Osmoprotection by proline accumulation induced by rainfall variations in three steppe plants species Aristida pungens, Retama raetam and Astragalus armatus under Mediterranean Arid bioclimate

Abstract

Since the middle of the last century, the Algerian steppe vegetation has been in continuous decline, which could be subject to environmental constraints that go against the sustainable development of a fragile environment exposed to climatic variations. Good management of this environment would be based on understanding the mechanisms of tolerance of steppe plant communities to the rainfall variations of the territory where they live. In the present study, for four years (2019- 2022), during the spring season, under arid bioclimate in the central Algerian Laghouat steppe region (Mokrane site), the relative water content (RCW) and the accumulated proline content were measured in the fresh leaves of three plant species (R. raetam, A. armatus and A. pungens). Also, a climatic synthesis of the study site was carried out. The aridity index of the site was found to be 0.06, and annual rainfall differences > 150 mm have sometimes been observed. The site is characterized by 11 months of drought over the year. During the 04 years, 2019 was the rainiest year receiving 238.88mm precipitation. During the 04 years of measurement, RCW revealed the existence of significant differences (P<0.05) for each of the three species. In R. raetam, the RWC was between 18.6 and 49.6%; for A. armatus 12 and 33.31% and for A. pungens 12.04 and 77.42% respectively. Between 2019 and 2022, the proline content also showed significant differences (P<0.05) for each of the three species. In R. raetam it was between 0.13- 1.4 mmol/g FM, for A. armatus between 0.26 - 0.96 mmol/g FM and between 0.20 -1.12 mmol/g FM for A. pungens. Pearson correlations revealed that annual cumulative rains were weakly correlated with RWC, but the correlation was strong and in a negative direction with accumulated proline. These results demonstrated that adaptation of the three species to rainfall variations is based on a tolerance mechanism driven by proline synthesis.