Changes in response to drought stress of triticale and maize genotypes differing in drought tolerance

Direct effects and after-effects of soil drought for 7 and 14 d were examined on seedling dry matter, leaf water potential (ψ), leaf injury index (LI), and chlorophyll (Chl) content of drought (D) resistant and sensitive triticale and maize genotypes. D caused higher decrease in number of developed leaves and dry matter of shoots and roots in the sensitive genotypes than in the resistant ones. Soil D caused lower decrease of ψ in the triticale than maize leaves. Influence of D on the Chl b content was considerably lower than on the Chl a content. In triticale the most harmful D impact was observed for physiologically younger leaves, in maize for the older ones. A period of 7-d-long recovery was too short for a complete removal of an adverse influence of D.     

Branch development controls leaf area dynamics in grapevine (Vitis vinifera) growing in drying soil

BACKGROUND AND AIMS: Soil water deficit is a major abiotic stress with severe consequences for the development, productivity and quality of crops. However, it is considered a positive factor in grapevine management (Vitis vinifera), as it has been shown to increase grape quality. The effects of soil water deficit on organogenesis, morphogenesis and gas exchange in the shoot were investigated. METHODS: Shoot organogenesis was analysed by distinguishing between the various steps in the development of the main axis and branches. Several experiments were carried out in pots, placed in a greenhouse or outside, in southern France. Soil water deficits of various intensities were imposed during vegetative development of the shoots of two cultivars ('Syrah' and 'Grenache N'). KEY RESULTS: All developmental processes were inhibited by soil water deficit, in an intensity-dependent manner, and sensitivity to water stress was process-dependent. Quantitative relationships with soil water were established for all processes. No difference was observed between the two cultivars for any criterion. The number of leaves on branches was particularly sensitive to soil water deficit, which rapidly and strongly reduced the rate of leaf appearance on developing branches. This response was not related to carbon availability, photosynthetic activity or the soluble sugar content of young expanding leaves. The potential number of branches was not a limiting factor for shoot development. CONCLUSIONS: The particularly high sensitivity to soil water deficit of leaf appearance on branches indicates that this process is a major determinant of the adaptation of plant leaf area to soil water deficit. The origin of this particular developmental response to soil water deficit is unclear, but it seems to be related to constitutive characteristics of branches rather than to competition for assimilates between axes differing in sink strength.     

Lipidomic reprogramming associated with drought stress priming‐enhanced heat tolerance in tall fescue (Festuca arundinacea)

Stress priming by exposing plants to a mild or moderate drought could enhance plant tolerance to subsequent heat stress. Lipids play vital roles in stress adaptation, but how lipidomic profiles change, affecting the cross‐stress tolerance, is largely unknown. The objectives of this study were to perform lipidomics, to analyse the content, composition, and saturation levels of lipids in leaves of tall fescue (Festuca arundinacea) following drought priming and subsequent heat stress, and to identify major lipids and molecular species associated with priming‐enhanced heat tolerance. Plants were initially exposed to drought for 8 days by withholding irrigation and subsequently subjected to 25 days of heat stress (38/33°C day/night) in growth chambers. Drought‐primed plants maintained significantly higher leaf relative water content, chlorophyll content, photochemical efficiency, and lower electrolyte leakage than nonprimed plants under heat stress. Drought priming enhanced the accumulation of phospholipids and glycolipids involved in membrane stabilization and stress signalling (phosphatidic acid, phosphatidylcholine, phosphatidylinositol, phosphatidylglycerol, and digalactosyl diacylglycerol) during subsequent exposure to heat stress. The reprogramming of lipid metabolism for membrane stabilization and signalling in response to drought priming and subsequent exposure to heat stress could contribute to drought priming‐enhanced heat tolerance in cool‐season grass species.     

Interactions of drought and low temperature stress on lipid and fatty acid composition of cucumber genotypes differing in growth response at suboptimal temperature

The effects of drought stress and/or low temperature stress on total lipid and phospholipid content and fatty acid composition of leaves of cucumber ( Cucumis sativus L.) genotypes differing in growth response at suboptimal temperature were studied. Both drought and low temperature resulted in reduced growth, especially in cv. Farbio, the genotype least tolerant to low temperature. Drought resulted in an increase in total lipid and phospholipid per g fresh weight. On a lipid basis no change in phospholipids or fatty acid content was observed. The fatty acid composition was changed by drought and low temperature, resulting in an increase in the degree of unsaturation. The genotype-specific reaction to treatment for total lipid content and the degree of unsaturation point to the possibility of a genetic origin for drought-induced lipid changes, which may be used in a breeding program for improved growth at suboptimal temperature.     

Differences in hydraulic architecture account for near-isohydric and anisohydric behaviour of two field-grown Vitis vinifera L. cultivars during drought

A comparative study on stomatal control under water deficit was conducted on grapevines of the cultivars Grenache, of Mediterranean origin, and Syrah of mesic origin, grown near Montpellier, France and Geisenheim, Germany. Syrah maintained similar maximum stomatal conductance (g_max) and maximum leaf photosynthesis (A_max) values than Grenache at lower predawn leaf water potentials, Ψ_leaf, throughout the season. The Ψ_leaf of Syrah decreased strongly during the day and was lower in stressed than in watered plants, showing anisohydric stomatal behaviour. In contrast, Grenache showed isohydric stomatal behaviour in which Ψ_leaf did not drop significantly below the minimum Ψ_leaf of watered plants. When g was plotted versus leaf specific hydraulic conductance, K_l, incorporating leaf transpiration rate and whole‐plant water potential gradients, previous differences between varieties disappeared both on a seasonal and diurnal scale. This suggested that isohydric and anisohydric behaviour could be regulated by hydraulic conductance. Pressure‐flow measurements on excised organs from plants not previously stressed revealed that Grenache had a two‐ to three‐fold larger hydraulic conductance per unit path length (K_h) and a four‐ to six‐fold larger leaf area specific conductivity (LSC) in leaf petioles than Syrah. Differences between internodes were only apparent for LSC and were much smaller. Cavitation detected as ultrasound acoustic emissions on air‐dried shoots showed higher rates for Grenache than Syrah during the early phases of the dry‐down. It is hypothesized that the differences in water‐conducting capacity of stems and especially petioles may be at the origin of the near‐isohydric and anisohydric behaviour of g.     

Developmental changes in the diurnal water budget of the grape berry exposed to water deficits

The diurnal water budget of developing grape (Vitis vinifera L.) berries was evaluated before and after the onset of fruit ripening (veraison). The diameter of individual berries of potted ‘Zinfandel’ and ‘Cabernet Sauvignon’ grapevines was measured continuously with electronic displacement transducers over 24 h periods under controlled environmental conditions, and leaf water status was determined by the pressure chamber technique. For well-watered vines, daytime contraction was much less during ripening (after veraison) than before ripening. Daytime contraction was reduced by restricting berry or shoot transpiration, with the larger effect being shoot transpiration pre-veraison and berry transpiration post-veraison. The contributions of the pedicel xylem and phloem as well as berry transpiration to the net diurnal water budget of the fruit were estimated by eliminating phloem or phloem and xylem pathways. Berry transpiration was significant and comprised the bulk of water outflow for the berry both before and after veraison. A nearly exclusive role for the xylem in water transport into the berry was evident during pre-veraison development, but the phloem was clearly dominant in the post-veraison water budget. Daytime contraction was very sensitive to plant water status before veraison but was remarkably insensitive to changes in plant water status after veraison. This transition is attributed to an increased phloem inflow and a partial discontinuity in berry xylem during ripening.     

Water stress induces different levels of photosynthesis and electron transport rate regulation in grapevines

A, net CO₂ assimilation rate
E, leaf transpiration
ETR, electron transport rate
F_s, fluorescence yield at steady state
F_m and F_m', maximal fluorescence levels when all PSII reaction centres are closed in dark- and light-acclimated leaves, respectively
F_o and F_o', initial fluorescence levels when all PSII reaction centres are closed in dark- and light-acclimated leaves, respectively
F_v/F_m, efficiency of excitation capture by open PSII in dark-adapted leaves
ΔF/F_m', actual photochemical efficiency of PSII
g, stomatal conductance
NPQ, non-photochemical quenching of chlorophyll fluorescence
PPFD, photosynthetic photon flux density
Ψ_PD and Ψ_MD, leaf water potential at pre-dawn and midday, respectively
Rl, estimated photorespiration rate
I₁ and I₂, Irrigation treatments
R, Recovery treatment
D₁ and D₂, drought treatments
HD₁ and HD₂, hard drought treatments

Diurnal time courses of chlorophyll fluorescence and gas-exchange rates were measured in young potted grapevines (Vitis vinifera L. cv. Tempranillo) subjected to different conditions of water supply under Mediterranean summer conditions. The irrigated plants exhibited typical diurnal patterns for all measured parameters, showing a correspondence between electron transport rate, net CO₂ assimilation and stomatal conductance. Mild decreases in soil-water availability led to different degrees of down-regulation of photosynthesis and increased nonphotochemical quenching of chlorophyll fluorescence. A good correspondence between electron transport rate and CO₂ assimilation was still maintained, suggesting a coregulation of both photosynthetic processes. In contrast, a severe water deficit induced a drastic down-regulation of photosynthesis and breakage of the above-mentioned link. Both midday net CO₂ assimilation and electron transport rate significantly correlated with pre-dawn water potential (Ψ_PD) (r² = 0·65 and r² = 0·92, P < 0·001, respectively). However, when field data were analysed, the relationship between electron transport rate and Ψ_PD was not maintained, although net CO₂ assimilation was similarly correlated with Ψ_PD. Interestingly, the steady-state chlorophyll fluorescence yield was a good indicator of plant water stress.     

Osmotic adjustment of chickpea (Cicer arietinum) is not associated with changes in carbohydrate composition or leaf gas exchange under drought

Genetic differences in osmotic adjustment (OA) have been reported among chickpea (Cicer arietinum) cultivars. In this study eight advanced breeding lines (ABLs) derived from a cross between CTS 60543 (high OA) and Kaniva (low OA) and Tyson (medium OA) and Kaniva, along with the parents, were evaluated for OA, leaf carbohydrate composition and leaf gas exchange under dryland field conditions in India. The water potential (WP) decreased to lower values (less than −2.5 MPa) in Tyson, M 110 and M 86 than in the other genotypes. With decrease in WP, OA increased by 0.5 MPa in Kaniva and CTS 60543 to 1.3 MPa in M 55. As the decrease in WP varied with genotype, when OA was regressed against WP M 39 and M 55 had greater increases in OA with decrease in WP than the remaining nine genotypes, including the parents. As WP decreased, leaf starch content decreased while total soluble sugars, hexoses and sucrose increased: the decrease in starch was much smaller in M 93 and M 129 than in Tyson and M 51, but genotypic differences could not be detected in the increase in total sugars, hexoses or sucrose. The rates of photosynthesis and transpiration decreased as the WP became more negative, but M 129 reached low rates of photosynthesis (2 μmol m⁻² s⁻¹) and transpiration at a WP of −1.7 MPa, whereas Tyson reached the same low rate at −2.4 MPa. While OA varied among the chickpea genotypes, the differences were not associated with the changes in carbohydrate composition or the rates of gas exchange at low values of WP. Further, the degree of OA of the 11 genotypes was not the same as when they were selected for differences in OA under rainout shelter conditions in the field in Australia, suggesting that OA may show poor stability depending upon the stress level, location or physiological stage of the plant. This suggests that OA is not a valuable drought-resistance trait to select for in chickpea breeding programmes.     

干旱胁迫条件下6种喀斯特主要造林树种苗木叶片水势及吸水潜能变化

水势是反映植物水分亏缺或水分状况的一个直接指标,可用来确定植物受干旱胁迫的程度和抗旱能力高低。本文研究了6种喀斯特造林树种苗木在干旱胁迫条件下叶片水势及其吸水潜能的变化。结果表明：（1）随着胁迫强度的增加,6种树种不同生长时期,其叶片水势均表现出下降趋势,且不同干旱胁迫强度之间差异显著（p<0.002）。在干旱胁迫下,所有树种叶片水势均以生长旺期的下降幅度最大,生长末期次之,生长初期最小。在生长旺期,6个树种叶片水势最低值分别比对照下降了2.21 Mpa、2.14 Mpa、3.57 Mpa、2.89Mpa、4.02Mpa和3.07Mpa。（2）侧柏苗木在生长初期轻度干旱条件下,其叶片水势胁迫指数只有0.150;在中度干旱胁迫条件下,其胁迫指数增加到0.559;在重度干旱胁迫条件下,达0.716,叶片水势下降超过70%。香樟苗木在生长初期轻度干旱胁迫条件下,其叶片水势胁迫指数就已达0.603,叶片水势下降超过了60%;在中度和重度干旱胁迫条件下,其水势胁迫指数相差不大。其它树种苗木的胁迫指数亦有与侧柏或香樟相似的变化趋势。（3）6个树种苗木在干旱胁迫条件下平均叶片水势与土壤水势差值大小排序为,生长初期：刺槐（1.261Mpa）>香樟（0.850 Mpa）>滇柏（0.846 Mpa）>侧柏（0.568 Mpa）>构树（0.524 Mpa）>杜英（0.219 Mpa）;生长旺期：香樟（2.994 Mpa）>刺槐（2.68 Mpa）>侧柏（2.028 Mpa）>滇柏（2.008 Mpa）>杜英（1.824 Mpa）>构树（1.543 Mpa）;生长末期：刺槐（0.692 Mpa）>构树（0.687 Mpa）>滇柏（0.653 Mpa）>侧柏（0.354 Mpa）>香樟（0.338 Mpa）>杜英（0.262 Mpa）。（4）干旱胁迫复水24h后,不同生长阶段苗木叶片水势恢复指数随干旱胁迫强度的增加而逐渐减小。叶片水势恢复度按生长时期排序为：生长末期>生长旺期>生长初期。（5）利用隶属函数累加法将6个树种苗木的吸水潜能大小可排序为：侧柏>滇柏>刺槐>香樟>构树>杜英。     

Characterization and early detection of grapevine (Vitis vinifera) stress responses to esca disease by in situ chlorophyll fluorescence and comparison with drought stress

Esca disease, as well as other trunk diseases of grapevine, is an important wood disease that impedes the water transport in plants by clogging the xylem vessels. This type of effect is not detectable for years, due to the long latency time of the disease. In a field experiment, the susceptibility of Vitis vinifera cv. Cabernet sauvignon and Merlot to esca disease was evaluated by visual assessment of foliar symptoms and by necrosis and white rot indexes. C. sauvignon was highly susceptible and Merlot was tolerant to esca. The characteristics of fast chlorophyll a fluorescence transient were investigated in attached leaves by using the so-called JIP-test. The fluorescence transient was analyzed and plants without visible esca foliar symptoms were compared with those showing symptoms. In C. sauvignon, alteration of the photosynthetic apparatus could be detected 2 months before the appearance of foliar symptoms in autumn. To our knowledge, this is the first report of early detection of esca disease using a nondestructive method. For Merlot, only one JIP-test parameter was affected. However, when both cultivars were compared, the relationship of the performance index (defined by the density of reaction centers (RCs) and by the yields φ_Po and ψ_o; PI_ABS = [RC/ABS][φ_Po/(1 − φ_Po)][ψ_o/(1 − ψ_o)]) versus the calculated rate of the electron transfer [probability that an absorbed photon moves an electron further than $Q_{\text{A}}^{-}$; φ_Eo = φ_Poψ_o = (TR_o/ABS)(ET_o/TR_o) = ET_o/ABS = (1 − F₀/F_M)(1 − V_J)] permitted us to separate the highest performing cultivar Merlot from the susceptible C. sauvignon. Also, the method used allowed us to detect modification of the photosystem II (PS II) performance in greenhouse-grown Riesling × Sylvaner after a drought stress. Finally, the comparison of the fluorescence transients of esca-affected and drought-stressed grapevines provided information on the differentiated functional-behavior patterns of PS II for the two stress types. These results suggest that esca infection cannot simply be interpreted as a water transport deficit through xylem dysfunction, but that other reaction mechanisms in the plants must be considered. The possibility to use fast chlorophyll a fluorescence monitoring as a wood decay early detection tool is discussed.     

Leaf hydraulics and drought stress: response, recovery and survivorship in four woody temperate plant species

Efficient conduction of water inside leaves is essential for leaf function, yet the hydraulic-mediated impact of drought on gas exchange remains poorly understood. Here we examine the decline and subsequent recovery of leaf water potential ( Ψ _leaf), leaf hydraulic conductance ( K _leaf), and midday transpiration ( E ) in four temperate woody species exposed to controlled drought conditions ranging from mild to lethal. During drought the vulnerability of K _leaf to declining Ψ _leaf varied greatly among the species sampled. Following drought, plants were rewatered and the rate of E and K _leaf recovery was found to be strongly dependent on the severity of the drought imposed. Gas exchange recovery was strongly correlated with the relatively slow recovery of K _leaf for three of the four species, indicating conformity to a hydraulic-stomatal limitation model of plant recovery. However, there was also a shift in the sensitivity of stomata to Ψ _leaf suggesting that the plant hormone abscisic acid may be involved in limiting the rate of stomatal reopening. The level of drought tolerance varied among the four species and was correlated with leaf hydraulic vulnerability. These results suggest that species-specific variation in hydraulic properties plays a fundamental role in steering the dynamic response of plants during recovery.     

Quantitative analysis of the phenotypic variability of shoot architecture in two grapevine (Vitis vinifera) cultivars

BACKGROUND AND AIMS: Plant architecture and its interaction with agronomic practices and environmental constraints are determinants of the structure of the canopy, which is involved in carbon acquisition and fruit quality development. A framework for the quantitative analysis of grapevine (Vitis vinifera) shoot architecture, based on a set of topological and geometrical parameters, was developed for the identification of differences between cultivars and the origins of phenotypic variability. METHODS: Two commercial cultivars ('Grenache N', 'Syrah') with different shoot architectures were grown in pots, in well-irrigated conditions. Shoot topology was analysed, using a hidden semi-Markov chain and variable-order Markov chains to identify deviations from the normal pattern of succession of phytomer types (P0-P1-P2), together with kinematic analysis of shoot axis development. Shoot geometry was characterized by final internode and individual leaf area measurements. KEY RESULTS: Shoot architecture differed significantly between cultivars. Secondary leaf area and axis length were greater for 'Syrah'. Secondary leaf area distribution along the main axis also differed between cultivars, with secondary leaves preferentially located towards the basal part of the shoot in 'Syrah'. The main factors leading to differences in leaf area between the cultivars were: (a) slight differences in main shoot structure, with the supplementary P0 phytomer on the lower part of the shoot in 'Grenache N', which bears a short branch; and (b) an higher rate and duration of development of branches bearing by P1-P2 phytomers related to P0 ones at the bottom of the shoot in 'Syrah'. Differences in axis length were accounted for principally by differences in individual internode morphology, with 'Syrah' having significantly longer internodes. This trait, together with a smaller shoot diameter, may account for the characteristic 'droopy' habit of 'Syrah' shoots. CONCLUSIONS: This study highlights the architectural parameters involved in the phenotypic variability of shoot architecture in two grapevine cultivars. Differences in primary shoot structure and in branch development potential accounted for the main differences in leaf area distribution between the two cultivars. By contrast, shoot shape seemed to be controlled by differences in axis length due principally to differences in internode length.     

Up-regulation of lipid metabolism and glycine betaine synthesis are associated with choline-induced salt tolerance in halophytic seashore paspalum

Choline may affect salt tolerance by regulating lipid and glycine betaine (GB) metabolism. This study was conducted to determine whether alteration of lipid profiles and GB metabolism may contribute to choline regulation and genotypic variations in salt tolerance in a halophytic grass, seashore paspalum (Paspalum vaginatum). Plants of Adalayd and Sea Isle 2000 were subjected to salt stress (200-mM NaCl) with or without foliar application of choline chloride (1 mM). Genotypic variations in salt tolerance and promotive effects of choline application on salt tolerance were associated with both the up-regulation of lipid metabolism and GB synthesis. The genotypic variations in salt tolerance associated with lipid metabolism were reflected by the differential accumulation of phosphatidylcholine and phosphatidylethanolamine between Adalayd and Sea Isle 2000. Choline-induced salt tolerance was associated with of the increase in digalactosyl diacylglycerol (DGDG) content including DGDG (36:4 and 36:6) in both cultivars of seashore paspalum and enhanced synthesis of phosphatidylinositol (34:2, 36:5, and 36:2) and phosphatidic acid (34:2, 34:1, and 36:5), as well as increases in the ratio of digalactosyl diacylglycerol: monogalactosyl diacylglycerol (DGDG:MGDG) in salt-tolerant Sea Isle 2000. Choline regulation of salt tolerance may be due to the alteration in lipid metabolism in this halophytic grass species.     

Photosynthesis, leaf conductance and water relations of in vitro cultured grapevine rootstock in relation to acclimatisation

Leaf net CO₂ uptake and leaf photosynthetic capacity were investigated in micropropagated 41B grapevine rootstock (Vitis vinifera‘Chasselas’×Vitis berlandieri, Mill. De Gr.) plants grown in the presence of four sucrose concentrations (6.25, 12.5, 25.0 or 37.5 g l^?1). Sucrose concentration in the medium during growth in vitro did not affect the leaf photosynthetic performance of plants neither before nor after transplantation. The maximum photosynthetic rate, measured as CO₂-dependent O₂ evolution, was 7.3 µmol m^?2 s^?1 before transplanting and 15.4 µmol m^?2 s^?1 one month after transplantation. The maximum quantum yield of O₂ evolution (on the basis of incident light) was about 0.07 for all sucrose treatments both before and after transplantation. Dry biomass before transplanting was highest in plants grown with 25.0 or 37.5 g l^?1 sucrose in the medium. One month after transplantation the highest dry biomass was also observed for the same treatments. Survival of plants was 100% for all treatments. Leaf conductance to water vapour was always higher in plants before than after transplantation. Both before and after transplanting it increased with increasing light intensity and decreased slightly with increasing CO₂ molar ratio in in vitro plants. Stomata of plants before transplantation were unresponsive to vapour pressure deficit. In vitro plants experience an acute water stress when they are maintained with the whole root system in water and exposed to ambient controlled conditions in a growth chamber. However, there was no wilting of the leaves when similar plants with roots cut off were left in the same conditions. Hydraulic conductivity was low at both root and shoot-root connection levels. It is likely that water supply could be limiting during transplantation because of the low root and root-stem connection conductivity. Water uptake by roots rather than water loss from the shoots would be of primary importance for the maintenance of water balance during acclimatisation.     

Growth response of Halimium halimifolium at four sites with different soil water availability regimes in two contrasted hydrological cycles

The relationship between water availability and plant growth response in Halimium halimifolium (L.) Willk throughout two years with contrasted precipitation (300 and 850 mm) was examined by measuring vegetative growth and midday leaf water potential in four sandy soil sites with different water availability in Doñana National Park, Spain. H. halimifolium, Cistaceae is mostly restricted to sandy substrates close to coastal Mediterranean areas. At Doñana National Park this species is the main component of stable sand vegetation. Vegetative growth started in March, ending in July. The maximum shoot elongation rate (110 mm/year) and number of branches (8.3 branches/year) occurred in plants growing in the most hygrophytic site (MN) in both the wet and dry years. Plants at this site exhibited higher midday water potentials throughout the year. In contrast, the minimum shoot elongation rate (40 mm/year) and midday water potential (–4.0 MPa) occurred in Monte Intermedio plants (MI) in the dry year, although the water table was shallower than in Monte Blanco (MB). In the wet year the minimum shoot and branch elongation were recorded in MB. The number of leaves per branch for a single main shoot was higher (55 leaves/branch) in the driest area (MB), but these leaves had the smallest area. ANOVA showed significant differences in growth response and midday water potential between the four sites. A stepwise multiple linear regression showed that midday water potential, water table depth and monthly average temperature were the variables most closely associated with shoot elongation rate. We conclude that under severe dryness, the expected patterns of greater growth in sites with better water supply may differ from compared with the expected growth pattern in normal conditions.     

Water stress effects on leaf elongation,leaf water potential,transpiration, and nutrient uptake of rice,maize, and soybean

A pot experiment was conducted in the greenhouse to determine and compare the responses of rice (Oryza sativa L. var, IR 36), maize (Zea mays L. var. DMR-2), and soybean (Glycine max [L.] Merr. var. Clark 63) to soil water stress. Leaf elongation, dawn leaf water potential, transpiration rate, and nutrient uptake in stressed rice declined earlier than in maize and soybean. Maize and soybean, compared with rice, maintained high dawn leaf water potential for a longer period of water stress before leaf water potential. Nutrient uptake under water stress conditions was influenced more by the capacity of the roots to absorb nutrients than by transpiration. Transport of nutrients to the shoots may occur even at reduced transpiration rate It is concluded that the ability of maize and soybean to grow better than rice under water stress conditions may be due to their ability to maintain turgor as a result of the slow decline in leaf water potential brought about by low, transpiration rate and continued uptake of nutrient, especially K, which must have allowed osmotic adjustment to occur.     

Differences in the response of sunflower (Helianthus annuus) subjected to flooding and drought stress

Wample, R. L. and Thornton, R. K. 1984. Differences in the response of sunflower ( Helianthus annuus ) subjected to flooding and drought stress.
Comparison of drought- and flood-stressed sunflower plants ( Helianthus annuus L. hybrid 894) showed some similarities in response but differences in the mechanisms responsible for the responses to stress. Drought–stressed plants showed typical reductions in leaf water potential with increasing stress accompanied by increased leaf resistance. Photosynthesis declined while photorespiration increased after 48 and 96 h of drought stress. A primary reason for reduced photosynthesis in drought-stressed plants was increased stomatal resistance. No significant 0change in leaf water potential or in leaf resistance in flooded plants was found in this study. However, photosynthesis declined in a manner similar to that in drought-stressed plants and photorespiration showed only a transient increase at 48 h. Dark respiration was significantly higher at 48 and 96 h but the magnitude of the increase cannot account for the reduction in photosynthesis. Since the photosynthetic rate of flooded plants declined while stomata remained open, an effect at a more fundamental level is suggested and is thought to be related to disruption of carbohydrate transport.     

土壤水分胁迫对拉瑞尔小枝水分参数的影响

采用压力室法在土壤水势为-0.021、-0.121、-0.698、-0.968 MPa 4种情况下对大田种植的1年生Larrea tridentata的小枝水势进行测定,并绘制PV曲线,通过PV曲线求解各水分参数,用以判定土壤水分胁迫对L.tridentata生理特性的影响。研究结果表明:供水良好的情况下,L.tridentata水势日变化呈双峰曲线,随着土壤水分含量的减少,峰值逐渐变得不明显。在土壤水分胁迫条件下,L.tridentata有一定的渗透调节和保持膨压的能力,它一方面通过细胞壁弹性和拥有较高的束缚水含量来保持膨压,另一方面原生质具有较强的忍耐脱水的能力。随着土壤干旱胁迫的逐渐加重,其耐脱水能力提高,保持膨压的能力逐渐减弱。通过对其在不同土壤水分胁迫条件下渗透调节和维持膨压能力的综合评价,得出其在4种土壤水分状况下的综合抗旱指数分别为0.25、0.17、0.933、0.657,说明随着土壤水分含量的逐渐减少,L.tridentata能逐渐提高自身抵御干旱的能力以适应干旱;通过抗旱模型的判定得出L.tridentata属于高水势延迟脱水型耐旱树种。     

Changes in lipid composition in the tissues of fresh-water plant <Emphasis Type="Italic">Hydrilla verticillata</Emphasis> induced by accumulation and elimination of heavy metals

Qualitative and quantitative composition of lipids was investigated in fresh-water vascular plant Hydrilla verticillata (L. fil.) Royle in the course of the accumulation and elimination of heavy metals (HM). The plants were incubated in 100μM solutions of metal nitrates for 10 days. The accumulation of Cu²⁺, Zn²⁺, and Pb²⁺ and their elimination from the plants depended on the duration of exposure and chemical nature of the metal. Accumulation of lead and copper salts was the greatest on the 3rd day, and zinc, on the 10th day. It was associated with changes in the composition of total lipids, polar lipids, and fatty acid (FA). Copper ions suppressed lipid metabolism stronger than other metals. Zn²⁺ and Pb²⁺ induced the accumulation of biomass and elevated the content of some phospholipids and glycolipids. The detected changes (decrease or increase) were observed both during the incubation with HM and within an afterstress period when the plants recovered in the medium free of metals. Judging by their effect on the content of lipids and FA, HM form a series: Cu²⁺ > Zn²⁺ > Pb²⁺. The responses of plant lipid metabolism to the metals of various chemical nature are discussed.     

Changes in lipid content and composition during the development of N-nitrosodiethylamine induced hepatocarcinoma

Alterations in lipid content and composition in the N-nitrosodiethylamine-induced hepatocarcinoma were investigated. Rats were administrated with N-nitrosodiethylamine in the drinking water for 12 weeks followed by normal tap water for another 6 weeks. The cholesterol content in the liver was increased shortly after the administration of N-nitrosodiethylamine and remained elevated after the removal of the nitrosoamine from the water. The phosphatidylethanolamine level was elevated during N-nitrosodiethylamine administration with a concomitant reduction in phosphatidylcholine level. Lysophosphatidylcholine and sphingomyelin levels were increased during the last four weeks of the study. The level of phosphatidylinositol was substantially reduced after eight weeks of N-nitrosodiethylamine treatment, and remained low during the post-treatment period. We postulate that changes in lysophosphatidylcholine and sphingomyelin may be a compensatory mechanism for maintaining the asymmetrical distribution of choline-containing lipids in the outer leaflet of the membrane. The elevated level of cholesterol may be a useful indicator for the early detection of N-nitrosodiethylamine-induced hepatocarcinoma.