Decrease In Leaf Water Potential Research Articles

Dew absorption by leaf trichomes in Caragana korshinskii: An alternative water acquisition strategy for withstanding drought in arid environments.

Investigating plant morphological traits can provide insights into plant drought tolerance. To date, many papers have focused on plant hydraulic responses to drought during dehydration, but atmospheric water absorption by trichomes to mitigate drought stress by influencing leaf hydraulics in plant species that inhabit arid environments has been largely ignored. The experiment in this study was designed to assess how dew absorbed by leaf trichomes helps Caragana korshinskii withstand drought. The results showed that under a drought stress and dew (DS & D) treatment, C. korshinskii displayed a strong capacity to absorb dew with trichomes; exhibited slow decreases in leaf water potential (Ψleaf ), leaf hydraulic conductivity (Kleaf ), and gas exchange; experienced 50% Kleaf and gas exchange losses at lower relative soil water content levels than plants treated with drought stress and no dew (DS & ND); and experienced 50% Kleaf loss (Kleaf P50 ) at similar Ψleaf levels as DS & ND plants. Its congener C. sinica, which does not have leaf trichomes, displayed little ability to absorb dew under drought stress and did not show any remarkable improvement in the above parameters under the DS & D treatment. Our results indicated that leaf trichomes are important epidermal dew-uptake structures that assist in partially sustaining the leaf hydraulic assimilation system, mitigate the adverse effects of drought stress and contribute to the distribution of C. korshinskii in arid environments.

EFFECTS OF DIFFERENT SOURCES OF IRRIGATION WATER ON THE GROWTH OF ZINNIA ELEGANS L. UNDER DROUGHT STRESS

The application of deficit irrigation water strategies to floriculture may make a significant contribution to irrigation water conservation. The purpose of this research was to evaluate the effects of different irrigation regimes for Zinnia ‘Solmar Yellow’ plants grown in an open field using different sources of irrigation water. Zinnia plants were grown in a field under three irrigation regimes, corresponding to 100% (control) of field capacity, 75%, and 50% of the irrigation needs. The water used for irrigation was derived from three sources: groundwater, distilled water, and blended water (50% ground-water + 50% distilled-water). In this investigation the vegetative growth, flower yield, pigment characteristics, ion content, leaf water potential, and leaf osmotic potential of plants exposed to these treatments were determined. Under the imposed drought conditions, the irrigation regimes with high or moderate quality water had the following effects: (i) a negative effect on the vegetative growth and flower yield, but a later flowering date; (ii) higher levels of leaf pigments in both distilled water and blended water irrigations at the 100% level; (iii) a decrease in leaf water potential and leaf osmotic potential; and (iv) a decrease in calcium, magnesium, and potassium ion contents but an increase in chloride and sodium ions under distilled water irrigation. In conclusion, irrigation with blended water (50% + 50%) at the 100% and/or 75% levels can be recommended for open field-grown Zinnia ‘Solmar Yellow’ production to enhance host plant tolerance to saline water and decrease the high cost burden of water desalinization.

An ABA-flavonoid relationship contributes to the differences in drought resistance between different sea buckthorn subspecies.

Drought is the most severe abiotic stress and hinders the normal growth and development of plants. Sea buckthorn (Hippophae rhamnoides Linn.) is a typical drought-resistant tree species. In this study, the leaves of the H. rhamnoides ssp. sinensis ('FN') and H. rhamnoides ssp. mongolica ('XY') were selected during drought-recovery cycles for RNA sequencing, and physiological and biochemical analyses. The results revealed that drought stress significantly decreased leaf water potential, net photosynthetic rate and stomatal conductance in both sea buckthorn subspecies. Similarly, the contents of flavone, flavonol, isoflavone and flavanone significantly decreased under drought stress in 'XY'. Conversely, in 'FN', the flavone and abscisic acid (ABA) contents were significantly higher under drought stress and recovered after rehydration. Meanwhile, 4618 and 6100 differentially expressed genes (DEGs) were identified under drought stress in 'FN' and 'XY', respectively. In total, 5164 DEGs were observed in the comparison between 'FN' and 'XY' under drought stress. This was more than the 3821 and 3387 DEGs found when comparing the subspecies under control and rehydration conditions, respectively. These DEGs were mainly associated with carotenoid biosynthesis, flavonoid biosynthesis, photosynthesis and plant hormone signal transduction. Six hub DEGs (ABCG5, ABCG22, ABCG32, ABCG36, ABF2 and PYL4) were identified to respond to drought stress based on weighted gene co-expression network analysis and Basic Local Alignment Search Tool (BLAST) analysis using DroughtDB. These six DEGs were annotated to play roles in the ABA-dependent signaling pathway. Sixteen RNA sequencing results involving eight genes and similar expression patterns (12/16) were validated using quantitative real-time Polymerase Chain Reaction (PCR). The biochemical and molecular mechanisms underlying the regulation of drought responses by ABA and flavonoids in sea buckthorn were clarified. In this study, gene co-expression networks were constructed, and the results suggested that the mutual regulation of ABA and flavonoid signaling contributed to the difference in drought resistance between the different sea buckthorn subspecies.

Assessing suitability of Andrographis paniculata genotypes for rain-fed conditions in semi-arid climates

Medicinal plants are generally suggested for degraded land or areas having low rain-fall. Andrographis paniculata is an important medicinal plant known for its diterpene lactone i.e. andrographolide. We exposed 26 genotypes of A. paniculata to rain-fed condition during early-season rain-fed (ESRF) and mid-season rain-fed (MSRF) conditions and compared with the control to assess their suitability in semi-arid climate region of Gujarat, India. The study was performed during two consecutive years 2016–2017 in split plot design with rain-fed conditions as main-plot treatment and genotypes as sub-plot treatment in three replications. The gaseous exchange parameters taken at 85∼100 days after transplanting exhibited mean photosynthesis rate was 20.5 μmol CO2 m−2 s−1 ranging between 15.9 μmol CO2 m−2 s−1 and 24.0 μmol CO2 m−2 s−1. Exceeding 7% decrease in stomatal conductance was recorded compared to the control plants under imposed rain-fed condition. The mean value of transpiration rate was 4.8 mmol H2O m−2 s−1. The mean value of water use efficiency was 4.6. MSRF condition decreased leaf water potential from −0.517 to −1.189 Mpa. The dry herbage decreased by 29.2% due to MSRF condition as compared the control. The andrographolide yield per plant suffered significantly and under ESRF condition it reduced mainly due to reduction in andrographolide content. Reduced andrographolide yield per plant in MSRF condition was mainly due to reduction in herbage yield. Results revealed that ESRF and MSRF condition characterized by erratic rainfall pattern and dry spell is not beneficial for quality production in A. paniculata. Based on the least decrease in andrographolide, yield two genotypes viz., AP 6 and AP 12 identified to be suitable for ESRF condition and two genotypes viz., AP 19 and AP 6 suitable for MSRF condition. Overall, four genotypes, AP 35, AP 39, AP 61 and AP 24 were suitable as the promising genotypes having high andrographolide yield.

Responses of functional traits to seven-year nitrogen addition in two tree species: coordination of hydraulics, gas exchange and carbon reserves.

Atmospheric nitrogen (N) deposition has been observed to impact plant structure and functional traits in terrestrial ecosystems. Although the effect of N deposition on plant water use has been well-evaluated in laboratories and in experimental forests, the linkages between water and carbon relations under N deposition are unclear. Here, we report on hydraulics, gas exchange and carbon reserves of two broad-leaved tree species (Quercus mongolica and Fraxinus mandshurica) in mature temperate forests after a seven-year experiment with different levels of N addition (control (CK), low (23kgNha-1yr-1), medium (46kgNha-1yr-1) and high (69kgNha-1yr-1)). We investigated variation in hydraulic traits (xylem-specific hydraulic conductivity (Ks), native percentage loss of conductivity (PLC) and leaf water potential), xylem anatomy (vessel diameter and density), gas exchange (maximum net photosynthesis rate and stomatal conductance) and carbon reserves (soluble sugars, starch and total nonstructural carbohydrates (NSC)) with different N addition levels. We found that medium N addition significantly increased Ks and vessel diameter compared to control, but accompanied increasing PLC and decreasing leaf water potential, suggesting that N addition results in a greater hydraulic efficiency and higher risk of embolism. N addition promoted photosynthetic capacity via increasing foliar N concentration but did not change stomatal conductance. In addition, we found increase in foliar soluble sugar concentration and decrease in starch concentration with N addition, and positive correlations between hydraulic traits (vessel diameter and PLC) and soluble sugars. These coupled responses of tree hydraulics and carbon metabolism are consistent with a regulatory role of carbohydrates in maintaining hydraulic integrity. Our study provides an important insight into the relationship of plant water transport and carbon dynamics under increasing N deposition.

Salt Tolerance and Na Allocation in Sorghum bicolor under Variable Soil and Water Salinity.

Salinity is a major constraint for plant growth in world areas exposed to salinization. Sorghum bicolor (L.) Moench is a species that has received attention for biomass production in saline areas thanks to drought and salinity tolerance. To improve the knowledge in the mechanisms of salt tolerance and sodium allocation to plant organs, a pot experiment was set up. The experimental design combined three levels of soil salinity (0, 3, and 6 dS m−1) with three levels of water salinity (0, 2–4, and 4–8 dS m−1) and two water regimes: no salt leaching (No SL) and salt leaching (SL). This latter regime was carried out with the same three water salinity levels and resulted in average +81% water supply. High soil salinity associated with high water salinity (HSS-HWS) affected plant growth and final dry weight (DW) to a greater extent in No SL (−87% DW) than SL (−42% DW). Additionally, HSS-HWS determined a stronger decrease in leaf water potential and relative water content under No SL than SL. HSS-HWS with No SL resulted in a higher Na bioaccumulation from soil to plant and in translocation from roots to stem and, finally, leaves, which are the most sensitive organ. Higher water availability (SL), although determining higher salt input when associated with HWS, limited Na bioaccumulation, prevented Na translocation to leaves, and enhanced selective absorption of Ca vs. Na. At plant level, higher Na accumulation was associated with lower Ca and Mg accumulation, especially in No SL. This indicates altered ion homeostasis and cation unbalance.

Transcripts and ABA-dependent signaling in response to drought stress in Hippophae rhamnoides L

This study revealed the ABA-dependent signaling pathway and flavonoid synthesis pathway of sea buckthorn under drought conditions from plant physiology and gene expression levels. As climate changes and temperatures rise, sea buckthorn (Hippophae rhamnoides L.) is increasingly exposed to numerous challenges, particularly aridity. In this study, the leaves of sea buckthorn were harvested from plants in drought-recovery cycles and selected for RNA sequencing to uncover the underlying genetic basis of drought stress response through physiological and biochemical analyses. The results revealed that drought conditions significantly (p < 0.05) decreased leaf water potential, net photosynthetic rate, and stomatal conductance, Abscisic acid (ABA) and flavone content significantly (p < 0.05) increased under drought conditions and recovered after rehydration. Compared with the control and recovery irrigation conditions, respectively, 7734 and 7338 genes were differentially expressed under drought stress. Major differentially expressed genes involved in ABA-dependent signaling and flavonoid biosynthesis pathways were identified. Six hub genes of the co-expression network were blasted against the Drought Stress Gene Database and were found to have direct relationships with 25 genes there were related to cellular responses to stimuli. Five hub genes and seven drought transcription factors were validated by RT-qPCR. This study elucidated the molecular mechanism of the ABA-dependent signaling pathway that affects stomatal closure and flavonoid biosynthesis in antioxidant systems under drought conditions in sea buckthorn. The identified six hub genes will serve as a valuable resource and provide essential information for improving sea buckthorn tolerance to drought conditions.

Optimizing irrigation and determining the most sensitive development stage to drought in barley (Hordeum vulgare L.) in a semi-arid environment

Rising temperatures and increasing water scarcity, which are already important issues, are expected to intensify in the near future due to global warming. Optimizing irrigation in agriculture is a challenge. Understanding the response of crop development stages to water deficit stress provides an opportunity for optimizing irrigation. Here we studied the response of two barley varieties (Rihane, Martin), to water deficit stress at three development stages (tillering, stem elongation, and heading) by measuring water status and grain yield components in a field experiment in Tunisia. The three stages were selected due to their importance in crop growth and grain development. Water deficit stress was initiated by withholding water for 21 days at the three stages with subsequent re-watering. Water deficit led to a progressive decrease in leaf water potential. In both varieties, heading was the stage most sensitive to water deficit. Leaf water potential measurements indicated that water deficit stress was more severe during heading, which to some extent may have influenced the comparison between growth stages. During heading, the number of ears per plant and weight of a thousand grains were reduced by more than 70% and 50%, respectively compared with stress at tillering. Comparison of yield components showed differences between the two barley varieties only when the water deficit was produced during the tillering stage.

Single and combined effects of heat and water stress and recovery on cotton (Gossypium hirsutum L.) leaf physiology and sucrose metabolism

High temperatures and water-deficit stress limit cotton production around the world. Their individual effects on plant physiology and metabolism have been extensively studied, however, their combination has received considerably less attention. To that end, growth chamber experiments were conducted using cotton (Gossypium hirsutum L.) cultivar ST5288B2F and the objectives were to discern physiological and metabolic alterations after heat and water stress application (single or combined) and recovery, during cotton's vegetative stage. Under water stress conditions, leaf physiological parameters were suppressed and changes in carbohydrate levels, due to alterations in sucrose-metabolizing enzymes activities, were observed. Heat stress alone increased carbohydrate content, and activities of sucrose-degrading enzymes, while leaf physiology remained unaffected. The combined stress did exacerbate decreases in leaf water potential and soluble acid invertase activity, but the rest of the responses were similar to those of water stress. After stress alleviation, leaf physiological parameters of water-stressed plants did not manage to recover and substantial decreases were observed in leaf starch levels and activities of sucrose-cleaving enzymes, while the majority of parameters of heat-shocked plants returned to control levels. Recovery of the plants subjected to the combined stress was comparable to that of water-stressed plants, but significant differences were observed in carbohydrate levels and sucrose synthase activity. Our study demonstrated that under combined stress and post-stress conditions, water stress was the dominant factor affecting cotton leaf physiology and sucrose metabolism, highlighting however, the unique responses of some traits that could not be deduced from the additive effects of the single stresses.

Auxin and proline producing rhizobacteria mitigate salt-induced growth inhibition of barley plants by enhancing water and nutrient status

Although inoculation with plant growth-promoting rhizobacteria (PGPR) can improve crop salt tolerance, it is not always clear how these beneficial microbes affect plant ionic and water status. To investigate this phenomenon, three salt-tolerant bacteria were used to inoculate barley plants cultivated under salt stress. The bacterial strains Bacillus mojavensis S1, B. pumilus S2 and Pseudomonas fluorescens S3 showed an increase in IAA and proline production when cultivated on 100 and 200 mM NaCl supplemented medium. A salt-sensitive barley cultivar Rihane was grown at 0 and 100 mM of NaCl, with or without bacterial inoculation. Salt treatment decreased shoot dry weight of uninoculated plants by about 25%. In uninoculated plants, salinity decreased leaf water potential 0.8 MPa, increased roots and shoots Na+ concentrations by approximately 59% and 89% respectively and increased proline concentration. Bacterial inoculation with strains S1 and S3 prevented salt-induced reduction of shoot dry weights respectively by 54% and 46%, and root dry weights by almost 40%. These two bacterial strains enhanced stomatal conductance and CO2 assimilation of plants subjected or not to salt. Under saline conditions, all bacterial strains decreased root and shoot Na+ concentrations, improved leaf water potential and the strain S1 maintained it close to control values. Salinity stress was mainly alleviated in barley plants after inoculation with S1 and S3 strains, having respectively high proline and IAA productions under 200 mM of NaCl, which contribute to the alleviation of salt stress and stimulate root development, enhancing water and nutrient uptake by plants. Future prospects of the PGP potential of halotolerant bacterial species will extend their application in agriculture.

Partial root zone drying irrigation, planting methods and nitrogen fertilization influence on physiologic and agronomic parameters of winter wheat

The effectiveness of water-saving irrigation strategies such as partial root zone drying (PRD) should be explored to ensure food security as the availability of water for irrigation declines and population increases. PRD is easily performed by localized irrigation method; however very small percentage of irrigated area is under this irrigation method and main irrigation method is furrow irrigation that should be adapted to PRD. In this respect, present study was conducted to explore the effects of PRD in furrow irrigation strategies on physiological and agronomic behavior of winter wheat. The field experiment included two irrigation strategies (variable alternate furrow irrigation (VAFI) as PRD and ordinary furrow irrigation (OFI), two different planting method (in-furrow planting and on-ridge planting) and three nitrogen rates (0, 150, and 300 kg N ha−1) over 2015–2016 and 2016–2017. Results showed that decreasing leaf water potential (LWP) during the stem elongation stage resulted in increasing the sensitivity of winter wheat to water stress and yield reduction. The leaf photosynthesis rate (An) was not significantly lowered in VAFI (PRD) in comparison with that obtained in OFI. The VAFI strategy reduced the stomatal conductance (gs) about 12% and 7% in comparison with that obtained in OFI in the first and second year, respectively that were statistically significant. The lower slope of linear relationship between leaf transpiration efficiency (An/Tr) and vapor pressure deficit (VPD) in VAFI strategy indicated that with increasing VPD, leaf transpiration efficiency was higher than that obtained in OFI. As a consequence, VAFI strategy as PRD was effective in increasing An/Tr and can be an alternative irrigation management in winter wheat farms with limited water supplies. Although, in-furrow planting showed higher efficiency in increasing yield in comparison with that obtained in on-ridge planting, on-ridge planting showed higher effects on leaf transpiration efficiency. Furthermore, there was no significant difference between two application rates of nitrogen (150 kg N ha−1 and 300 kg N ha−1) for different parameters; therefore, application of 150 kg N ha−1 can be suggested as an effective rate to increase winter wheat yield. Consequently, in areas with scarce water and furrow irrigation, combination of VAFI, in-furrow planting and 150 kg N ha−1 is recommended to achieve optimum yield with possibility of saving water during the winter wheat growing season.

Drought tolerance in cork oak is associated with low leaf stomatal and hydraulic conductances

Abstract: To investigate the role of seeds origin in drought tolerance, the response to water deprivation of cork oak seedlings differing in climatic conditions at their geographical origin was compared. Gafour is the provenance from the driest site and Feija is the provenance from the wettest site. Net photosynthesis (An), stomatal conductance (gs) and leaf water potential were measured during dehydration. A delayed decrease in leaf water potential is observed after water withholding in Gafour as compared to Feija leaves. At the onset of dehydration, An and gs were higher in Feija. After withholding watering, Gafour leaves were able to maintain a higher An and gs than Feija leaves. Most likely, drought tolerance in Gafour leaves is associated to their lower gs under well-hydrated conditions. The stomatal density (Ds) and specific leaf area (SLA) were not different in well-watered leaves but, leaf hydraulic conductance was lower in Gafour leaves when compared to Feija leaves. Our results suggested that lower stomatal and hydraulic conductances of Gafour leaves could be involved in bringing about the better resistance to dehydration.

Postinvasive Bacterial Resistance Conferred by Open Stomata in Rice.

Stomata are leaf pores that regulate gas exchange and water transpiration in response to environmental cues. They also function in innate immunity by limiting pathogen entry through actively closing in so-called stomatal defense. However, roles of stomata in plant disease resistance are not fully elucidated, especially in monocots. Here, we report that non-race specific resistance of the rice abscisic acid-deficient mutant Osaba1 to Xanthomonas oryzae pv. oryzae is due to increased stomatal conductance. Reducing stomatal conductance in the Osaba1 mutant increases its susceptibility to X. oryzae pv. oryzae. Artificial opening of stomata in wild-type plants leads to enhanced resistance to X. oryzae pv. oryzae. The rice mutant es1-1 with constitutively higher stomatal conductance exhibits strong resistance to X. oryzae pv. oryzae. Additionally, Osaba1 and es1-1 are resistant to X. oryzae pv. oryzicola. The data support that open stomata confer postinvasive resistance against bacterial pathogens in rice, and such resistance probably results from decreased leaf water potential. Our findings reveal a novel role of stomata in plant immunity through modulation of leaf water status, which provides physiological insight into the interactions between plant, pathogen, and environment.

Mycorrhizal inoculation on compost substrate affects nutritional balance, water uptake and photosynthetic efficiency in Cistus albidus plants submitted to water stress

The use of composted manure as alternative substrate can be suitable to produce ornamental potted plants. However, under water stress this substrate can result an additional stress for plants due to its physicochemical properties. In these conditions, mycorrhizae application can improve water and nutrients efficiency. The experiment was carried out in a growth chamber with a first phase (I) in which both inoculated and non-inoculated Cistus albidus L. plants at two substrates (commercial and mixtures of composted manure) were well irrigated and a second phase (II) in which the plants were submitted to water stress. Glomus iranicum (Blaszk., Kovacs & Balazs) var. tenuihypharum sp. nova was well established in cistus roots, but water stress hindered mycorrhizal proliferation in compost, which resulted in plants with smaller leaf and root biomass. The plants in compost had the highest Cl, K, Na, P and Zn contents in leaf; mycorrhizae reduced the Na and increased phosphorus, especially when the substrate was well-watered. Water stress decreased leaf water potential (Ψl), and mycorrhizae induced higher Ψl values in both substrates. Compost induced leaf osmotic adjustment, lower gas exchange and photochemical quenching parameters (Fv/Fm, Y(II)) values. Mycorrhizal plants had higher Y(II) and qP values than non-inoculated plants. Compost decreased relative chlorophyll content in both phases, but in inoculated plants these values increased under water stress. C. albidus plants growing in compost maintain a good nutritional balance and efficient osmotic regulation. Under water stress, plants suffer more stress than plants in commercial substrate, as reflected by the lipid peroxidation and Pn values.

Hydraulic conductivity in stem of young plants of Jatropha curcas L. cultivated under irrigated or water deficit conditions

Jatropha curcas L. can survive situations of water deficiency, in which carbon assimilation and growth rates are severely affected, which can ultimately result in low productivity. With the objective of evaluating the hydraulic conductivity of stem xylem and its relationship with leaf gas exchange under water deficiency, two-month old plants of ten genotypes of J. curcas from an improved population were cultivated under water restriction (soil water content of 14%) or under full irrigation (soil water content of 22%) for 60 days. Water deficit led to significant increase of leaf area-specific hydraulic conductivity (LSCn) in genotype CNPAE 517 and decrease in CNPAE 556, 557, 559, 569 and 570. Of those five genotypes, only in CNPAE 556 there was no decrease of leaf water potential measured around 4 h. Genotypes CNPAE 516, 517 and 520 can be highlighted, where elevated rate of net photosynthesis were observed even under water restriction. Changes in the anatomy of the xylem vessels, as well as in root biomass when submitted to water deficiency favored a greater or lesser drought tolerance of the genotypes when the native or potential hydraulic conductivity were analyzed. In summary, high plasticity for hydraulic and anatomical traits, as observed for the genotypes CNPAE 516, 517 and 520 must be considered for further investigation on the tradeoffs between hydraulic conductivity and productivity, in the search for genetic material suitable for cultivation in areas subject to short periods of soil water deficit.

Effect of Salinity Stress on the Morphology and Physiology of Five Different Coleus Species

Introduction Salinity stress is one of the most deleterious abiotic stress factors that affect the growth, productivity and physiology of plants. Salinity imposes negative effect on the plant growth by decreasing leaf water potential, inducing morphological and physiological changes, production o

Exogenous proline improves osmoregulation, physiological functions, essential oil, and seed yield of fennel

Proline is an amino acid with pivotal role in plant responses to environmental constraints. Effects of its foliar application (20mM) on physiological functions of 12 fennel (Foeniculum vulgare Mill.) genotypes at the presence of different moisture conditions (non-stress control and drought stress) was studied in a 2-year field study. Drought led to notable increases in mean leaf polyphenol, proline and total soluble carbohydrates and essential oil concentrations, despite decreases in carotenoids and chlorophyll concentrations, leaf water potential, relative water content, plant above-ground dry mass and water use efficiency. Exogenous proline resulted in significant increases in mean carotenoids, polyphenol, chlorophyll, proline, total soluble carbohydrates and essential oil concentrations and relative water content, but it caused a decrease in leaf water potential. Proline amendment positively affected plant water relations, due mostly to enhancement in osmoregulation, as certain genotypes with greater mean leaf proline concentration and relative water content appeared to produce greater above-ground dry mass, when exposed to the external proline. Ameliorative effects of exogenous proline tended to be greater in drought-stressed plants, as it led to the enhancement of chlorophyll concentration and relative water content of fennel in drought conditions. Genotypes Urmia and Yazd were found to be able to withstand better against drought and benefit more from external proline. Our findings suggest that while indigenous proline is the most sensitive osmoticum in fennel’s response to drought, its external amendment may bring about improvements in water relations and osmoregulatory measure in this medicinal plant.

Physiological behavior of cassava plants (Manihot esculenta Crantz) in response to infection by Xanthomonas axonopodis pv. manihotis under greenhouse conditions

Cassava is one of the main sources of energy for human populations in tropical countries. Cassava production can be severely reduced by diseases, such as the vascular bacteriosis (bacterial blight) caused by Xanthomonas axonopodis pv. manihotis (Xam). In this study, the physiological behavior of plants from two cassava varieties, one resistant and one susceptible to infection by the Xam CIO151 strain was evaluated. The plants of the susceptible variety presented increased stomatal resistance, decreased leaf water potential and increased proline content compared with the resistant variety. On the other hand, the inoculated plants from the two varieties showed an increased accumulation of total sugars starting at 7 days post-inoculation compared with the non-inoculated plants.

Stomatal conductance increases with rising temperature

ABSTRACTStomatal conductance directly modifies plant water relations and photosynthesis. Many environmental factors affecting the stomatal conductance have been intensively studied but temperature has been largely neglected, even though it is one of the fastest changing environmental variables and it is rising due to climate change. In this study, we describe how stomata open when the temperature increases. Stomatal conductance increased by ca 40% in a broadleaf and a coniferous species, poplar (Populus deltoides x nigra) and loblolly pine (Pinus taeda) when temperature was increased by 10 °C, from 30 °C to 40 °C at a constant vapor pressure deficit of 1 kPa. The mechanism of regulating stomatal conductance by temperature was, at least partly, independent of other known mechanisms linked to water status and carbon metabolism. Stomatal conductance increased with rising temperature despite the decrease in leaf water potential, increase in transpiration, increase in intercellular CO2 concentration and was decoupled from photosynthesis. Increase in xylem and mesophyll hydraulic conductance coming from lower water viscosity may to some degree explain temperature dependent opening of stomata. The direct stomatal response to temperature allows plants to benefit from increased evaporative cooling during the heat waves and from lower stomatal limitations to photosynthesis but they may be jeopardized by faster depletion of soil water.

Effects of rainfall exclusion on leaf gas exchange traits and osmotic adjustment in mature canopy trees of Dryobalanops aromatica (Dipterocarpaceae) in a Malaysian tropical rain forest.

Climate change exposes vegetation to unusual levels of drought, risking a decline in productivity and an increase in mortality. It still remains unclear how trees and forests respond to such unusual drought, particularly Southeast Asian tropical rain forests. To understand leaf ecophysiological responses of tropical rain forest trees to soil drying, a rainfall exclusion experiment was conducted on mature canopy trees of Dryobalanops aromatica Gaertn.f. (Dipterocarpaceae) for 4 months in an aseasonal tropical rain forest in Sarawak, Malaysia. The rainfall was intercepted by using a soft vinyl chloride sheet. We compared the three control and three treatment trees with respect to leaf water use at the top of the crown, including stomatal conductance (gsmax), photosynthesis (Amax), leaf water potential (predawn: Ψpre; midday: Ψmid), leaf water potential at turgor loss point (πtlp), osmotic potential at full turgor (π100) and a bulk modulus of elasticity (ε). Measurements were taken using tree-tower and canopy-crane systems. During the experiment, the treatment trees suffered drought stress without evidence of canopy dieback in comparison with the control trees; e.g., Ψpre and Ψmid decreased with soil drying. Minimum values of Ψmid in the treatment trees decreased during the experiment, and were lower than πtlp in the control trees. However, the treatment trees also decreased their πtlp by osmotic adjustment, and the values were lower than the minimum values of their Ψmid. In addition, the treatment trees maintained gs and Amax especially in the morning, though at midday, values decreased to half those of the control trees. Decreasing leaf water potential by osmotic adjustment to maintain gs and Amax under soil drying in treatment trees was considered to represent anisohydric behavior. These results suggest that D. aromatica may have high leaf adaptability to drought by regulating leaf water consumption and maintaining turgor pressure to improve its leaf water relations.