Is photosynthetic activity responsible for the stimulating effect of light on ABA-induced proline accumulation in barley leaves?

In hydrated barley leaf segments incubated in solution for 7 h, the accumulation of proline induced by 100 mu mol/L ABA with the synergistic interaction of KCl was stimulated by white, blue (460 nm) and red (660 nm) light. With 30 mmol/L KCl concentration, the stimulating effect of light reached a plateau at a photon fluence of 120, 40 and 10 mu mol sec(-1) m(-2) for white, blue and red light, respectively. The contents of proline at the plateau level were similar with the different lights. DCMU effectively inhibited the hormonal process both in the light and in the dark. Experiments with etiolated barley leaves showed that also in these leaves the hormonal process occurred in the dark. The light stimulated, as in the case of green leaves, ABA-induced proline accumulation in the leaves without differentiated chloroplasts and the effect of white, blue and red light showed a considerable effectiveness at low light intensity. The stimulation of the three lights reached a plateau in the presence of 30 mmol/L KCl and at the same photon irradiance as that for green leaves. In etiolated, light-incubated leaves, ABA inhibited chlorophyll synthesis as a function of its concentration and the inhibition was almost complete at 100 mu mol/L concentration. The comparison of chlorophyll content and accumulated proline content in green and etiolated leaves showed that the capability of proline accumulation in the light is independent of chlorophyll content. The results indicated that photosynthesis cannot be responsible for light-stimulation of proline accumulation induced by exogenously supplied ABA in hydrated barley leaves.