PLANT PHYSIOLOGY , Vol 114, Issue 1 47-53, Copyright © 1997 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Asymmetric Distribution of Acetylcholinesterase in Gravistimulated Maize Seedlings
Y. S. Momonoki
Faculty of Bioindustry, Tokyo University of Agriculture, 196 Yasaka, Abashiri, Hokkaido 09924 Japan
Acetylcholinesterase (AChE) activity has previously been studied by this
laboratory and shown to occur at the interface between the stele and cortex
of the mesocotyl of maize (Zea mays L.) seedlings. In this work we studied
the distribution of AChE activity in 5-d-old maize seedlings following a
gravity stimulus. After the stimulus, we found an asymmetric distribution
of the enzyme in the coleoptile, the coleoptile node, and the mesocotyl of
the stimulated seedlings using both histochemical and colorimetric methods
for measuring the hydrolysis of acetylthiocholine. The hydrolytic
capability of the esterase was greater on the lower side of the
horizontally placed seedlings. Using the histochemical method, we localized
the hydrolytic capability in the cortical cells around the vascular stele
of the tissues. The hydrolytic activity was inhibited 80 to 90% by
neostigmine, an inhibitor of AChE. When neostigmine was applied to the corn
kernel, the gravity response of the seedling was inhibited and no
enzyme-positive spots appeared in the gravity-stimulated seedlings. We
believe these results indicate a role for AChE in the gravity response of
maize seedlings.
