Endogenous gibberellins in Lolium perenne and influence of defoliation on their contents in elongating leaf bases and in leaf sheaths

Gibberellin (GA) levels in leaf sheaths and in elongating leaf bases of per ennial ryegrass (Lolium perenne L. cv. Bravo) were monitored in undefoliate d and defoliated plants. Nine C-13-hydroxylated GAs (GA(8), GA(97), GA(29), GA(1), GA(,20), GA(44), GA(19), GA(17), GA(53)) and one C-13-non-hydroxyla ted GA (GA(9)) were identified by combined gas chromatography-mass spectrom etry in leaf extracts. The total level of GA(8), GA(29), GA(1), GA(20), GA( 44), GA(19) and GA(53), determined by selected ion monitoring, was 7 times higher in elongating leaf bases than in mature leaf sheaths. In both leaf t issues, defoliation induced an increase in GA(53) level, while GA(20) and G A(1) levels decreased, suggesting that the GA(53) --> GA(44), as well as GA (19) --> GA(20), conversions were slowed down. The roles of GA(1) in the co ntrol of leaf elongation and fructan mobilization following defoliation are discussed.