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 selection", which demonstrates improved survival in summer drought, and two from the white clover cultivar "Grasslands Kopu", a more drought-sensitive cultivar, are compared in terms of their responses to a water deficit. Plants of each genotype were grown in a temperature-controlled glasshouse and a water deficit imposed through deprivation. Proline content and the relative abundance of soluble carbohydrates were determined in mature leaf tissue excised from water-sufficient plants, from plants after a short-term period of water deprivation (prior to the onset of a significant change in leaf water potential (psi(t)) and from plants after a longer period of water deprivation (after a significant change in psi(t)). Proline accumulated in concert with the onset of a significant change in psi(t); the highest content of 2.7 mg/g FW being measured in the Syrian selection genotypes compared with 2.4 mg/g FW measured in Kopu. In water-sufficient leaf tissue, pinitol 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 deprivation, pinitol was again an abundant soluble carbohydrate but the proportion of sucrose (in the Syrian selection genotypes) and fructose (in the Kopu genotypes) had increased to comprise significant levels in the leaf tissue. After a longer period of water deprivation, pinitol was again the major sugar present and represented a significantly higher proportion of leaf soluble carbohydrate (p=0.003) in the Kopu genotypes when compared with the Syrian selection genotypes. The results show that pinitol is the major soluble sugar present in mature leaves of white clover when subjected to a significant water deficit.