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 gibber ellins (GAs) present in young fruit of pea (Pisum sativum L.). The rel ative importance of these GAs in controlling fruit growth and their bi osynthetic origins were investigated in cv. Alaska. In addition, the n on-13-hydroxylated active GAs, GA(4) and GA(7), were identified for th e first time in young seeds harvested 4 d after anthesis, although the y are minor components and are not expected to play major physiologica l roles. The GA(1) content is maximal in seeds and pods at 6 d after a nthesis, the time of highest growth rate of the pod (Garcia-Martinez e t al. 1991, Planta 184: 53-60), whereas gibberellic acid (GA(3)), whic h is present at high levels in seeds 4-8 d after anthesis, has very lo w abundance in pods. Gibberellins A(19), A(20) and A(29) are most conc entrated in seeds at, or shortly after, anthesis and their abundance d eclines 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 devel opment. Measurement of the GA content of the pods at 4 d after anthesi s 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 endo genous GA(1) in pods from pollinated ovaries is just sufficient to giv e 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 de velopment. The distribution of GAs within the seeds at 4 d post anthes is 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 equall y between testa and endosperm and GA(4) was localised mainly in the en dosperm. Of the GAs analysed, only GA(3) and GA(20) were detected in t he embryo. Metabolism experiments with intact tissues and cell-free fr actions 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-oxida se activities, the endosperm, 3 beta-hydroxylase and 20-oxidase activi ties. Both tissues also produced 16,17-dihydrodiols. However, GA(1) an d 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 G A(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.