The role of photooxidation processes in carbon and nitrogen metabolism at photosynthesis of the wheat flag

摘要

Assimilation of ~(14)CO_2 and distribution of ~(14)C among radiolabelled products of photosynthesis in me leaves of wheat plants (Triticum aestivum L.) fertilized by urea and Ca(NO_3)_2 were investigated Assimilation of ~(14)CO_2 was canned out m the leaf chamber under two carbon dioxide concentrations (0.03% and 0.3 % ) and two oxygen concentrations (21% and 1% ). The Warburg's effect (inhibition of ~(14)C assimilation by oxygen) under 0.03 % CO_2 concentration was observed only in non-fertilized plants. Under these conditions the reaction to oxygen in urea-fertilized plants was not observed whereas the Warburg's antieffect in the plant fertilized by Ca(NO_3)_2 was detected. The Warburg's antieffect was observed in plants of all variants under saturating CO_2 concentration. Under intensive nitrogen nutrition independent of the nitrogen forms carbon removal from the Calvin cycle via glycolate pathway was increased and non-reduced transformation of 3-PGA was observed. The first pathway was more pronounced in nitrate-fertilized plants and the second one, in urea-fertilized plants. Under the conditions of limitation of Rubisco-oxygenase activity (0.3 % CO_2 and 1% O_2) the synthesis intensity for glycolate metabolism products was declined in control and urea-Fertilized plants but was enhanced in the nitrate-ferttiized plants variant. It is concluded that the mechanism of glycolate formation is activated via transketolase reaction in fertilized plants, and the products of nitrate reduction play the role of oxidants in nitrate-fertilized plants while the superoxide radical plays this role in urea-fertilized plants.