Kinetics of maize leaf elongation IV. Effects of (+)- and (-)-abscisic acid |
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Authors: | Cramer G; Krishnan K; Abrams S |
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Institution: | Department of Biochemistry, Mail Stop 200, University of Nevada, Reno, NV 89557, USA; Plant Biotechnology Institute, National Research Council of Canada, 110 Gymnasium Road, Saskatoon, Saskatchewan, SK, S7N 0W9, Canada; Corresponding author |
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Abstract: | Abscisic acid (ABA) is involved in many of the responses of plants to
environmental stress. This study focuses on the inhibitory effect of ABA on
leaf expansion. In addition, the effects of (+)-ABA, the natural form of
ABA, were compared to the effects of (-)-ABA. Leaf elongation rates
(LER) were measured for the 3rd leaf of maize plants.
ABA concentrations were measured by RIA for total ABA and an ELISA specific
for (+)-ABA. ABA was added to the hydroponic solution and changes in the
LER were measured over time. ABA could inhibit
LER within 30 min ad reached steady-state
LER within 4 h. Internal ABA concentrations in the
growing zone of the leaf also reached steady-state concentrations after 4
h. This effect of ABA was reversible, because LER was
fully restored upon removal of externally applied ABA, and internal
concentrations of ABA in the growing zone returned to normal levels,
whereas ABA concentrations remained elevated in mature tissue. Thus,
steady-state LER was highly correlated with the
steady-state internal ABA concentration of the growing zone. ABA inhibited
leaf expansion by increasing the apparent cell wall yield threshold; no
other growth parameters were affected. The (-)-enantiomer of ABA had much
less effect on LER than (+)-ABA when compared upon an
external concentration basis. Internal ABA concentrations rationalized the
response, showing that (-)-ABA accumulation was very low, most likely due
to low uptake rates. From this analysis, it was determined that
LER was equally sensitive to internal concentrations
of (+)- or (-)-ABA. |
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