POLLINATION INCREASES GIBBERELLIN LEVELS IN DEVELOPING OVARIES OF SEEDED VARIETIES OF CITRUS

Reproductive and vegetative tissues of the seeded Pineapple cultivars of sweet orange (Citrus sinensis L.) contained the following C-13 hydr oxylated gibberellins (GAs): GA(53), GA(17), GA(19), GA(20), GA(1), GA (29), and GA(8), as well as GA(97), 3-epi-GA(1), and several uncharact erized GAs. The inclusion of 3-epi-GA(1) as an endogenous substance wa s based on measurements of the isomerization rates of previously added [H-2(2)]GA(1). Pollination enhanced amounts of GA(19), GA(20), GA(29) , and GA(8) in developing ovaries. Levels of GA(1) increased from 5.0 to 9.5 ng/g dry weight during anthesis and were reduced thereafter. Th e amount of GA in mature pollen was very low. Emasculation reduced GA levels and caused a rapid 100% ovary abscission. This effect was parti ally counteracted by either pollination or application of GA(3). In po llinated ovaries, repeated paclobutrazol applications decreased the am ount of GA and increased ovary abscission, although the pattern of con tinuous decline was different from the sudden abscission induced by em asculation. The above results indicate that, in citrus, pollination in creases GA levels and reduces ovary abscission and that the presence o f exogenous GA(3) in unpollinated ovaries also suppresses abscission. Evidence is also presented that pollination and GAs do not, as is gene rally assumed, suppress ovary abscission through the reactivation of c ell division.