PLANT PHYSIOLOGY , Vol 105, Issue 3 937-940, Copyright © 1994 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
The Response to Gravity Is Correlated with the Number of Statoliths in Chara Rhizoids
J. Z. Kiss
Department of Botany, Miami University, Oxford, Ohio 45056
In contrast to higher plants, Chara rhizoids have single membrane-bound
compartments that appear to function as statoliths. Rhizoids were generated
by germinating zygotes of Chara in either soil water (SW) medium or
artificial pond water (APW) medium. Differential-interference-contrast
microscopy demonstrated that rhizoids from SW-grown plants typically
contain 50 to 60 statoliths per cell, whereas rhizoids from APW-grown
plants contain 5 to 10 statoliths per cell. Rhizoids from SW are more
responsive to gravity than rhizoids from APW because (a) SW rhizoids were
oriented to gravity during vertical growth, whereas APW rhizoids were
relatively disoriented, and (b) curvature of SW rhizoids was 3 to 4 times
greater throughout the time course of curvature. The growth rate of APW
rhizoids was significantly greater than that of SW-grown rhizoids. This
latter result suggests that APW rhizoids are not limited in their ability
for gravitropic curvature by growth and that these rhizoids are impaired in
the early stages of gravitropism (i.e. gravity perception). Plants grown in
APW appeared to be healthy because of their growth rate and the vigorous
cytoplasmic streaming observed in the rhizoids. This study is comparable to
earlier studies of gravitropism in starch-deficient mutants of higher
plants and provides support for the role of statoliths in gravity
perception.
