Global warming may cause overwintering plants to lose tolerance to low temperatures owing to de-acclimation caused by winter temperature fluctuations. The effect of elevated temperatures is regulated by the endogenous levels of phytohormones, including brassinosteroids, which allow the maintenance of high productivity under stressful conditions This study examined barley (Hordeum vulgare) de-acclimation tolerance using two mutant lines: BW084, harbouring a mutation in the HvCPD gene, and BW312, harbouring a mutation in the HvBRI1 gene. Both mutants were more tolerant to de-acclimation than the reference cultivar and displayed downregulation of chloroplast genes expression in response to de-acclimation, but differed in physiological traits related to photosynthesis and soluble carbohydrates metabolism. After 1 day of de-acclimation, biosynthesis mutant BW084 was characterized by a greater increase in the net photosynthesis rate than signalling mutant BW312. In turn after 10 days of de-acclimation, signalling mutant BW312 was characterized by the largest decrease in the fructan pool and degree of polymerization in leaves and crowns while biosynthesis mutant BW084 showed a significantly smaller decrease. In both mutants, de-acclimation tolerance was associated with maintenance of optimal tissue hydration, as evidenced by lower osmotic potential and higher cell hydration compared to the reference cultivar.
Pociecha et al. (Tue,) studied this question.
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