Abstract
The levels of ATP, ADP and AMP, the activity of phosphatases, and the ability for oxidative phosphorylation were studied in roots of pea (Pisum sativum) plants grown in media salinized either with NaCl or Na2SO4. In response to salinity, the ATP level in the roots decreased, whereas the ADP level increased slightly. As a result, the ADP:ATP ratio in the tissue increased with increasing salinity in the growth medium. The AMP level in the tissue was not affected by salinity.
Phosphatase activity (using p-nitrophenyl phosphate and ATP as substrates), in the soluble and in the mitochondrial fractions from roots grown in NaCl-salinized media, was considerably higher than in the control roots. In the mitochondrial fraction of the roots grown in Na2SO4-salinized media, such an increase was not observed.
The phosphorylating activity of mitochondria was depressed by the two types of salinity, but was more sensitive to NaCl salinity. In mitochondrial suspensions prepared from roots exposed to salinity, practically no phosphorylation could take place if nicotinamide adenine dinucleotide was omitted from the reaction mixture; but even when added, the restoration of phosphorylative ability was not complete. Addition of NaCl to the reaction mixture did not affect the activity of the phosphatases. Addition of Na2SO4 to the reaction mixture depressed, in some cases, the activity of the acid phosphatase. Phosphorylative activity was affected, however, by both types of salinity: presence of either NaCl or Na2SO4 at − 1 atm in the reaction mixture increased phosphorylative activity, and higher concentrations (−3 and −5 atm) depressed it.
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