Turgor Differences and Water Stress in Maize and Sorghum Leaves During Drought and Recovery

The pressure potentials (turgor pressure) in leaves of maize(Zea mays L.) and grain sorghum (Sorghum vulgare Pers.) plantssubjected to water stress in a controlled environment were estimatedfrom measurements of water and osmotic potentials. Changes inturgor pressure were larger in sorghum than in maize duringthe development of water stress and after re-watering. It issuggested that this indicates a lower cell wall elasticity insorghum than in maize. This fact may affect some of the physiologicalactivities of sorghum     

Diurnal and Seasonal Changes in Leaf Water Potential Components and Elastic Properties in Response to Water Stress in Apple Trees

Apple trees are very drought tolerant, having the capability to grow and carry on photosynthesis even at low water potentials. Much of the tolerance is due to the ability of apple leaves to maintain turgor potentials at levels conducive to growth and stomatal opening. Diurnally, leaf turgor is maintained through decreases in osmotic potentials (due to active solute accumulation), osmotic adjustment, or to concentration of solutes via tissue water loss. These two processes combined may decrease osmotic potentials by as much as 1.65 MPn during the day. Seasonally, osmotic potentials remain fairly constant, but leaf elasticity increases, allowing growth to continue and stomata to remain open us water and turgor potentials become progressively lower. Release of stored water from plant tissues to the transpiration stream is another means of preventing water potentials from reaching critical values for stomatal closure. A combination of a number of these physiological adaptations may account for much of the drought tolerance in apple trees.     

Behavior of Corn and Sorghum under Water Stress and during Recovery

Corn (Zea mays L.) and sorghum (Sorghum vulgare, Pers.) plants were grown in a vermiculite-gravel mixture in controlled environment chambers until they were 40 days old. Water was withheld until they were severely wilted, and they were then rewatered. During drying and after rewatering stomatal resistance was measured with a diffusion porometer each morning, and water saturation deficit and water potential were measured on leaf samples. The average resistance of the lower epidermis of well watered plants was lower for corn than for sorghum. When water stress developed, the stomata began to close at a higher water potential in corn than in sorghum. The stomata of both species began to reopen normally soon after the wilted plants were rewatered, and on the 2nd day the leaf resistances were nearly as low as those of the controls. The average leaf water potential of well watered corn was −4.5 bars; that of sorghum, −6.4 bars. The lowest leaf water potential in stressed corn was −12.8 bars at a water saturation deficit of 45%. The lowest leaf water potential in stressed sorghum was −15.7 bars, but the water saturation deficit was only 29%. At these values the leaves of both species were tightly rolled or folded and some injury was apparent. Thus, although the average leaf resistance of corn is little lower than that of sorghum, corn loses much more of its water before the stomata are fully closed than does sorghum. The smaller reduction in water content of sorghum for a given reduction in leaf water potential is characteristic of drought-resistant species.     

Stomatal Behavior and Water Status of Maize, Sorghum, and Tobacco under Field Conditions: II. At Low Soil Water Potential

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), leaf resistance (r₁), leaf water potential (ψ), osmotic potential (π), and turgor potential (P) were followed concurrently in crops of maize (Zea mays L. cv. Pa602A), sorghum (Sorghum bicolor [L.] Moench cv. RS 610), and tobacco (Nicotiana tabacum L. cv. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were low. The r₁, measured with a ventilated diffusion porometer, of the leaves in the upper canopy decreased temporarily after sunrise [~0530 hours Eastern Standard Time] as I increased, but then r₁ increased again between 0700 and 0830 hr Eastern Standard Time as the ψ, measured with a pressure chamber, decreased rapidly from the values of −7, −4 and −6 bars at sunrise to minimal values of −18, −22 and −15 bars near midday in the maize, sorghum, and tobacco, respectively. The π, measured with a vapor pressure osmometer, also decreased after sunrise, but not to the same degree as the decrease in ψ, so that a P of zero was reached in some leaves between 0730 and 0800 hours. The lower (more negative) π of leaves in the upper canopy than those in the lower canopy gave the upper leaves a higher P at a given ψ than the lower leaves in all three species; leaves at intermediate heights had an intermediate P. This difference between leaves at the three heights in the canopy was maintained at all values of ψ. The r₁ remained unchanged over a wide range of P and then increased markedly at a P of 2 bars in maize, −1 bar in sorghum, and near zero P in tobacco: r₁ also remained constant until ψ decreased to −17, −20, and −13 bars in leaves at intermediate heights in maize, sorghum, and tobacco, respectively. In all three species r₁ of leaves in the upper canopy increased at more negative values of ψ than those at the base of the canopy, and in tobacco, leaves in the upper canopy wilted at more negative values of ψ than those in the lower canopy.     

Stomatal Behavior and Water Status of Maize, Sorghum, and Tobacco under Field Conditions: I. At High Soil Water Potential

Diurnal changes in the vertical profiles of irradiance incident upon the adaxial leaf surface (I), stomatal resistance (r_s), leaf water potential (ψ), osmotic potential (π), and turgor potential (P) were followed concurrently in crops of maize (Zea mays L. var. Pa 602A), sorghum (Sorghum bicolor [L.] Moench var. RS610), and tobacco (Nicotiana tabacum L. var. Havanna Seed 211) on several days in 1968 to 1970 when soil water potentials were high. In all three crops the r_s, measured with a ventilated diffusion porometer, the ψ, measured with the pressure chamber, the π, measured with a vapor pressure osmometer, and the calculated P, decreased from sunrise to reach minimum values near midday and then increased again in the afternoon. The diurnal range of all the variables was greater for leaves in the upper canopy than for those in the lower canopy. P was observed to decrease with decreasing ψ, but never became zero. Sorghum had a higher P at a ψ of, say −10 bars, than did maize, and maize had a higher P than tobacco at the same ψ. Moreover, at the same ψ the upper leaves in all canopies had a higher P than the lower leaves. When compared at high irradiances, r_s did not increase as ψ declined to −13, −15, and −10 bars or as P declined to 0.3, 3.5, and 1.2 bars in maize, sorghum, and tobacco, respectively. The relation between r_s and I in the upper, nonsenescent leaves of all three crops fits a hyperbolic curve, but the response varied with species and leaf senescence. The adaxial and abaxial epidermises had the same response of r_s to I in maize and sorghum, whereas in tobacco the adaxial epidermis had a higher r_s than the abaxial epidermis at all values of I. At equal values of I, tobacco had the lowest leaf resistance (r_l) and maize had the highest r_l. Senescent maize leaves had nonfunctional stomata, whereas the lowermost sorghum leaves had higher stomatal resistances on average than the other leaves.     

Growth, Turgor, Water Potential, and Young's Modulus in Pea Internodes

The relations between longitudinal growth, Young's modulus, turgor, water potential, and tissue tensions have been studied on growing internodes of etiolated pea seedlings in an attempt to apply some physical concepts to the growth of a well-known plant material. The modulus has been determined by the resonance frequency method and expressed as E_tissue It increases nearly proportional to the turgor pressure and is at water saturation more than 50 times higher than at plasmolysis. E_tissue is higher in the epidermis than in the ground parenchyma. Indoleacetic acid causes a decrease in Etissue Other properties have been studied on intact and split segments of internodes in solutions of graded mannitol additions. — The following tentative picture of the normal course of the growth has been obtained. Auxin induces growth both in the periphery (epidermis) and in the central core (parenchyma) under a decrease in E_tissue This is followed by an increase of E_tissue which is independent of auxin but depending upon the turgor pressure. It is assumed to involve internal structural changes of the cell walls of the type of creep. The rapid growth takes place in a dynamic system with a low water potential despite favourable water conditions. Epidermis and parenchyma grow equally rapid without tissue tensions. — Such can be produced artificially by splitting of segments and water uptake. The parenchyma thereby loses its sensitivity to auxin. This is the background of the split stem test for auxin. — E_tissue increases when growth is slowing down, probably owing to both synthesis of wall substance and structural changes within the wall. The cells attain a more static condition with E_tissue higher in epidermis than in parenchyma. This leads to the normal tissue tensions. — The result agrees with growth according to the multi-net-principle. The cause of the low water potential and low turgor is discussed with reference to the dynamic nature of both growth and water transport and a probably low matric potential of the streaming water. The decrease in E_tissue following auxin addition is small but is the net difference between an auxin-induced decrease and an increase through the assumed creep.     

Plants under Climatic Stress: VI. Chilling and Light Effects on Photosynthetic Enzymes of Sorghum and Maize

The activity of several photosynthetic enzymes was unaltered by exposure of sorghum or maize to low temperatures (10 C) and light (170 w m⁻²). Two light-activated C₄-pathway enzymes, NADP-malate dehydrogenase and pyruvate Pi dikinase, were reduced in activity, and this was largely attributable to a loss of enzyme rather than to incomplete enzyme activation. Loss of NADP-malate dehydrogenase was more marked in sorghum than in maize, and in both species no loss occurred at 10 C when light levels were reduced from 170 to 50 w m⁻². A light-dependent, low temperature-induced loss of catalase activity was also observed in maize leaves.     

供氮形态与部位对局部根区水分胁迫下玉米水分吸收与利用的影响

试验以玉米品种'金海五号'幼苗为材料,在分根条件下采用聚乙二醇(PEG-6000)模拟局部根区水分胁迫,设置3种供氮形态(硝态氮、铵态氮、两者各占50%的混合氮)和2种供氮部位(水氮同区,氮加入到无PEG侧;水氮异区,氮加入到含PEG侧),研究局部根区水分胁迫下氮形态与供应部位对玉米水分吸收和利用的调节与作用机制,为局部根区灌溉水分高效利用提供理论依据.结果发现:(1)同一氮形态下水氮同区供应的植株蒸腾速率、耗水量、木质部汁液流速和生物量较高,加有硝态氮源处理无PEG侧根系的导管数目及单一氮形态处理无PEG侧根系的导管直径较高,但木质部汁液、叶片中脱落酸(ABA)浓度以及水分利用效率均较低.(2)同一供氮部位下,植株的蒸腾速率、耗水量、木质部汁液流速和生物量的顺序均为混合氮>硝态氮>铵态氮依次,但单一铵态氮处理植株的ABA浓度较高,水分利用效率较高.研究表明,同一氮形态下水氮同区供应植株生长较好、水分吸收能力较强,但水氮异区供应下植株的水分利用效率较高;同一供氮部位下,植株生长和水分吸收能力的顺序为混合氮>硝态氮>铵态氮,但单供铵态氮植株的水分利用效率较高.     

Turgor Regulation in a Brackish Water Charophyte, Lamprothamnium succinctum III. Changes in Cytoplasmic Free Amino Acids and Sucrose Contents during Turgor Regulation

Cytoplasm and cell sap of Lamprothamnium succinctum were analyzedseparately for the contents of free amino acids and sucroseto find whether they contribute to turgor regulation. In thevacuole, both amino acids and sucrose were found to be minorcomponents contributing to the generation of osmotic pressure.Their amounts were almost insensitive to changes in externalosmotic pressure. In the cytoplasm, both amino acids and sucrosein the cytoplasm contributed about 20% to the osmotic pressure.Hypotonic treatment did not affect the contents of either, buthypertonic treatment, while not affecting the amino acid contents,caused a significant increase in sucrose content. The cytoplasmicsucrose content increased linearly with an increase in externalosmotic pressure, accounting for 40% of the increased osmoticpressure. ¹ Present address: Department of Biology, Osaka Medical College,Sawaragi-cho, Takatsuki, Osaka 569, Japan ² Present address: Department of Applied Physiology, NationalInstitute of Agrobiological Resources, Yatabe, Tsukuda, Ibaragi305, Japan (Received November 25, 1986; Accepted March 18, 1987)     

Physiological Changes in Cultured Sorghum Cells in Response to Induced Water Stress : II. Soluble Carbohydrates and Organic Acids

Eight cultivars Sorghum bicolor (L.) Moench were grown as callus cultures under induced, prolonged water stress (8 weeks), with polyethylene glycol in the medium. Concentrations of soluble carbohydrates and organic acids in callus were measured at the end of the growth period to determine differences in response to prolonged water stress. Sucrose, glucose, fructose, and malate were the predominant solutes detected in all callus at all water potentials. All cultivars had high levels of solutes in the absence of water stress and low levels in the presence of prolonged water stress. However, at low water potentials, low levels of solutes were observed in drought-tolerant cultivar callus and high solute levels were observed in drought-susceptible cultivar callus. Estimated sucrose concentrations were significantly higher in water-stressed, susceptible cultivar callus. Large solute concentrations in susceptible cultivar callus were attributed to osmotic adjustment and/or reduced growth during water stress.     

Water Stress and --SH-Dependent Physiological Activities in Young Maize Plants

In young maize plants, water stress affects the —SH-dependentactivities: photosynthesis and dark respiration are reducedto about 60% at the wilting point; protein synthesis is inhibitedeven by moderate stress; and nitrate reductase activity is immediatelyinhibited also, prior to significant changes in the water statusof the plant As protoplasmatic protein denaturation occurs,protein —SS—increases at the expense of —SH,with consequent decrease of the —SH/—SS— ratio.The linear correlation between —SH/—SS— ratioand —SH-dependent activities suggests a strict dependencebetween them. A moderate increment both in rhodanese activityand labile sulphide content has been also demonstrated at thebeginning of the stress.     

Transpiration Induces Radial Turgor Pressure Gradients in Wheat and Maize Roots

Previous studies have shown both the presence and the absence of radial turgor and osmotic pressure gradients across the cortex of roots. In this work, gradients were sought in the roots of wheat (Triticum aestivum) and maize (Zea mays) under conditions in which transpiration flux across the root was varied This was done by altering the relative humidity above the plant, by excising the root, or by using plants in which the leaves were too young to transpire. Roots of different ages (4-65 d) were studied and radial profiles at different distances from the tip (5-30 mm) were measured. In both species, gradients of turgor and osmotic pressure (increasing inward) were found under transpiring conditions but not when transpiration was inhibited. The presence of radial turgor and osmotic pressure gradients, and the behavior of the gradient when transpiration is interrupted, indicate that active membrane transport or radial solvent drag may play an important role in the distribution of solutes across the root cortex in transpiring plants. Contrary to the conventional view, the flow of water and solutes across the symplastic pathway through the plasmodesmata cannot be inwardly directed under transpiring conditions.     

Mechanical Stress in the Shoot Apices of Euphorbia, Lycopersicon, and Pisum under controlled Turgor

Cuts were made in the surface of the shoot apices of Euphorbialathyris, tomato (Lycopersicon esculentum), and Pea (Pisum sativum)while they were completely immersed in water or aqueous mannitolat various concentrations, or in near-saturated air. Gapingoccurred all over the apical dome of Euphorbia and on the tomatoapex at the site of emergence of the primordial bulge. Maximumgaping occurred in near-saturated air and under water, and wasprogressively reduced with increasing osmotica. It is concludedthat the gaping results from tension in the surface cells andis not caused by superficial drying out. No gaping occurred in the axil of the newly formed primordiumof the tomato nor anywhere in the apex of the pea. Histologicalevidence suggests that these tissues are under lateral compression. The mechanical stresses involved are discussed in relation tothe morphology of the apices together with existing data onthe distribution of cell division during primordia formation.     

Growth Inhibition, Turgor Maintenance, and Changes in Yield Threshold after Cessation of Solute Import in Pea Epicotyls

The dependence of stem elongation on solute import was investigated in etiolated pea seedlings (Pisum sativum L. var Alaska) by excising the cotyledons. Stem elongation was inhibited by 60% within 5 hours of excision. Dry weight accumulation into the growing region stopped and osmotic pressure of the cell sap declined by 0.14 megapascal over 5 hours. Attempts to assay phloem transport via ethylenediaminetetraacetate-enhanced exudation from cut stems revealed no effect of cotyledon excision, indicating that the technique measured artifactual leakage from cells. Despite the drop in cell osmotic pressure, turgor pressure (measured directly via a pressure probe) did not decline. Turgor maintenance is postulated to occur via uptake of solutes from the free space, thereby maintaining the osmotic pressure difference across the cell membrane. Cell wall properties were measured by the pressure-block stress relaxation technique. Results indicate that growth inhibition after cotyledon excision was mediated primarily via an increase in the wall yield threshold.     

Proline Metabolism and Transport in Maize Seedlings at Low Water Potential

The growing zone of maize seedling primary roots accumulatesproline at low water potential. Endosperm removal and excisionof root tips rapidly decreased the proline pool and greatlyreduced proline accumulation in root tips at low water potential.Proline accumulation was not restored by exogenous amino acids.Labelling root tips with [¹⁴C]glutamate and [¹⁴C]proline showedthat the rate of proline utilization (oxidation and proteinsynthesis) exceeded the rate of biosynthesis by five-fold athigh and low water potentials. This explains the reduction inthe proline pool following root and endosperm excision and theinability to accumulate proline at low water potential. Theendosperm is therefore the source of the proline that accumulatesin the root tips of intact seedlings. Proline constituted 10% of the amino acids released from the endosperm. [¹⁴C]Prolinewas transported from the scutellum to other parts of the seedlingand reached the highest concentration in the root tip. Less[¹⁴C]proline was transported at low water potential but becauseof the lower rate of protein synthesis and oxidation, more accumulatedas proline in the root tip. Despite the low biosynthesis capacityof the roots, the extent of proline accumulation in relationto water potential is precisely controlled by transport andutilization rate.     

Glutamine Synthetase Activity, Relative Water Content and Water Potential in Maize Submitted to Drought

Primer screening and optimization for random amplified polymorphic DNA (RAPD) analysis of cashew (Anacardium occidentale L.) was investigated. Among four series (A, B, D and N) of 10-mer primers, A-series performed better amplification of fragments than other series. The maximum amplification fragments was obtained using OPA-02, OPA-03, OPA-09, OPB-06, OPB-10, OPD-03, OPD-05 and OPN-03 primers. The primers OPA-02 and OPN-03 produced maximum number of DNA fragments in Anacardium occidentale cv. H-320. Primers (OPB-08 and OPN-05 performed a least number of amplification fragments. RAPD profile also indicate that some primer did not produce good amplification. The primer OPA-02 amplified 12 number of polymorphic bands in 20 cultivars of cashew. Only one DNA fragment was produced in A. occidentale cv. Vridhachalam - 2 (M-44/3) by using the primer OPA-02. This revised version was published online in July 2006 with corrections to the Cover Date.     

未分胁迫下不同抗旱性小麦芽鞘膨压和IAA及ABA含量变化（简报）

水分胁迫条件下,小麦细胞膨压下降与芽鞘生长抑制呈正相关。不同品种单位膨压升高引起的伸长生长有差异。水分胁迫0、3、8、20、32、45h后,抗旱性强的品种芽鞘中IAA含量及IAA／ABA比值在接近生长最快的时刻出现高峰;抗旱性差的品种IAA含量及IAA／ABA比值的高峰出现的时间与生长最快的时间不一致。单位膨压升高引起芽鞘长度增加大的品种,腔迫处理后IAA含理及IAA／ABA相对较高或下降程度相对较小;而BA含理升高则相反,抗旱性弱的品种胁迫处理后ABA含量增加相对较多。     

Carbon Balance of Sorghum Plants during Osmotic Adjustment to Water Stress

The daily (24-hour) carbon balances of whole sorghum plants (Sorghum bicolor L. Moench cv BTX616) were continuously measured throughout 15 days of water stress, followed by rewatering and 4 more days of measurements. The plants were grown under controlled environment conditions typical of warm, humid, sunny days. During the first 12 days, osmotic potentials decreased in parallel with decreased water potentials to maintain pressure potentials near 0.5 kilojoules per kilogram (5 bars). Immediately before rewatering on day 15, the water potential was −3.0 kilojoules per kilogram. Osmotic adjustment at this point was 1.0 kilojoules per kilogram, as measured by the decrease in the water potential at zero turgor from its initial value of −1.4 kilojoules per kilogram.

Gross input of carbon was less but the fraction retained was greater because a smaller fraction was lost through respiration in stressed plants than in unstressed plants. This was attributed to a lower rate of biomass synthesis, and conversely a higher rate of storage of photosynthate, due to inhibition of leaf expansion. The reduction in the cost associated with biomass synthesis more than balanced any metabolic cost of osmotic adjustment. The net daily gain of carbon was always positive in the stressed plants.

There was a large burst of respiration on rewatering, due to renewed synthesis of biomass from stored photosynthate. Over the next 3 days, osmotic adjustment was lost and the daily carbon balance returned to that typical of nonstressed plants. Thus, osmotic adjustment allowed the stressed plants to accumulate biomass carbon throughout the cycle, with little additional metabolic cost. Carbon stored during stress was immediately available for biomass synthesis on rewatering.

     

水分胁迫下花生叶片AhNCED1蛋白表达与气孔开度的变化

研究了水分胁迫下不同花生抗旱品种叶片气孔开度和相对含水量变化,分析TAhNCEDI基因和AhNCED1蛋白进行表达情况,发现水分胁迫下,叶片相对含水量下降,叶片气孔开度降低,叶片AhNCED1基因和AhNCED1蛋白表达增强。抗旱品种较之敏旱品种在响应水分胁迫初期时（1h）AhNCED1基因和AhNCED1蛋白表达较强,叶片气孔开度下降较快,引发气孔关闭,其叶片相对含水量较高,保水能力较强。ABA合成抑制剂naproxen处理后,叶片AhNCED1基因和AhNCED1蛋白的表达减弱,气孔开度快速增加,水分胁迫下花生叶片AhNCED1蛋白表达可能影响气孔开闭。