Exogenous application of putrescine at pre-anthesis enhances the thermotolerance of wheat (Triticum aestivum L.).

Antioxidant enzymes, besides being involved in various developmental processes, are known to be important for environmental stress tolerance in plants. In this study, the effect of treatment of 2.5 mM putrescine (Put), heat stress (HS -42°C for 2 h) and their combination on the expression and activity of antioxidant enzymes was studied at pre-anthesis in the leaves of two wheat (Triticum aestivum L.) cultivars — HDR77 (thermotolerant) and HD2329 (thermosusceptible). We observed that 2.5 mM Put before HS significantly enhanced the transcript levels of superoxide dismutase (SOD), catalase (CAT), cytoplasmic and peroxisomal ascorbate peroxidase (cAPX, pAPX) in both the cultivars. However, the activities of antioxidant enzymes (SOD, CAT, APX and GR), as well as accumulation of antioxidants (ascorbic acid and total thiol content) were higher in HDR77 than in HD2329 in response to the treatment 2.5 mM Put + HS. No significant change was observed in the proline accumulation in response to HS and combined treatment of 2.5 mM Put + HS. A decrease in the H2O2 accumulation, lipid peroxidation and increase in cell membrane stability (CMS) were observed in response to 2.5 mM Put + HS treatment, as compared to HS treatment alone in both the cultivars; HDR77 was, however, more responsive to 2.5 mM Put + HS treatment. Put (2.5 mM) treatment at pre-anthesis thus modulated the defense mechanism responsible for the thermotolerance capacity of wheat under the heat stress. Elicitors like Put, therefore, need to be further studied for temporarily manipulating the thermotolerance capacity of wheat grown under the field conditions in view of the impending global climate change.

Genome Wide Identification of Target Heat Shock Protein90 Genes and Their Differential Expression against Heat Stress in Wheat.

Aims: To study the genetic and transcript profiling of the genes specifying cytosolic HSP90s in Triticum aestivum. Study Design: Random sampling. Place and Duration of Study: Indian Agricultural Research Institute, New Delhi, India, between August to December, 2011. Methodology: We include C-306 (thermotolerant) and PBW343 (thermosusceptible) cultivars of wheat for the study. Total RNA was isolated using Trizol method and gene was identified and isolated using RT-PCR. In silico characterization was done using different bioinformatic tools. Quantitative real time PCR was carried out using BioRad CFX96 platform and Pfaffl’s method was used for the comparative change in fold expression of the gene. Results: Here, we report cloning of an HSP90 gene from C-306 wheat cultivar having an ORF of 700 amino acids. Genome Blast identified 3 different clusters of reference sequence on chromosome no 4, 8 and 9 having LOC 100125696 and showing maximum homology with HSP90 reported from Triticum aestivum. Pure amino acid composition revealed highest composition of glutamic acid followed by lysine and leucine whereas, cysteine composition was lowest. Protein characterization showed the existence of 10 networks of coevolved amino acids. Quantitative real time PCR showed 1.5, 4.5, 5 & 7.4 fold increase in expression of HSP90 in case of C-306 compared to 2.5, 6.4, 6.9 & 5.6 fold increase in case of PBW343 at vegetative (root & shoot), pollination and milky dough stage. Multiple co-chaperones of HSP90 were observed by immunoblot assay in response to differential heat shock. Conclusion: This investigation proves that HSP90 is one of the key components of defense mechanism in wheat against heat stress which requires the formation of cochaperone complexes with HSP70 for its functional activity. There is a need to exploit the transcription factors associated with HSP90 and its regulation and differential expression in order to use it for developing thermotolerant wheat cultivars.