PLANT PHYSIOLOGY , Vol 108, Issue 4 1471-1477, Copyright © 1995 by American Society of Plant Biologists
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DEVELOPMENT AND GROWTH REGULATION |
Diurnal Regulation of Leaf Blade Elongation in Rice by CO2 (Is it Related to Sucrose-Phosphate Synthase Activity?)
S. P. Seneweera, A. S. Basra, E. W. Barlow and J. P. Conroy
School of Horticulture, University of Western Sydney, Hawkesbury, Bourke Street, Richmond, New South Wales 2753, Australia
The relationship between leaf blade elongation rates (LER) and
sucrose-phosphate synthase (SPS) activity was investigated at different
times during ontogeny of rice (Oryza sativa L. cv Jarrah) grown in flooded
soil at either 350 or 700 [mu]L CO2 L-1. High CO2 concentrations increased
LER of expanding blades and in vivo activity (Vlimiting) SPS activity of
expanded blades during the early vegetative stage (21 d after planting
[DAP]), when tiller number was small and growing blades were strong
carbohydrate sinks. Despite a constant light environment, there was a
distinct diurnal pattern in LER, Vlimiting SPS activity, and concentration
of soluble sugars, with an increase in the early part of the light period
and a decrease later in the light period. The strong correlation (r = 0.65)
between LER and Vlimiting SPS activity over the diurnal cycle indicated
that SPS activity played an important role in controlling blade growth. The
higher Vlimiting SPS activity at elevated CO2 at 21 DAP was caused by an
increase in the activation state of the enzyme rather than an increase in
Vmax. Fructose and glucose accumulated to a greater extent than sucrose at
high CO2 and may have been utilized for synthesis of cell-wall components,
contributing to higher specific leaf weight. By the mid-tillering stage (42
DAP), CO2 enrichment enhanced Vlimiting and Vmax activities of source
blades. Nevertheless, LER was depressed by high CO2, probably because
tillers were stronger carbohydrate sinks than growing blades.
