Physiological and Agronomic Responses of Four Rice Varieties to Drought in the Rainforest.

The present investigation tested the hypothesis that there would be variation in physiological responses to water deficit among rice varieties from different production ecologies, with contrasting tolerance to water deficit under repeated cycle of soil moisture deficit, at reproductive growth stage. A screen house and a field trial were conducted at International Institute of Tropical Agriculture, Ibadan and Ikenne (Latitude 6° 52' N, Longitude 3° 43' E) respectively. Both experiments had rice varieties ('IR 64', 'WAB 56-104', 'IR 77298-1-2-B-10' and 'NERICA 4') and stress status (stress and control) as treatment factor's, arranged in a randomised complete block design with three replicates. In both trials, the physiological mechanism that underpins varietal differences with repeated cycles of water deficit at the reproductive growth stage was more balanced water status, improved foliar characters, efficient photosynthetic capacity and higher grain yield in comparatively drought tolerant upland rice varieties ('NERICA 4' and 'WAB 56-104'), as opposed with the results for the drought susceptible cultivar 'IR 64'. A converse pattern was observed on water stressed rice, despite fewer cycles of water deficit on the field. The results could have suggested that the initiation of water deficit is the rate limiting step rather than its intensity at the reproductive growth stage

Estimation of soil water deficit in an irrigated cotton field with infrared thermography

Plant growth and soil water deficit can vary spatially and temporally in crop fields due to variation in soil properties and/or irrigation and crop management factors. We conducted field experiments with cotton (Gossypium hirsutum L.) over two seasons during 2007-2009 to test if infrared thermography can distinguish systematic variation in deficit irrigation applied to various parts of the field over time. Soil water content was measured with a neutron probe and thermal images of crop plants were taken with a thermal infrared camera. Leaf water potential and stomatal conductance were also measured on selected occasions. All measurements were made at fixed locations within three replicate plots of an irrigation experiment consisting of four soil-water deficit treatments. Canopy temperature related as well with soil water within the root zone of cotton as the stomatal conductance index derived from canopy temperature, but it neglected the effect of local and seasonal variation in environmental conditions. Similarities in the pattern of spatial variation in canopy temperature and soil water over the experimental field indicates that thermography can be used with stomatal conductance index to assess soil water deficit in cotton fields for scheduling of irrigation and to apply water in areas within the field where it is most needed to reduce water deficit stress to the crop. Further confidence with application of infrared thermography can be gained by testing our measurement approach and analysis with irrigation scheduling of other crops

Defisit Air Pada Berbagai Fase Pertumbuhan dan Pengaruhnya Terhadap Karakter Kuantitatif Beberapa Genotipe Kacang Tanah

This study aims to determine the effect of water deficit at various phases of plant growth on the quantitative characters of several peanut genotypes. This study used a completely randomized design-split plot design.  The water deficit consisted of 6 treatments: d0 = no water deficit, d1 = water deficit from germination to harvest, d2 = water deficit from germination to age 25 days after planting (dap) (vegetative phase), d3 = water deficit from age 26  to 50 dap (flowering phase to pod formation), d4 = water deficit from age 51 dap to 75 dap (seed filling phase), and d5 = water deficit from age 75 dap to 100 dap (seed ripening phase until harvest). The peanut genotype used consisted of 10 genotypes. The results showed that water deficit in various phases of plant growth resulted in different quantitative characters in several peanut genotypes. Genotype G3T4 produced heaviest dry pod weight of 12.7 g plant-1 in water deficit from germination to harvest. Genotype G200-I produced heaviest dry pod weight of 11.5 g per plant-1 in water deficit in the vegetative phase. Genotype G3T4 produced heaviest dry pod weight of 13.3 g per plant in water deficit the generative phase. Genotype G300-II produced heaviest the dry pod weight of 11.7 g per plant-1 in the water deficit of the seed filling phase. Genotypes G2D2, G2T3 and G200-I produced the heaviest dry pod weight of 11.0 g per plant-1 in the water deficit of the seed ripening phase

Regulation of ethylene biosynthesis in Festuca novae-zelandiae (Hack.) Cockayne and in Festuca aruninaceae (Schreb.) in response to a water deficit : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Plant Biology at Massey University, Palmerston North, New Zealand

Changes in ethylene evolution and the associated biosynthetic enzyme ACC oxidase to a water deficit, were examined in intact leaves of Fostuca novae-zelandiae and F. arundinacea cultivar 'Roa' (syn. Schedonorus phoenix). The aim was to establish a role, or otherwise, for ACC oxidase as a regulator of ethylene biosynthesis in response to a water deficit. While ACC synthase has long been recognised as the major rate-limiting enzyme in ethylene biosynthesis, there is mounting evidence to suggest that ACC oxidase may also regulate the ethylene biosynthesic pathway in higher plants. Leaf tissues from the two species were harvested at regular intervals during the experimental dry-down, and dissected into two leaf zones, regions enclosed by the ligule. comprising the meristematic and elongating leaf zone (the enclosed tissue), and exposed regions composing the mature green leaf zones. Leaf proline content and the rate of leaf elongation (LER) were used as internal and external indicators of physiological changes in response to the water-deficit. Ethylene evolution in response to a water-deficit was found to be tissue-specific in F.arundinacea. In the rapidly expanding leaf zones, i.e. enclosed tissue, ethylene was maintained at levels similar to control tissue. In the mature green regions of leaves, ethylene followed changes in the leaf elongation rate (LER) with observed peaks in ethylene evolution occurnng approximately 48 hours after a rapid decline in the LER. This burst of ethylene was found to precede any accumulation of proline. Increases in the proline content in both leaf zones, only became significant after the ethylene evolution had subsided to below base levels. This stage-specific ethylene evolution in leaves suggests preferential protection of the rapidly expanding leaf cells, an observation that has been documented by other authors. ACO specific enzyme activity was greatest at soil water contents of ca. 9% in the enclosed and 10% in the exposed leaf tissues of F.arundinacea. On further purification of the enzyme, two novel proteins were recognised by polyclonal antibodies in water-stressed leaves of F.arundinacea. A 32 kDa protein was identified in the enclosed leaf tissue and a 37 kDa protein was identified in the exposed leaf tissue, by SDS-PAGE. These proteins eluted from a Mono Q column at different points in the separation process, i.e at salt concentrations of 320-340 and 300-320 mM NaCI respectively, indicating that they may represent two distinct isoforms of the ACO enzyme. Both proteins are active at pH 7.5 with saturating substrate (ACC) and co-substrate (Na ascorbate) concentrations of 1 mM and 30 mM respectively, and co-factor concentrations of 0.02 mM Fe² + and 30 mM NaHCO₃. When compared with results from western analyses, maximum specific enzyme activity correlated well with the water-deficit induced protein from partially purified enclosed leaf tissue, but only loosely with the protein identified in the exposed leaf tissue. The presence of high molecular weight proteins in both the crude and the purrfied (Mono Q) leaf extracts of F.arundinacea together with the novel proteins, suggests that the ACO enzyme in this species may exist as a dimer In F.novae-zelandiae, the presence of high molecular weight molecules m the crude and partially purified (Sephadex G-25) extracts also suggests dimensation of the enzyme in this species. From this study however, it is not possible to establish a clear regulatory role for the ACO enzyme in ethylene biosynthesis in either F.arvndinacea or F.novae-zelandiae While two novel water-deficit-induced proteins were associated with increased ACO activity in purified leaf extracts of F. amndinacea, there was no obvious correlation between ethylene evolution and enzyme activity

Delaying chloroplast turnover increases water-deficit stress tolerance through the enhancement of nitrogen assimilation in rice.

Abiotic stress-induced senescence in crops is a process particularly affecting the photosynthetic apparatus, decreasing photosynthetic activity and inducing chloroplast degradation. A pathway for stress-induced chloroplast degradation that involves the CHLOROPLAST VESICULATION (CV) gene was characterized in rice (Oryza sativa) plants. OsCV expression was up-regulated with the age of the plants and when plants were exposed to water-deficit conditions. The down-regulation of OsCV expression contributed to the maintenance of the chloroplast integrity under stress. OsCV-silenced plants displayed enhanced source fitness (i.e. carbon and nitrogen assimilation) and photorespiration, leading to water-deficit stress tolerance. Co-immunoprecipitation, intracellular co-localization, and bimolecular fluorescence demonstrated the in vivo interaction between OsCV and chloroplastic glutamine synthetase (OsGS2), affecting source-sink relationships of the plants under stress. Our results would indicate that the OsCV-mediated chloroplast degradation pathway is involved in the regulation of nitrogen assimilation during stress-induced plant senescence

Extensive tissue-specific transcriptomic plasticity in maize primary roots upon water deficit

Water deficit is the most important environmental constraint severely limiting global crop growth and productivity. This study investigated early transcriptome changes in maize (Zea mays L.) primary root tissues in response to moderate water deficit conditions by RNA-Sequencing. Differential gene expression analyses revealed a high degree of plasticity of the water deficit response. The activity status of genes (active/inactive) was determined by a Bayesian hierarchical model. In total, 70% of expressed genes were constitutively active in all tissues. In contrast, \u3c3% (50 genes) of water deficit-responsive genes (1915) were consistently regulated in all tissues, while \u3e75% (1501 genes) were specifically regulated in a single root tissue. Water deficit-responsive genes were most numerous in the cortex of the mature root zone and in the elongation zone. The most prominent functional categories among differentially expressed genes in all tissues were ‘transcriptional regulation’ and ‘hormone metabolism’, indicating global reprogramming of cellular metabolism as an adaptation to water deficit. Additionally, the most significant transcriptomic changes in the root tip were associated with cell wall reorganization, leading to continued root growth despite water deficit conditions. This study provides insight into tissue-specific water deficit responses and will be a resource for future genetic analyses and breeding strategies to develop more drought-tolerant maize cultivars