PLANT PHYSIOLOGY , Vol 108, Issue 4 1487-1494, Copyright © 1995 by American Society of Plant Biologists
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WHOLE PLANT, ENVIRONMENTAL, AND STRESS PHYSIOLOGY |
Early Iron Deficiency Stress Response in Leaves of Sugar Beet
T. L. Winder and J. N. Nishio
Department of Botany, University of Wyoming, Laramie, Wyoming 82071-3165
Iron nutrient deficiency was investigated in leaves of hydroponically grown
sugar beets (Beta vulgaris) to determine how ribulose-1,5-bisphosphate
carboxylase/oxygenase (Rubisco) gene expression is affected when thylakoid
components of photosynthesis are diminished. Rubisco polypeptide content
was reduced by 60% in severely iron-stressed leaves, and the reduction was
directly correlated to chlorophyll content. The concentration of Rubisco
protein in iron-stressed leaves was found to be regulated by availability
of mRNAs, and CO2 fixation by Rubisco was reduced from 45 [mu]mol CO2 m-2
s-1 in extracts from iron-sufficient leaves to 20 [mu]mol CO2 m-2 s-1 in
extracts from severely stressed leaves. The rate of CO2 fixation was
directly correlated to leaf chlorophyll content. Rubisco in iron-sufficient
control leaves was 59% activated, whereas in severely stressed leaves grown
under the same light, Rubisco was 43% activated. RNA synthesis was reduced
by about 50% in iron-deficient leaves, but 16S and 25S rRNA and ctDNA were
essentially unaffected by iron stress.
