Silicon Improves the Tolerance to Water-Deficit Stress Induced by Polyethylene Glycol in Wheat (Triticum aestivum L.) Seedlings

Drought stress usually causes a serious yield reduction in wheat production. Silicon (Si) has been reported to be able to alleviate drought stress damage; however, the mechanism is still poorly understood. In this article, the effects of Si (as sodium silicate) on some parameters related to oxidative damage, proline, soluble sugar, and inorganic ions in the leaves of wheat under 20% (w/v) polyethylene glycol (PEG-6000) simulative drought stress are investigated. PEG stress depressed the growth of shoot and root and decreased leaf water potential and chlorophyll concentration. Addition of 1.0 mM Si could partially improve the growth of shoot (but not root) and increase the leaf chlorophyll concentrations of stressed plants. Inclusion of Si in culture solution also maintained leaf water potential of stressed plants at the same level as that of the control plants. PEG stress induced significant accumulation of leaf hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) as well as an increase in electrolyte leakage, which were all decreased by added silicon. These results suggest that stress-induced membrane lipid peroxidation could be partly alleviated by added silicon. Moreover, the results were also supported by the observation that PEG stress-induced decrease in glutathione concentration in the leaves was reversed by added silicon. The proline concentration in the leaves was markedly increased under PEG stress, whereas added silicon partially reversed this. PEG stress decreased the leaf soluble sugar concentration. There were significant negative regressions between proline concentration and both shoot dry weight and leaf chlorophyll concentrations, whereas there were positive regressions between the proline concentration and both H₂O₂ and MDA concentrations in the leaves, supporting the view that proline accumulation is a symptom of stress damage rather than stress tolerance. Addition of Si obviously increased Si accumulation in the shoot. Analyses of Na, Mg, K, and Ca showed no accumulation of these ions in the shoot (on the basis of per tissue dry weight) under water stress, and added Si even decreased their concentrations. These results suggest that under short-term PEG-induced water stress conditions (1 week), antioxidant defense, rather than osmotic adjustment, contributed to the improved wheat growth by Si.     

Improved Phosphorus Uptake by Wheat Plant (Triticum aestivum L.) with Rhizosphere Fluorescent Pseudomonads Strains Under Water-Deficit Stress

Journal of Plant Growth Regulation - The aim of this study was to characterize fluorescent pseudomonads isolates of dryland wheat for salinity and drought tolerance and plant growth-promoting (PGP)...     

Nitrogen and Photosynthesis in the Flag Leaf of Wheat (Triticum aestivum L.)

Wheat (Triticum aestivum L. cv Yecora 70) plants were grown with various concentrations of nitrate nitrogen available to the roots. Sampling of flag leaves began after they had reached full expansion and continued throughout senescence. Rates of gas exchange, ribulose-1,5-bisphosphate (RuP₂) carboxylase activity, and the amounts of chlorophyll, soluble protein, nitrogen, and phosphorus were determined for each flag leaf. Rate of CO₂ assimilation was uniquely related to total leaf nitrogen irrespective of nutrient treatment, season, and leaf age. Assimilation rate increased with leaf nitrogen, but the slope of the relationship declined markedly when leaf nitrogen exceeded 125 millimoles nitrogen per square meter. Chlorophyll content and RuP₂ carboxylase activity were approximately proportional to leaf nitrogen content. As leaves aged, RuP₂ carboxylase activity and calculated Hill activity declined in parallel. With normal ambient partial pressure of CO₂, the intercellular partial pressure of CO₂ was always such that rate of assimilation appeared colimited by RuP₂ carboxylation and RuP₂ regeneration capacity.

The initial slope of rate of CO₂ assimilation against intercellular partial pressure of CO₂ varied nonlinearly with carboxylase activity. It is suggested that this was due to a finite conductance to CO₂ diffusion in the wall and liquid phase which causes a drop in CO₂ partial pressure between the intercellular spaces and the site of carboxylation. A double reciprocal plot was used to obtain an estimate of the transfer conductance.

     

Effect of Water Deficit on Sporogenesis in Wheat (Triticum aestivum L.)

Plants of Triticum aestivum L., cv. Gabo, were grown in a glasshousefor 4 weeks and then transferred to a controlled environmentwith 20±1 °C temperature and 16 h photoperiod. Theywere subjected to water deficit by withholding the water supplyduring various stages of floral development, including thoseimmediately before meiosis and all stages until just after anthesis. The proportion of apparently normal florets which produced grainwas reduced when water deficit occurred during and immediatelyafter meiosis in the generative tissues. The effect of thisreduced grain set on total grain yield was partially compensatedby an increase in the weight of the remaining grains. Cross-pollinationbetween stressed and well-watered plants showed that grain setwas reduced as a direct consequence of the induction of malesterility by water stress, whereas female fertility was unaffected.A large proportion of the anthers on water-stressed plants weresmall and shrivelled, did not dehisce normally and containedpollen which was devoid of normal cytoplasmic constituents andshowed no staining reaction with triphenyl tetrazolium chloride.This effect on male fertility was not a result of desiccationof the sporogenous tissue, but an indirect outcome of the decreasein water potential elsewhere in the plant. Water stress, Triticum aestivum L., wheat, pollen, sporogenesis, grain set, male sterility     

外源水杨酸对光抑制条件下小麦叶片光合作用的影响

以浓度为50、100、200 mg·kg-1的水杨酸(SA)预先处理灌浆期的小麦叶片,可有效防护强光所致的氧化损伤,维持较高的超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性,减轻丙二醛(MDA)积累.叶片在光抑制条件下,可维持较高的通过PSⅡ电子传递速率(Fm/Fo)、PSⅡ原初光化学效率(Fv/Fm)、PSⅡ量子效率(ΦPSⅡ)、光化学猝灭系数(qP)、净光合速率(Pn)和较低的非光化学猝灭系数(qNP).其中,以较低浓度SA(50 mg·kg-1)的效果较好.     

水杨酸和阿斯匹林对小麦盐害的缓解作用

盐胁迫条件下水杨酸和阿斯匹林能提高小麦种子发芽率、发芽指数和活力指数,降低幼苗叶片质膜透性和盐胁迫对细胞膜的伤害,提高幼苗体内超氧化物歧化酶、过氧化物酶等细胞保护酶的活性,减少膜脂过氧化作用产物丙二醛的积累,降低根系Ｎａ＋和提高根系Ｋ＋ 的向上运输选择性。所有这些变化都有利于缓解盐胁迫对小麦的伤害,提高其对盐胁迫的适应性。     

Effects of Kinetin on Tiller Bud Elongation in Wheat (Triticum aestivum L.)

Experiments are described in which at four stages of developmentmain tillers of wheat (Triticum aestivum L.) were isolated andinserted in test-tubes containing distilled water or kinetin.Leaves and leaf sheaths were split off to expose a lateral budapproximately 3 mm long whose growth was measured during a periodof 8 days. Kinetin at 6 ppm promoted bud elongation and dry-weightgain at all stages of development and in different light intensitiesand photoperiods. Reducing assimilate supply either by partialdefoliation of the main tiller or treatment with DCMU inhibitedbud growth during the early part of development, an effect whichwas relieved by kinetin. TIBA applied to prevent auxin transportincreased bud growth at the first two but not later stages ofdevelopment. Kinetin also inhibited nodal root growth consistently. At least two phases of bud control in grasses have to be considered,the first being the imposition of apical dominance after initiationof floral organs and stem elongation, the second being the releaseof buds from inhibition around ear emergence. Imposition ofbud inhibition appears to be a function of auxin and assimilatesupply, and at this stage the promoting effects of kinetin maybe through its action of mobilizing flow of assimilates. Therelease of buds at a later stage is apparently not associatedwith auxin, and kinetin may no longer be concerned with assimilateflow but rather with overcoming an inhibitory effect on budgrowth emanating from the leaves.     

Free Polyamines in Senescing Wheat(Triticum aestivum L.)

The free polyamine content of flag leaves, peduncles, rachis,glumes, and grains of wheat (Triticum aestivum L., cv. Castell)plants, ripening under field conditions, has been investigatedduring three consecutive growing seasons. Putrescine was quantitativelythe most important of all polyamines detected in these organs.Concentrations were highest in the grains, glumes and flag leaves.No correlation was found between polyamine content and the onsetof senescence of flag leaves and other organs. Excised primaryleaves, however, showed a decrease in polyamine content in thedark and also in light/dark cycles, but in the latter case onlyafter an initial increase. Sink removal of otherwise intactwheat plants caused an accumulation of putrescine in flag leavesat the later stages of senescence, whereas removal of all otherleaves was without any significant effect. Putrescine was alsorecovered in phloem-exudate samples collected throughout theperiod of grain development. In both grains and glumes, peakconcentrations of polyamines were found early during seed development. Key words: Triticum aestivum, polyamines, ripening, senescence     

小麦幼苗期水分胁迫所诱导基因表达谱的初步分析

利用抑制差减杂交(Suppression Subtractive Hybridization,SSH)和高密度点阵膜技术研究小麦2叶幼苗期水分胁迫诱导表达基因。通过筛选具有1530个克隆的SSH文库,获得181个阳性克隆。序列同源性比较和功能查询结果发现,83．2％的水分胁迫诱导表达基因分别与不同逆境胁迫条件下表达的基因具有较高的同源性,这些基因在生物体内的功能都是直接或间接对细胞遭受逆境胁迫起保护作用。其中17个EST未找到同源性较高的匹配序列,已经在GenBank注册。用反向Northern、RT-PCR和Northern进一步检验所获得的功能已知EST,初步建立了小麦幼苗期水分胁迫诱导的基因表达谱。     

小麦品种的耐肥性与光合作用

本试验以耐肥性不同的三个冬小麦品种为试材,研究了品种的耐肥性与光合作用的关系。结果表明,旗叶的光合速率顺序为: 泰山一号(中度耐肥)>济南13(高度耐肥)>昌乐5号(不耐肥)。光合速率的绝对值虽因不同年度间环境条件的不伺而有所变动,但品种间的差别则保持相对稳定。增施氮肥,能使昌乐5号的光合速率明显降低,而泰山—和济南13的光合速率则因增施氮肥受到显著的促进。     

Interactive Effects of Salinity and Ozone Pollution on Photosynthesis,Stomatal Conductance,Growth, and Assimilate Partitioning of Wheat (Triticum aestivum L.)

Plants of an Egyptian cultivar of wheat (Triticum aestivum L. cv. Giza 63) were exposed in open-top chambers (OTCs) for 8 h d^–1 for up to 75 d to a factorial combination of two levels of salinity (0 and 50 mM NaCl) and two levels of O₃ (filtered air and 50 mm³ m^–3). Exposure to 50 mm³ m^–3 O₃ significantly decreased stomatal conductance (g _s), net photosynthetic rate (P _N), and chlorophyll (Chl) content by 20, 25, and 21 %, respectively. This reduction resulted in a change in assimilate allocation in favour of shoot growth leading to a decrease in root to shoot ratio and eventually to a decrease in relative growth rate (RGR) of both root and shoot. There was a very large reduction in yield parameters, especially in the number of ears/plant and 1 000-grain mass. Soil salinity significantly reduced P _N and g _s by 17 and 15 %, respectively, while Chl content was increased by 17 %. Root growth was decreased leading to an increase in root/shoot ratio. Yield parameters were decreased due to salt stress. There was antagonistic interaction between salinity (50 mM NaCl) and O₃ (50 mm³ m^–3) showing that salinity effectively protects against the adverse effects of O₃ by increasing g _s during O₃ fumigation.     

Effect of Water Deficit on Self-thinning Line in Spring Wheat （Triticum aestivum L.） Populations

Monocultures of spring wheat （Triticum aestivum L.） were grown at overcrowded densities （10 000 and 3 000 plants per m^2） under well-watered and water-stressed conditions to investigate the effects of water deficits on self-thinning. The results showed that density reduction in water-stressed populations was delayed compared with that In well-watered populations. Populations grown In well-watered conditions conformed to the -3/2- power law. Compared with the well-watered condition, there was no significant decrease of the self-thinning line under water-stressed conditions In this experiment, although the rate of average shoot blomass accumulatlon decreased. This result Implied that the exponent of the -3/2-power equation Is not as sensitive as the rate of average shoot blomass accumulation to water stress. Further analysis indicated that, In each density treatment, the lines of the height versus shoot blomass relationships did not differ significantly between the two water conditions. However, the Intercepts of the height versus shoot blomass relationships were greater In the higher-density populations （10 000/m^2） than those In the lower-density populations （3 000/m^2）. These results showed that water deficit did not change plant geometry In this experiment. That Is to say, shoot competition for light remains constant at a given blomass, although root competition for water becomes more serious In water deficit conditions. Based on these results and previous reports we propose that, to affect the thinning line slope, changes In symmetric competition are not as efficient as changes In asymmetric competition.     

牛磺酸对小麦幼苗生长的生理效应

采用牛磺酸溶液培育小麦幼苗,测定10、100、500、1 000、5 000 mg/L的牛磺酸对小麦幼苗的光合作用PS Ⅱ光化学效率、细胞膜相对透性和膜脂过氧化以及生长的影响.结果表明,与对照组相比,适宜浓度的牛磺酸处理可促进小麦幼苗的生长,使其根长、株高、单株幼苗的干重和鲜重增加,并在一定程度上提高叶片的光化学效率,降低细胞膜相对透性和膜脂过氧化产物的含量;最适处理浓度约为500 mg/L.说明牛磺酸对小麦幼苗细胞膜有一定的保护作用.     

甜菜碱对NaCl胁迫下小麦细胞保护酶活性的影响

本文以小麦为材料,研究甜菜碱对ＮａＣｌ胁迫下小麦幼苗细胞保护酶系统的影响。结果表明,外源甜菜碱能够提高ＮａＣｌ胁迫下小麦幼苗超氧化物歧化酶、过氧化物酶等细胞保护酶的活性,抑制过氧化作用产物丙二醛的积累,降低叶片质膜透性和盐害对细胞膜的伤害。所有这些变化都有利于提高ＮａＣｌ胁迫下小麦幼苗细胞膜的稳定性、完整性和对ＮａＣｌ胁迫的适应性     

甜菜碱对NaCl胁迫下小麦细胞保护酶活性的影响

本文以小麦为材料,研究甜菜碱对NaCl胁迫下小麦幼苗细胞保护酶系统的影响。结果表明,外源甜菜碱能够提高NaCl胁迫下小麦幼苗超氧化物歧化酶、过氧化物酶等细胞保护酶的活性,抑制过氧化作用产物丙二醛的积累,降低叶片质膜透性和盐害对细胞膜的伤害。所有这些变化都有利于提高NaCl胁迫下小麦幼苗细胞膜的稳定性、完整性和对NaCl胁迫的适应性。     

Floret Initiation and Development in Spring Wheat (Triticum aestivum L.)

The number and developmental stages of florets were determinedin each spikelet of the spike in the main shoots of spring wheat.Samples were taken frequently from plants grown in a phytotronand in a nitrogen application field-test. Ten stages of development,from floret initiation until anthesis, were recognized and described. Inter-spikelet variation in the total number of initiated floretswas rather small. However, the number of florets at advancedstages of development, as well as the number of grains, washighest in the central spikelets in which florets initiatedfirst. Floret initiation did not proceed beyond spike emergence,whereafter the distal florets and the spikelet apex degenerated.Grain-set was restricted to florets which had developed at leastto the stage of visible anther lobes at spike emergence. Thenumber of these florets was increased significantly by nitrogenapplication. Wheat, Triticum aestivum L., spikelet, floret, grain set, nitrogen     

小麦抗倒性研究进展

倒伏是严重影响小麦子粒产量和品质的一个重要因素。本文系统阐述了小麦茎秆形态和结构特性、茎秆化学成分与抗倒伏关系以及抗倒性的遗传和分子标记等方面的最新研究进展。株高、基部节间长度与抗倒性呈负相关;而基部节间粗度、秆壁厚、单位长度干重与抗倒性呈正相关。茎秆机械组织细胞层数、厚度,维管束数目、面积以及髓腔大小与抗倒性密切相关。茎秆化学成分中纤维素、木质素以及碳水化合物含量和硅、钾元素含量与抗倒性呈正相关。小麦抗倒性呈数量性状遗传特征,除受多对主基因控制外,可能还受微效修饰基因作用。采用分子标记技术已将抗倒性以及与抗倒性相关的茎秆形态性状进行了QTL定位。     

Studies on the Efficiency of Energy Conversion in Photosynthetic Parts of Wheat Plants (Triticum aestivum L.)

This paper describes the photosynthetic response to light intensityduring a typical day for three parts of the wheat plant (basalleaves, flag leaf and ear) at five successive stages of growthfrom the seedling stage to maturity. The results are examinedin relation to the respiration rate of these organs, and theirangle of erectness, chlorophyll content, stomatal size and distribution.The efficiency of fixation and retention of solar energy byphotosynthesis is calculated for each part. For each organ efficiencydeclines with increasing maturity, but throughout their photosyntheticlife, ears are shown to be more efficient than flag leaves,which in turn are more efficient than basal leaves. The reverseapplies if the calculation is made over the entire life of theplant. The results suggest ways of increasing the dry matterproduction potential in wheat.     

Colchicine-induced Paracrystals in Root Cells of Wheat (Triticum aestivum L.)

Tubulin conformations other than microtubules in the meristematiccells of wheat roots grown in the presence of 2 mM colchicinesolution were investigated by immunofluorescence and electronmicroscopy. In the affected cells microtubules disappeared andwere replaced by tubulin fluorescent strands that occurred inthe cortical cytoplasm. With increasing time of exposure tocolchicine the tubulin strands became better organized and occurredalso in the subcortical cytoplasm and finally they were restrictedto the area around the nucleus. In prophase and preprophasecells thick strands occupied the cortical cytoplasmic zone wherein normal cells a preprophase microtubule band (PMB) was expectedto be assembled. In the colchicine-treated cells electron microscopy revealedan accumulation of paracrystalline aggregates, which initiallyoccurred along the cell wall and later deeper in the cytoplasm,in the perinuclear regions and the cytoplasmic invaginationsof the nucleus. In transverse planes the paracrystalline strandsappear to consist of hexagonal subunits in a 'honeycomb' arrangement,while in longitudinal and oblique sections they exhibit variableimages. Since their distribution coincides with that of thetubulin strands visualized by immunofluorescence, they are consideredto be the same structure. Therefore, the paracrystals consistof, or at least contain, tubulin. They are most likely to bepolymers of tubulin-colchicine complexes.Copyright 1995, 1999Academic Press Wheat roots, colchicine, immunofluorescence, electron microscopy, tubulin paracrystals, Triticum aestivum L