Stress-induced Accumulation of Osmoprotectants in four Plantago Species

Abstract

We have studied whether two common osmolytes - proline (Pro) and glycine betaine (GB) - accumulate in plants of different Plantago species in response to salt and water stress, which would suggest that these compatible solutes and ‘osmoprotectants` fulfil a functional role of in the plants` stress tolerance mechanisms. Plants of P. coronopus, P. major, P. crassifolia and P. lagopus were treated with increasing NaCl concentrations or subjected to water stress, under controlled conditions in the greenhouse. GB and Pro contents in control, non-stressed plants were relatively low and, in most cases, did not change, or increased only moderately when the plants were maintained without water or were grown in the presence of up to 400 mM NaCl, for four weeks. However, higher salt concentrations (450 - 600 mM NaCl), which these taxa never encounter in their natural habitats, induced a significant accumulation of Pro in all species but P. major, the most salt-sensitive one. These data indicate that GB and Pro do not act as functional osmolytes in Plantago species, and do not contribute to osmotic adjustment under natural conditions; however, these plants have the potential to activate Pro-mediated mechanisms of salt tolerance at very high, artificial salinity levels.