Water-Stress Induced Changes in Concentrations of Proline and Other Solutes in Growing Regions of Young Barley Leaves

Riazi, A., Matsuda, K. and Arslan, A. 1985. Water-stress induced changes in concentrations of proline and other solutes in growing regions of young barley leaves.—J. exp. Bot. 36: 1716–1725. Young, intact barley Hordeum vulgare L. cv. ‘Arivat’ seedlings stressed with PEG or NaCl were measured for water status and levels of proline, sugars and inorganic cations in growing (basal 1.0 cm) and other areas of leaves. In growing regions, reductions in ψn were found within 1 h in seedlings stressed with PEG (−0.8 M Pa) but 4 h were required before proline increased and proline accounted for less than 5% of the osmotic adjustment after 24 h. Increases in proline occurred to a lesser extent in expanded mid-blade regions where osmotic adjustment was less. After one or more days stress, proline levels in basal tissues were 10 × higher than in mid-blade tissues, and proline increases in these and intervening tissues occurred without loss of turgor. When seedlings were stressed for extended periods with mild to moderate concentrations of PEG, proline elevations in basal to mid-blade areas were proportional to reductions in tissue ψ and ψn NaCl-stress led to similar responses except prohne increases per unit decrease in ψx, were 2–3 × greater than in PEG-stressed tissues. Time-course studies showed levels of inorganic cations were not altered in the growing areas during the first few h of PEG-induced stress, but glucose increased as ψx, decreased. The results showed that proline increase is not the cause but could be a consequence of osmotic adjustment, and its increase is not due to cell death. They also provided independent evidence that stress responses of growing tissues differ substantially from expanded areas in young barley leaves.