars (Kemb10, SPK004, KSP20, Yan Shu 1 and Zapallo) were analysed for their sensory characteristics and changes herein during storage under tropical conditions. Nine descriptors for sweet potato were derived after brainstorming and quantitative descriptive analysis (QDA). These were: floury, smooth, soft, chestnutty, sweet, fibrous, grainy, moist and discoloration. Significant differences were observed among the cultivars profiles. A principal component analysis (PCA) revealed two principal components (PC1 and PC2) explaining in total 68% of the variation. PC1 explained 52% and correlated with textural properties, and PC2 explained 16% of the variation and correlated with flavour components. The results suggest that differences between sweet potato cultivars are mainly determined by textural components. Storage had most effect on the sweet and chestnutty characteristics, and did not affect the texture characteristics. Overall the changes during storage were less significant than the differences between the cultivars.

Under marketing conditions in tropical developing countries sweetpotatoes have a shelf-life of only 1 to 2 weeks. Storage trials conducted under simulated tropical marketing conditions showed that root shrivelling due to weight loss and rotting are the two major forms of deterioration. Measurement of respiration rates indicated that under these conditions weight loss is primarily (86%) due to water loss. Under these environmental conditions rotting is promoted by water loss, which is therefore the driving force of deterioration. For the cultivars studied, a large range in rates of weight loss was found, which was consistent between seasons, suggesting that breeding for extended shelf-life is feasible. A range of root quality characteristics were assessed, including dry matter content, sugar content, surface area, initial weight, rough weevil ( Blosyrus spp.) damage, latex production, cortex thickness and hardness of the tissue. Multiple regression models for rates of weight loss indicated that dry matter content and root monosaccharide content were important controlling factors. Cultivars with low dry matter content and with high monosaccharide levels lose less weight. The two characteristics are related, and we do not know which more directly affects rates of weight loss. Other root characteristics were less important, although it was found that root size and pre-harvest rough weevil damage had significant effects.

Sweetpotato weevils ( Cylas spp.) constitute a major constraint upon sweetpotato production and utilization world-wide. Attempts to breed for resistance to Cylas spp. have had limited success. However, there are reports of variation in the susceptibility to weevil attack in the field among cultivars in East Africa. Field trials were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine the extent to which sweetpotato cultivars presently available in East Africa consistently differ in their susceptibility to field infestation by Cylas spp. and to identify the plant factors that determine the levels of susceptibility. Several methods to assess levels of field infestation were tested, and their relative merits are discussed. Significant cultivar differences in susceptibility to Cylas spp. infestation were observed for four out of six trials carried out over 2 years. The exceptions were cases where infestation levels were either very low or very high. Linear...

The response of the sweetpotato weevil Cylas puncticollis (Coleoptera: Brentidae) to roots of different sweetpotato cvs was investigated as part of a project to examine the factors that affect susceptibility of sweetpotato cvs to weevil infestation in the field. Laboratory experiments were conducted at two sites (Ukiriguru and Kibaha) in Tanzania and at one site (Serere) in Uganda to determine if the harvested storage roots of sweetpotato cvs differed in their acceptability to C. puncticollis or if any root antibiosis towards C. puncticollis existed. For all experiments cultivar effects for the total number of emerging adults were significant to at least 10% and in most cases were much more significant. At Ukiriguru and Kibaha, the results showed reasonable consistency between years, and of the four cultivars used at both sites, fewer C. puncticollis adults emerged from roots of Sinia and Budagala than from SPN/0 and Mwanamonde on all occasions. A relationship between laboratory experiments and crown dama...

Fresh produce has been recognised as a healthy food, thus there is increasing consumer demand for fresh fruit and vegetables. The shelf-life of fresh produce, however, is relatively short and is limited by microbial contamination or visual, textural and nutritional quality loss. There are many methods to reduce/eliminate microorganisms present in food and ozone treatment is one of them. The use of ozone by the fresh produce industry is a good alternative to chemical treatments, e.g. the use of chlorine. The effectiveness of ozone as an antimicrobial agent has previously been reviewed and has been updated here, with the latest findings. The main focus of this review is on the effects of ozone on the fresh produce quality, defined by maintenance of texture, visual quality, taste and aroma, and nutritional content. Furthermore, ozone has been found to be efficient in reducing pesticide residues from the produce. The treatments that have the ability to reduce microbial contamination of the product without having an adverse effect on its visual, textural and nutritional quality can be recommended and subsequently incorporated into the supply chain. A good understanding of all the benefits and limitations related to the use of ozone is needed, and relevant information has been reviewed in this paper.

Grain yields of eight representative semidwarf spring wheat (Triticum aestivum L.) cultivars released in northwest Mexico between 1962 and 1988 have increased linearly across years as measured in this region during 6 yr under favorable management and irrigation. To understand the physiological basis of this progress and possibly assist future selection for grain yield, leaf traits were determined during 3 yr in the same study. Stomatal conductance (g(S)), maximum photosynthetic rate (A(max)), and canopy temperature depression (CTD), averaged over the 3 yr, were closely and positively correlated with progress in the 6-yr mean yield. The correlation was greatest with g(S) (r = 0.94 P < 0.01). Compared with the overall yield increase of 27%, g(S) increased 63%, A(max) increased 23%, and canopies were 0.6 degree C cooler. Carbon-13 isotope discrimination was also positively associated with yield progress (r = 0.71, P < 0.05), but other leaf traits such as flag leaf area, specific leaf weight, percentage N and greeness were not, nor was crop growth rate around anthesis. The causal basis of the leaf activity interrelationships is reasonably clear, with both increased intercellular CO2 concentration and increased mesophyll activity contributing to the increase in A(max). However, causal links to the yield progress, and the accompanying increase in kernels per square meter, are not clear. It is concluded that g(S) and CTD should be further investigated as potential indirect selection criteria for yield.

A comparison has been made between the changes in absorption spectra and chlorophyll fluorescence emission occurring upon the induction of non-photochemical dissipation of excitation energy (qE) in isolated thylakoids and those accompanying the aggregation of detergent-solubilised spinach light-harvesting complex (LHCII). In support of a recent hypothesis for the mechanism of qE (Horton et al. (1991) FEBS Lett. 292, 1–4), it was found that absorbence changes at 530 nm were associated with qE and LHCII aggregation. Antimycin A inhibited these changes and prevented LHCII aggregation, as indicated by the electrophoretic mobility of the complex and its low-temperature fluorescence spectrum. An antimycin-insensitive partial aggregation of LHCII was associated with an absorbance change at 505 nm. Low concentration of detergent caused disaggregation of LHCII and the reversal of qE. These data are discussed in terms of the relationship between structural change in LHCII and the mechanism of non-photochemical quenching of chlorophyll fluorescence in thylakoids.

Exposure of chromatophores of Rhodobacter capsulatus to a high light intensity (10 000 μE m −2 s −1 ) in the presence of oxygen results in non-photochemical quenching of bacteriochlorophyll fluorescence and a decrease in the quantum yield of charge separation at the reaction centre. Several observations support the hypothesis that this is due to the formation of a quencher in the light-harvesting antennae. The relationship between quenching of the maximum fluorescence yield F m and the dark-level fluorescence yield F o fits theoretical predictions for antenna quenching, while the decrease in photochemical quantum yield is proportional to the decrease in F v / F m (where F v = F m — F o ). The number of functional reaction centres appears to be unchanged. No change in redox dependence of charge separation can be detected, suggesting that no damage of the reaction centre occurs. It is suggested that the quencher is formed by the oxidation of some species. Consistent with this, quenching is inhibited by the removal of oxygen. Aerobic quenching can be observed in mutants lacking either the outer light-harvesting complex LHII or both the reaction centre and the inner light-harvesting complex LHI indicative of quenching throughout the light-harvesting apparatus. Under anaerobic conditions there is still some light-dependent inhibition of quantum yield of charge separation by a distinct process that does not effect F v / F m . The mechanism of this process is unknown

The pH dependence of maximum chlorophyll fluorescence yield (Fm) was examined in spinach thylakoids in the presence of nigericin to dissipate the transthylakoid pH gradient. 3-(3',4'-dichlorophenyl)-1,1-dimethylurea (DCMU) was present to eliminate photochemical quenching. Thylakoids were prepared from dark adapted leaves ('dark' thylakoids) or preilluminated leaves ('light' thylakoids). In the latter there had been approximately 50% conversion of the xanthophyll violaxanthin to zeaxanthin, while no conversion had occurred in the former. In the presence of a reductant such as ascorbate, antimycin A sensitive quenching was observed (half maximal quenching at 5 μM), whose pH dependence differed between the two types of thylakoid. Preillumination of leaves resulted in more quenching at pH values where very little quenching was observed in 'dark' thylakoids (pH 5-7.6). This was similar to activation of high-energy-state quenching (qE) observed previously (Rees D, Young A, Noctor G, Britton G and Horton P (1989) FEBS Lett 256: 85-90). Thylakoids isolated from preilluminated DTT treated leaves, that contained no zeaxanthin, behaved like dark thylakoids. A second form of quenching was observed in the presence of ferricyanide, that could be reversed by the addition of ascorbate. This was not antimycin A sensitive and showed the same pH dependence in both types of thylakoid. The former type of quenching, but not the latter, showed similar low temperature fluorescence emission spectra to qE, and was considered to occur by the same mechanism.

A new hypothesis is presented to explain the major molecular process that regulates the efficiency of light harvesting by chloroplast membranes. It is proposed that in excess light the decrease in the thylakoid lumen pH causes an increase in aggregation of the light harvesting complexes of photosystem II resulting in formation of an efficient pathway for non-radiative dissipation of excitation energy. The aggregation is potentiated by the conversion of violaxanthin to zeaxanthin. This hypothesis is based upon (i) similarity between the spectroscopic changes associated with energy dissipation and those observed upon aggregation of isolated light harvesting complex; and (ii) the link between changes in light scattering and increased energy dissipation.

Thylakoids isolated from light-treated spinach leaves (‘light’ thylakoids) which contain significant zeaxanthin levels show amplification of high-energy-state chlorophyll fluorescence quenching (qE) with respect to the transthylakoid pH gradient, when compared to thylakoids from dark-adapted leaves (‘dark’ thylakoids) which contain no zeaxanthin. In 77 K fluorescence emission spectra q E in ‘dark’ thylakoids shows maximal quenching with respect to fluorescence yield near 680 nm, whereas in ‘light’ thylakoids additional quenching occurs near 700 nm, which is associated with the appearance of a chlorophyll species absorbing at long wavelengths. It is suggested that this long-wavelength species is associated with an aggregated state of LHC II.

The quenching of variable fluorescence yield (qN) and the quenching of dark level fluorescence yield (q0) directly atributable to high-energy-state fluorescence quenching (qE) was studied to distinguish between energy dissipation in the antenna and light harvesting complexes (antenna quenching) and energy dissipation at the reaction centres (reaction centre quenching). A consistent relationship was obtained between qN and q0 in barley leaves, the green alga Dunaliella C9AA and in pea thylakoids with 2,3,5,6-tetramethyl-p-phenylene diamine (DAD) as mediator of cyclic electron flow around PS 1. This correlated well with the relationship obtained using m-dinitrobenzene (DNB), a chemical model for antenna quenching, to quench fluorescence in Dunaliella C9AA or pea thylakoids. The results also correlated reasonably well with theoretical predictions by the Butler model for antenna quenching, but did not correlate with the predictions for reaction centre quenching. It is postulated that qE quenching therefore occures in the antenna and light harvesting complexes, and that the small deviation from the Butler prediction is due to PS 2 heterogeneity.

The parameter фp (= rate of photosynthetic O2evolution(incident light × qQ) reflects the efficiency of O2 evolution by PS II reaction centres with respect to incident light, independent of the redox state of the primary electron acceptor QA (Weis, E. and Berry, J.A. (1987) Biochim. Biophys. Acta 894, 198–208). During whole chain electron transfer to methyl viologen in spinach thylakoids decreases in фp of more than 50% were observed in the presence of a transthylakoid pH gradient. Evidence was obtained that there are two components of фp decrease; one is associated with non-photochemical dissipation of chlorophyll excitation, observed as nonphotochemical fluorescence quenching (qNP), while a second component is not associated with fluorescence changes. The evidence for the latter was obtained using thylakoids that were suspended in low magnesium, or in the presence of antimycin A, so that they would develop only low levels of qNP. It is proposed that this component is due to electron cycling around the PS II reaction centre, and that the cycle is closely related to the transthylakoid pH gradient. The cycle can be observed during electron flow through PS II only, to o-phenylene diamine, and therefore does not appear to be controlled by the redox state of components beyond PS II in the electron transfer chain. Reversible фp decreases observed in uncoupled thylakoids at low pH suggest that the cycle may be controlled by the pH of the intrathylakoid space, and not the pH gradient per se. Measurements made during the approach to steady state, in which the development qNP is slower that the formation of the pH gradient, are consistent with the suggestion that the contribution to фp changes by qNP can be determined by the ratio of variable to maximum fluorescence yield (Genty, B., Briantais, J.-M. and Baker, N.R. (1989) Biochim. Biophys. Acta 990, 87–92).

Although sweetpotato is primarily grown for home consumption, marketing is becoming increasingly important, and in this case, short shelf-life of the roots is a major constraint. An assessment of the levels of damage of sweetpotatoes when they arrive at urban markets indicated that between 49% and 93% roots exhibited some form of damage. The major types of damage noted were breakages, cuts, infestation by weevils (Cylas spp.), rotting and superficial scuffing. All forms of damage, except superficial scuffing, lead to a shortened shelf-life due to both increased fresh weight loss and rotting. Superficial scuffing increased the rate of rotting but not of weight loss. It was estimated, based on the six cases considered, that the damage resulted in a reduction of shelf-life of between 23% and 47%. Key Words: Ipomoea batatus, post-harvest losses, Tanzania (African Crop Science Journal 2001 9(1): 301-308)

The yield of photosynthetic O2 evolution was measured in cultures of Dunaliella C9AA over a range of light intensities, and a range of low temperatures at constant light intensity. Changes in the rate of charge separation at Photosystem I (PS I) and Photosystem II (PS II) were estimated by the parameters ΦPS I and ΦPS II . ΦPS I is calculated on the basis of the proportion of centres in the correct redox state for charge separation to occur, as measured spectrophotometrically. ΦPS II is calculated using chlorophyll fluorescence to estimate the proportion of centres in the correct redox state, and also to estimate limitations in excitation delivery to reaction centres. With both increasing light intensity and decreasing temperature it was found that O2 evolution decreased more than predicted by either ΦPS I or ΦPS II. The results are interpreted as evidence of non-assimilatory electron flow; either linear whole chain, or cyclic around each photosystem.

Light-dependent quenching of room-temperature chlorophyll fluorescence associated with the “energisation” of the thylakoid membrane is usually referred to as qE; improvements in the analysis of chlorophyll fluorescence yield (1,2) allow its quantification. qE is generally taken to reflect an increase in energy dissipation by non-radiative pathways (heat) at Photosystem 2. This increased dissipation has been implicated in the control of electron transport through PS2 (3,4) and in protection of PS2 reaction centres against photoinhibition (5). However, the mechanistic links between the onset of ΔpH and the increased energy dissipation remain obscure.

Photoinhibition of higher plants encompasses a range of phenomena, many of which stem from the requirement to harmlessly dissipate excess light energy. These responses to light stress are manifest as a decrease in the quantum yield of photosynthesis and a quenching of chl fluorescence and primarily affect PS II. In intact plants a number of processes have been suggested to protect the photosynthetic apparatus from the potentially harmful effects of excessive light when dissipation through photosynthesis itself is exceeded. These include ΔpH [1], phosphorylation [2] and the xanthophyll cycle [3]. When the capacity of these processes is exceeded direct damage to a component or components involved in the photochemistry of PS II takes place [4,5,6].

With increasing incident light the efficiency of photosynthesis (Φs = rate of photosynthetic O2 evolution/incident light intensity) tends to decrease. As processes beyond photosystem 2 (PS2) become rate limiting, QA becomes progressively reduced, such that PS2 centres are no longer able to carry out charge separation (closed centres). This is observed as a decrease in the coefficient of fluorescence quenching by photochemistry, qQ, which indicates the proportion of excitation energy delivered to PS2 centres that is captured by ‘open’ centres. Unless a limitation develops at PS2 itself Φs should decrease in proportion to qQ. However it has been found that this is not the case in vivo, and that the parameter Φp (= Φs/qQ), considered to reflect intrinsic quantum yield of PS2, decreases with increasing incident light [1,2]. It has been suggested that this decrease in Φp is related to the non-photochemical dissipation of excitation observed as fluorescence quenching (qNP) [1,2]. In this paper we describe work carried out to determine the mechanism of Φp changes by studying in vitro systems. Although we observe changes in Φp directly related to qNP, we also confirm the observation of Oxborough and Horton [3] that Φp changes can be observed independently of qNP.

Sweet potato is an important staple food crop in East Africa, but under local marketing conditions it has a shelf life of generally no longer than 2 weeks. As a result, the potential for marketing over longer distances is limited. The role of changes in sensory properties and weight loss as limiting factors for shelf-life were investigated. The important sensory attributes of five sweet potato cultivars were determined in discussion sessions with four taste panels and were: floury, sweet, chestnutty, grainy, smooth, soft, fibrous, discoloration, and moist. The sensory profiles of the five cultivars (KSP20, Kemb10, Yanshu 1, Pumpkin, and SPK004) differed significantly (P < 0.001). However, after 4 and 8 weeks under simulated tropical storage conditions (26 °C, 80% to 90% RH) no significant changes in the attributes were detected in most cases (P > 0.05). Changes in sensory properties were therefore not considered to limit shelf life. Shelf life experiments in Tanzania under simulated marketing conditions (26 + 5 °C, 50% to 60% RH) with 29 local cultivars revealed that roots with high rates of weight loss also rot rapidly. It was found that weight losses (primarily due to water loss) were high and varied significantly among cultivars (12% to 45% loss in 21 days). Further studies will investigate the structure and strength of the periderm as the main barrier to water loss to facilitate future cultivar selection.

31P nuclear magnetic resonance (NMR) saturation transfer has been used to measure enzymatic flux through the creatine phosphokinase reaction in the direction of ATP synthesis in the human forearm muscle flexor digitorum superficialis. Modification of the ratio method for measurement of spin-lattice relaxation (R. Freeman, H. D. W. Hill, and R. Kaptein, J. Mags. Reson. 7, 82 (1972) was tested and used to appreciably shorten the duration of the measurement. Under conditions of steady state work intracellular pH decreased slightly by 0.06 units and the spin-lattice relaxation time of phosphocreatine in muscle was unchanged, while flux from phosphocreatine to ATP was 64 ± 10% of the resting value. This is contrary to the increase in flux of 155% predicted from previous saturation transfer studies carried out in vitro on rabbit skeletal muscle creatine phosphokinase using metabolite concentrations to mimic those in vivo (E. A. Shoubridge, J. L. Bland, and G. K. Radda, Biochim. Biophys. Acta 805, 72 (1984). This discrepancy could be accounted for by an underestimation of the ADP concentrations to which the enzyme is exposed due to inaccurate assumptions about the total metabolite concentrations, or possibly by compartmentation of creatine phosphokinase and its reactants. © 1989 Academic Press, Inc.

The thylakoid membranes of higher plants possess several mechanisms that control both the distribution and rate of dissipation of absorbed light. These mechanisms, which allow regulation of photosynthetic electron transport in response to alteration in external and internal factors, can be observed as the various processes that quench chlorophyll fluorescence. By using the 'light-doubling techniques’, together with analysis of quenching relaxation, it is possible to assess quantitatively the extents of these regulatory processes and to allow their interrelations to be studied. These techniques can be applied to in vitro systems or to leaves, and can be particularly useful when applied with electron-transport measurements and when models are used to aid interpretation. Results of quenching analysis at different light intensities in isolated thylakoids, intact chloroplasts, protoplasts, algae and leaves of a variety of species are presented.

The relaxation of the non-photochemical quenching of chlorophyll fluorescence has been investigated in cells of the green alga Dunaliella following illumination. The relaxation after the addition of DCMU or darkening was strongly biphasic. The uncoupler NH4Cl induced rapid relaxation of both phases, which were therefore both energy-dependent quenching, qE. The proportion of the slow phase of qE increased at increasing light intensity. In the presence of the inhibitors rotenone and antimycin the slow phase of qE was stabilised for in excess of 15 min. NaN3 inhibited the relaxation of almost all the qE. The implications of these results are discussed in terms of the interpretation of the non-photochemical quenching of chlorophyll fluorescence in vivo and the mechanism of qE.

The quantitative relationship between energy-dependent quenching of chlorophyll fluorescence (qE) and trans-thylakoid pH difference (ΔpH, estimated with 9-aminoacridine) was compared in chloroplasts from leaves preilluminated at low oxygen in the absence of CO2 with chloroplasts from leaves darkened under the same conditions. The extent of both phenomena was varied by changes in actinic light intensity. Chloroplasts from preilluminated leaves contained high levels of zeaxanthin (up to 15% of total carotenoid) and were capable of forming qE at lower ΔpH values than chloroplasts from dark-adapted leaves, which lacked zeaxanthin. Infusion of dithiothreitol into leaves prior to preillumination prevented the light-induced formation of zeaxanthin; chloroplasts prepared from these leaves showed the same relationship between qE and ΔpH observed in chloroplasts fom dark-adapted leaves. The rate of appearance and disappearance of the change in relationship between qE and ΔpH upon leaf preillumination and darkening was closely matched by the kinetics of synthesis and degradation of zeaxanthin. The quantitative relationship between qE and quenching of the dark-level of fluorescence (F0) was very similar in chloroplasts from preilluminated or dark-adapted leaves, containing disparate amounts of zeaxanthin. In both sets of chloroplasts, qE was inhibited by antimycin A. These latter observations suggest that the formation of qE involves mechanistically similar features in chloroplasts containing or lacking zeaxanthin. Overall, the data are discussed in terms of action of zeaxanthin as a ‘quenching amplifier’, functioning physiologically to allow qE formation in the absence of high ΔpH potentially prohibitive to high rates of CO2 fixation.