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Modification of Carbon Partitioning, Photosynthetic Capacity, and
O2 Sensitivity in Arabidopsis Plants with Low
ADP-Glucose Pyrophosphorylase Activity1
Jindong Sun,
Thomas W. Okita, and
Gerald E. Edwards*
Institute of Biological Chemistry (J.S., T.W.O., G.E.E.),
Department of Botany (J.S., G.E.E.), Washington State University,
Pullman, Washington 99164
Wild-type Arabidopsis plants, the
starch-deficient mutant TL46, and the near-starchless mutant TL25 were
evaluated by noninvasive in situ methods for their capacity for net
CO2 assimilation, true rates of photosynthetic
O2 evolution (determined from chlorophyll fluorescence
measurements of photosystem II), partitioning of photosynthate into
sucrose and starch, and plant growth. Compared with wild-type plants,
the starch mutants showed reduced photosynthetic capacity, with the
largest reduction occurring in mutant TL25 subjected to high light and
increased CO2 partial pressure. The extent of stimulation
of CO2 assimilation by increasing CO2 or by
reducing O2 partial pressure was significantly less for the starch mutants than for wild-type plants. Under high light and moderate
to high levels of CO2, the rates of CO2
assimilation and O2 evolution and the percentage inhibition
of photosynthesis by low O2 were higher for the wild type
than for the mutants. The relative rates of
14CO2 incorporation into starch under high
light and high CO2 followed the patterns of photosynthetic
capacity, with TL46 showing 31% to 40% of the starch-labeling rates
of the wild type and TL25 showing less than 14% incorporation.
Overall, there were significant correlations between the rates of
starch synthesis and CO2 assimilation and between the rates
of starch synthesis and cumulative leaf area. These results indicate
that leaf starch plays an important role as a transient reserve, the
synthesis of which can ameliorate any potential reduction in
photosynthesis caused by feedback regulation.
1
This research was supported by grants from the
U.S. Department of Agriculture (USDA) (no. 95-37306-2195 to T.W.O. and
G.E.E.) and the Department of Energy (no. DE-FG0687ER136 to T.W.O.).
This research study falls under the purview of Hatch Project 0119, College of Agriculture and Home Economics, Washington State University, and of the USDA North Central 142 Regional Project.
*
Corresponding author; e-mail edwards{at}wsu.edu; fax
1-509-335-3517.
Plant Physiol. (1999) 119: 267-276
Copyright Clearance Center: 0032-0889/99/119//10
© 1999 American Society of Plant Physiologists
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