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We examined the distribution of plants in sandy rangelands with different degrees of desertification in (i) Horqin and Mu Us sandy lands in north China, (ii) Darfur district in north-west Sudan and (iii) southern Tunisia. The severity of desertification in these areas was classified as light, moderate, severe or extreme. The following vegetation changes were observed with increasing severity of desertification: a decrease in the number of plant species, an increase in drought-tolerant plants, a decrease in the proportion of palatable grasses and the occurrence of some species in only one category of desertification, whereas other species occurred in several categories. Plant species with unique niche requirements were identified and recommended as indicators of the degree of desertification for particular areas. We discuss the characteristics of species in areas with severe desertification and the method of using plant species as indicators of the extent of desertification. [ABSTRACT FROM AUTHOR]

Abstract: In the North China Plain (NCP), more than 70% of irrigation water resources are used for winter wheat (Triticum aestivum L.). A crucial target of groundwater conservation and sustainable crop production is to develop water-saving agriculture, particularly for winter wheat. The purpose of this study was to optimize irrigation scheduling for high wheat yield and water use efficiency (WUE). Field experiments were conducted for three growing seasons at the Wuqiao Experiment Station of China Agriculture University. Eleven, four and six irrigation treatments, consisting of frequency of irrigation (zero to four times) and timing (at raising, jointing, booting, flowering and milking stage), were employed for 1994/95, 1995/96 and 1996/97 seasons, respectively. Available water content (AWC), rain events, soil water use (SWU), evapotranspiration (ET) and grain yield were recorded, and water use efficiency (WUE) and irrigation water use efficiency (IWUE) were calculated. The results showed that after a 75-mm pre-sowing irrigation, soil water content and AWC in the root zone of a 2-m soil profile during sowing were 31.1% (or 90.7% of field capacity) and 16.1%, respectively. Rainfall events were variable and showed a limited impact on AWC. The AWC decreased significantly with the growth of wheat. At the jointing stage no water deficits occurred for all treatments, at the flowering stage water deficits were found only in the rain-fed treatment, and at harvest all treatments had moderate to severe soil water deficits. The SWU in the 2-m soil profile was negatively related to the irrigation water volume, i.e. applying 75mm irrigation reduced SWU by 28.2mm. Regression analyses showed that relationships between ET and grain yield or WUE could be described by quadratic functions. Grain yield and WUE reached their maximum values of 7423kg/ha and 1.645kg/m3 at the ET rate of 509 and 382mm, respectively. IWUE was negatively correlated with irrigated water volume. From the above results, three irrigation schedules: (1) pre-sowing irrigation only, (2) pre-sowing irrigation+irrigation at jointing or booting stage, and (3) pre-sowing irrigation+irrigations at jointing and flowering stages were identified and recommended for practical winter wheat production in the NCP. [Copyright &y& Elsevier]

An environmentally controlled experiment was conducted in growth chambers to investigate the interactive effects of salinity and air humidity on two cultivars of tomato (Lycopersicon esculentum Mill.), Daniela (relatively salt tolerant) and Naomi (relatively salt sensitive). One month after germination, the plants were exposed for 15 days to factorial combinations of two salinity levels, 0 (control) and 80 mM sodium chloride (NaCl), and two relative humidity (RH) levels, 30% and 70%. The NaCl treatment decreased the growth of cv. Naomi by 34% and 21% at 30% and 70% RH, respectively, while there was no decrease in the growth of cv. Daniela at 30% RH and only a slight decrease at 70% RH. Under NaCl treatment, cv Daniela had significantly lower Na+concentrations in leaves and stems and a higher root-to-shoot ratio than cv. Naomi at both relative humidities. Salt tolerance of cv. Daniela may be related to its high root-to-shoot ratio and its ability to exclude Na+from the shoot. NaCl-treated plants of cv. Daniela had a lower biomass at 70% than at 30% RH. Conversely, NaCl-treated plants of cv. Naomi had a greater biomass at 70% compared with 30% RH. The ameliorating effects of high RH on NaCl-induced growth reductions in cv. Naomi could be attributed to an increase in leaf area, root growth, photosynthetic rate, and stomatal conductance and a decrease in Cl- concentration in leaves. The overall findings of this study suggest that the growth of salt-sensitive tomato cultivars under saline conditions could be improved by increasing air humidity. [ABSTRACT FROM AUTHOR]

Experiments were conducted in an environmentally controlled growth chamber to evaluate the role of the root system in the salt tolerance of two soybean (Glycine max(L.) Merr.) cultivars, Tachiyutaka and Dare, that differ in salt tolerance. Young plants were submitted to 0 (control), 40, 80, and 120 mM NaCl treatments for 3, 23, and 30 days in three experiments, respectively. The most significant differences between the two cultivars were obtained in 40 mM NaCl. Under this condition, compared with salt sensitive cv. Tachiyutaka, tolerant cv. Dare showed a higher relative shoot and root growth (Dare: 70 and 63%, Tachiyutaka: 42 and 42%, respectively), water extraction ability (Dare: 0.18 g cm-2 d-1 for transpiration and 0.98 g m-1 d-1 for water uptake, Tachiyutaka: 0.13 g cm-2 d-1 and 0.81 g m-1 d-1 respectively), root pressure (Dare: 5.68 mg g-1 for root exudate, Tachiyutaka: 0.32 mg g-1), better root osmotic adjustment (Dare: -0.61 MPa for osmotic potential, Tachiyutaka: -0.59 MPa), and less sodium (Na+) accumulation in plant tissue (Dare: 0.1, 0.4, and 9.2 mg g-1 in leaf, stem, and root, respectively, Tachiyutaka: 1.4, 3.5, and 11.6 mg g-1). The difference in salt tolerance between the two cultivars is attributed to the root system. The salt tolerance of cv. Dare is associated with high water uptake, and Na+ and chloride (Cl-) exclusion of the roots. [ABSTRACT FROM AUTHOR]

The effects of defoliation on soybean [Glycine max (L.) Merr.] growth and yield have been well studied, but relatively little is known about its nitrogen (N) accumulation after defoliation. An experiment was conducted to examine soybean recovery and N accumulation following defoliation. The indeterminate cultivar ('Tousan 69') was planted in a greenhouse, and two defoliation treatments (no defoliation and 67% defoliation) were imposed at the R2 stage when plants had at least one flower in the two uppermost nodes. At 0, 15, 30 and 45 days after defoliation (DAD), plants were destructively sampled to measure dry mass production, nitrogen accumulation and nitrogen fixation. Seed yield and N concentration also were measured at maturity. Neither the seed yield nor its N concentration was affected by defoliation. Although defoliation temporarily reduced soybean dry weight and N accumulation during 15 DAD, defoliated plants completely recovered their dry weight and N accumulation 30 DAD. There was little difference in N concentration between defoliated and non defoliated plants, indicating that N acquisition was restored during the recovery process. Recovery of N accumulation in defoliated plant was due to complete recovery of N2-fixing ability and maybe related to improvement in N absorption after defoliation. [ABSTRACT FROM AUTHOR]

Effects of silicon (Si) application on photosynthesis of solution-cultured cucumber seedlings were investigated under osmotic stress and unstressed conditions. In unstressed conditions, silicon application had no effect on growth and photosynthetic parameters. The responses of the photosynthetic parameters to abruptly imposed osmotic stress did not differ between silicon treatments. After 1 week exposure to osmotic stress, growth reduction was observed, but it was less severe in seedlings grown with silicon than in those without silicon. Although there were no differences between silicon treatments in stomatal conductance, transpiration rate, cuticular transpiration, or xylem sap exudation rate under osmotic stress, leaf intercellular carbon dioxide (CO2) concentration was significantly lower and photosynthetic rate tended to be higher in seedlings supplied with silicon. These results suggested that the silicon-induced alleviation of growth reduction under osmotic stress in cucumber was due to amelioration of stress-induced damage of leaf tissues rather than to improvement of leaf water status. [ABSTRACT FROM AUTHOR]

Effects of silicon application on stomatal conductance in sorghum were investigated. Sorghum seedlings were grown in culture solution containing 0 or 1. 67mM silicon. On ninth day after giving silicon treatment, when there were no differences in shoot and root growth between the silicon-supplied and silicon-deficient treatments, seedlings were exposed to gradually increasing light intensity, combination of sudden increase and decrease in light intensity, and water stress induced by mixing sorbitol with the culture solution. There was increased stomatal conductance with increasing light intensity and no significant difference was observed between the two silicon treatments. Under water stress, the stomatal conductance of silicon-supplied seedlings was higher than that of silicon-deficient seedlings. The higher stomatal conductance in silicon-supplied seedlings under water stress was attributed to increased leaf water potential due to silicon-induced enhancement of hydraulic conductance. The results indicated that silicon application could affect stomatal conductance in sorghum seedlings through the modification of plant water relations. [Copyright &y& Elsevier]

An experiment was conducted to determine if salinity stress alters the response and tolerance of soybean to defoliation. Four soybean [ Glycine max (L.) Merr.] cultivars (‘Tachiutaka,’ ‘Tousan 69,’ ‘Dare’ and ‘Enrei’) in a growth chamber were exposed to two salinity treatments (0 and 40 mM NaCl) and two defoliation treatments (with and without defoliation). The interactive effects of salinity stress and defoliation on growth rate, leaf expansion, photosynthetic gas exchange, and sodium (Na + ) accumulation were determined. The decrease in growth rate resulting from defoliation was more pronounced in plants grown under salinity stress than in those grown without the stress. Without salinity stress, defoliated plants of all four cultivars had leaf-expansion similar rates to those of the undefoliated ones, but the photosynthetic rates of their remaining leaves were higher than those of undefoliated plants. However, with salinity stress, defoliated ‘Tachiutaka’ and ‘Tousa 69’ had lower leaf expansion and photosynthetic rates than undefoliated plants. For cultivars ‘Dare’ and ‘Enrei,’ the defoliated plants had leaf-expansion rates similar to undefoliated ones, but the photosynthetic rate of the remaining leaves did not increase. Except for cultivar ‘Dare,’ defoliated plants grown under salinity stress had higher Na + accumulation in leaves than undefoliated ones, and this result may be related to slow leaf expansion and photosynthesis. Salinity stress negatively affects soybean response and tolerance of defoliation, and the effects varied according to the salt tolerance of the cultivar. [ABSTRACT FROM AUTHOR]

To analyze how silicon (Si) fertilizer improves plant growth under water stress, we investigated the growth and root responses of sorghum seedlings to Si application. Seedlings were grown hydroponically at two Si levels (0 and 1.78 mM) and under two water stress conditions simulated with polyethylene glycol. The reduction in dry weight due to stress was alleviated by Si application, accompanied by an increase in root water uptake. Silicon application decreased the osmotic potential of the roots without affecting their water content, showing that osmotic adjustment occurred to increase water uptake. An assessment of root solutes suggested that soluble sugar and amino acids (alanine and glutamic acid) were osmolytes responsible for this adjustment. Root anatomical traits related to water transport were not affected by the Si application. These results improved our understanding of the physiological mechanisms that underlie the Si-induced increases in sorghum growth and water uptake under water stress. [ABSTRACT FROM AUTHOR]

Sorghum [Sorghum bicolor (L.) Moench] was grown hydroponically with or without 50 ppm silicon (Si), and exposed to water stress from 10 days after sowing (DAS). At 15 and 23 DAS, we measured dry weight and diurnal variations in photosynthetic rate (PN), stomatal conductance (gs), transpiration rate (T), leaf water potential (ψL), and water uptake rate (23 DAS only). The reduction in dry weight at 23 DAS caused by water stress was ameliorated by silicon. Under water stress, silicon-treated seedlings showed higher gs, PN, and T than untreated ones. ψL remained almost constant within treatments throughout the daytime. Water uptake rate was reduced by water stress, but the reduction was ameliorated by silicon. We conclude that silicon enhanced water uptake and gs, improving water supply to the leaves. These effects of silicon occurred soon after exposure to water stress. [ABSTRACT FROM AUTHOR]

To clarify whether silicon application could improve root growth of rye (Secale cereale L.) under drought, a pot experiment was conducted under two soil water regimes (soil water contents were kept at 0.015-0.030 or above 0.050 g g-1 for dry and well-watered conditions, respectively). Silicon increased dry weight of rye but did not affect shoot/root ratio under the well-watered condition, while it lowered the ratio under the dry condition. Water use and leaf water potential were increased by silicon under the well-watered condition, although photosynthetic rate, stomatal conductance and water use efficiency were not affected. Under the dry condition, silicon-supplied ryes showed higher photosynthetic rate, stomatal conductance, water use and leaf water potential than silicon-deficient ones. These results suggested that silicon increased dry matter production of ryes under drought, enabling them to allocate more assimilates to root. This resulted in lowering of the shoot/root ratio and better adaptation to drought. [ABSTRACT FROM AUTHOR]

In this study, it was verified whether silicon (Si) affected plant hydraulic resistance, which was one of the significant factors affecting water uptake. Sorghum bicolor (L.) Moench. was grown hydroponically under varying silicon levels and exposed to osmotic stresses. Under osmotic stress, reduction in growth, photosynthesis, and transpiration were alleviated as supplied silicon levels increased. These alleviative effects were ascribed to enhancement of water uptake. Although shoot/root ratio was not affected by silicon, estimated apparent hydraulic resistance was lower in silicon-supplied sorghum than silicon-deficient one under osmotic stress. Simultaneous measurement of transpiration and water uptake rates indicated that under osmotic stress silicon-deficient sorghums showed unbalanced water relation that transpiration rate exceeded water uptake rate, while they were balanced in silicon-supplied sorghums. The results indicated that silicon improved hydraulic resistance, allowing sorghum to avoid from decrease in water uptake rate that happens to silicon-deficient sorghum under water stress. [ABSTRACT FROM AUTHOR]

Three diploid ( Triticum boeoticum, AA; Aegilops speltoides, BB and Ae. tauschii, DD), two tetraploid (T. dicoccoides, AABB and T. dicoccon, AABB) and one hexaploid (T. vulgare, AABBDD) varieties of wheat, which are very important in the evolution of wheat were chosen in this study. A pot experiment was carried out on the wheat under different water and nutrient conditions (i) to understand the differences in biomass, yield, water use efficiency (WUE), and nutrient (N, P and K) use efficiency (uptake and utilization efficiency) among ploidies in the evolution of wheat; (ii) to clarify the effect of water and nutrient conditions on water and nutrient use efficiency; and (iii) to assess the relationship of water and nutrient use efficiency in the evolution of wheat. Our results showed that from diploid to tetraploid then to hexaploid during the evolution of wheat, both root biomass and above-ground biomass increased initially and then decreased. Water consumption for transpiration decreased remarkably, correlating with the decline of the growth period, while grain yield, harvest index, WUE, N, P and K uptake efficiency, and N, P and K utilization efficiency increased significantly. Grain yield, harvest index and WUE decreased in the same order: T. vulgare > T. dicoccon > T. dicoccoides > Ae. tauschii > Ae. speltoides > T. boeoticum. Water stress significantly decreased root biomass, above-ground biomass, yield, and water consumption for transpiration by 47–52%, but remarkably increased WUE. Increasing the nutrient supply increased wheat above-ground biomass, grain yield, harvest index, water consumption for transpiration and WUE under different water levels, but reduced root biomass under drought conditions. Generally, water stress and low nutrient supply resulted in the lower nutrient uptake efficiency of wheat. However, water and nutrient application had no significant effects on nutrient utilization efficiency, suggesting that wheat nutrient utilization efficiency is mainly controlled by genotypes. Compared to the other two diploid wheats, Ae. squarrosa (DD) had significant higher WUE and nutrient utilization efficiency, indicating that the D genome may carry genes controlling high efficient utilization of water and nutrient. Significant relationships were found between WUE and N, P and K utilization efficiency. (Handling editor: Jin-Zhong Cui) [ABSTRACT FROM AUTHOR]

Conserving irrigation water resources is a most important measure for sustainable wheat production in the North China Plain. In the present study, the effect of phosphorus (P) application for saving irrigation water was evaluated. The application of fertilizer P increased nitrogen and phosphorus uptake, shoot biomass, head number, seed number and, consequently, grain yield, and increased soil water use and seasonal evapo-transpiration. The lower the volume of irrigation water applied, the more obvious were these effects. When winter wheat was basally fertilized with 88.5 kg P 2 O 5 /ha and irrigated with 90 mm at the jointing stage, the highest fertilizer P use efficiency, apparent P recovery and net profit (due to irrigation and/or fertilizer P) were obtained. The results suggested that fertilizer P should be used for saving irrigation water resources in the North China Plain. [ABSTRACT FROM AUTHOR]

Ethylene involvement in germination of Striga hermonthica (Del.) Benth., an important root parasitic weed on poaceous crops, was investigated at the physiological and molecular levels. Seeds, conditioned at 30°C for 14 days, were treated with ethylene, ethephon or 1-aminocyclopropane-1-carboxylic acid (ACC). Ethylene consistently induced low germination. Ethephon and ACC effectively stimulated germination at concentrations of 0.01 and 1 mM , respectively. In contrast to ethylene, both ethephon and ACC acted in a concentration-dependent manner. Germination induced by the synthetic strigolactone GR24 was inhibited by aminoethoxyvinylglycine (AVG) and 1-methylcyclopropene. ACC reversed the inhibition caused by AVG. When seeds were treated with GR24 in sealed vials, ethylene concentration in headspace gas increased prior to the onset of germination. Total RNA extracted from germinating seeds 12 h after GR24 treatment was used for PCR-based amplification of cDNA fragments encoding the ACC synthase- and oxidase-active site domains. Two distinct cDNA fragments encoding ACC synthase (SHACS1 and SHACS2 ) and one encoding ACC oxidase (SHACO1 ) were cloned and sequenced. Southern analysis suggested that each of the cloned genes was present as a single copy in the genome of S. hermonthica . Northern analyses showed that SHACS1 exhibited a temporal change in expression peaking at 10 h after GR24 treatment, which coincided with a steady increase in ethylene concentration. SHACS2 was expressed at a low level with a similar trend. SHACO1 exhibited a temporal change in expression peaking at 15 days during conditioning, when seed response to GR24 was maximal. In summary, expression of ACC synthase and ACC oxidase genes was found to be responsive to a germination stimulant and to conditioning, respectively. The implications of these findings with respect to germination of S. hermonthica under field conditions are discussed. [ABSTRACT FROM AUTHOR]

Bamboo is a silicon accumulating plant. In leaves, the major place of silicon (Si) deposition is the epidermis, with the highest concentration of Si in silica cells. In bamboo roots, the deposition of Si is found only in endodermal cell walls. The silicification of leaves and roots was examined in the economically important bamboo plant Phyllostachys heterocycla, using an environmental scanning electron microscope coupled with X-ray microanalysis, as well as gravimetric quantification. The content of Si on a dry weight basis measured by gravimetric quantification was 7.6% in leaves and 2.4% in roots, respectively. Moreover, quantification of EDX data showed high Si impregnation of the inner tangential endodermal walls. Si content in this part of the root endodermal cell walls was even higher than that in the outer leaf epidermal walls, where conspicuous deposition of Si often occurs in grass plants. [ABSTRACT FROM AUTHOR]

Summary • The dynamics of silica deposition and Si aggregates formation in inner tangential walls of root endodermal cells, which occurs as an additional stage of endodermal development in sorghum (Sorghum bicolor ), were studied. • An environmental scanning electron microscope (ESEM) and X-ray microanalyzer (EDAX) were used to study sorghum roots grown hydroponically with Si (+ Si medium) and without Si (– Si medium). • Silica aggregates were absent in roots of plants cultivated in – Si medium. However, their additional formation on fully mature and thickened endodermal cell walls took place when plants grown in – Si medium were transferred to + Si medium. The beginning of Si aggregates formation was observed and Si deposition detected 2 h after transfer to + Si medium. • By dipping the apical root half in + Si medium, the silica aggregates were formed in the endodermis at the basal part of the root. This supports the hypothesis of outward Si transport from the xylem to the endodermis rather than radial inward Si movement and its deposition at the point of the apoplastic barrier represented by the endodermis. [ABSTRACT FROM AUTHOR]

(+)-Strigol was isolated from Menispermum dauricum root culture filtrate. Its identity was confirmed by HPLC, 1H NMR, UV and MS, and on the basis of its CD spectrum. This is the first report on isolation of strigolactone from aseptic plant culture. [Copyright &y& Elsevier]

Describes the isolation and identification of chlorinated alkaloids in Menispermum dauricum root culture. Conversion reactions among alkaloids; X-ray crystallographic analysis of alkaloids; Biosynthetic relationships among alkaloids.