Enhanced thermotolerance of the vegetative part of MT-sHSP transgenic tomato line

Transgenic tomato (Lycopersicon esculentum Mill.) line was developed that over-expressed tomato MT-sHSP to study the role of MT-sHSP in imparting tolerance to high temperature to vegetative part. T0 and T1 generation lines of transgenic tomato and wild type were used for molecular and physiological characterization for thermotolerance. Plants were grown at optimum (26/20 °C) and two supra-optimum, viz. ST1 (30/22 °C) and ST2 (32/25 °C) day/night temperature cycles. Plant height, leaf area, as well as assimilation (PN), leaf cell membrane thermostability (LCMT), and night respiration were recorded. The T0 and T1 lines showed increased thermotolerance under both supra-optimum temperatures. Moreover, PN did not limit the vegetative and reproductive growth under elevated temperatures. After exposure to heat-shock, the wild type and during growth at elevated temperature the transgenic line accumulated proline in the leaf, though more in wild type. Results of the LCMT clearly showed that wild type possessed more heat acclimation potential during growth at elevated temperature than the transgenic line. Further, the expression of MT-sHSP by both the transgenic and wild type under optimum temperature and after heat-shock, respectively, showed that transformation of tomato genome for high temperature tolerance could be a reality; the transformation by itself did not affect the expression of the gene for MT-sHSP. We found that a correlation exists between thermotolerance and both T0 and T1 generations of tomato plants and also inheritance of the MT-sHSP gene in T1 progeny. It is assumed that MT-sHSP is just not expressed by plants under heat-shock, but has a unique function involved in thermotolerance. Specific role of the MT-sHSP in thermotolerance, however, need to be ascertained by in vitro studies.