D. Subrahmanyam

Effects of chromium toxicity on leaf photosynthetic characteristics and oxidative changes in wheat (Triticum aestivum L.)

Cr(VI) significantly reduced rates of net photosynthesis and transpiration and of stomatal conductance. Cr(VI) did not affect the Fv/Fm ratio of chlorophyll fluorescence implying that the primary photochemical processes in photosystem 2 were not affected. However, the efficiency of excitation capture by open PS2 centres, in vivo quantum yield of PS2 photochemistry, and electron transport rate were significantly reduced by Cr(VI). The coefficient of photochemical quenching was reduced with a concomitant increase in coefficient of non-photochemical quenching, suggesting reduced demand for ATP and NADPH due to inhibition of CO2 assimilation. Lipid peroxidation was increased by Cr(VI) and the activities of superoxide dismutase and catalase (CAT) were increased. However, the CAT activity was reduced by high Cr(VI) concentration. The activities of ascorbate peroxidase and glutathione reductase were significantly reduced by Cr(VI) treatment.

Influence of water stress on leaf photosynthetic characteristics in wheat cultivars differing in their susceptibility to drought

A gradual reduction in leaf water potential (Ψleaf), net photosynthetic rate (PN), stomatal conductance, and transpiration rate was observed in two drought tolerant (C 306 and K 8027) and two susceptible (RW 893 and 899) genotypes subjected to water stress. The extent of reduction was lower in K 8027 and C 306 and higher in RW 893 and RW 899. Rewatering the plants after 5 d of stress restored PN and other gas exchange traits in all four cultivars. Water stress had no significant effect on variable to maximum fluorescence ratio (Fv/Fm) indicating that water stress had no effect on primary photochemistry of photosystem 2 (PS2). However, water stress reduced the efficiency of excitation energy transfer (F′v/F′m) and the quantum yield of electron transport (ΦPS2). The reduction was more pronounced in susceptible cultivars. Water stress had no significant effect on photochemical quenching, however, the non-photochemical quenching increased by water stress.

Genotype × Environment Interactions of Yield Traits in Backcross Introgression Lines Derived from Oryza sativa cv. Swarna/Oryza nivara

Advanced backcross introgression lines (BILs) developed from crosses of Oryza sativa var. Swarna/O. nivara accessions were grown and evaluated for yield and related traits. Trials were conducted for consecutive three seasons in field conditions in a randomized complete block design with three replications. Data on yield traits under irrigated conditions were analyzed using the Additive Main Effect and Multiplicative Interaction (AMMI), Genotype and Genotype × Environment Interaction (GGE) and modified rank-sum statistic (YSi) for yield stability. BILs viz., G3 (14S) and G6 (166S) showed yield stability across the seasons along with high mean yield performance. G3 is early in flowering with high yield and has good grain quality and medium height, hence could be recommended for most of the irrigated locations. G6 is a late duration genotype, with strong culm strength, high grain number and panicle weight. G6 has higher yield and stability than Swarna but has Swarna grain type. Among the varieties tested DRRDhan 40 and recurrent parent Swarna showed stability for yield traits across the seasons. The component traits thousand grain weight, panicle weight, panicle length, grain number and plant height explained highest genotypic percentage over environment and interaction factors and can be prioritized to dissect stable QTLs/ genes. These lines were genotyped using microsatellite markers covering the entire rice genome and also using a set of markers linked to previously reported yield QTLs. It was observed that wild derived lines with more than 70% of recurrent parent genome were stable and showed enhanced yield levels compared to genotypes with higher donor genome introgressions.

Genome-wide changes in microRNA expression during short and prolonged heat stress and recovery in contrasting rice cultivars

Highlight Heat susceptible and tolerant rice genotypes have different landscapes of miRNAs and the tolerant genotypes show efficient recovery mediated by miRNAs. Roots regulate miRNAs more sensitively than shoots during heat stress.

Design and development of the multispectral payload for TWSAT mission

Third World Satellite (TWSAT) is a small satellite of the Indian Space Research Organization (ISRO), weighing approximately 100 kg. This spacecraft will carry a 37-meter ground resolution, four band multispectral optical payload. This is a low cost, quick to develop, payload for studies of coastal regions, forestry, agriculture and related applications. The payload features four identical lens assemblies, each of which is designed to operate in a particular spectral band by using an appropriate band pass filter. The optical design is innovative in being usable over a spectral range of 450 to 860 nm. The design of the lens assembly is very compact, and as a result the payload is also small and commensurate with a small satellite. This payload is expected to reduce cost drastically compared to previous payloads by using qualified, commercial components to a large extent. The mechanical design of the payload features a monolithic, light weighted, aluminum main structure. This structure supports the lens assemblies on one side, and the detector head assemblies on the other side. This paper presents the optical and mechanical design of the electro-optic module, and the various tests proposed to be carried out to qualify the payload for space use.

14CO2 Assimilation and 14C-photosynthate Translocation in Different Leaves of Sunflower

Chlorophyll and nitrogen contents were highest in leaves of middle position, similarly as photosynthetic efficiency represented by 14C fixation (maxima in leaf 5 from the top). All the leaves lost 14C after 2 weeks of 14CO2 exposure. However, the reduction in radioactivity was less in young upper leaves than in the mature lower leaves. Leaves exported 14C-photosynthates to stem both above and below the exposed leaf. Very little radioactivity was recovered from the seeds of plants in which only first or second leaves were exposed to 14CO2 implying thereby that the carbon contribution of first two leaves to seed filling was negligible. The contribution of leaves to seed filling increased with the leaf position up to the sixth leaf from the top and after the seventh leaf their contribution to seed filling declined gradually.

Physical interaction of RTBV ORFI with D1 protein of Oryza sativa and Fe/Zn homeostasis play a key role in symptoms development during rice tungro disease to facilitate the insect mediated virus transmission

Rice tungro disease is caused by the combined action of Rice tungro bacilliform virus (RTBV) and Rice tungro spherical virus (RTSV). The RTBV is involved in the development of symptoms while RTSV is essential for virus transmission. We attempted to study the mode of action of RTBV in the development of symptoms. The tungro disease symptoms were attributed to viral interference in chlorophyll and carotenoids biosynthesis, photosynthesis machinery, iron/zinc homeostasis, and the genes encoding the enzymes associated with these biological processes of rice. The adverse effects of virus infection in photosystem II (PSII) activity was demonstrated by analyzing the Fv/Fm ratio, expression of psbA and cab1R genes, and direct interaction of RTBV ORF I protein with the D1 protein of rice. Since ORF I function is not yet known in the RTBV life cycle, this is the first report showing its involvement in regulating host photosynthesis process and symptoms development.

Identification of rice landraces with promising yield and the associated genomic regions under low nitrogen

With the priority of the low input sustainable rice cultivation for environment friendly agriculture, NUE of rice becomes the need of the hour. A set of 472 rice genotypes comprising landraces and breeding lines were evaluated for two seasons under field conditions with low and recommended nitrogen and >100 landraces were identified with relative higher yield under low nitrogen. Donors were identified for higher N uptake, N translocation into grains and grain yield under low N. Grains on secondary branches, N content in grain and yield appears to be the selection criterion under low N. Through association mapping, using minimum marker set of 50 rice SSR markers, 12 genomic regions were identified for yield and yield associated traits under low nitrogen. Four associated genomic regions on chromosomes 5, 7 and 10 were fine mapped and QTL for yield under low N were identified from the marker delimited regions. Three candidate genes viz., 2-oxoglutarate /malate translocator (Os05g0208000), alanine aminotransferase (Os07g0617800) and pyridoxal phosphate-dependent transferase (Os10g0189600) from QTL regions showed enhanced expression in the genotypes with promising yield under low N. Marker assisted selection using SSR markers associated with three candidate genes identified two stable breeding lines confirmed through multi-location evaluation.

Studies on root anatomy, morphology and physiology of rice grown under aerobic and anaerobic conditions

With the changing climate and rainfall abrasions, there is a gradual shift in the system of rice cultivation from traditional transplanted anaerobic to aerobic system. Studies on the root anatomical and morpho-physiological traits provide insights about the adaptation under aerobic conditions. We investigated the root anatomical and morpho-physiological traits in anaerobic (BPT 5204) and aerobic (CR Dhan 202) adapted rice genotypes grown under anaerobic and aerobic conditions. It was observed that the formation of fewer aerenchyma, thickened root and larger xylem area were critical anatomical traits associated with aerobic adaptation as compared to anaerobic conditions. The root length of CR Dhan 202 significantly increased under aerobic condition which may be attributed to its aerobic adaptation in terms of water acquisition. The photosynthetic rate was significantly higher in CR Dhan 202xa0as compared to that of BPT 5204 under the aerobic condition. The morpho-physiological results showed that the root length, total dry weight and photosynthetic rate are the key parameters for imparting aerobic adaptation. These root anatomical and morpho-physiological traits associated with the adaptation can be used as screening criteria for phenotyping and selection of genotypes suitable for aerobic system of cultivation. Such study is expected to expedite the development of rice aerobic varieties in aerobic breeding programmes.

Characterization of backcross introgression lines derived from Oryza nivara accessions for photosynthesis and yield

Improvement of photosynthetic traits is a promising strategy to break the yield potential barrier of major food crops. Leaf photosynthetic traits were evaluated in a set of high yielding Oryza sativa, cv. Swarnau2009×u2009Oryza nivara backcross introgression lines (BILs) along with recurrent parent Swarna, both in wet (Kharif) and dry (Rabi) seasons in normal irrigated field conditions. Net photosynthesis (PN) ranged from 15.37 to 23.25xa0µmol (CO2) m−2xa0s−1 in the BILs. Significant difference in PN was observed across the seasons and genotypes. Six BILs showed high photosynthesis compared with recurrent parent in both seasons. Chlorophyll content showed minimum variation across the seasons for any specific BIL but significant variation was observed among BILs. Significant positive association between photosynthetic traits and yield traits was observed, but this association was not consistent across seasons mainly due to contrasting weather parameters in both seasons. BILs 166s and 248s with high and consistent photosynthetic rate exhibited stable high yield levels in both the seasons compared to the recurrent parent Swarna. There is scope to exploit photosynthetic efficiency of wild and weedy rice to identify genes for improvement of photosynthetic rate in cultivars.