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

Abstract

The effect of GA<sub>3</sub> 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 <sup>14</sup>C0<sub>2</sub> assimilation preceded diminished export of current photosynthates. In plants with K<sup>+</sup>-deficit, transfer for 3 days from low- to high-K solution stimulated photosynthesis without effect on <sup>14</sup>C-export. Three days after GA<sub>3</sub> treatment of the swollen hypocotyl <sup>14</sup>C0<sub>2</sub> assimilation was stimulated while <sup>14</sup>C-retention in the blades was diminished, but only in low-K plants. In Tetra low-K plants with poorly developed storage organs, treatment with GA<sub>3</sub> 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 GA<sub>3</sub> even in K-deficient plants; the swollen hypocotyl was already developed before K depletion from the nutrient solution. Nevertheless, in Saxa plants, GA<sub>3</sub> 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 GA<sub>3</sub> 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 GAY