Do phytohormones influence the uptake and metabolism of sucrose in spikelets of wheat?

Effects of GA(3), ABA and kinetin on C-14-sucrose uptake and invertase acti vity were studied in three cultivars of wheat (Triticum aestivum L.), namel y HD 2329, PEW 343 and Kalyansona, using detached ears cultured in a liquid medium containing phytohormones for 6 h (short culturing) or 3 days (long- culturing). During long culturing, addition of GA(3) and kinetin at 100 mu M increased the accumulation of free sugars in all the cultivars, but C-14- sucrose uptake and its conversion to starch was enhanced only in Kalyansona , suggesting differential hormonal responsiveness of the cultivars. Similar ly, invertase activity especially that of neutral invertase was enhanced by GA(3) and kinetin. ABA inhibited both sucrose uptake, starch and invertase activity in all the cultivars. These results suggest that gibberellin and cytokinin are positive modulators of grain sink activity, whereas ABA is a negative modulator. Hormonal stimulation of sink activity was reflected in increased dry matter accumulation and the starch content of grains.