Effects of abscisic acid, fusicoccin, and potassium on growth and morphogenesis of leaves and internodes in dark-grown rice seedlings

Abstract

We investigated the effects of abscisic acid (ABA), fusicoccin (FC) and potassium on the appearance of “MC” or “non-MC” type rice (Oryza sativa L.) seedlings. The MC type seedling referred to a seedling which only consisted of mesocotyl and coleoptile (the undeveloped leaves were enclosed by the coleoptile),whereas non-MC type seedling was the seedling consisted of greatly elongated leaves and internodes. Seedlings were grown on 0.8 % agar medium in the presence or absence of ABA, FC and KCl under aseptic conditions at 30 °C in the dark for 14 days. In cv. ‘Basmati 217’, MC type cultivar, 2 × 10-2 M KCl or 10-6 M FC both reduced the frequency of occurrence of the MC type seedlings among the investigated plants. Mesocotyl growth was inhibited about 45% by KCl and 90% by FC. In cv. 'JC 91', non-MC type cultivar, 1.5 × 10-6 M ABA increased the percentage of the MC type seedlings and reduced coleoptile growth by 78% and second leaf growth by 87% However, during this treatment mesocotyl growth was stimulated by 195%. The effects of ABA were almost entirely overcome by FC. Thus, the action of these substances results in a drastic change in the morphological development of dark-grown rice seedlings. Since it has been reported that FC stimulates the development of K+ uptake coupled to H+ extrusion and ABA inhibits this function, we suggest that ABA and FC may regulate the morphogenesis of leaves and internodes of rice seedlings via the H+/K+ ion exchange system.