Aruna Tyagi

Role of phytosterols in drought stress tolerance in rice

Phytosterols are integral components of the membrane lipid bilayer in plants. They regulate membrane fluidity to influence its properties, functions and structure. An increase in accumulation of phytosterols namely campesterol, stigmasterol and β-sitosterol was observed in rice as seedlings matured. The levels of the major phytosterol, β-sitosterol in N22 (drought tolerant) rice seedlings was found to increase proportionately with severity of drought stress. Its levels were 145, 216, 345 and 364 μg/g FW after subjecting to water stress for 3, 6, 9 and 12 days respectively, while for IR64 (drought susceptible), levels were 137, 198, 227 and 287 μg/g FW at the same stages. Phytosterols were also found to increase with maturity as observed at 30, 50 and 75 days after planting. The activity of HMG-CoA reductase (EC 1.1.1.34) which is considered to be a key limiting enzyme in the biosynthesis of phytosterols was 0.55, 0.56, 0.78 and 0.85 μmol/min/L at 3, 6, 9 and 12 days of water stress in N22 and 0.31, 0.50, 0.54 and 0.65 μmol/min/L in case of IR64 respectively. The elevation in the levels of phytosterols as well as the activity of HMG-CoA reductase during drought stress indicates the role of phytosterols in providing tolerance to stress.

Functional validation of a drought-responsive AP2/ERF family transcription factor-encoding gene from rice in Arabidopsis

A water-deficit stress (WDS)-responsive transcription factor-encoding gene isolated from drought-tolerant Oryza sativa L. cv. N-22 corresponding to the AP2/ERF family and named AP2/ERF-N22, when overexpressed in Arabidopsis under a constitutive promoter, showed improved turgor and less wilting as compared to wild-type plants under WDS. However, the transgenic plants showed phenotypic aberrations such as stunted growth, smaller silique size, reduced number of seeds and delayed flowering. Physio-biochemical analysis of T2 plants revealed higher relative water content, membrane stability index, capacity to scavenge reactive oxygen species and increased levels of proline, carotenoids, wax and abscisic acid content under WDS. Higher abscisic acid content resulted in reduced stomatal conductance and transpiration rate. The reduced chlorophyll content also leads to reduced photosynthetic rate and efficiency. Thus, this gene may be exploited for enhanced drought tolerance in crop plants.

Molecular Response to Water Stress in Lathyrus sativus

Studies on response of Lathyrus sativus plants to water stress showed that the plants recovered to pre-stressed level if revived within first seven days of stress. After 12 days of stress period, root weight of stressed plants was 10 times lesser than control. Lipoxygenase expression was the highest in leaves followed by very low levels in stems and undetectable in roots. Lox A and B messengers were respectively 3 and 1.5 fold more in stressed leaves than control. A −22kD polypeptide was observed in stressed plants on SDS-PAGE.

Elicitor-Induced Biochemical and Molecular Manifestations to Improve Drought Tolerance in Rice (Oryza sativa L.) through Seed-Priming

Rice (Oryza sativa L.) is one of the major grain cereals of the Indian subcontinent which face water-deficit stress for their cultivation. Seed-priming has been reported to be a useful approach to complement stress responses in plants. In the present study, seed-priming with hormonal or chemical elicitor [viz. methyl jasmonate (MJ), salicylic acid (SA), paclobutrazol (PB)] showed significant increase in total phenolic content, antioxidant activity and expression of Rice Drought-responsive (RD1 and RD2) genes (of AP2/ERF family) in contrasting rice genotypes (Nagina-22, drought-tolerant and Pusa Sugandh-5, drought-sensitive) under drought stress. However, decrease in lipid peroxidation and protein oxidation was observed not only under the stress but also under control condition in the plants raised from primed seeds. Expression analyses of RD1 and RD2 genes showed upregulated expression in the plants raised from primed seeds under drought stress. Moreover, the RD2 gene and the drought-sensitive genotype showed better response than that of the RD1 gene and the drought-tolerant genotype in combating the effects of drought stress. Among the elicitors, MJ was found to be the most effective for seed-priming, followed by PB and SA. Growth and development of the plants raised from primed seeds were found to be better under control and drought stress conditions compared to that of the plants raised from unprimed seeds under the stress. The present study suggests that seed-priming could be one of the useful approaches to be explored toward the development of simple, cost-effective and farmer-friendly technology to enhance rice yield in rainfed areas.

Isolation of a Novel Early Drought Responding Partial cDNA Sequence from Rice by Differential Display of mRNA

Total RNA isolated from control as well as stressed rice seedlings was reverse transcribed and subjected to radioactive PCR for differential display. A partial cDNA corresponding to moisture stress was isolated and sequenced. The clone showed homology to lysine transport protein /lysine specific permease.

Construction and Screening of Barley Genomic Library with a B1-Hordein Gene Probe

Barley genomic library from cv NP113 was made in a replacement vector EMBL-3. The titre was found to be 1.25 x 106 per μg of genomic DNA. The recombinants were screened using a B1-hordein DNA probe. One clone contained a positively hybridizing 4 kb fragment.

Regulation of phytosterol biosynthetic pathway during drought stress in rice

Plants respond to drought stress in the form of various physio-biochemical and molecular changes at both cellular and molecular levels. Drought stress causes the destruction of cell membranes by disintegration of membrane lipids. One of the major groups of membrane lipids that plays important role in preserving the integrity of cell membranes is phytosterols. HMG-CoA reductase (HMGR) is the principal enzyme in the biosynthesis of plant sterols, synthesized via mevalonic acid pathway. Phospholipid: sterol acyltransferase (PSAT) is another important enzyme that plays an important role in turnover of phytosterols into steryl esters and helps maintain homeostasis of membrane lipids. In this study, the expression of both HMGR and PSAT genes in drought sensitive (IR64) and drought tolerant (N22) rice cultivars under applied drought conditions were found to be elevated. The increase in expression of these genes was proportional to the level of severity of applied drought stress. This is substantiated by the negative correlation of HMGR and PSAT expression to relative water content (RWC) and membrane stability index (MSI). Expression of PSAT was also found to be positively correlated to ABA content and HMGR expression.