Plant Physiology 70:1634-1636 (1982)
© 1982 American Society of Plant Biologists
Articles
Estimation of Osmotic Parameters Accompanying Zeatin-Induced Growth of Detached Cucumber Cotyledons 1
David L. Rayle,
Cleon W. Ross2 and
Nina Robinson3
Department of Botany, San Diego State University, San Diego, California 92181,
Department of Botany and Plant Pathology, Colorado State University, Fort Collins, Colorado 80523
Water potential ( ), the osmotic potential ( ), and the pressure potential (p) of detached cotyledons isolated from Cucumis sativus L. cv Marketer seedlings after 0, 1.5, and 3 days growth with and without zeatin were determined. From zero time to 3 days, cotyledons incubated without exogenous zeatin exhibited a slight decrease in (from –0.4 to –1.0 bars), while those grown with zeatin developed even more negative values (about –4 bars). Both groups showed rising values (decreases in solutes per unit volume), but this rise was more dramatic in those treated with zeatin. These data indicate that the capacity of zeatin-treated cotyledons to take up water more rapidly than controls and thus expand faster must be due to wall loosening, as reflected in p values which declined during 3 days from about +11 bars to about +1.4 bars.
It was also found that freshly detached cotyledons or those grown without exogenous zeatin exhibited osmoregulation in polyethylene glycol (PEG) solutions. That is, while cotyledons initially lost H2O into certain PEG solutions, their values decreased over time and they began absorbing water after 1 to 4 hours. After 3 days growth, zeatin-treated cotyledons had lost most of this capacity of osmoregulate. It seems likely that osmoregulation in cotyledons not treated with zeatin is due to wall loosening rather than changes in . Zeatin-treated cotyledons with already loosened walls may not have this option to deal with water stress and thus simply come to equilibrium with external PEG solutions.
2 To whom requests for reprints should be addressed.
3 Present address: Department of Biochemistry and Biophysics, University of California, Davis, CA 95616.
1 Supported by National Science Foundation Grant PCM 79-22139 to Colorado State University.
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