The involvement of gibberellins with the internode length and flowering genotypes of Pisum

This study was primarily concerned with the involvement of gibberellins in the control of internode length in a range of genotypes of Pisum sativum L. Shoots of tall peas (Le) are shown by lettuce hypocotyl and rice seedling bioassays to contain a relatively large amount of a polar gibberellin-like substance which is either absent from or present in only small amounts in dwarf peas (Ls). This biochemical difference can be attributed to a genetic difference at the Le locus. Preliminary results using unrelated pure breeding tall and dwarf lines were confirmed by the use of an F2 progeny segregating for the Le/le pair of alleles. The polar gibberellin-like substance in shoots of tall peas is tentatively identified by GCMS-MIM as GA1. In tall peas, the GA1-like substance is located mainly in the actively growing and elongating apical region of the shoot. Its level is much reduced in mature leaf and stem tissue, perhaps explaining the lack of a graft transmissible effect of the tall and dwarf phenotypes. GA20 is the major active gibberellin in dwarf peas and the GA20-like substance is also shown to be located mainly in the apical region of the shoot of both tall and dwarf peas. Shoots of the extremely short plants with mutant na are found by bioassay to contain undetectable levels of gibberellin-like substances. This is confirmed by the use of near isogenic lines differing at the Na locus. Results from graft and feed experiments using the gibberellin deficient na Le and na is plants suggest that the Le gene controls the conversion of GA20 to the GA1-like compound by promoting 31β-hydroxylation (as evidenced by high activity in the rice seedling bioassay using cv. Waito C). In contrast to their action in the shoot, the na and Le genes do not influence the gibberellin-like content of immature seed, suggesting that the action of genes controlling gibberellin biosynthesis or metabolism can be organ or tissue specific. In an F2 progeny, shoots of slender and dwarf segregates show no large differences in gibberellin content that would explain the large phenotypic difference. The slender phenotype (la cry8 ) can be mimicked in dwarf peas with the application of non-limiting quantities of GA3 . However, as slender peas appear insensitive to changes in gibberellin levels, it is suggested that genes at the La and Cry loci are influencing some process at or beyond the activation of the gibberellin receptor site. The gibberellin content of a range of different flowering genotypes was examined to provide evidence for or against a reported link between the flowering genes Sn and Hr and gibberellin metabolism. The results do not support the theory that the primary action of these genes is to control gibberellin metabolism. The results do show an apparent drop in the level of the GA20-like substance with the onset of apical senescence in some lines making the comparison of early flowering to later flowering genotypes difficult