Effect of gibberellic acid on growth and carbohydrate metabolism of developing tubers of potato (Solanum tuberosum) [potato tubers, starch synthesizing enzymes]
1981
Mares, D.J. (Sydney Univ. (Australia). Plant Breeding Inst. Narrabri) | Marschner, H. | Krauss, A.
Potato plants (Solanum tuberosum L. cv. Ostara) were grown in aerated water culture in a controlled environment. When the tubers had reached a diameter of 1-3 cm, ('14)C-labelled or unlabelled gibberellic acid(GA(,3)) was applied to the surface of the stolons at points approximately 1 cm from the developing tubers, and treatment continued for 10 days. Significant quantities of GA(,3) moved into tuber tissue within 2-4 days of hormone application. This influx of GA(,3) was accompanied by a marked reduction in both the activity of ADPG-pyrophosphorylase and the ratio ADPG-pyrophosphorylase/starch phosphorylase and an increase in the activity of UDPG-pyrophosphorylase. Starch phosphorylase activity initially increased slightly but then fell, whereas the activity of starch synthase remained constant throughout the experiment. The soluble sugar composition of the tubers changed qualitatively towards a pattern characteristic of growing stolon tips prior to tuber initiation, but there was no clear evidence of net starch degradation. Changes in the activities of the enzymes were observed prior to noticeable effects of the hormone on tuber growth rate or the development of new stolons at the tuber eyes. GA(,3)-treated tubers imported more ('14)C from labelled photosynthate than expected on the basis of growth rate. However, the capacity to convert soluble-('14)C to ethanol-insoluble-('14)C (predominantly starch) was reduced in comparison with non-treated tubers. The observed changes in carbohydrate composition and enzyme activities indicate that GA(,3) induces a drastic change in potato tuber metabolism towards a pattern characteristic for the termination of the storage process.
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