Decrease In Leaf Water Potential Research Articles

Efficient fog harvesting by Stipagrostis sabulicola (Namib dune bushman grass)

Stipagrostis sabulicola, an endemic grass species of the central Namib Desert, grows on dune fields under conditions of very low annual precipitation punctuated by regular nocturnal fog events. The objective of this study is to determine to what extent S. sabulicola relies on water supply by fog harvesting. The following parameters were monitored: 1) climate, 2) stem runoff, 3) leaf water potential (LWP) and 4) soil water content (SWC). Collected fog water was 5.0 L (liter) per m −2 leaf surface and therefore a total harvest of 4–5 L per fog event for a medium-sized mound of S. sabulicola. SWC close to a mound increased substantially during a fog event, with SWC at about 2.2% within a mound. LWP of S. sabulicola ranged between −1.7 MPa and −3.5 MPa. On days without fog, LWP was highest during the morning and decreased during the afternoon. No significant decrease of LWP occurred during days following a fog event. The increase of SWC at the plant base during a fog event indicates that fog harvest of S. sabulicola occurs mainly via stem flow with subsequent absorption by the root system and that fog catchment therefore represents a substantial water source for this species.

Silicon application and drought tolerance mechanism of sorghum

Pot experiments were conducted at the PMAS, Arid Agriculture University, Rawalpindi, Pakistan during 2007 repeated during 2008 to study the effect of silicon and nanoirrigation (W40) on drought tolerance mechanism of sorghum. According to experimental design, the silicon fertilization was divided into two levels: control (no application of potassium silicate) Si0 and application of silicon Si200 (200 mlL-1 of potassium silicate per kg of soil). Irrigation was divided into two levels: crop upper limit (40 mm) irrigation denoted as W40 and without irrigation, crop lower limit as Wo. Each treatment was replicated three times with two sorghum cultivars: PARC SS-2 (drought tolerant) and Johar-1(drought susceptible). The results showed that increase in silicon leads to increase in leaf area index (LAI), specific leaf weight (SLW), chlorophyll content (SPAD), leaf dry weight (LDW), shoot dry weight (SDW), root dry weight (RDW), total dry weight (TDW) and remarkably decrease in leaf water potential and shoot to root ratio in sorghum cultivars compared to control treatment. When silicon concentration is applied with irrigation LAI, SPAD, LDW, SDW, RDW, TDW, net assimilation rate (NAR), relative growth rate (RGR), leaf area ratio (LAR) and water use efficiency (WUE) increased by 30, 31, 40, 30, 28, 30, 27, 35, 32, 30 and 36% respectively as compared to water deficient treatment. These results suggest that silicon application may be useful to improve the drought tolerance of sorghum through the enhancement of water uptake ability. Key words: Drought, leaf water potential, leaf area ratio, net assimilation rate, relative growth rate, nano-irrigation.

Stomatal sensitivities to changes in leaf water potential, air humidity, CO2 concentration and light intensity, and the effect of abscisic acid on the sensitivities in six temperate deciduous tree species

To characterise the stomata of six temperate deciduous tree species, sets of stomatal sensitivities to all the most important environmental factors were measured. To compare the importance of abscisic acid (ABA) in the different stomatal responses, the effect of exogenous ABA on all the stomatal sensitivities was determined.Almost all the stomatal sensitivities: the sensitivity to a decrease in leaf water potential, air humidity, CO2 concentration ([CO2]) and light intensity, and to an increase in [CO2] and light intensity were the highest in the slow-growing species, and the lowest in the fast-growing species. Drought increased the sensitivity to the environmental changes that induce a decrease in the stomatal conductance, and decreased the sensitivity to the changes that induce an increase in this conductance. The sensitivities of the slow-growers were most strongly affected by drought and ABA. Therefore the success of the slow-growers in their ecological niches can be based on the highly sensitive and strictly regulated responses of their stomata. The fast-growers had the highest sensitivity to an increase in leaf water potential and this sensitivity was sharply reduced by drought and ABA. Thus, the dominance of the trees in riparian areas can be based on the ability of their stomata to quickly reach high conductance in well-watered conditions and to efficiently decrease this rate during drought.Stomatal sensitivities to the hydraulic environmental factors (water potentials in plant and air) had higher values in well-watered trees and a more pronounced response to drought than the sensitivities to the photosynthetic environmental factors ([CO2] and light intensity). Thus, the hydraulic factors most likely prevail over the photosynthetic factors in determining stomatal conductance in these species.In response to exogenous ABA, the rates of stomatal closure, following a decrease in air humidity and light intensity, and an increase in [CO2], were accelerated. Stomatal opening following an increase in air humidity and light intensity and a decrease in [CO2] was replaced by slow closing. The rate of stomatal opening following an increase in leaf water potential was reduced. As the sensitivities to changes in light were modified less by the ABA than the other stomatal sensitivities, the prediction of stomatal responses on the basis of the sensitivity to light alone should be excluded in stomatal models.

Potassium deficiency affects water status and photosynthetic rate of the vegetative sink in green house tomato prior to its effects on source activity

The potassium requirement of green house tomatoes is very high for vegetative growth and fruit production. Potassium deficiency in plants takes long time for expression of visible symptoms. The objective of this study is to detect the deficiency early during the vegetative growth and define the roles of aquaporin and K-channel transporters in the process of regulation of water status and source–sink relationship. The tomato plants were grown hydroponically inside green house of Hiroshima University, Japan and subjected to different levels of K in the rooting medium. Potassium deficiency stress decreased photosynthesis, expansion and transport of 14C assimilates of the source leaf, but the effects became evident only after diameter expansion of the growing stem (sink) was down-regulated. The depression of stem diameter expansion is assumed to be associated with the suppression of water supply more than photosynthate supply to the organ. The stem diameter expansion is parameterized by root water uptake and leaf transpiration rates. The application of aquaporin inhibitor (AgNO 3) decreased leaf water potential, stem expansion and root hydraulic conductance within minutes of application. Similar results were obtained for application of the K-channel inhibitors. These observations suggested a close relationship between stem diameter expansion and activities of aquaporins and K-channel transporters in roots. The deficiency of potassium might have reduced aquaporin activity, consequently suppressing root hydraulic conductance and water supply to the growing stem for diameter expansion and leaf for transpiration. We conclude that close coupling between aquaporins and K-channel transporters in water uptake of roots is responsible for regulation of stem diameter dynamics of green house tomato plants.

Reduced irrigation and rootstock effects on vegetative growth, yield and its components, and leaf physiological responses of Shiraz

Background and Aims: The study investigated whether rootstocks can modify grapevine responses to reduced irrigation. Methods and Results: Drip-irrigated Shiraz vines on eight rootstocks were subjected to industry standard and 30% reduced irrigation regimes over four seasons. Reducing irrigation decreased pruning weights and yield, but did not consistently affect irrigation water use index (IWUI). It increased leaf Δ13C. Reduced irrigation and elevated vapour pressure deficit (VPD) were associated with decreases in leaf water potential (ψl), leaf stomatal conductance and assimilation rate. Reducing irrigation raised leaf transpiration efficiency, whereas elevated VPD lowered it. These effects of reduced irrigation were independent of rootstock. Vines grafted to 101-14 had a higher ψl and achieved the highest yield and IWUI. The yields of vines grafted to Ramsey, Schwarzmann and 140 Ruggeri were also high. Vines grafted to 101-14, Ramsey and 1103 Paulsen had the higher rates of leaf assimilation. Rootstock did not affect Δ13C. Conclusion: The gain in leaf transpiration efficiency caused by reducing irrigation was not associated with a gain in IWUI. Rootstocks 101-14, Ramsey, Schwarzmann and 140 Ruggeri achieved higher yields and IWUI under both standard and reduced irrigation regimes. Significance of the Study: Among grafted vines growing on saline soil but receiving non-saline irrigation water and subject to a 30% reduction in irrigation, the yield responses of vines grafted on rootstocks rated as having good drought tolerance were the same as those of vines grafted on rootstocks rated as having poor drought tolerance.

Erratum to: Exploitation of patchy soil water resources by the clonal vine Ficus tikoua in karst habitats of southwestern China

The karst habitats of southwestern China are characterized by a highly heterogeneous distribution of water resources. We hypothesized that the clonal integration between connected ramets of the clonal vine Ficus tikoua was an important adaptive strategy to the patchy distribution of water resources in these habitats. We grew ramet pairs (each consisting of a parent and an offspring ramet) in both homogeneously and heterogeneously watered conditions. The offspring ramets were well-watered, whereas their connected parent ramets were randomly assigned to four water treatments: well-watered, mild water stress, moderate water stress, and severe water stress. Increasing water stress decreased leaf water potential, relative water content, net assimilation rate, maximum quantum yield of PSII (F v/F m), and biomass of the parent ramets. Subjecting the parents to water stress significantly increased root biomass and root mass ratio (RMR) of their offspring ramets. Exploitation of plentiful water resources through the increased adventitious roots connected to another soil patch permitted the complete restoration of water relations and photosynthetic capacity of offspring ramets after an initial depression. Water relations and gas exchange of the parents were not affected by the water supply to their connected offspring ramets, suggesting that offspring ramets hardly exported water to the stressed parents. However, net assimilation rate and proline content of the offspring ramets increased when they were connected to water-stressed parents. The compensatory photosynthetic responses of offspring ramets connected to stressed parents revealed an increasing trend as the experiment progressed. Morphological and physiological plasticity of F. tikoua in response to heterogeneous water resources allow them to adapt to karst habitats and be suitable candidates for vegetation restoration projects.

Allelopathic Effects of Chromolaena Odorata L. (R. M. King and Robinson – (Awolowo Plant’)) Toxin on Tomatoes (Lycopersicum esculentum Mill)

Allelopathic effects of Chromolaena odorata L. (R. M. KING AND ROBINSON) aqueous leaf extract and residues incorporated in the soil on the growth and water status of Lycopersicon esculentum Mill were studied. Significant growth reductions in Lycopersicon esculentum were observed from additions of C. odorata aqueous – leaf extract at concentrations as low as 1g fresh weight in 40ml of water. Reduction in growth was accompanied by decreases in leaf water potential. Incorporation of C. odorata leaf material into the soil in which L esculentum Mill seedlings were germinated and grown caused significant depression in growth over the 2-week test period with addition of 2g residue to 80g soil. Allelochemicals released from C. odorata plants and residue are suggested as a possible explanation for yield reductions in crops in fields where C. odorata plants are present. One mechanism of toxic action on seedlings involved interference with water balance

Sensitivity of stem and petiole hydraulic conductance of deciduous trees to xylem sap ion concentration

Hydraulic conductance of stem and petioles increased in response to an increase in xylem sap ion concentration, and decreased in response to a decrease in the ion concentration in six temperate deciduous tree species. The ion sensitivity of hydraulic conductance of stem and petioles was higher than the ion sensitivity of the stem alone. The ion sensitivity was lowest in the earliest developmental stages of the xylem, and had a seasonal maximum in the second half of summer. The ion sensitivity was highest in slow-growing species and lowest in fast-growing species. The ion sensitivity correlated negatively with mean radius of xylem conduits, hydraulic conductance of stem and petioles, hydraulic conductance of leaf laminae, and stomatal conductance, and positively with response of the hydraulic conductance of leaf laminae to HgCl2, and stomatal response to a decrease in leaf water potential or abscisic acid. It was concluded that the high ion sensitivity of xylem hydraulic conductance is a relevant characteristic of slow growth and a conservative water use strategy.

5-Aminolevulinic acid improves photosynthetic gas exchange capacity and ion uptake under salinity stress in oilseed rape (Brassica napus L.)

Salinity is one of the major constraints in oilseed rape (Brassica napus L.) production. One of the means to overcome this constraint is the use of plant growth regulators to induce plant tolerance. To study the plant response to salinity in combination with a growth regulator, 5-aminolevulinic acid (ALA), oilseed rape plants were grown hydroponically in greenhouse conditions under three levels of salinity (0, 100, and 200 mM NaCl) and foliar application of ALA (30 mg/l). Salinity depressed the growth of shoots and roots, and decreased leaf water potential and chlorophyll concentration. Addition of ALA partially improved the growth of shoots and roots, and increased the leaf chlorophyll concentrations of stressed plants. Foliar application of ALA also maintained leaf water potential of plants growing in 100 mM salinity at the same level as that of the control plants, and there was also an improvement in the water relations of ALA-treated plants growing in 200 mM. Net photosynthetic rate and gas exchange parameters were also reduced significantly with increasing salinity; these effects were partially reversed upon foliar application with ALA. Sodium accumulation increased with increasing NaCl concentration which induced a complex response in the macro-and micronutrients uptake and accumulation in both roots and leaves. Generally, analyses of macro- (N, P, K, S, Ca, and Mg) and micronutrients (Mn, Zn, Fe, and Cu) showed no increased accumulation of these ions in the leaves and roots (on dry weight basis) under increasing salinity except for zinc (Zn). Foliar application of ALA enhanced the concentrations of all nutrients other than Mn and Cu. These results suggest that under short-term salinity-induced stress (10 days), exogenous application of ALA helped the plants improve growth, photosynthetic gas exchange capacity, water potential, chlorophyll content, and mineral nutrition by manipulating the uptake of Na+.

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.

Physiological and biochemical traits involved in the genotypic variability to salt tolerance of Tunisian Cakile maritima

Abstract Cakile maritima (family: Brassicaceae) was collected from three provenances belonging to different bioclimatic stages (humid, semi arid and arid) in Tunisia to study their eco‐physiological and biochemical responses to salinity. Seedlings were cultivated on inert sand for 20 days under NaCl treatments (0, 100, 200, 400 mm NaCl). Plant response to salinity was provenance‐ and salt‐dependent. At 100 mm NaCl, growth parameters (leaf biomass, area, number per plant and relative growth rate) were improved in plants from Jerba (originating from arid bioclimatic stage) compared with the control, while growth was reduced in those from Tabarka (from humid area). High salt levels (400 mm NaCl) decreased the plant growth in the three provenances, but plants in Tabarka were the most salt sensitive. The relative salt tolerance of plants from Jerba and Bekalta provenances was associated with low levels of malondialdehyde as well as of electrolyte leakage and endoproteolytic activity. Salt reduced leaf hydration, the decrease in water content being dose‐dependent and more pronounced in Tabarka. Increase in salinity led to significant increase in leaf succulence and decrease in leaf water potential, especially in Jerba plants. The plants from the latter displayed the highest leaf levels of Na+ and Cl−, proline, soluble carbohydrates, soluble proteins, and polyphenols. Overall, the higher salt tolerance of plants from Jerba provenance, and to a lower extent of those from Bekalta, may be partly related to their better capacity for osmotic adjustment and to limit oxidative damage when salt‐challenged.

Chromium Alters Iron Nutrition and Water Relations of Spinach

ABSTRACT Spinach (Spinacea oleracea L. cv. ‘Banarasi’), known to be responsive to potentially toxic elements, was investigated for chromium (Cr6 +) effect on iron metabolism and water relations. After 40 days growth in sand culture, a set of plants was supplied with 100 and 400 μM Cr6 + (potassium dichromate, K2Cr2O7), superimposed over the complete nutrient solution (control). Excess Cr6 + produced visual symptoms of toxicity and increased accumulation of Cr, more in roots than in leaves. Decreased concentration of chlorophylls and the activities of heme enzymes, catalase and peroxidase in excess Cr6 + may suggest interference of Cr in iron metabolism of plants. These changes associated with decrease in iron (Fe) accumulation in Cr6 + treated plants, indicate that by reducing absorption of Fe, Cr6 + impairs the Fe requiring steps of chlorophyll and heme biosynthesis. In spite of lower water saturation deficit, the leaves of Cr6 + treated plants showed a decrease in leaf water potential, associated with increase in diffusive resistance and lowering of transpiration rate along with proline accumulation indicates water stress. The changes observed in water stress parameters in Cr6 + treated plants indicate that excess supply of Cr6 + reduces the physiological availability of water.

Drought reduced monoterpene emissions from the evergreen Mediterranean oak <i>Quercus ilex</i>: results from a throughfall displacement experiment

Abstract. The effects of water limitations on the emission of biogenic volatile organic compounds are not well understood. Experimental approaches studying drought effects in natural conditions are still missing. To address this question, a throughfall displacement experiment was set up in a natural forest of Quercus ilex, an evergreen Mediterranean oak emitting monoterpenes. Mature trees were exposed in 2005 and 2006 either to an additional drought, to irrigation or to natural drought (untreated control). In both years, absolute monoterpene emission rates as well as the respective standard factors of the trees exposed to normal and additional drought strongly declined during the drought periods. Monoterpene emissions were lower in year 2006 than in year 2005 (factor 2) due to a more pronounced summer drought period in this respective year. We observed a significant difference between the irrigation and additional drought or control treatment: irrigated trees emitted 82% more monoterpenes during the drought period 2006 than the trees of the other treatments. However, no significant effect on monoterpene emission was observed between normal and additional drought treatments, despite a significant effect on leaf water potential and photochemical efficiency. During the development of drought, monoterpene emissions responded exponentially rather than linearly to decreasing leaf water potential. Emissions rapidly declined when the water potential dropped below −2 MPa and photosynthesis was persistently inhibited. Monoterpene synthase activities measured in vitro showed no clear reduction during the same period. From our results we conclude that drought significantly reduces monoterpene fluxes of Mediterranean Holm oak forest into the atmosphere due to a lack of primary substrates coming from photosynthetic processes.

Carbon isotope discrimination in leaf juice of Acacia mangium and its relationship to water-use efficiency

Using the PMS pressure chamber and isotope mass spectrometer (MAT-252), the leaf juice of Acacia mangium was obtained, and the carbon isotope discrimination (D) representing the most recently fixed carbon in the juice was determined. At the same time, the water-use efficiency of A. mangium was estimated. The results indicated that the carbon isotope ratio in the air of forest canopy (δa), 10 m high a bove ground averaged − 7.57 ± 1.41 ‰ in cloudy days, and − 8.54±0.67‰ in sunny days, respectively. The diurnal change of the carbon isotope ratio in the photosynthetic products of the leaf juice (δp) was of saddle type in cloudy days, but dropped down from morning to later afternoon in sunny days. A strong negative correlation between δp and leaf-to-air vapor pressure deficit (D) was observed in sunny days, but a slight change in δp was found in cloudy days. The δp also decreased with decreasing leaf water potential (Ψ), reflecting that water stress could cause the decrease of δp. The carbon isotope discrimination of the leaf juice was positively correlated with the ratio between intercellular (Pi) and atmospheric (Pa) partial pressure of CO2. For A. mangium, the isotope effect on diffusion of atmospheric CO2 via stomata was denoted by a = 4.6‰, and that in net C3 diffusion with respect to Pi was indicated by b = 28.2‰. The results were in reasonable accord with the theoretically diffusive and biochemical fractionation of carbon isotope. It was defined that carbon isotope discrimination of photosynthetic products in A. mangium leaf juice was in proportion to that from photosynthetic products in dry material. The water-use efficiency estimated by the carbon isotope discrimination in leaf juice, fit well with that measured by gas exchange system (R2 = 0.86, p < 0.0001). The application of leaf juice in measuring the stable carbon isotope discrimination would reduce the effects of fluctuating environmental factors during the synthesis of dry matter, and improve the ecophysiological studies on carbon and water balance when scaling from the plant to canopy in the fields.

Salicylic acid improves acclimation to salt stress by stimulating abscisic aldehyde oxidase activity and abscisic acid accumulation, and increases Na + content in leaves without toxicity symptoms in Solanum lycopersicum L.

Pre-treatment with 10(-4)M salicylic acid (SA) in hydroponic culture medium provided protection against salinity stress in tomato plants (Solanum lycopersicum L. cv. Rio Fuego). The effect of 10(-7) or 10(-4)M SA on the water status of plants was examined in relation to the biosynthesis and accumulation of abscisic acid (ABA) in order to reveal the role of SA in the subsequent response to salt stress. Both pre-treatments inhibited the K+(86Rb+) uptake of plants, reduced the K+ content of leaves, and caused a decrease in leaf water potential (psi(w)). Due to the changes in the cellular water status, SA triggered the accumulation of ABA. Since the decrease in psi(w) proved to be transient, the effect of SA on ABA synthesis may also develop via other mechanisms. In spite of osmotic adaptation, the application of 10(-4)M, but not 10(-7)M SA, led to prolonged ABA accumulation and to enhanced activity of aldehyde oxidase (AO1, EC.1.2.3.1.), an enzyme responsible for the conversion of ABA-aldehyde to ABA, both in root and leaf tissues. AO2-AO4 isoforms from the root extracts also exhibited increased activities. The fact that the activities of AO are significantly enhanced both in the leaves and roots of plants exposed to 10(-4)M SA, may indicate a positive feedback regulation of ABA synthesis by ABA in this system. Moreover, during a 100mM NaCl treatment, higher levels of free putrescine or spermine were found in these leaves or roots, respectively, than in the salt-stressed controls, suggesting that polyamines may be implicated in the protection response of the cells. As a result, Na+ could be transported to the leaf mesophyll cells without known symptoms of salt toxicity.

Effect of partial rootzone drying on growth, gas exchange, and yield of tomato ( Solanum lycopersicum L.)

Three levels of partial rootzone drying (PRD) were evaluated and compared with conventional irrigation, in terms of gas exchange, water relations, growth, yield, fruit quality, and water use efficiency in tomato ( Solanum lycopersicum L.) saladette-type plants growing in pots with volcanic material and drip irrigation. There were four treatments, a control, in which available water (AW) in the whole root system was allowed to fall to 90%; PRD90-30, in which on one side of the divided root AW was allowed to fall to 90% and on the other side it was allowed to fall to 30%; PRD70-30, in which on one side of the divided root AW was allowed to fall to 70% and on the other side it was allowed to fall to 30%; PRD50-30, in which on one side of the divided root AW was allowed to fall to 50% and on the other side it was allowed to fall to 30%. When each treatment reached the desired AW level they were then irrigated. At the same time, when on one side AW reached values ≤30% irrigation was shifted to the other side. Results showed a significant decrease of leaf water potential up to 14% in PRD plants compared with control. Shoot dry weight and leaf area decreased in relation to substrate available water in PRD plants. Stomatal conductance and transpiration rate were lower, up to 31 and 18%, respectively, in plants with PRD compared with control. However, CO 2 assimilation rate was similar among treatments which along with the reduction of transpiration in PRD plants, increased instantaneous water use efficiency by 28, 25, and 33% in PRD90-30, PRD70-30, and PRD50-30 treatments, respectively, compared to control. Yield, number of fruits and fruit total soluble solids content were similar among treatments. An increase of 25% in fruit titratable acidity was reached in PRD50-30. Fruit firmness increased up to 31% in PRD treatments. PRD treatments allowed a water irrigation saving up to 46%.

Spatial covariance in resources affects photosynthetic rate and water potential, but not the growth of Glechoma longituba fragments

Glechom longituba is a widespread clonal plant and usually experiences diverse patchiness of its growing sites. The hypothesis was tested that spatial covariance in resources differentially affects the growth and physiology of G. longituba. Plants were exposed to two patchy habitats where above- and below-ground resources were either positively or negatively associated, and to four control habitats. When equal amounts of resources were given, G. longituba fragments from two patchy habitats had similar biomass, root weight ratio, leaf weight ratio, fluorescence yield, specific petiole length, and specific root length; fragments under reciprocal patchiness significantly increased photosynthetic rate and decreased leaf water potential. Biomass of clones grown in patchy habitats was equal or less than that of counterparts from the control habitats, not supporting the notion that clonal growth is more advantageous in patchy habitats than in uniform habitats. In addition, no evidence was detected for spatial division of labour because biomass allocation to roots and leaves was similar in patchy habitats compared with the control habitats.

Biochemical responses to drought stress in mulberry (Morus alba L.): evaluation of proline, glycine betaine and abscisic acid accumulation in five cultivars

Five popularly grown mulberry cultivars (K-2, MR-2, TR-10, BC2-59 and S-13) were subjected to drought stress by withholding irrigation, to obtain leaf water potentials (Ψw) ranging from −0.75, −1.50 and −2.25 MPa. Accumulation of proline, glycine betaine and abscisic acid (ABA) were quantified in control and water stressed mulberry leaves. The activities of enzymes involved in proline accumulation including glutamate dehydrogenase (EC1.4.1.2-4), pyrroline-5-carboxylate synthetase (EC 1.2.1.41), pyrroline-5-carboxylate reductase (EC1.5.1.2), ornithine transaminase (EC 2.6.1.13) were significantly enhanced in the leaves of all the cultivars with decreasing leaf water potentials, while the activities of proline dehydrogenase (EC 1.5.1.2) were reduced with progressive increase in water stress. Accumulation of proline, glycine betaine and abscisic acid was relatively higher in S-13 and BC2-59 compared to K-2, MR-2 and TR-10 under water deficit conditions. Our results demonstrate that S-13 and BC2-59 have superior osmoprotectant mechanisms under water-limited growth regimes.

The ER luminal binding protein (BiP) mediates an increase in drought tolerance in soybean and delays drought-induced leaf senescence in soybean and tobacco

The ER-resident molecular chaperone BiP (binding protein) was overexpressed in soybean. When plants growing in soil were exposed to drought (by reducing or completely withholding watering) the wild-type lines showed a large decrease in leaf water potential and leaf wilting, but the leaves in the transgenic lines did not wilt and exhibited only a small decrease in water potential. During exposure to drought the stomata of the transgenic lines did not close as much as in the wild type, and the rates of photosynthesis and transpiration became less inhibited than in the wild type. These parameters of drought resistance in the BiP overexpressing lines were not associated with a higher level of the osmolytes proline, sucrose, and glucose. It was also not associated with the typical drought-induced increase in root dry weight. Rather, at the end of the drought period, the BiP overexpressing lines had a lower level of the osmolytes and root weight than the wild type. The mRNA abundance of several typical drought-induced genes [NAC2, a seed maturation protein (SMP), a glutathione-S-transferase (GST), antiquitin, and protein disulphide isomerase 3 (PDI-3)] increased in the drought-stressed wild-type plants. Compared with the wild type, the increase in mRNA abundance of these genes was less (in some genes much less) in the BiP overexpressing lines that were exposed to drought. The effect of drought on leaf senescence was investigated in soybean and tobacco. It had previously been reported that tobacco BiP overexpression or repression reduced or accentuated the effects of drought. BiP overexpressing tobacco and soybean showed delayed leaf senescence during drought. BiP antisense tobacco plants, conversely, showed advanced leaf senescence. It is concluded that BiP overexpression confers resistance to drought, through an as yet unknown mechanism that is related to ER functioning. The delay in leaf senescence by BiP overexpression might relate to the absence of the response to drought.

Root signals and stomatal closure in relation to photosynthesis, chlorophyll a fluorescence and adventitious rooting of flooded tomato plants

An investigation was carried out to determine whether stomatal closure in flooded tomato plants (Solanum lycopersicum) results from decreased leaf water potentials (psi(L)), decreased photosynthetic capacity and attendant increases in internal CO(2) (C(i)) or from losses of root function such as cytokinin and gibberellin export. Pot-grown plants were flooded when 1 month old. Leaf conductance was measured by diffusion porometry, the efficiency of photosystem II (PSII) was estimated by fluorimetry, and infrared gas analysis was used to determine C(i) and related parameters. Flooding starting in the morning closed the stomata and increased psi(L) after a short-lived depression of psi(L). The pattern of closure remained unchanged when psi(;L) depression was avoided by starting flooding at the end rather than at the start of the photoperiod. Raising external CO(2) concentrations by 100 micromol mol(-1) also closed stomata rapidly. Five chlorophyll fluorescence parameters [F(q)'/F(m)', F(q)'/F(v)', F(v)'/F(m)', non-photochemical quenching (NPQ) and F(v)/F(m)] were affected by flooding within 12-36 h and changes were linked to decreased C(i). Closing stomata by applying abscisic acid or increasing external CO(2) substantially reproduced the effects of flooding on chlorophyll fluorescence. The presence of well-aerated adventitious roots partially inhibited stomatal closure of flooded plants. Allowing adventitious roots to form on plants flooded for >3 d promoted some stomatal re-opening. This effect of adventitious roots was not reproduced by foliar applications of benzyl adenine and gibberellic acid. Stomata of flooded plants did not close in response to short-lived decreases in psi(L) or to increased C(i) resulting from impaired PSII photochemistry. Instead, stomatal closure depressed C(i) and this in turn largely explained subsequent changes in chlorophyll fluorescence parameters. Stomatal opening was promoted by the presence of well-aerated adventitious roots, implying that loss of function of root signalling contributes to closing of stomata during flooding. The possibility that this involves inhibition of cytokinin or gibberellin export was not well supported.