Role of Gibberellins in Stem Elongation and Flowering in Radish

Abstract

The relationship among gibberellins, CCC, vernalization, and photoperiod in the flowering response of radish, Raphanus sativus L., cv. Miyashige-sofuto, was studied. The optimal condition for flowering was vernalization and a 16-hour photoperiod; GA(3) had no additional effect. Gibberellin A(3) (60 mug total) was not able to induce flowering in nonvernalized plants grown on 8-hour days, but it did increase the percentage of nonvernalized plants that flowered under long days from 60 to 100.Gibberellin content of vernalized seedlings increased within the first 24 hours after seedlings were transferred to the greenhouse. Content reached a peak in the first 4 days after transfer and thereafter remained constant. Essentially no gibberellin was found in 2 day-old non-vernalized (control) seedlings of comparable size to the vernalized ones. Gibberellin content in the controls reached a peak on the fourth day of growth in the greenhouse; thereafter, it decreased steadily.Bolting was inhibited slightly by CCC when applied during vernalization; it was almost completely inhibited when CCC was applied after seed vernalization. Extraction experiments revealed that CCC actually reduced the gibberellin content when applied during or after vernalization. The dwarfing agent, however, had essentially no effect on flowering. We concluded that gibberellins likely play a direct role in bolting of ;Miyashige-sofuto' radish, but probably are not directly functional in initiating flowering.