Search

Tuber dormancy and sprouting are commercially important potato traits as long-term tuber storage is necessary to ensure year-round availability. Premature dormancy release and sprout growth in tubers during storage can result in a significant deterioration in product quality. In addition, the main chemical sprout suppressant chlorpropham has been withdrawn in Europe, necessitating alternative approaches for controlling sprouting. Breeding potato cultivars with longer dormancy and slower sprout growth is a desirable goal, although this must be tempered by the needs of the seed potato industry, where dormancy break and sprout vigour are required for rapid emergence. We have performed a detailed genetic analysis of tuber sprout growth using a diploid potato population derived from two highly heterozygous parents. A dual approach employing conventional QTL analysis allied to a combined bulk-segregant analysis (BSA) using a novel potato whole-exome capture (WEC) platform was evaluated. Tubers were assessed for sprout growth in storage at six time-points over two consecutive growing seasons. Genetic analysis revealed the presence of main QTL on five chromosomes, several of which were consistent across two growing seasons. In addition, phenotypic bulks displaying extreme sprout growth phenotypes were subjected to WEC sequencing for performing BSA. The combined BSA and WEC approach corroborated QTL locations and served to narrow the associated genomic regions, while also identifying new QTL for further investigation. Overall, our findings reveal a very complex genetic architecture for tuber sprouting and sprout growth, which has implications both for potato and other root, bulb and tuber crops where long-term storage is essential.

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.

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.

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 effect of continuous exposure to ozone at 0.45, 0.9 and 2 μmol mol−1 on quality changes during the storage of red and green chilli peppers at 10 °C was investigated. Ozone at 0.45 and 0.9 μmol mol−1 reduced disease incidence in red peppers, with no further benefits at 2 μmol mol−1. Ozone at 0.9 μmol mol−1 reduced weight loss during storage and improved firmness maintenance. Skin colour was bleached in red peppers exposed to ozone at 2 μmol mol−1, and in green ones at all tested doses. Total phenolic content was not affected by ozone but antioxidant activity was reduced in green chilli peppers exposed to ozone at 2 μmol mol−1, due to lower ascorbic acid content in those samples. Ozone at 0.9 μmol mol−1 extended the shelf-life of chilli peppers.

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.

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.

The effect of continuous exposure to ozone on quality changes during the storage of red bell peppers, cucumbers and zucchini was investigated. Peppers were stored at 14 °C and were exposed to ozone at 0.1 and 0.3 μmol mol−1, while cucumbers and zucchini were stored at 12 and 8 °C, respectively, and exposed to ozone at 0.1 μmol mol−1. The content of fructose (2.75 g/100 g FW) and glucose (2.00 g/100 g FW) in red bell peppers exposed to ozone at 0.1 μmol mol−1 was increased by 8 and 7%, respectively, when compared to controls. Continuous exposure to ozone at 0.3 μmol mol−1, on the other hand, had no effect on fructose (2.52 g/100 g FW) and glucose (1.88 g/100 g FW) content. The content of vitamin C was significantly enhanced in red bell peppers exposed to ozone at 0.1 and 0.3 μmol mol−1 after 7 d of storage, however, this effect was not maintained. After 14 d, vitamin C content in peppers exposed to ozone at 0.1 μmol mol−1 was not significantly different from the control, whereas it was reduced at 0.3 μmol mol−1. Total phenolics content was increased in peppers exposed to ozone at 0.1 μmol mol−1, but was unaffected at 0.3 μmol mol−1. Continuous exposure of red bell peppers to ozone at 0.1 and 0.3 μmol mol−1 had no significant effect on weight loss, texture and colour. In cucumbers and zucchini, continuous exposure to ozone at 0.1 μmol mol−1 reduced weight loss by more than 40% and improved texture maintenance, while having no significant effect on their biochemistry. The findings from this study suggest that continuous exposure to ozone at 0.1 μmol mol−1 is a promising method for shelf-life extension of cucumbers and zucchini. Even though in red bell peppers continuously exposed to ozone at 0.1 μmol mol−1 sugars and phenolics content was increased, further work is still needed to better understand the exact mechanism of ozone action and its potential for the industrial use.

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 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).

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.

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 extent of energy-dependent quenching of chlorophyll fluorescence in broken spinach chloroplasts has been quantitatively related to the size of the thylakoid proton gradient as measured by the quenching of 9-aminoacridine fluorescence by titration at constant irradiance with the uncoupler nigericin or by change in irradiance. It was found that chloroplasts prepared from leaves that had been pre-illuminated with strong light for 30 min showed energy-dependent quenching at a lower proton gradient than chloroplasts prepared from dark-adapted leaves. Measurement of the carotenoid composition of the thylakoids showed that light treatment raised the ratio of zeaxanthin: violaxanthin. The possible dependence of energy-dependent quenching on xanthophyll composition and the physiological implications of this light-activation process to the regulation of photosynthetic electron transport are discussed.

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.