Gravitropic response of acetylcholinesterase and IAA-inositol synthase in lazy rice [Oryza sativa]

We previously observed that gravistimulation changes the localization of acetylcholinesterase (AChE) and IAA-inositol synthase in maize shoots. In the present study, we analyzed the localization patterns of these enzymes in a lazy strain of rice, which lacks gravitropic responses. AChE was detected by color development due to enzymic reaction in the coleoptile of dark-grown rice plants under a light microscope. IAA-inositol synthase was detected immunochemically using an anti-IAA-inositol synthase polyclonal antibody. Gravistimulation was given by moving 5-d-old rice seedlings from a vertical to a horizontal position. AChE and IAA-inositol synthase in both normal and lazy rice strains were both distributed asymmetrically in the vascular bundles in the lower half of the horizontally oriented coleoptile at the 90th min. At the 4th h, they were distributed asymmetrically in normal rice, but symmetrically in the lazy rice. The immunoreaction of IAA-inositol synthase in the lazy rice was weak compared to that of the normal rice. Neostigmine bromide inhibited AChE activity and asymmetric distribution of IAA-inositol synthase in both normal and lazy rice strains. The results showed that AChE responded to gravistimulus, and consequently controlled the distribution of IAA-inositol synthase in both normal and lazy rice strains.