M. Udaya Kumar

Leaf cuticular wax amount and crystal morphology regulate post-harvest water loss in mulberry (Morus species)

Mulberry leaves are the sole source of food for silkworms (Bombyx mori), and moisture content of the detached leaves fed to silkworms determines silkworm growth and cocoon yield. Since leaf dehydration in commercial sericulture is a serious problem, development of new methods that minimize post-harvest water loss are greatly needed. In the present study, variability in moisture retention capacity (MRC, measured as leaf relative water content after one to 5 h of air-drying) was examined by screening 290 diverse mulberry accessions and the relationship between MRC and leaf surface (cuticular) wax amount was determined. Leaf MRC varied significantly among accessions, and was found to correlate strongly with leaf wax amount. Scanning electron microscopic analysis indicated that leaves having crystalline surface waxes of increased facet size and density were associated with high MRC accessions. Leaf MRC at 5 h after harvest was not related to other parameters such as specific leaf weight, and stomatal frequency and index. This study suggests that mulberry accessions having elevated leaf surface wax amount and crystal size and density exhibit reduced leaf post-harvest water loss, and could provide the foundation for selective breeding of improved cultivars.

Activation tagging in indica rice identifies ribosomal proteins as potential targets for manipulation of water‐use efficiency and abiotic stress tolerance in plants

We have generated 3900 enhancer-based activation-tagged plants, in addition to 1030 stable Dissociator-enhancer plants in a widely cultivated indica rice variety, BPT-5204. Of them, 3000 were screened for water-use efficiency (WUE) by analysing photosynthetic quantum efficiency and yield-related attributes under water-limiting conditions that identified 200 activation-tagged mutants, which were analysed for flanking sequences at the site of enhancer integration in the genome. We have further selected five plants with low Δ13 C, high quantum efficiency and increased plant yield compared with wild type for a detailed investigation. Expression studies of 18 genes in these mutants revealed that in four plants one of the three to four tagged genes became activated, while two genes were concurrently up-regulated in the fifth plant. Two genes coding for proteins involved in 60S ribosomal assembly, RPL6 and RPL23A, were among those that became activated by enhancers. Quantitative expression analysis of these two genes also corroborated the results on activating-tagging. The high up-regulation of RPL6 and RPL23A in various stress treatments and the presence of significant cis-regulatory elements in their promoter regions along with the high up-regulation of several of RPL genes in various stress treatments indicate that they are potential targets for manipulating WUE/abiotic stress tolerance.

Enhancement of water status by calcium pretreatment in groundnut and cowpea plants subjected to moisture stress

SummaryThe effect of calcium in the water relations and tolerance to moisture deficits was tested in groundnut and cowpea. In both species, enrichment of tissue with calcium resulted in maintenance of a higher water status under stress associated with low proline accumulation. The extent of membrane damage (as reflected by the absorbance at 273 nm) was lesser in leaves of plants fed with higher levels of Ca++ when subjected to simulated stress. The rate of water loss from the leaves of Ca++-enriched plants was also lower. The possible role of Ca++ in inducing membrane stability and maintenance of higher water status is discussed.

Genotypic variation in carbon exchange rate, functional leaf area and productivity in finger millet (Eleusine coracana gaertn.): An approach to identify desirable plant types for higher water use efficiency under rainfed conditions

Abstract Earlier field studies in finger millet showed the lack of a direct relationship between the leaf area duration and the grain productivity and biomass production of finger millet under rainfed conditions, indicating that there are genotypes with high productivity in spite of a low assimilation leaf area. In this study, an attempt was made to investigate the genotypic differences in stomatal frequency (F), leaf area (LA), leaf area duration (LAD), total stomatal number per plant (LA × F), and the relationship of these parameters to biomass production, grain yield and photosynthetic rate in 100 medium-duration genotypes. The differences in stomatal number per plant amongst genotypes was, as expected, influenced more by the leaf area than by the stomatal frequency of leaves at any canopy position. There were several genotypes with a consistently low leaf area but having a productivity under rainfed conditions that was equivalent to that of the high leaf area types. Mean biological yield and grain productivity were not significantly different between the two groups, although the differences in both LAD and stomatal number per plant were significant. Genotypes with a consistently low leaf area per plant associated with high biomass and grain yield were selected on the broad assumption that these genotypes may also show smaller canopy water loss under rainfed conditions, due to a low transpirational area. Photosynthetic 14 CO 2 fixation and gas exchange studies showed that the rate of leaf carbon fixation was two-fold higher in genotypes that had a consistently low leaf area but were able to produce dry matter and grain yield in the same amount as the high leaf area types. Such genotypes are desirable for rainfed or drought situations.

Regulation of water loss under moisture stress in sunflower genotypes: stomatal sensitivity in relation to stomatal frequency, diffusive resistances and transpiration rate, at different canopy positions

Transpiration rate, diffusive resistances, canopy conductances and water potentials were determined at three canopy positions in non·stressed and stressed plants of sunflower hybrid BSH·1 and five other cultivars of sunflower under field conditions. The leaf area (LA) and stomatal frequency (f) was determined at the three canopy positions in field.grown plants and the total number of stomata per plant was calculated as the product of LA and f. These variables were then related to the dry·matter accumulation and seed yield in these cultivars. Cultivars with either a high leaf area or high number of stomata per plant were more productive under non-stress conditions. Under stress conditions, cultivars differed in the extent of change in conductance (g) and transpiration rate at different canopy positions. In the hybrid BSH·1, g was low at all levels in the canopy associated with a higher (less negative) water potential and this hybrid had lower transpiration rates at all canopy levels under stress although the number of stomata per plant was high. Stomatal sensitivity associated with a higher threshold water potential for stomatal closure is discussed as a possible explanation for the higher dry.matter accumulation and productivity of hybrid sunflower BSH·1 under moisture stress conditions.

Ectopic expression of Arabidopsis Target of Rapamycin (AtTOR) improves water-use efficiency and yield potential in rice

The target of Rapamycin (TOR) present in all eukaryotes is a multifunctional protein, regulating growth, development, protein translation, ribosome biogenesis, nutrient, and energy signaling. In the present study, ectopic expression of TOR gene of Arabidopsis thaliana in a widely cultivated indica rice resulted in enhanced plant growth under water-limiting conditions conferring agronomically important water-use efficiency (WUE) trait. The AtTOR high expression lines of rice exhibited profuse tillering, increased panicle length, increased plant height, high photosynthetic efficiency, chlorophyll content and low ∆13C. Δ13C, which is inversely related to high WUE, was as low as 17‰ in two AtTOR high expression lines. These lines were also insensitive to the ABA-mediated inhibition of seed germination. The significant upregulation of 15 stress-specific genes in high expression lines indicates their contribution to abiotic stress tolerance. The constitutive expression of AtTOR is also associated with significant transcriptional upregulation of putative TOR complex-1 components, OsRaptor and OsLST8. Glucose-mediated transcriptional activation of AtTOR gene enhanced lateral root formation. Taken together, our findings indicate that TOR, in addition to its multiple cellular functions, also plays an important role in response to abiotic stress and potentially enhances WUE and yield related attributes.

The Balance between Leaf Area and Photosynthetic Activity in Determining Productivity of Fox-tail Millet ( Setaria italica ) under Rain-fed Conditions

The relationship of leaf weight ratio (LWR), leaf area ratio (LAR), stomatal frequency and dry matter (DM) production with yield and with photosynthetic efficiency, as reflected by 14 CO 2 fixation rate, was studied in fox-tail millet ( Setaria italica ) for three consecutive years. Several genotypes were identified which combined small leaf area and/or low stomatal numbers per plant with productivity under rain-fed conditions equal to that of genotypes with large stomatal numbers. 14 CO 2 studies in these genotypes showed that the rate of carbon fixation by the leaves was greater, at any canopy position, than in the corresponding large LA/large DM types. Genotypes with consistently small stomatal numbers per plant, associated with good dry matter accumulation and productivity, may also show small transpirational water loss under rain-fed or drought conditions. It is concluded that such genotypes are desirable for better productivity under these conditions.

Determination of carbonic anhydrase activity using infra-red gas analysis

Abstract A technique for the estimation of carbonic anhydrase (CA) using the infra-red-gas analyser (IRGA) has been developed. Instead of determining pressure changes in the dehydration reaction catalysed by the enzyme, the IRGA was used to determine the increase in carbon dioxide content in the enzymatic and non-enzymatically catalysed dehydration reaction. The reliability of this method was assessed using pure carbonic anhydrase. Although the method has not been compared with other methods, the known sensitivity of the IRGA (resolution of 0.1–1.0 μmol/mol) was exploited. The differences in CA activity of two finger millet (Eleusine coracana) genotypes differing markedly in photosynthetic rate but showing similar leaf conductances was assessed.