Uday V. Pathre

Comparative transcriptomic analysis of roots of contrasting Gossypium herbaceum genotypes revealing adaptation to drought

BackgroundRoot length and its architecture govern the adaptability of plants to various stress conditions, including drought stress. Genetic variations in root growth, length, and architecture are genotypes dependent. In this study, we compared the drought-induced transcriptome of four genotypes of Gossypium herbaceum that differed in their drought tolerance adaptability. Three different methodologies, namely, microarray, pyrosequencing, and qRT–PCR, were used for transcriptome analysis and validation.ResultsThe variations in root length and growth were found among four genotypes of G.herbaceum when exposed to mannitol-induced osmotic stress. Under osmotic stress, the drought tolerant genotypes Vagad and GujCot-21 showed a longer root length than did by drought sensitive RAHS-14 and RAHS-IPS-187. Further, the gene expression patterns in the root tissue of all genotypes were analyzed. We obtained a total of 794 differentially expressed genes by microarray and 104928 high-quality reads representing 53195 unigenes from the root transcriptome. The Vagad and GujCot-21 respond to water stress by inducing various genes and pathways such as response to stresses, response to water deprivation, and flavonoid pathways. Some key regulatory genes involved in abiotic stress such as AP2 EREBP, MYB, WRKY, ERF, ERD9, and LEA were highly expressed in Vagad and GujCot-21. The genes RHD3, NAP1, LBD, and transcription factor WRKY75, known for root development under various stress conditions, were expressed specifically in Vagad and GujCot-21. The genes related to peroxidases, transporters, cell wall-modifying enzymes, and compatible solutes (amino acids, amino sugars, betaine, sugars, or sugar alcohols) were also highly expressed in Vagad and Gujcot-21.ConclusionOur analysis highlights changes in the expression pattern of genes and depicts a small but highly specific set of drought responsive genes induced in response to drought stress. Some of these genes were very likely to be involved in drought stress signaling and adaptation, such as transmembrane nitrate transporter, alcohol dehydrogenase, pyruvate decarboxylase, sucrose synthase, and LEA. These results might serve as the basis for an in-depth genomics study of Gossypium herbaceum, including a comparative transcriptome analysis and the selection of genes for root traits and drought tolerance.

Desiccation-induced physiological and biochemical changes in resurrection plant, Selaginella bryopteris

Selaginella bryopteris is a lycophyte resurrection plant, which incurves during desiccation and recovers on availability of moisture. The aim of the study was to test and understand the various physiological and biochemical changes the fronds undergo during desiccation and rehydration, to get an insight as to how this plant adapts and survives through the dry phase. Upon desiccation, S. bryopteris fronds showed drastic inhibition in net photosynthesis (A) and maximal photochemical efficiency of PSII (F(v)/F(m)) however, chlorophyll content did not show much variation. Dark respiration (R(d)) continued even at 10% relative water content (RWC), and showed a burst after rehydration, which is proposed to be crucial to establish protection mechanisms. Desiccation caused an enhanced production of reactive oxygen species (ROS) and increased lipid peroxidation. Proline accumulation increased substantially by 11-fold. Sucrose and starch contents decreased upon desiccation as compared to control. The antioxidative enzymes viz. superoxide dismutase (SOD), ascorbate peroxidase (APX) and catalase (CAT) along with soluble acid invertase increased during desiccation. S. bryopteris shows mechanical as well as physiological mechanisms for tolerance to extreme levels of desiccation stress. The rapid and almost complete recovery of F(v)/F(m) after rehydration clearly indicates the absence of marked photoinhibitory or thermal injury to PSII during desiccation. This along with the homoiochlorophyllous characteristics enables S. bryopteris to recover its A. The antioxidant metabolism further plays an important role in the desiccation tolerance of S. bryopteris.

Metabolic and histopathological alterations of Jatropha mosaic begomovirus-infected Jatropha curcas L. by HR-MAS NMR spectroscopy and magnetic resonance imaging

Alterations in the anatomical structures, sap translocation and metabolic profiles in Jatropha curcas L. (Euphorbiaceae), infected with Jatropha mosaic virus (JMV) have been investigated using MRI and HR-MAS NMR spectroscopy. The contrast of MRI images distinguishes abnormalities in anatomical structures of infected and healthy stem. The HR-MAS NMR spectroscopic analysis indicated that viral infection significantly affected the plant metabolism. Higher accumulation of TCA cycle intermediates, such as citrate and malate, in JMV-infected plants suggested a higher rate of respiration. The respiration rate was more than twofold as compared to healthy ones. The viral stress also significantly increases the concentrations of alanine, arginine, glutamine, valine, GABA and choline as compared to healthy ones. Microscopic examination revealed severe hyperplasia caused by JMV with a considerable reduction in the size of stem cells. Lower concentration of glucose and sucrose in viral-infected stem tissues indicates decreased translocation of photosynthates from leaves to stem due to hyperplasia caused by JMV. The MR images distinguished stele, cortical and pith regions of JMV-infected and healthy stems. Contrast of T1- and T2-weighted images showed significant differences in the spatial distribution of water, lipids and macromolecules in virus-infected and healthy stem tissues. The results demonstrated the value of MRI and HR-MAS NMR spectroscopy in studying viral infection and metabolic shift in plants. The present methodology may help in better understanding the metabolic alterations during biotic stress in other plant species of agricultural and commercial importance.

First molecular identification of a begomovirus in India that is closely related to Cassava mosaic virus and causes mosaic and stunting of Jatropha curcas L.

The association of a begomovirus with Jatropha mosaic disease has been found in north India. The begomovirus possessed highest identities and closest relationships withIndian andSri Lankan cassava mosaic virus isolates.

Midday depression in photosynthesis: Effect on sucrose-phosphate synthase and ribulose-1,5-bisphosphate carboxylase in leaves of Prosopis juliflora (Swartz) DC

The midday depression in net photosynthetic rate (PN) and stomatal conductance (gs) in Prosopis juliflora was studied in relation to two key enzymes of carbon metabolism. Diurnal gas exchange measurements carried out in autumn on P. juliflora showed a pronounced depression in PN and gs along with a decrease in apparent carboxylation efficiency (CE*) during midday. The activities of sucrose-phosphate synthase (SPS) and ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) also showed large diurnal fluctuations. Initial RuBPCO activity (that present in vivo) and total activity (fully carbamylated activity) increased gradually with increase in irradiance, in the morning reaching a maximum by 08:00 h. The RuBPCO activity declined sharply during midday due to decrease in initial activity. The drop in the % activation of RuBPCO indicated that the deactivation of RuBPCO was achieved via a decarbamylation mechanism. There was a marked similarity in the diurnal patterns of SPS activity and the PN. During a diurnal rhythm, SPS activity increased after irradiation, reaching a maximum at 08:00 h and then declined during midday. Diurnal fluctuations in SPS activity could be due to the changes in the amount of protein (changes in Vmax) as well as to the changes in kinetic properties (changes in Vlim). Hence the midday decline in photosynthesis is closely associated with the regulation of RuBPCO and SPS activities.

Expression of GhNAC2 from G. herbaceum , improves root growth and imparts tolerance to drought in transgenic cotton and Arabidopsis

NAC proteins are plant-specific transcription factors that play essential roles in regulating development and responses to abiotic and biotic stresses. We show that over-expression of the cotton GhNAC2 under the CaMV35S promoter increases root growth in both Arabidopsis and cotton under unstressed conditions. Transgenic Arabidopsis plants also show improved root growth in presence of mannitol and NaCl while transgenic cotton expressing GhNAC2 show reduced leaf abscission and wilting upon water stress compared to control plants. Transgenic Arabidopsis plants also have larger leaves, higher seed number and size under well watered conditions, reduced transpiration and higher relative leaf water content. Micro-array analysis of transgenic plants over-expressing GhNAC2 reveals activation of the ABA/JA pathways and a suppression of the ethylene pathway at several levels to reduce expression of ERF6/ERF1/WRKY33/ MPK3/MKK9/ACS6 and their targets. This probably suppresses the ethylene-mediated inhibition of organ expansion, leading to larger leaves, better root growth and higher yields under unstressed conditions. Suppression of the ethylene pathway and activation of the ABA/JA pathways also primes the plant for improved stress tolerance by reduction in transpiration, greater stomatal control and suppression of growth retarding factors.

Diurnal and seasonal changes in photosynthesis and photosystem 2 photochemical efficiency in Prosopis juliflora leaves subjected to natural environmental stress

The plants of Prosopis juliflora growing in northern India are exposed to large variations of temperature, vapour pressure deficits (VPD), and photosynthetic photon flux density (PPFD) throughout the year. Under these conditions P. juliflora had two short periods of leaf production, one after the winter season and second after summer, which resulted in two distinct even aged cohorts of leaves. In winter with cold nights (2–8 °C) and moderate temperatures during the day, the plants showed high rates of photosynthesis. In summer the midday temperatures often reached <45 °C and plants showed severe inhibition of photosynthesis. The leaves of second cohort appeared in July and showed typical midday depression of photosynthesis. An analysis of diurnal partitioning of the absorbed excitation energy into photochemistry showed that a smaller fraction of the energy was utilised for photochemistry and a greater fraction was dissipated thermally, further the photon utilisation for photochemistry and thermal dissipation is largely affected by the interaction of irradiance and temperature. The plants showed high photochemical efficiency of photosystem 2 (PS2) at predawn and very little photoinhibition in all seasons except in summer. The photoinhibition in summer was pronounced with very poor recovery during night. Since P. juliflora exhibited distinct pattern of senescence and production of new leaves after winter and summer stress period, it appeared that the ontogenic characteristic together with its ability for safe dissipation of excess radiant energy in P. juliflora contributes to its growth and survival.

Reflectance and cyclic electron flow as an indicator of drought stress in cotton (Gossypium hirsutum).

The response and the functioning of the photosynthetic machinery of cotton, Gossypium hirsutum during water stress was studied by leaf optical properties, linear (ETRII) and cyclic electron flow (CEF) and chlorophyll a fluorescence. We observed that in G. hirsutum, during water limitation, Chlorophyll b showed the best correlation with reflectance at 731 nm and is a better indicator of drought. Fv/Fm was observed to be very insensitive to mild water stress. However, during severe water stress the leaves exhibit considerable inhibition in Fv/Fm and an increase in anthocyanin levels by about 20‐fold. CEF was very responsive to mild water stress. The mild drought stress caused large decrease in the ability of the leaves to utilize the light energy. Photosystem I and photosystem II is protected from photoinhibition by high CEF and nonphotochemical quenching under mild water stress. While during severe drought stress, linear electron flow showed a sharp decrease in comparison to CEF. CEF play a major role in G. hirsutum leaves during mild as well as under severe water stress condition and is thus a good indicator of water stress.

The Field Performance of some Accessions of Jatropha Curcas L. (Biodiesel Plant) on Degraded Sodic Land in North India

Twenty four accessions of Jatropha curcas L. (JCL) were planted on a degraded sodic land in Lucknow, India, in which growth and yield traits were measured over five years (2006–2010). There was a large variation in growth and yield among these accessions, and the average seed yield (118 g plant−1) and oil content (30%) of JCL on the sodic land were sufficiently low to make it an economically feasible venture for biofuel production. The seed:fruit, kernel:seed ratios and the 100 seed test weight were also measured. In order to make it an economically viable proposition, some preliminary screening were done to assort the superior accessions (CSMCRI-C1, NBPGR-Urlikanchan, NBPGR-Chhatrapati, and NBPGR-Hansraj), on the basis of growth and yield traits, that have attained an average height of 264.6–344.6 cm, with an 8.5- to 10-cm collar diameter, 41–57 branches per plant, a 209- to 290-cm canopy spread, a 178–246 g plant−1 seed yield, and a 27–38% oil content at five years. Though they do not correlate well between growth/yield and gas exchange parameters (photosynthetic rate, transpiration, stomatal conductance, and water use efficiency), even then these markers are useful to screen out a large number of accessions at an early stage before the yield starts or stabilizes to increase the land use efficiency. The changes in soil properties after five years of the plantations showed reduction in soil pH and electrical conductivity, with a parallel increase in organic carbon, organic nitrogen, microbial biomass, and dehydrogenase activity, indicating that JCL had a modest ability to reclaim the sodic soils.

Purification and properties of leucine aminotransferase from soybean seedlings

Two isoenzymes of leucine aminotransferase (LAT I and LAT II) were extracted and partially purified from etiolated soybean seedlings. LAT I accounted for about 87% and LAT II about 13% of the total LAT activity. LAT I was eluted from a DEAE-cellulose column with a buffer having lower ionic strength than LAT II. Both isoenzymes gave pH optima of 8.9. Kinetic data for the forward reaction were consistent with the accepted ping-pong bi-bi mechanism for aminotransferases. Isoenzymes were inhibited by excess of substrate and product. Inhibition by the substrate analogue maleate suggested that both substrates utilized the same catalytic site of the enzyme. Hydroxylamine inhibited the aldehyde form of the LAT while the amino form was found to be inert.