Effect of GA3 on photosynthate allocation and invertase activity in radish plants grown on different potassium levels

The effect of GA3 application to the swollen hypocotyl was studied in radish cultivars Saxa and Tetra Iłowiecka, supplied with various amount of K and grown in greenhouse in hydroponic culture. In low-K plants of both compared cultivars, strong depression of 14C02 assimilation preceded diminished export of current photosynthates. In plants with K+-deficit, transfer for 3 days from low- to high-K solution stimulated photosynthesis without effect on 14C-export. Three days after GA3 treatment of the swollen hypocotyl 14C02 assimilation was stimulated while 14C-retention in the blades was diminished, but only in low-K plants. In Tetra low-K plants with poorly developed storage organs, treatment with GA3 caused their better supply with current photosynthates at the expense of the roots. In the Saxa cultivar, the pattern of photosynthate allocation was only slightly affected by GA3 even in K-deficient plants; the swollen hypocotyl was already developed before K depletion from the nutrient solution. Nevertheless, in Saxa plants, GA3 prolonged not only growth of the storage organ, but also enhanced acid invertase which at that time was greatly diminished in low- and high-K plants. In contrast, the relatively high activity of invertase in Tetra cv. was not affected by GA3 treatment in low-K plants and was even depressed in high-K plants. This suggests that growth and accumulation of substances in the storage organ of radish plants and acid invertase activity greatly differ in their response to applied GA