Effects of shade, drought and daughter cladodes on the CO2 uptake by cladodes of Opuntia ficus-indica

The effects of shade on the physiology of opuntias have received little attention, notwithstanding that shade regularly occurs in both wild stands and cultivated populations. This research evaluates the effects of shade on the physiology of cladodes of Opuntia ficus‐indica, with and without daughter cladodes, as they are exposed to progressive drought. The stress caused by shade, drought and daughter cladodes reduced photosynthesis by mother cladodes and was associated with decreases in relative water content, parenchyma thickness and chlorophyll content. Shade exacerbated the physiological drought of mother cladodes imposed by daughter cladodes and by reduced soil water content.     

Effect of mannitol and glucose-induced osmotic stress on growth,water relations,and solute composition of cell suspension cultures of poplar (Populus deltoides var.Occidentalis) in relation to anthocyanin accumulation

Summary A cell suspension culture of poplar (Populus deltoides (Marsh.) Bartr. var.occidentalis Rydb.), accumulating the anthocyanin pigment, cyanidin 3-glucoside, in the lag phase of culture growth, was subjected to osmotic stress with glucose and mannitol. Osmotic stress treatments resulted in growth suppression and higher anthocyanin accumulation compared with unstressed cells. Both an increase in the proportion of pigmented cells and an increase in the concentration of anthocyanin in the pigmented cells were responsible for high anthocyanin content of cultured cells subjected to osmotic stress. The osmotic stress induced by glucose suppressed growth more than that by mannitol and produced higher anthocyanin levels. Only small amounts of [U-¹⁴C]mannitol were taken up and metabolized by the cells. Stressed cells accumulated sugars and free amino acids to a different extent resulting in altered cell sugar-to-amino acid ratios. The accumulation of osmotically active solutes and cell growth suppression may both be responsible for the accumulation of anthocyanin in stressed cells.     

Triadimefon reduces transpiration and increases yield in water stressed plants

The total free amino acid pools in radicles of watermelon seeds, investigated during imbibition of water at 25°C, were higher under the most (darkness) than under the least (continuous broad spectrum far-red light) favourable light regime for germination. When seeds were imbibed in an appropriate osmotic solution of PEG-6000 (fully suppressing germination), in darkness or under continuous red or far-red light, the biochemical analyses of the radicles after 1,2,3 and 4 days from the onset of imbibition show that while the total soluble sugar content remains rather constant in all treatments, significant changes are observed in the total free amino acid pools. After the first day, a considerable increase characterizes the "darkness" pool in contrast to a moderate one under red, while the "far-red" pool remains constant. Ultimately, at 4 days, the three pools are 190,142 and 123% of the 0 day radicle one. The qualitative free amino acid determination of the 4 day darkness and far-red pools shows a considerably increased percentage contribution of glutamic acid, arginine and citrulline in the "darkness" pool. The free amino acid increase in non-illuminated radicles may be correlated to germinability; moreover, it is evidently a phytochrome-mediated, pre-germinatory event, probably due to the hydrolysis of proteins (known to be rich in glutamic acid and arginine), stored in the radicle.     

Drought-induced variations of water relations parameters in Olea europaea

The effects of water stress on water potential components, tissue water content, mean elastic modulus and the osmoregulation capacity of olive (Olea europaea L. cv. Coratina) leaves was determined. Artificial rehydration of olive leaf tissues altered the P-V relationships so that a plateau phenomenon occurred. Points in the P-V curve in the region affected by the plateau, generally up to –0.5 MPa, were corrected for all the samples analyzed. In the corrected P-V relationship, an osmotic adjustment was found in drought-stressed leaf tissues. Osmotic potentials at full turgor (_{0 (sat)}) and osmotic potential at turgor-loss (_{0 (TVT)}) decreased from –2.06±0.01 MPa and –3.07±0.16 MPa in controls to –2.81±0.03 MPa and –3.85±0.12 MPa in most stressed plants. Osmotic adjustment values obtained from the P-V curves agreed with those obtained using an osmometer. An active osmotic adjustment of 1.42 MPa was also observed in 1–4 mm- diameter roots. Mannitol is the main carbohydrate involved in osmotic potential decrease in all treatments. The maximum elastic modulus increased from 11.6±0.95 MPa in the controls to 18.6±0.61 MPa in the most stressed plants.     

Growth and osmoregulation in Pisum sativum subhooks as affected by gibberellic acid and cotyledon excision

Growth stimulation by gibberellic acid (GA) of the Alaska pea ( Pisum sativum L.) subhook was observed within 6 h after its application; the stimulation being larger in cuttings with cotyledons than in decotylized ones. The osmotic potential in the subhook increased as it grew, the rate of its increase being faster in cuttings without than in cuttings with cotyledons. GA had no effect on the change in the osmotic potential until 8 h after GA application, but afterwards it suppressed the increase in cuttings with cotyledons. This GA effect was not observed in decotylized cuttings. Changes in the osmotic potential were well correlated with changes in the concentration of soluble sugars, but not with changes in amino acids and K⁺, Soluble sugars accumulated in the subhook of cuttings with and without cotyledons in proportion to growth, irrespective of the presence or absence of GA. Cotyledon excision suppressed sugar accumulation, and GA promoted it in cuttings with cotyledons but not in decotylized ones. These results suggest that GA stimulates the translocation of sugars from the cotyledons to the subhook and, thereby, maintains the osmotic potential low, resulting in enhanced growth.     

Cyclitols and carbohydrates in leaves and roots of 13 Eucalyptus species suggest contrasting physiological responses to water deficit

In many tree species, physiological adaptations to drought include the accumulation of osmotically active substances and/or the presence of particular compatible solutes, among them cyclitols. Recently, the cyclitol quercitol was identified in species of Eucalyptus, a diverse genus whose speciation is probably driven by adaptation to water availability. We subjected seedlings of 13 Eucalyptus species from different ecosystems ('mesic' and 'xeric') and different sub-generic taxonomic groups to 10 weeks of water deficit (WD) treatment. Pre-dawn water potentials (psi(pdwn)) and relative water content (RWC) were determined in shoots, and total osmolality, soluble low-molecular-weight carbohydrates and cyclitols were measured in leaves and roots. Responses to water deficit followed two distinct patterns: Eucalyptus species from 'mesic' environments adjusted concentrations of sucrose (through increased levels of sucrose and decreases in RWC) in response to water deficit, whereas 'xeric' species increased concentrations of quercitol (through reductions in RWC). In root tissues, only species from xeric environments contained high levels of quercitol and mannitol, increasing under WD conditions. We suggest that the former (mesic) strategy may be beneficial to respond to short-lasting drought conditions, because sucrose is easily metabolized, whereas the latter (xeric) strategy may relate to an effective acclimation to longer-lasting drought. These physiological response groups are also related to taxonomic groups within the genus.     

Gas exchange and growth responses to elevated CO2 and light levels in the CAM species Opuntia ficus-indica

Gas exchange and dry-weight production in Opuntia ficus-indica, a CAM species cultivated worldwide for its fruit and cladodes, were studied in 370 and 750 μmol mol⁻¹ CO₂ at three photosynthetic photon flux densities (PPFD: 5, 13 and 20 mol m⁻² d⁻¹). Elevated CO₂ and PPFD enhanced the growth of basal cladodes and roots during the 12-week study. A rise in the PPFD increased the growth of daughter cladodes; elevated CO₂ enhanced the growth of first-daughter cladodes but decreased the growth of the second-daughter cladodes produced on them. CO₂ enrichment enhanced daily net CO₂ uptake during the initial 8 weeks after planting for both basal and first-daughter cladodes. Water vapour conductance was 9 to 15% lower in 750 than in 370 μmol mol⁻¹ CO₂. Cladode chlorophyll content was lower in elevated CO₂ and at higher PPFD. Soluble sugar and starch contents increased with time and were higher in elevated CO₂ and at higher PPFD. The total plant nitrogen content was lower in elevated CO₂. The effect of elevated CO₂ on net CO₂ uptake disappeared at 12 weeks after planting, possibly due to acclimation or feedback inhibition, which in turn could reflect decreases in the sink strength of roots. Despite this decreased effect on net CO₂ uptake, the total plant dry weight at 12 weeks averaged 32% higher in 750 than in 370 μmol mol⁻¹ CO₂. Averaged for the two CO₂ treatments, the total plant dry weight increased by 66% from low to medium PPFD and by 37% from medium to high PPFD.     

Intrinsic morphology and spatial distribution of non-structural carbohydrates contribute to drought resistance of two mulberry cultivars

• Drought is one of the most adverse environmental stresses limiting plant growth and productivity. However, the underlying mechanisms regarding metabolism of non-structural carbohydrates (NSC) in source and sink organs are still not fully elucidated in woody trees.
• Saplings of mulberry cv Zhongshen1 and Wubu were subjected to a 15-day progressive drought stress. NSC levels and gene expression involved in NSC metabolism were investigated in roots and leaves. Growth performance and photosynthesis, leaf stomatal morphology, and other physiological parameters were also analysed.
• Under well-watered conditions, Wubu had a higher R/S, with higher NSC in leaves than in roots; Zhongshen1 had a lower R/S with higher NSC in roots than leaves. Under drought stress, Zhongshen1 showed decreased productivity and increased proline, abscisic acid, ROS content and activity of antioxidant enzymes, while Wubu sustained comparable productivity and photosynthesis. Interestingly, drought resulted in decreased starch and slightly increased soluble sugars in leaves of Wubu, accompanied by notable downregulation of starch-synthesizing genes and upregulation of starch-degrading genes. Similar patterns in NSC levels and relevant gene expression were also observed in roots of Zhongshen1. Concurrently, soluble sugars decreased and starch was unchanged in roots of Wubu and leaves of Zhongshen1. However, gene expression of starch metabolism in roots of Wubu was unaltered, but in leaves of Zhongshen1 starch metabolism was more activated.
• These findings revealed that intrinsic R/S and spatial distribution of NSC in roots and leaves concomitantly contribute to drought resistance in mulberry.

     

Water relations of Capsicum genotypes under water stress

Pepper species and cultivars, Capsicum annuum cv. Bell Boy, C. annuum cv. Kulai and C. frutescens cv. Padi, differing in drought tolerance were investigated for their water relations, stomatal responses and abscisic acid (ABA) content during water stress. C. frutescens cv. Padi exhibited a greater osmotic adjustment than C. annuum cultivars. Stomatal conductance of cv. Bell Boy was more sensitive to water stress than that of cvs. Kulai and Padi. In all pepper genotypes, stomatal closure was triggered in the absence of a large decrease in leaf water status. ABA content in xylem sap and leaf was higher in C. annum cultivars compared to C. frutescens cv. Padi. This revised version was published online in July 2006 with corrections to the Cover Date.     

Influence of drought and flowering on growth and water relations of perennial ryegrass populations

Spring-sown (vegetative) and autumn-sown (flowering) swards of Lolium perenne cvs Melle, Aurora and their hybrid growing in 0.9 m deep bins of soil in the glasshouse were compared, a) as drought progressed from June to August 1986, and b) after cutting, fertilising and re-watering.
During drought, vegetative plants produced more herbage, had initially higher leaf extension rates, had longer and wider leaves, maintained more tillers, had lower mortality, adjusted osmotic potential more effectively and had stomata less sensitive to stress than did flowering plants. On re-watering, previously stressed flowering plants regrew more slowly than the irrigated controls, whereas previously stressed vegetative plants regrew more rapidly than the controls.
Aurora was the most drought-resistant population, mainly because of low tiller death rates. The hybrid tended to have the lowest leaf water potentials and conductances and grew poorly during drought. Possible underlying physiological mechanisms are discussed.     

Water storage and osmotic pressure influences on the water relations of a dicotyledonous desert succulent

Abstract Water storage and nocturnal increases in osmotic pressure affect the water relations of the desert succulent Ferocactus acanthodes, which was studied using an electrical circuit analog based on the anatomy and morphology of a representative individual. Transpiration rates and osmotic pressures over a 24-h period were used as input variables. The model predicted water potential, turgor pressure and water flow for various tissues. Plant capacitances, storage resistances and nocturnal increases in osmotic pressure were varied to determine their role in the water relations of this dicotyledonous succulent. Water coming from storage tissues contributed about one-third of the water transpired at night: the majority of this water came from the nonphotosynthetic, water storage parenchyma of the stem. Time lags of 4 h were predicted between maximum transpiration and maximum water uptake from the soil. Varying the capacitance of the plant caused proportional changes in osmotically driven water movement but changes in storage resistance had only minor effects. Turgor pressure in the chlorenchyma depended on osmotic pressure, but was fairly insensitive to doubling or halving of the capacitance or storage resistance of the plant. Water uptake from the soil was only slightly affected by osmotic pressure changes in the chlorenchyma. For this stem succulent, the movement of water from the chlorenchyma to the xylem and the internal redistribution of water among stem tissues were dominated by nocturnal changes in chlorenchyma osmotic pressure, not by transpiration.     

Combined effects of drought and high temperature on water relations of wheat and sorghum

Drought and high temperature are major factors limiting crop production. The two stresses occur together in many regions, but they usually are investigated separately. This study tested the hypothesis that high temperature interacts with drought to affect water relations, and the effect is greater in heat-sensitive wheat (Triticum aestivum L.) than in sorghum (Sorghum bicolor L. Moench). Wheat and sorghum were grown in soil that was well watered or not watered in controlled chambers at 15/10, 25/20, 35/30 and 40/35 °C day/night. Soil water content (SWC), leaf relative water content (RWC), leaf water potential (), leaf osmotic potential (), leaf turgor potential (P) and osmotic adjustment (OA) were determined at 2-d intervals. All values held nearly constant at all temperatures when soil was well watered but were affected strongly by high temperature when water was withheld. The combined stresses reduced SWC, RWC, Psi and , and unevenly raised P over time, particularly in sorghum. Sorghum also exhibited marked OA at high temperature, which was usually lethal to wheat. High temperature appeared to interact with drought to affect water relations by altering SWC and not by influencing OA. The results demonstrated that crops maintain nearly stable water relations regardless of temperature when moisture is ample, but high temperature strongly affects water relations when water is limiting. Increasing the thermotolerance of wheat might improve its potential to acclimate to both high temperature and drought.     

Influences of soil volume and an elevated CO2 level on growth and CO2 exchange for the Crassulacean acid metabolism plant Opuntia ficus-indica

Effects of the current (38 Pa) and an elevated (74 Pa) CO₂ partial pressure on root and shoot areas, biomass accumulation and daily net CO₂ exchange were determined for Opuntia ficus-indica (L.) Miller, a highly productive Crassulacean acid metabolism species cultivated worldwide. Plants were grown in environmentally controlled rooms for 18 weeks in pots of three soil volumes (2 600, 6 500 and 26 000 cm³), the smallest of which was intended to restrict root growth. For plants in the medium-sized soil volume, basal cladodes tended to be thicker and areas of main and lateral roots tended to be greater as the CO₂ level was doubled. Daughter cladodes tended to be initiated sooner at the current compared with the elevated CO₂ level but total areas were similar by 10 weeks. At 10 weeks, daily net CO₂ uptake for the three soil volumes averaged 24% higher for plants growing under elevated compared with current CO₂ levels, but at 18 weeks only 3% enhancement in uptake occurred. Dry weight gain was enhanced 24% by elevated CO₂ during the first 10 weeks but only 8% over 18 weeks. Increasing the soil volume 10-fold led to a greater stimulation of daily net CO₂ uptake and biomass production than did doubling the CO₂ level. At 18 weeks, root biomass doubled and shoot biomass nearly doubled as the soil volume was increased 10-fold; the effects of soil volume tended to be greater for elevated CO₂. The amount of cladode nitrogen per unit dry weight decreased as the CO₂ level was raised and increased as soil volume increased, the latter suggesting that the effects of soil volume could be due to nitrogen limitations.     

干旱调控下小麦RIL群体灌浆期茎秆可溶性碳水化合物积累与转运的遗传分析

以小麦RIL群体(陇鉴19×Q9086,F₈)120个株系及其亲本为供试材料,研究雨养(DS)和正常灌溉(WW)条件下,小麦灌浆期不同发育阶段主茎不同节位可溶性碳水化合物(WSC)含量、转运率及其对籽粒的贡献率,以及穗粒重的遗传特点及各目标性状间的相关性.结果表明: 在两种水分条件下,小麦RIL群体各目标性状变异广泛,变异系数在2.7%～62.1%(DS)和1.9%～52.1%(WW),多样性指数在0.61～0.90(DS)和0.64～0.89(WW),且存在超亲分离.各目标性状表型受基因型、水分环境、节位和发育时期的显著影响.其中,WSC含量受发育时期的影响较大,WSC转运率具有显著的水分和节位主导效应,而WSC转运对籽粒的贡献率受基因型、节位和水分的共同作用.开花初期和灌浆中期WSC含量、花前WSC转运率对籽粒的贡献率之间普遍表现为显著或极显著正相关,且干旱条件下其相关系数更高.各目标性状的遗传力较低(hB₂在干旱条件下为0.31～0.56,灌溉条件下为0.44～0.67),控制各目标性状的遗传基因对数在6～29对(DS)和3～19对(WW).表明该群体对所考察性状有贡献的等位基因在其后代群体中得到广泛分离,其表达易受水分环境的影响,符合典型数量性状特点.     

极端干旱对草甸草原优势植物非结构性碳水化合物的影响

植物光合作用产生的非结构性碳水化合物(NSCs)水平可以反映植物和生态系统对环境变化的响应程度。近年来, 草原极端干旱事件的发生频率和持续时间增加趋势明显, 对生态系统结构和功能产生深远影响。该研究以内蒙古呼伦贝尔草甸草原为研究对象, 通过连续4年减少66%生长季降水量的控制实验来模拟极端干旱事件, 分析草原6种优势物种和植物功能群NSCs各组分对极端干旱的响应规律与机制。结果显示, 由于植物生物学、光合特性以及生理生态等特性的差异, 不同物种对干旱胁迫的响应具有明显差异。这表明草地植物NSCs组分及其利用策略对干旱胁迫的响应具有物种特异性, 从而导致其生物量的不同响应。将6种植物分为禾草和非禾草两类, 发现干旱显著增加了禾草的淀粉含量, 但对其可溶性糖含量无显著影响; 相反, 干旱显著增加了非禾草功能群的可溶性糖含量, 对其淀粉含量无显著影响, 表明不同功能群采取了不同的干旱应对策略。禾草选择将光合作用固定的能量进行储存以应对干旱胁迫, 其生物量对干旱响应不敏感; 而非禾草选择将能量以可溶性糖的形式直接供植物生长利用以及抵御干旱胁迫, 其生物量对干旱响应较为敏感。这一发现可为预测在全球气候变化背景下草甸草原生态系统结构与功能对极端干旱的响应提供科学参考。     

Effects of water stress and rewatering on leaf water relations of lemon plants

Potted two-year-old lemon plants (Citrus limon (L.) Burm. fil.) cv. Fino, growing under field conditions were subjected to drought by withholding irrigation for 13 d. After that, plants were re-irrigated and the recovery was studied for 5 d. Control plants were daily irrigated maintaining the soil matric potential at about -30 kPa. Young leaves of control plants presented higher leaf conductance (g1) and lower midday leaf water potential (Ψmd) than mature ones. Young leaves also showed higher leaf water potential at the turgor loss point (Ψtlp) than mature leaves. In both leaf types g1 decreased with increased vapour pressure deficit of the atmosphere. From day 1 of the withholding water, predawn and midday leaf water potentials (Ψpd and Ψmd) decreased, reaching in both cases minimum values of -5.5 MPa, with no significant differences between mature and young leaves. Water stress induced stomatal closure, leaf rolling and partial defoliation. No osmotic adjustment was found in response to water stress in either leaf type, but both were able to enhance the cell wall elasticity (elastic adjustment). After rewatering, leaf water potential recovered quickly (within 2 d) but g1 did not. This revised version was published online in July 2006 with corrections to the Cover Date.     

Effects of accumulation of 3-O-methylglucose on growth and osmotic regulation in Chlorella emersonii

Abstract. The effect of accumulation of 3- O -methylglucose (MG) on growth and steady-stale concentrations of the endogenous osmotic solutes proline and sucrose was studied in Chlorella emersonii grown at external osmotic pressure (II) of 0.08-1.64 MPa. NaCL was used as osmoticum. The total solute content of the cells was manipulated by supplying 2 mol m⁻³ MG for 4 and 48 h. MG accumulated to 50–230 mol m⁻³ within 4h and was not metabolized. Uptake of MG resulted in decreases in concentrations of proline and sucrose, the two solutes mainly responsible for osmotic adaptation of C. emersonii to high II. After 4 or 48 h growth in the presence of MG, the decreases in concentration of proline and sucrose were as predicted from the contribution of MG to the total solute content of the cell.     

Gas exchange parameters, water relations and carbohydrate partitioning in leaves of field-grown Prunus domestica following fruit removal

The effect of fruit removal on gas exchange, water relations, chlorophyll and non-structural carbohydrate content of leaves from mature, field-grown plum trees ( Prunus domestica L. cv. Stanley) was determined over 2 consecutive growing seasons. Removal of fruits during stage II of fruit development decreased CO₂ assimilation rate within 24 h from 12.6 to 8.5 μmol m^-2 s^-1 in 1986, and from 12.1 to 10.2 μmol m^-2 s^-1 in 1987. Depression of net photosynthesis persisted for at least 5 days and was greatest in the early afternoon. Recovery of the CO₂ assimilation rate to pretreatment levels coincided in defruited trees with vegetative growth that was more than 5-fold that of fruiting trees in the first 6 weeks after fruit removal in 1986. Estimated photorespiration was similar in both fruiting and defruited trees. The stomatal contribution to the decrease of CO₂ assimilation rate, calculated from assimilation/intercellular CO₂ curves, ranged from 31 to 46%. Defruiting did not affect leaf water potential, but decreased leaf osmotic potential. Leaf levels of chlorophyll, fructose, glucose, sorbitol and sucrose were not affected by defruiting, whereas starch content increased up to 51% in leaves of defruited trees within 24 h after fruit removal. However, because of the small starch pool present in plum leaves (<1.9% dry weight) it is unlikely that starch accumulation was responsible for the observed decline in CO₂ assimilation rate after fruit removal. The decrease of CO₂ assimilation rate is discussed in relation to the hypothesis of assimilate demand regulating photosynthesis through a feedback mechanism.