The localization, metabolism and biological activity of gibberellins in maturing and germinating seeds of Pisum sativum cv. Progress No. 9

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Abstract
Gibberellin A20 (GA20), GA29 and GA29-catabolite were quantified in cotyledons, embryonic axes, and testas of Pisum sativum cv. Progress No. 9 throughout the final stages of seed maturation and during germination. Stable isotope-labelled GAs were used as internal standards in conjunction with combined gas chromatography-mass spectrometry. Gibberellin A20 and GA29 were mainly located in the cotyledons of maturing seeds, and GA29-catabolite was predominantly located in the testa. Stable isotope- and radio-labelled GA20 and GA29 were fed to both intact seeds developing in vivo, and to isolated seed parts cultured in vitro. The combined results of in-vivo and in-vitro feeds indicated that GA20 is metabolised to GA29 in the cotyledons, that GA29 is transported from the cotyledons to the testa, and that GA29 is metabolised to GA29-catabolite in the testa. Although the metabolism of GA20 in the cotyledons and of GA29 in the testa has been shown definitively, the mobility of GA29 has not yet been demonstrated directly. During seed desiccation and germination GA29-catabolite and products arising from it are transferred from the testa into the embryo. There is no evidence of a physiological function for GA29-catabolite in germination or early seedling growth. Use of a growth retardant indicates that seedling growth, but not germination, is dependent on de-novo GA biosynthesis.

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