Gibberellins in internodes and ears of wheat containing different dwarfing alleles

Gibberellins (GAs) belonging to the main early 13-hydroxylation GA pathway (GA(1), GA(3), GA(8), GA(17), GA(19), GA(20), GA(29), GA(44) and GA(53)) were identified by full-scan GC-mass spectrometry in rapidly expanding stem internodes and young ears of wheat. In addition, GA(97) (2 beta-hydroxy GA(53)) and GA(98) (2 beta-hydroxy GA(44)) were detected in reproductive, but not vegetative, tissues. Conversely, some members of the non-13-hydroxylation GA pathway (GA(4), GA(9) and GA(34)) were present in stem internodes but not in young ears. Later members of the main GA pathway (GA(19) --> GA(20) --> GA(1) --> GA(8)) were quantified by GC-selected ion monitoring in stem internodes and ears. In the rht (tall) line, GA(19) >>> GA(20) approximate to GA(1) << GA(8) during the main phase of expansion growth of both stem internodes and ears, suggesting that the conversion of GA(19) to GA(20) is a rate-limiting step on the GA pathway. In vegetative stem internodes, GA(1) concentration increased in proportion to the severity of the Rht1 (semi-dwarf) and Rht3 (dwarf) phenotypes but, at certain stages of Rht3 internode development, the expected decrease in GA(19) content, relative to the GA-responsive, rht (tall) line, did not occur and both GA(19) and GA(1) accumulated. In very young ears of both tall and dwarf lines, the concentrations of GA(20) and GA(8) were high, suggesting low 3 beta-(GA(20) to GA(1)) and high 2 beta-(GA(1) to GA(8)) hydroxylase activities prior to the period of rachis elongation. The Rht alleles had no effect on either GA content or rates of ear rachis elongation during the main phase of ear growth, providing indirect evidence that Rht genes are not expressed in expanding wheat ears. (C) 1998 Elsevier Science Ltd. All rights reserved.