PLANT PHYSIOLOGY , Vol 107, Issue 4 1313-1321, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Leaf Phosphate Status, Photosynthesis, and Carbon Partitioning in Sugar Beet (IV. Changes with Time Following Increased Supply of Phosphate to Low-Phosphate Plants)
I. M. Rao and N. Terry
Department of Plant Biology, University of California, Berkeley, California 94720
Changes in photosynthesis, carbon partitioning, and growth following
resupply of orthophosphate (Pi) to moderately P-deficient plants (low-P)
were determined for sugar beets (Beta vulgaris L. cv F58-554H1) cultured
hydroponically in growth chambers. One set of plants was supplied with 1.0
mM Pi in half-strength Hoagland solution (control plants), and a second set
(low-P plants) was supplied with 0.05 mM Pi. At the end of 2 weeks, the
low-P plants were resupplied with 1.0 mM Pi. Low-P plants rapidly
accumulated large amounts of Pi, and the photosynthesis rate increased to
control values within 4 to 6 h. The rate of photosynthesis appeared to be
controlled by ribulose-1,5-bisphosphate (RuBP); low P reduced
photosynthesis and RuBP levels, and P resupply increased photosynthesis and
RuBP in a manner parallel with time. Low-P treatment reduced adenylate
levels substantially but not nicotinamide nucleotides; adenylate levels
recovered to control values over 3 to 6 h. With low P, more photosynthate
is allocated to non-P carbon compounds (e.g. starch, sucrose) than to sugar
phosphates. When P is resupplied, sugar phosphates increase as starch and
sucrose pools decrease; this increase in leaf (chloroplast) sugar
phosphates was most likely responsible for the increases in RuBP and
photosynthesis and may have increased adenylate levels (through enhanced
levels of ribose-5-phosphate).
