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.