Gibberellins in internodes and ears of wheat containing different dwarfing alleles
1998
Webb, S.E. | Appleford, N.E.J. | Gaskin, P. | Lenton, J.R.
Gibberellins (GAs) belonging to the main early 13-hydroxylation GA pathway (GA1, GA3, GA8, GA17, GA19, GA20, GA29, GA44 and GA53) were identified by full-scan GC-mass spectrometry in rapidly expanding stem internodes and young ears of wheat. In addition, GA97 (2 beta-hydroxy GA53) and GA98 (2 beta-hydroxy GA44) were detected in reproductive, but not vegetative, tissues. Conversely, some members of the non-13-hydroxylation GA pathway (G4, G9 and GA34) were present in stem internodes but not in young ears. Later members of the main GA pathway (GA19 leads to GA20 leads to GA1 leads to GA8) were quantified by GC-selected ion monitoring in stem internodes and ears. In the rht (tall) line, GA19 >>> GA20 approximately GA1 << GA8 during the main phase of expansion growth of both stem internodes and ears, suggesting that the conversion of GA19 to GA20 is a rate-limiting step on the GA pathway. In vegetative stem internodes, GA1 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 GA19 content, relative to the GA-responsive, rht (tall) line, did not occur and both GA19 and GA1 accumulated. In very young ears of both tall and dwarf lines, the concentrations of GA20 and GA8 were high, suggesting low 3 beta-(GA20 to GA1) and high 2 beta-(GA1 to GA8) 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.
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