The role of gibberellins A(1) and A(3) in fruit growth of Pisum sativum L and the identification of gibberellins A(4) and A(7) in young seeds

Gibberellins A(1) and A(3) are the major physiologically active gibberellins (GAs) present in young fruit of pea (Pisum sativum L.). The relative importance of these GAs in controlling fruit growth and their biosynthetic origins were investigated in cv. Alaska. In addition, the non-13-hydroxylated active GAs, GA(4) and GA(7), were identified for the first time in young seeds harvested 4 d after anthesis, although they are minor components and are not expected to play major physiological roles. The GA(1) content is maximal in seeds and pods at 6 d after anthesis, the time of highest growth rate of the pod (Garcia-Martinez et al. 1991, Planta 184: 53-60), whereas gibberellic acid (GA(3)), which is present at high levels in seeds 4-8 d after anthesis, has very low abundance in pods. Gibberellins A(19), A(20) and A(29) are most concentrated in seeds at, or shortly after, anthesis and their abundance declines rapidly with development, concomitant with the sharp increase in GA(1) and GA(3) content. Application of GA(1) or GA(3) to the leaf subtending an emasculated flower stimulated parthenocarpic fruit development. Measurement of the GA content of the pods at 4 d after anthesis indicated that only 0.002-0.5% of the applied GA was transported to the fruit, depending on dose. There was a linear relationship between GA(1) content and pod weight up to about 2 ng . (g FW)(-1), whereas no such correlation existed for GA(3) content. The concentration of endogenous GA(1) in pods from pollinated ovaries is just sufficient to give the maximum growth response. It is concluded that GA(1), but not GA(3), controls pod growth in pea; GA(3) may be involved in early seed development. The distribution of GAs within the seeds at 4 d post anthesis was also investigated. Most of the GA(1), GA(8), GA(19), GA(20) and GA(29) was present in the testa, whereas GA(3) was distributed equally between testa and endosperm and GA(4) was localised mainly in the endosperm. Of the GAs analysed, only GA(3) and GA(20) were detected in the embryo. Metabolism experiments with intact tissues and cell-free fractions indicated compartmentation of GA biosynthesis within the seed. Using C-14- labelled GA(12), GA(9), 2,3-didehydroGA(9) and GA(20) as substrates, the testa was shown to contain 13-hydroxylase and 20-oxidase activities, the endosperm, 3 beta-hydroxylase and 20-oxidase activities. Both tissues also produced 16,17-dihydrodiols. However, GA(1) and GA(3) were not obtained as products and it is unlikely that they are formed via the early 13-hydroxylation pathway. [C-14]gibberellin A(12), applied to the inside surface of pods in situ, was metabolised to GA(19), GA(20), GA(29), GA(29)-catabolite, GA(81) and GA(97), but GA(1) was not detected. Gibberellin A(20) was metabolised by this tissue to GA(29) and GA(29)-catabolite.

Peer reviewed