The effect of H2O2 on the photosynthetic biochemistry of Pisum sativum.
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Date
1990
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Abstract
To study the short-term effect of hydrogen peroxide on plant metabolism aminotriazole
(2 mM), a catalase inhibitor was applied through the transpiration stream of pea seedlings
and the gas exchange characteristics, ascorbate peroxidase, glutathione reductase and
catalase activities, and the levels of hydrogen peroxide, glutathione and formate were
determined. CO2 assimilation rates were inhibited after the addition of aminotriazole:
photorespiratory conditions (high 02 and low CO2 concentrations, high light intensities)
exascerbated the inhibition. CO2 response curves showed that aminotriazole reduced both
the RuBP regeneration rate and the efficiency of the carboxylation reaction of Rubisco.
The inhibition of the CO2 assimilation rate during the first 100 minutes after the addition
of aminotriazole was alleviated by feeding PGA through the transpiration stream. Catalase
activity was completely inhibited within 200 minutes of aminotriazole application, but there
was no concomitant increase in the hydrogen peroxide concentration, suggesting that
hydrogen peroxide is metabolised by an alternative mechanism. The treatment had no
effect on ascorbate peroxidase and glutathione reductase activities or total glutathione pool
size, but greatly increased formate levels. These results suggest that hydrogen peroxide is
metabolised by reacting with glyoxylate to form formate and CO2, The increased
production of formate may reduce the flow of carbon through the normal photorespiratory
pathway and may be used anapleurotically as a precursor of products of l-C metabolism
other than serine. This would prevent the return of photorespiratory carbon to the BensonCalvin
cycle in the form of 3-PGA. It is proposed that when RuBP regeneration levels are
low high formate levels may be an effector of Rubisco, and competitively inhibit the
binding of CO2 and 02. These results suggest that under photorespiratory conditions the
uninterrupted flow of carbon through the photorespiratory pathway is fundamental to the
functioning of photosynthetic metabolism.
Description
Thesis (M.Sc.)-University of Natal, Durban, 1990.
Keywords
Biochemistry., Photosynthesis., Theses--Botany.