The effects of gibberellic acid and 6-benzylaminopurine on chlorophyll synthesis in the primary leaves of Phaseoulus aureus (mung bean) have been investigated. These have been related to the role of the cotyledon and hypocotyl in controlling chlorophyll formation during illumination of the etiolated seedlings. The importance of the cotyledon to chlorophyll production declined with age after six days of etiolated growth and in five day old plants was of less significance than the presence of the hypocotyl. The presence of both organs resulted in interference and not an additive interaction. Gibberellic acid and 6-benzylaminopurine promoted and inhibited chlorophyll synthesis. The nature of the response was dependent on the concentration of the hormone and the age of the leaf. In the absence of photosynthesis, the activity of both hormones was altered. Gibberellic acid proved ineffective and 6-benzylaminopurine inhibitory. The addition of sucrose to this or the control system (+ photosynthesis) indicated that gibberellic acid was more responsive to carbohydrate supply than was 6-benzyl-aminopurine. An examination of different carbohydrate sources revealed that sucrose most affected the hormone-Induced responses. The interaction of the two hormones showed a strong synergistic response in five day old leaves. This was present at the higher concentrations of each hormone; the lower concentrations appeared antagonistic. Changes in the interaction were investigated with regard to age and substrate supply and were related to the level of endogenous gibberellin. Possible effects of the hormones on chloroplast replication and carbon dioxide exchange were also examined. The results are discussed in relation to the mode of action of the hormones and their role in the greening of primary leaves.
|Date of Award||1973|