Pinitol accumulation in mature leaves of white clover in response to a water deficit

In this study, two genotypes from the white clover breeding line 'Syrian se lection', which demonstrates improved survival in summer drought, and two f rom the white clover cultivar 'Grasslands Kopu', a more drought-sensitive c ultivar, are compared in terms of their responses to a water deficit. Plant s of each genotype were grown in a temperature-controlled glasshouse and a water deficit imposed through water deprivation. Proline content and the re lative abundance of soluble carbohydrates were determined in mature leaf ti ssue excised from water-sufficient plants, from plants after a short-term p eriod of water deprivation (prior to the onset of a significant change in l eaf water potential (psi(t))) and from plants after a longer period of wate r deprivation (after a significant change in psi(t)) Proline accumulated in concert with the onset of a significant change in psi(t); the highest cont ent of 2.7 mg/g FW being measured in the Syrian selection genotypes compare d with 2.4 mg/g FW measured in Kopu. In water-sufficient leaf tissue. pinit ol was the major soluble carbohydrate present, with a significantly higher content (p = 0.027) in terms of relative abundance in the Syrian selection genotypes when compared with the Kopu genotypes. After short-term water dep rivation, pinitol was again an abundant soluble carbohydrate but the propor tion of sucrose tin the Syrian selection genotypes) and fructose tin the Ko pu genotypes) had increased to comprise significant levels in the leaf tiss ue. After a longer period of water deprivation, pinitol was again the major sugar present and represented a significantly higher proportion of leaf so luble carbohydrate (p = 0.003) in the Kopu genotypes when compared with the Syrian selection genotypes. The results show that pinitol is the major sol uble sugar present in mature leaves of white clover when subjected to a sig nificant water deficit. (C) 2000 Elsevier Science B.V. All rights reserved.