ISHS Acta Horticulturae 179: V International Symposium on Growth Regulators in Fruit Production
AMMONIA, ARGININE, POLYAMINES AND FLOWER INITIATION IN APPLE |
| Author: | G.R. Edwards |
| Abstract:
Under controlled nutrient supply, flower initiation in the axillary meristems of maiden apple trees is significantly greater when nitrogen is supplied as NH4+ ions than when supplied as NO3- ions. The response occurs following even brief exposure to ammonium ions during an otherwise continuous nitrate supply. As little as 24 hours exposure is sufficient. Arginine is the major amino acid in the stems subtending axillary buds. Its concentration increases following exposure to ammonium ions and continues to rise over the following week whether or not the nitrogen source is changed back to nitrate. With a continuous nitrate supply the level of arginine is lower and declines over the period of a week. Other amino acids show similar differences. It seems that flower initiation in apple follows a slow natural increase or a sudden experimental upsurge in the level of reduced nitrogen, of which arginine is the major component. Simazine is known to increase the effectiveness of the nitrate reductase enzyme and should therefore increase the level of reduced nitrate in the tissues. The addition of 1 ppm simazine to nutrient solutions containing nitrate, either for 24 hours or one week, was found to be as effective as substituting ammonium for nitrate ions during similar periods of time. Simazine treatment therefore had the same effect as ammonium treatment both on the argenine level and on flower initiation. Arginine is an important precursor of the polyamines putrescine, spermidine and spermine. These have recently been shown to be correlated with cell division and morphogenesis in many plant systems. Infusion of polyamines into trees supplied with nitrate caused them to flower as profusely as trees exposed to ammonium ions. | |
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