Does proline accumulated in leaves of water deficit stressed barley plants confine cell membrane injury? I. Free proline accumulation and membrane injury index in drought and osmotically stressed plants

The aim of this work was to examine the relationship between proline accumulation and membrane injury in barley leaves suffering from the effects of water deficit. Water deficit stress was induced by water withholding or by immersing the roots in polyethylene glycol (PEG 6000) solution of osmotic potential -1.5 MPa. The effect of water stress on proline accumulation and on membrane injury was evaluated in leaf blades of several barley genotypes. Substantial differences in proline accumulation and membrane injury indices among most of the genotypes investigated were observed. It was found that in drought stressed plants a higher ability to accumulate proline positively correlates with lower membrane injury. Whereas, in osmotically stressed plants the highest proline accumulation in the leaves was noticed in genotype with the largest membrane injury. The possible role of proline in membrane protection under conditions of slow-acting drought or shock-acting osmotic stress is discussed.