Abstract
Summary Proline (Pro) is a versatile metabolite playing a role in the protection of plants against environmental stresses. To gain a deeper understanding of the regulation of Pro metabolism under predicted future climate conditions, including drought stress, elevated temperature and CO 2, we combined measurements in contrasting grassland species (two grasses and two legumes) at multiple organisational levels, that is, metabolite concentrations, enzyme activities and gene expression.Drought stress (D) activates Pro biosynthesis and represses its catabolism, and elevated temperature (DT) further elevated its content. Elevated CO 2 attenuated the DT effect on Pro accumulation.Computational pathway control analysis allowed a mechanistic understanding of the regulatory changes in Pro metabolism. This analysis indicates that the experimentally observed coregulation of multiple enzymes is more effective in modulating Pro concentrations than regulation of a single step. Pyrroline‐5‐carboxylate synthetase (P5CS) and pyrroline‐5‐carboxylate reductase (P5CR) play a central role in grasses (Lolium perenne, Poa pratensis), and arginase (ARG), ornithine aminotransferase (OAT) and P5CR play a central role in legumes (Medicago lupulina, Lotus corniculatus).Different strategies in the regulation of Pro concentrations under stress conditions were observed. In grasses the glutamate pathway is activated predominantly, and in the legumes the ornithine pathway, possibly related to differences in N‐nutritional status.
Highlights
Proline (Pro) is an essential proteinogenic amino acid, and is known as a stress defence molecule
In previous work we showed that elevated CO2 alleviated photosynthesis inhibition under drought stress conditions, and reduced stress impact through reducing photorespiration and formation of hydrogen peroxide (H2O2; AbdElgawad et al, 2015)
The activity of Pyrroline-5-carboxylate synthetase (P5CS) was induced by drought and elevated temperature, in the grass species but not in the legumes (Fig. 2d)
Summary
Proline (Pro) is an essential proteinogenic amino acid, and is known as a stress defence molecule. An increased rate of Pro biosynthesis can help to maintain higher NADP+: NADPH ratios and stabilize the redox balance (Hare & Cress, 1997; Szabados & Savoure, 2010). Other proposed functions of Pro include storage and transfer of energy (Abraham et al, 2003; Szabados & Savoure, 2010; Verslues & Sharma, 2010). Taken together, it is a remarkably multifunctional molecule involved in plant stress defence
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