Reduction In Osmotic Potential Research Articles

Effects of excessive nitrogen fertilizer and soil moisture deficiency on antioxidant enzyme system and osmotic adjustment in tomato seedlings

Long-term excessive application of nitrogen fertilizer induces secondary salinization of soil, which results in inhibiting plant growth. In addition, soil moisture deficiency also affects plant growth. To investigate the effects of excessive nitrogen fertilizer and soil moisture deficiency on the antioxidant enzyme system, plant water relations were analyzed through pressure-volume (P-V) curve, and photosynthetic light response parameters in tomato (Solanum lycopersicum L. Myoko) seedlings, an indoor experiment about 50 d was conducted using two irrigation water amounts based on field capacity (soil moisture deficiency: 50%-80%; adequate water: 70%-80%), two nitrogen fertilizer rates (moderate nitrogen; excessive nitrogen fertilizer: 0.585 g/pot) and two types of irrigation water (tap water and microbial diluent). The results showed that excessive nitrogen fertilizer (N) and soil moisture deficiency (W) reduced the biomass of tomato seedlings. In comparison to CK (combination of adequate water and tap water quality), microbial dilution (EM) increased plant biomass by 5.2%. Also, the nitrogen application increased chlorophyll relative contents (SPAD). The maximum net photosynthetic rate (Pc) decreased with nitrogen application and increased with EM application and irrigation amount. Excessive nitrogen application increased the plant nitrate reductase activity (NR). The plant NR in the N treatment showed a 13.0% increase compared to CK, and the plant NR in the treatment of nitrogen application with water deficiency (WN) increased 34.0% compared to water deficiency (W). After applying excessive nitrogen, N, EM-N, WN, EM-WN respectively increased the plant nitrate reductase activity by 13.0%, 22.9%, 34.0% and 28.6%, compared with the corresponding treatment with moderate nitrogen (i.e., CK, EM, W and EM-W). In addition, the activities of antioxidant enzymes [superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT)] in four treatments of nitrogen application (N, EM-N, WN, EM-WN) also increased significantly. Both soil moisture and nitrogen fertilizer significantly affect the parameters of osmotic adjustment, which is manifested in the reduction of osmotic potential (πFT), and the increase in the osmotic concentration (Cosm) and concentration difference (ΔCosm). But the decrease in the relative water content of apoplast (ζap), indicating that water deficiency and excessive nitrogen reduced the water absorption and water retention capacity of tomatoes to a certain extent. In conclusion, excessive nitrogen application and soil moisture deficiency inhibit plant growth significantly in this experiment. Meanwhile, microbial dilution can alleviate excessive nitrogen fertilizer and water stress to some extent, but the effect was not significant. Keywords: antioxidant enzyme, nitrogen, osmotic adjustment, pressure-volume curve, stress, tomato, water DOI: 10.25165/j.ijabe.20221502.5555 Citation: Zhang Y J, Yu S E, Li Z J, Chang T T, Xu Q C, Xu H L, et al. Effects of excessive nitrogen fertilizer and soil moisture deficiency on antioxidant enzyme system and osmotic adjustment in tomato seedlings. Int J Agric & Biol Eng, 2022; 15(2): 127–134.

γ-Aminobutyric Acid (GABA) Priming Improves Seed Germination and Seedling Stress Tolerance Associated With Enhanced Antioxidant Metabolism, DREB Expression, and Dehydrin Accumulation in White Clover Under Water Stress.

As an important plant growth regulator, the role of γ-aminobutyric acid (GABA) in regulating seeds germination was less well elucidated under water stress. The present study was conducted to investigate the impact of GABA pretreatment on seeds germination of white clover (Trifolium repens) under water deficient condition. Results demonstrated that seeds pretreated with 2μmol/l GABA significantly alleviated decreases in endogenous GABA content, germination percentage, germination potential, germination index, root length, and fresh weight along with marked reduction in mean germination time after 7days of germination under drought stress. In addition, seeds priming with GABA significantly increased the accumulation of soluble sugars, non-enzymatic antioxidants [reduced ascorbate, dehydroascorbic acid, oxidized glutathione (GSSG), and reduced glutathione (GSH)], and enzymes [superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR), glutathioe reductase, and monodehydroasorbate reductase (MDHR)] activities involved in antioxidant metabolism, which could be associated with significant reduction in osmotic potential and the accumulation of superoxide anion, hydrogen peroxide, electrical leakage, and malondialdehyde in seeds under drought stress. The GABA-pretreated seeds exhibited significantly higher abundance of dehydrin (DHN, 56 KDa) and expression levels of DHNs encoding genes (SK2, Y2K, Y2SK, and Dehydrin b) and transcription factors (DREB2, DREB3, DREB4, and DREB5) than the untreated seeds during germination under water-limited condition. These results indicated that the GABA regulated improvement in seeds germination associated with enhancement in osmotic adjustment, antioxidant metabolism, and DREB-related DHNs expression. Current study will provide a better insight about the GABA-regulated defense mechanism during seeds germination under water-limited condition.

Transcriptome analysis of upland cotton revealed novel pathways to scavenge reactive oxygen species (ROS) responding to Na2SO4 tolerance

Salinity is an extensive and adverse environmental stress to crop plants across the globe, and a major abiotic constraint responsible for limited crop production threatening the crop security. Soil salinization is a widespread problem across the globe, threatening the crop production and food security. Salinity impairs plant growth and development via reduction in osmotic potential, cytotoxicity due to excessive uptake of ions such as sodium (Na+) and chloride (Cl−), and nutritional imbalance. Cotton, being the most cultivated crop on saline-alkaline soils, it is of great importance to elucidate the mechanisms involved in Na2SO4 tolerance which is still lacking in upland cotton. Zhong 9835, a Na2SO4 resistant cultivar was screened for transcriptomic studies through various levels of Na2SO4 treatments, which results into identification of 3329 differentially expressed genes (DEGs) in roots, stems and leave at 300 mM Na2SO4 stress till 12 h in compared to control. According to gene functional annotation analysis, genes involved in reactive oxygen species (ROS) scavenging system including osmotic stress and ion toxicity were significantly up-regulated, especially GST (glutathione transferase). In addition, analysis for sulfur metabolism, results in to identification of two rate limiting enzymes [APR (Gh_D05G1637) and OASTL (Gh_A13G0863)] during synthesis of GSH from SO42−. Furthermore, we also observed a crosstalk of the hormones and TFs (transcription factors) enriched in hormone signal transduction pathway. Genes related to IAA exceeds the rest of hormones followed by ubiquitin related genes which are greater than TFs. The analysis of the expression profiles of diverse tissues under Na2SO4 stress and identification of relevant key hub genes in a network crosstalk will provide a strong foundation and valuable clues for genetic improvements of cotton in response to various salt stresses.

Over-expression of the Zea mays phytoglobin (ZmPgb1.1) alleviates the effect of water stress through shoot-specific mechanisms

Water deficit limits plant growth and development by interfering with several physiological and molecular processes both in root and shoot tissues. Through their ability to scavenge nitric oxide (NO), phytoglobins (Pgbs) exercise a protective role during several conditions of stress. While their action has been mainly documented in roots, it is unclear whether Pgb exercises a specific and direct role in shoot tissue. We used a Zea mays root-less system to assess how over-expression or down-regulation of ZmPgb1.1 influences the behavior of shoots exposed to polyethylene glycol (PEG)-simulated water deficit. Relative to their WT and ZmPgb1.1 down-regulating counterparts, PEG-treated shoots over-expressing ZmPgb1.1 exhibited a reduced accumulation of ROS and lipid peroxidation. These effects were ascribed to lower transcript levels of Respiratory Burst Oxidase Homolog (RBOH) genes encoding the ROS generating enzyme complex NADPH oxidase, and a more active antioxidant system. Furthermore, over-expression of ZmPgb1.1 attenuated the reduction in osmotic potential and relative water content experienced during water stress, an observation also demonstrated at a whole plant level, possibly through the retention of the expression of three aquaporins involved in water transfer and implicated in drought tolerance. Pharmacological treatments modulating NO and ethylene levels revealed that the ZmPgb1.1 action was mediated by ethylene synthesis and response, with NO acting as an upstream intermediate. Collectively we provide substantial evidence that ZmPgb1.1 exercises a direct role in shoot tissue, independent from that previously reported in roots, which confers tolerance to water stress.

Quantification of Germination Response of Millet (Panicum miliaceum L.) Seeds to Water Potential and Priming using Hydrotime Model

Abstract Seed germination is a complex biological process that is influenced by different environmental physical factors including temperature, water potential, salinity, pH and light, as well as intrinsic genetic factors. In such environments, the water needed for germination is available for only a short time, and consequently, successful crop establishment depends not only on rapid and uniform germination of the seedlot, but also on its ability to germinate under low water availability. All of these attributes can be analyzed through the hydrotime model (HT). Millet (Panicum miliaceum L.) is cultivated in arid and semi-arid regions of Iran. Therefore, in this study, using the hydrotime modeling approach, germination response of millet to priming (water and gibberellin 50 ppm at 15°C for 24 h) and water potential (0, -0.3, -0.6, -0.9, and -1.2 Mpa) was studied. Hydrotime (HT) model were fitted to cumulative germination of seeds and recorded in germination tests carried out at different water potentials (0, -0.3, -0.6, -0.9 and -1.2 MPa) and priming treatments (control, hydropriming and hormone priming). Results showed that, germination of millet decreased significantly with reduction of osmotic potential. Results indicated that the hydro-time constant (θH) for control, hydro-priming and hormone priming were 0.89, 0.79 and 0.67 MPa d, the water potential (Ψb(50)) for control, hydropriming and hormone priming were -0.89, -0.94 and -1.11 MPa, respectively. Results indicated that the use of hydrotime model in germination prediction could be useful to provide more accurate estimates for the timing of sowing and management of millet.

Black Medic (Medicago lupulina) Germination Response to Temperature and Osmotic Potential, and a Novel Growing Degree-Day Accounting Restriction for Heat-Limited Germination

AbstractBlack medic (Medicago lupulinaL.) is a problem weed species in Florida strawberry [Fragaria×ananassa(Weston) Duchesne ex Rozier (pro sp.) [chiloensis×virginiana]] production. It competes with the crop and hinders harvest efficiency. A reductionist approach is being undertaken to predictM. lupulinafield emergence to coordinate control tactics. Germination is the first model component to be developed. The objectives were to study the effect of osmotic potential and temperature on seed germination and to develop the germination component for reductionist emergence modeling. Trials were initiated using petri dishes in incubators to testM. lupulinagermination in response to osmotic potential (0 to −1 MPa) and constant (5 to 40 C) and fluctuating temperatures (35/25, 35/20, 25/15, and 25/10 C, 12/12-h duration).Medicago lupulinagerminated between 5 and 35 C. Optimal germination was between 10 and 20 C. Germination was negatively impacted by temperatures above the optimum. Fluctuating temperatures did not influence germination compared with constant temperatures. A reduction in osmotic potential from 0 to −0.25 MPa reduced germination from 43% to 14%. Three temperature-mediated germination trends were identified: standard increases and plateau up to 20 C, reduced germination between 20 and 35 C, and no germination at 40 C. A novel restriction to daily growing degree-day (GDD) accounting was developed for heat-limited germination. The germination restriction accounted for the optimum and maximum temperature, diminishing returns of exposure to higher temperatures, and the negative impact of higher temperatures above the optimum range. Determination logic and the new daily GDD accounting formula aligned GDD accumulation across all temperatures to be described by a Weibull formula (R2= 0.5199). Results establish the germination component for reductionist emergence modeling, but further study is required to account for dormancy and PRE growth.

Effects of temperature and water limitation on the germination of Stipagrostis ciliata seeds collected from Sidi Bouzid Governorate in Central Tunisia

Most ecological studies in North Africa reveal a process of continuous degradation of rangeland ecosystems as a result of overgrazing. This degradation appears across the decreasing of perennial grass diversity. Indeed, the majority of steppe ecosystems are characterized by a low density of perennial grass species at present. This study evaluated the effects of temperature and water limitation on the seed germination of Stipagrostis ciliata (Desf.) de Winter, a perennial grass species. The seeds were collected from the Bou Hedma Park, Sidi Bouzid Governorate, Central Tunisia. The thermal time and hydrothermal time models were used to describe the seed germination of S. ciliata under different water potentials and temperatures. The germination response of S. ciliata seeds in darkness was evaluated over a range of temperatures (15°C, 20°C, 25°C, 30°C and 35°C) and across a wide range of osmotic potentials (0.0,–0.2,–0.6,–1.2,–1.6 and –2.0 MPa) of the polyethylene glycol (PEG6000) solutions at each temperature level. Among the tested temperatures, 25°C was found to be the optimal temperature to the germination of S. ciliata seeds. The final germination percentage (75.2%) was obtained with distilled water. The progressive decrease of osmotic potential of the PEG6000 solutions inhibited the seed germination. However, the number of days to first germination was increased with a reduction of osmotic potential. A significant positive relationship was identified between final germination percentage of S. ciliata seeds and osmotic potential of the PEG6000 solutions, with R2 ranging from 0.5678 to 0.8761. Furthermore, a high degree of congruency between predicted and observed germination time course curves was observed. In general, S. ciliata exhibits a significant adaptation capacity for water limitation and high temperature in arid ecosystems.

Manipulating rainfall to study symptom expression of <i>Botrytis cinerea</i> infection in wine grapes

Manipulating rainfall to study symptom expression of <i>Botrytis cinerea</i> infection in wine grapes

Predicting Seed Germination of Safflower (Carthamus Tinctorius) Cultivars Using Hydrotime Model

Abstract Safflower (Carthamus tinctorius) is a highly branched, herbaceous, thistle-like annual plant. It is commercially cultivated for vegetable oil extracted from the seeds, which is cultivated under arid environments. In such environments, the water needed for germination is available for only a short time and, consequently, successful crop establishment depends not only on rapid and uniform germination of the seedlot, but also on its ability to germinate under low water availability. All of these attributes can be analyzed through the hydrotime model (HT). Safflower seeds were germinated in various polyethylene glycol (PEG 600) solutions to obtain water potentials of 0, -0.2, -0.4, -0.6, and -0.8 Mpa. Results indicated that germination of safflower cultivars decreased significantly with reduction of osmotic potential. The highest germination percentage for Sina (93.06 and 94.02%), Faraman (93.52 and 95.33%), Talaei (94.98 and 93.98%) and Kouseh (93.58 and 95.55%) cultivars were attained from distilled water (0 MPa) and -0.2 MPa, respectively. The hydrotime constant (θH) for Sina, Faraman, Talaei and Kouseh cultivars were 0.93, 0.84, 0.78 and 0.72 MPa d, and the water potential (Ψb(50)) for Sina, Faraman, Talaei and Kouseh cultivars were -0.56, -0.67, -0.64 and -0.77 MPa, respectively. Cumulative germination of safflower seed was higher in Kouseh cultivar, than in Sina, Faraman and Talaei cultivars. Results showed that, hydrotime model is suited to predicting seed germination of safflower seeds. In addition, the information gathered with this work allows us to build mathematical models to predict germination of safflower cultivars in the field under various environments.

Na+ Retention in the Root is a Key Adaptive Mechanism to Low and High Salinity in the Glycophyte, Talinum paniculatum (Jacq.) Gaertn. (Portulacaceae)

AbstractTalinum paniculatum is an important leafy vegetable and medicinal plant, used in many parts of South America, Africa and Asia. Its adaptation to abiotic stress has received little attention and therefore worthy of interest, especially as environmental conditions are rendering arable lands increasingly unfavourable for agriculture. Therefore, this study was undertaken to examine the influence of salt stress on the vegetative growth of the plant by subjecting seedlings to 0, 25, 50, 100, 200 and 300 mm NaCl stress for 10 days. The dry weight, ion concentrations, relative water content, oxidative damage, proline, osmotic potential and some antioxidants were determined. The plants were found to retain Na+ mainly in the root, with less affected leaf K+ concentration, and consequently very low shoot Na+/K+ ratios (<0.2) under all the stress treatments. The proline content significantly increased under the 100–300 mm treatments (18‐ to 244‐fold), with a corresponding significant reduction in osmotic potential and hence high osmotic adjustment. The antioxidant enzyme activities and non‐enzyme antioxidants showed significant increase only under the highest salinity. Taken together, these results suggest that shoot Na+ exclusion is characteristic of this plant and is mainly responsible for its adaptation to low salinity.

Estresse osmótico na germinação de sementes de Petiveria alliacea L.

RESUMOO trabalho teve como objetivo verificar os efeitos dos estresses hídrico e salino na germinação de sementes de Petiveria alliacea , bem como definir os limites máximos de tolerância da espécie a esses estresses. As sementes foram submetidas aos agentes osmóticos NaCl, CaCl2 e PEG nos potenciais à 0; -0,1; -0,2; -0,3; -0,4; -0,5; -0,6; -0,7; -0,8; -0,9 e -1,0 MPa sob temperatura constante de 25˚C e fotoperíodo de 12 horas, com avaliações diárias durante 30 dias. As variáveis analisadas foram porcentagem de germinação, índice de velocidade de germinação, tempo médio de germinação, índice de sincronização e frequência relativa da germinação. As sementes de P. alliacea sob estresse osmótico apresentam menor porcentagem e velocidade de germinação com a redução dos potencias osmóticos, principalmente com CaCl2. Em potenciais osmóticos mais negativos que -0,4; -0,5 e -0,7 MPa, respectivamente nos agentes CaCl2, NaCl, e PEG, não ocorre germinação. O padrão de distribuição da frequência relativa aumentou a polimodalidade, o tempo médio de germinação e o índice de sincronização da germinação com a redução dos potencias osmóticos.

Estresse hídrico e salino em sementes de soja classificadas em diferentes tamanhos

RESUMO A importância do tamanho das sementes tem sido relatada para várias espécies, visto que pode afetar a sua germinação e o vigor das plântulas, principalmente sob condições de estresse. Objetivou-se avaliar o efeito do tamanho das sementes na germinação e crescimento inicial de plântulas de soja (cultivares M9144RR e M8527RR), sob condições de estresse hídrico e salino. O estresse hídrico foi induzido por manitol e o salino por cloreto de sódio. Para a avaliação do efeito dos tratamentos, as sementes foram submetidas ao teste de germinação, primeira contagem de germinação e crescimento de plântulas. Utilizou-se delineamento inteiramente casualizado, com quatro repetições. Houve redução na germinação e no vigor das sementes de soja com a diminuição do potencial osmótico. Não foi observado efeito do tamanho das sementes sobre a germinação e comprimento das plântulas, porém, as sementes de maior tamanho resultaram em plântulas com maior massa seca, mesmo quando submetidas a condições de estresse hídrico e salino.

Tolerance of Mediterranean seagrasses (Posidonia oceanica and Cymodocea nodosa) to hypersaline stress: water relations and osmolyte concentrations

The present study examines for the first time the effects of increased salinity on water relations and osmolyte (carbohydrates and amino acids) concentrations in two Mediterranean seagrass species, Posidonia oceanica and Cymodocea nodosa, which are adapted to growth in environments with contrasting salinity and have a known differential sensitivity to alterations in ambient salinity. The specific aim was to obtain insights into their respective capacities to cope with natural or anthropogenically induced (e.g. desalination plants) hypersaline stress and its ecological implications. To this end, large plant fragments of both seagrass species were maintained for 47 days in a laboratory mesocosm system under ambient salinity (37 psu; control) and three chronic hypersaline conditions (39, 41 and 43 psu). Analyses of leaf-tissue osmolality indicated that both species followed a dehydration avoidance strategy, decreasing their leaf water potential (Ψw) as the external salinity increased, but using different physiological mechanisms: whereas P. oceanica leaves exhibited a reduction in osmotic potential (Ψπ), C. nodosa leaves maintained osmotic stability through a decrease in turgor pressure (Ψp) probably mediated through cell-hardening processes. Accordingly, the concentrations of soluble sugars and some amino acids (mainly Pro and Gly) suggested the activation of osmoregulatory processes in P. oceanica leaves, but not in C. nodosa leaves. Osmotic adjustments probably interfered with leaf growth and shoot survival of P. oceanica under hypersaline stress, whereas C. nodosa showed a more efficient physiological capacity to maintain plant performance under the same experimental conditions. These results are consistent with the more euryhaline ecological behaviour of C. nodosa and contribute to understanding the high vulnerability shown by P. oceanica to even mild increments in seawater salinity.

Metabolome and water homeostasis analysis of Thellungiella salsuginea suggests that dehydration tolerance is a key response to osmotic stress in this halophyte

Thellungiella salsuginea, a Brassicaceae species closely related to Arabidopsis thaliana, is tolerant to high salinity. The two species were compared under conditions of osmotic stress to assess the relationships between stress tolerance, the metabolome, water homeostasis and growth performance. A broad range of metabolites were analysed by metabolic fingerprinting and profiling, and the results showed that, despite a few notable differences in raffinose and secondary metabolites, the same metabolic pathways were regulated by salt stress in both species. The main difference was quantitative: Thellungiella had much higher levels of most metabolites than Arabidopsis whatever the treatment. Comprehensive quantification of organic and mineral solutes showed a relative stability of the total solute content regardless of the species or treatment, meaning that little or no osmotic adjustment occurred under stress. The reduction in osmotic potential observed in plants under stress was found to result from a passive loss of water. Thellungiella shoots contain less water than Arabidopsis shoots, and have the ability to lose more water, which could contribute to maintain a water potential gradient between soil and plant. Significant differences between Thellungiella and Arabidopsis were also observed in terms of the physicochemical properties of their metabolomes, such as water solubility and polarity. On the whole, the Thellungiella metabolome appears to be more compatible with dehydration. Osmotic stress was also found to impact the metabolome properties in both species, increasing the overall polarity. Together, the results suggest that Thellungiella copes with osmotic stress by tolerating dehydration, with its metabolic configuration lending itself to osmoprotective strategies rather than osmo-adjustment.

Root Osmotic Adjustment under Osmotic Stress in Maize Seedlings 1. Transient Change of Growth and Water Relations in Roots in Response to Osmotic Stress

The transient changes in seminal root elongation rate, osmotic potential, water potential, and turgor pressure in maize after the onset of stress treatments were examined using polyethylene glycol 6000 to evaluate the process of osmotic adjustment in root. Maize seedlings were exposed to different intensities of osmotic stress for 1, 3, 5, 10, and 20 minutes, and 2, 6, 12, and 24 hours. Seminal roots shrunk immediately after the onset of the −0.41 and −0.89 MPa stress treatments, due to dehydration. However, roots gradually resumed elongation from 5 minutes after the onset of the stress treatment. The osmotic potential in the root elongating zone dropped drastically with the onset of stress followed by a gradual decrease for 6 hours. We quantitatively analyzed the relative importance of the factors that contributed to the reduction of osmotic potential, and found that 46% reduction of osmotic potential was caused by tissue dehydration and 54% by solute accumulation 20 minutes after start of −0.89 MPa treatment. At hour 12, however, only 7% reduction of osmotic potential was caused by tissue dehydration and 93% by solute accumulation. In the root elongating zone, turgor pressure decreased immediately after the onset of the stress treatment due to the larger decline of water potential than that of the osmotic potential. However, from minute 20 onwards, turgor pressure started to recover due to osmotic adjustment. These results indicated that osmotic adjustment develops immediately after exposure to osmotic stress, especially in the root elongating zone, and substantially contributed to the maintenance of turgor pressure and root growth.

Water stress affects leaf anatomy, gas exchange, water relations and growth of two avocado cultivars

Two cultivars of avocado ( Persea americana Mill., ‘Fuerte’ and ‘Hass’) plants, grown in 50 l containers, were studied under two irrigation regimes for 6 months in order to evaluate the growth response and leaf physiological and anatomical changes induced by moderate water stress. Irrigation was applied when soil water potential reached at −0.03 and −0.5 MPa for the wet and dry treatments, respectively. Leaf anatomy changed in water-stressed leaves, which could have accounted for the decreased stomatal conductance. Photosynthesis is inhibited by reducing the diffusion of CO 2 to the chloroplast, both by stomatal closure and changes in mesophyll structure, which decreases the conductance to CO 2 diffusion within the leaf. Predawn leaf water potential ( Ψ) declined by 0.9 MPa for ‘Fuerte’ and 1.2 MPa for ‘Hass’ after 12 days of withholding water, whereas the turgor potential ( Ψ p) remained positive due to a decrease in the osmotic potential ( Ψ π) in both cultivars. The reduction in osmotic potential was mainly due to dehydration and only partly related to active accumulation of solutes. Tissue elasticity seems to be the predominant physiological mechanism of drought adaptation of avocado. Growth data suggests that ‘Hass’ seems to be more affected by moderate water stress.

The influence of cyst nematodes (Heterodera sacchari) and drought on water relations and growth of upland rice in Côte d'Ivoire

This study was undertaken to examine the influence of cyst nematodes (Heterodera sacchari) and drought stress, in isolation and combination, on the water status and growth of rice in Cote d'Ivoire. Drought is considered one of the main yield-limiting factors to upland rice in West Africa, while H. sacchari is emerging as a potentially serious pest. A field study conducted during 1997 at the West Africa Rice Development Association (WARDA) showed that under low water availability in sandy soil, damage to a nematode susceptible Oryza sativa (cv IDSA6) is significant. Visual drought score and physiological parameters were significantly affected (P≤0.01) in plots with a mean population density of 39.4 H. sacchari eggs ml-1 soil at 81 days after sowing, compared to plots with a mean density of 1.2 eggs ml-1. Stomatal conductance, leaf water potential and relative water content were lower, leaf chlorophyll content was greater, and near total yield losses were observed in higher nematode density plots. In 1-l pots following 5 days of imposed drought, the H. sacchari-resistant and drought-resistant O. glaberrima (cv CG14) showed a reduction in stomatal conductance of 73% and in leaf water potential by 0.96 MPa (54%). The effect of H. sacchari (473 eggs l-1 soil) inoculated as cysts to soil before sowing was similar but less severe. The combination of both stresses had similar but yet more pronounced effects than the single stresses on stomatal conductance, leaf water potential and leaf dry weight in CG14. IDSA6 responded in a similar manner to CG14, but less acutely to both stresses. Only the combined stresses resulted in a significant (P≤0.05) reduction in osmotic potential and root dry weight compared with the control, for either CG14 or IDSA6. It is suggested that H. sacchari increased the effects of drought and drought-related losses. This may give a false impression of drought susceptibility in field screening for cultivars, and complicate models which predict crop damage caused by nematodes.

The role of solute accumulation, osmotic adjustment and changes in cell wall elasticity in drought tolerance in Ziziphus mauritiana (Lamk.)

bulk tissue elastic modulus (wall rigidity) which resulted in turgor loss at the same h in both stressed Ber (Ziziphus mauritiana Lamk.) is a major fruit tree and unstressed leaves. The possible ecological signicrop of the north-west Indian arid zone. In a study of ficance of maintenance of turgor potential and cell the physiological basis of drought tolerance in this volume at low water potentials for drought tolerance species, two glasshouse experiments were conducted in Ziziphus is discussed. in which trees were droughted during single stresscycles. In the first experiment, during a 13 d drying Key words: Ziziphus mauritiana, drought, solute accumulacycle, pre-dawn leaf water (Y leaf ) and osmotic (Y p ) tion, osmotic adjustment, proline. potentials in droughted trees declined from ’0.5 and ’1.4 MPa to ’1.7 and ’2.2 MPa, respectively, for a decrease in relative water content (h) of 14%. During Introduction drought stress, changes in sugar metabolism were associated with significant increases in concentra- Drought is probably the most important factor limiting tions of hexose sugars (3.8-fold), cyclitol (scyllo- crop productivity world-wide (Jones and Corlett, 1992). inositol; 1.5-fold), and proline (35-fold; expressed per In semi-arid regions, where the amounts and patterns of unit dry weight), suggesting that altered solute parti- seasonal rainfall are often erratic and unpredictable, deeptioning may be an important factor in drought toler- rooting perennial species may exploit deep soil water ance of Ziziphus. On rewatering, pre-dawn Y leaf and h reserves. This facilitates production of yields in situations recovered fully, but Y p remained depressed by 0.4 MPa of high light coupled with drought, where shallow-rooted relative to control values, indicating that solute con- annual crops would normally fail. The use of perennials centration per unit water content had changed during may help buVer farmers’ production against year-to-year the drought cycle. fluctuations in yields from annual crop species. Under Evidence for osmotic adjustment was provided from such conditions, an ability to maintain cell water status a second study during which a gradual drought (e.g. through osmotic adjustment and/or leaf area adjustwas imposed. Pressure‐volume analysis revealed a ment) and cell integrity (by protecting cells against photo0.7 MPa reduction in osmotic potential at full turgor, and chemical oxidation) may be an advantage. There are with Y leaf at turgor loss depressed by ~1 MPa in many cases where plants growing in hostile environments drought-stressed leaves. Coupled with osmotic adjust- exhibit increased oxy-stress enzyme activities to combat lipid peroxidation by free radicals, hydrogen peroxide

Foliar dehydration tolerance of twelve deciduous tree species

The potential for foliar dehydration tolerance and maximum capacity for osmotic adjustment were compared among 12 temperate, deciduous tree species, under standardized soil and atmospheric conditions. Dehydration tolerance was operationally defined as lethal leaf water potential (Ψ): the Ψ of the last remaining leaves surviving a continuous, lethal soil drying episode. Nyssa sylvatica Marsh., and Liriodendron tulipifera L. were most sensitive to dehydration, having lethal leaf Ψ of -2.04 and -2.38 MPa, respectively. Chionanthus virginicus L., Quercus prinus L., Acer saccharum Marsh., and Quercus acutissima Carruthers withstood the most dehydration, with leaves not dying until leaf Ψ dropped to - 5.63 MPa or below. Lethal leaf Ψ (in MPa) of other, intermediate species were: Quercus rubra L. (-3.34), Oxydendrum arboreum (L.) D.C. (-3.98), Halesia carolina L. (-4.1 1), Acer rubrum L. (- 4.43), Quercus alba L. (-4.60), and Cornus florida L. (-4.88). Decreasing lethal leaf Ψ was significantly correlated with increasing capacity for osmotic adjustment. C. virginicus and Q. acutissima showed the most osmotic adjustment during the lethal soil drying episode, with osmotic potential at full turgor declining by 1.73 and 1.44 MPa, respectively. Other species having reductions in osmotic potential at full turgor exceeding 0.50 MPa were (in MPa) Q. prinus (0.89), A. saccharum (0.71), Q. alba (0.68), H. carolina (0.67), Q. rubra (0.60), and C. florida (0.52).

Drought Response of Low and High Maintenance Landscape Roses

Abstract Acclimation to drought was studied in the low-maintenance (Rosa hybrida) ‘Ferdy’ and ‘Pink Meidiland’, and the high-maintenance ‘Double Delight’ and ‘Paradise’. All plants were acclimated to drought with five consecutive, 4-day drought cycles, followed by a 2-day irrigation recovery period after the fifth drought cycle. Low-maintenance cultivars experienced less drought stress, as evidenced by higher leaf water potential, whole plant transpiration rate (E), relative water content, and leaf conductance on the final day of drought stress cycles. Morphologically, the low-maintenance cultivars had greater leaf cuticle weight than high-maintenance cultivars. Differences in the density and size of stomata and epidermal cells were not related to drought response. Low-maintenance cultivars had a smaller evaporative surface (smaller total leaf areas, smaller individual leaves, and reduced shoot dry weights). However, root : shoot ratios (root dry weight : top dry weight) and leaf area ratios (total leaf area : total plant dry weight) were comparable. Drought acclimation caused a greater reduction in osmotic potential of low-maintenance roses during the recovery period. Apparently, drought resistance in the low-maintenance roses was associated with increased cuticle thickness, reduced evaporative surface, and smaller individual leaves.