Pseudogibberellin A1 as an inhibitor of the GA3-induced growth of rice seedlings

Promotion of flowering in apple trees with gibberellin A4 and C-3 epi-gibberellin A 4

The proportion of spurs flowering on apple trees (Malus domestica Borkh. cv Golden Delicious) displaying a high degree of alternate-year flowering was increased in the "off" year by gibberellin A4 (GA4) and C-3 epi-GA4 applied in the previous year. When applied 4.5 weeks after anthesis amounts of GA4 ranging from 3 to 300 μg per spur and 25 or 50 μg of C-3 epi-GA4 per spur were effective. Treatments with GA4 made seven weeks after anthesis were less effective. A combination of 30 μg GA4 and 30 μg zeatin (6-(4-hydroxy-3-methylbut-trans-2-enylamino)purine) promoted flowering at both treatment times, and tended to be more effective than GA4 alone.

Activity of the aldehyde and alcohol of gibberellins A12 and A 14, two derivatives of gibberellin A 15 and four decomposition products of gibberellin A 3 in 13 plant bioassays

The biological activities of the aldehyde and alcohol of gibberellins (GAs) A12 and A14, 3α-OH-GA15, 3β-OH-GA15 wrong lactone (i.e. GA37 wrong lactone) and the four major decomposition products of GA3 (isogibberellic, allogibberic, epiallogibberic and Δ9(11)-dehydroallogibberic acids) were tested over a wide range of concentrations on 13 plant bioassays in order to ascertain certain of the structural requirements for biological activity. Generally modification of the basic GA-molecule decreased its activity in all assays except for derivatives of GA12 and GA14 (suggesting conversion of these derivatives to more polar, active GAs). Modification of the 3-OH from the usual 3β to 3α configuration markedly reduced activity. Neither the presence of an inverted lactone ring (i.e. 3β-OH-GA15 wrong lactone) nor changes to the lactone ring of GA3 (4→10) to form iso-GA3 (4→2) appreciably reduce activity. Further decomposition of GA3 to allogibberic and Δ9(11)-dehydroallogibberic acid reduced activity only slightly, but epimerization of allogibberic acid at C-9 essentially eliminated biological activity.

Metabolism of [(3)H]Gibberellin A 20 by plants of Bryophyllum daigremontianum under long- and short-day conditions

[(3)H]Gibberellin A20 ([(3)H]GA20), a native gibberellin of this plant, was injected into mature leaves of Bryophyllum daigremontianum (Hamet et Perr.) Berg. under long- and short-day conditions. It was converted, in order of decreasing yields, to GA29, 3-epi-GA1 (pseudo GA1), C/D-ring-rearranged GA20, and two minor, unidentified metabolites. Identifications were made by gas-liquid chromatography with radioactive monitoring using three different phases. Metabolism to 3-epi-GA1 was greater under short days, particularly in the treated leaf pair, although the absolute amount of GA29 was greater than that of 3-epi-GA1 under both photoperiods. The levels of radioactive metabolites in the shoots above the treated leaf pair gradually increased over a 51-day period, GA29 reaching 5 times the contten of 3-epi-GA1.