Photosynthesis, Photorespiration and Productivity of Wheat and Soybean Genotypes

The results of the numerous measurements obtained during the last 40 years on gas exchange rate using an infrared gas analyzer URAS-2T (Germany), phot osynthetic carbon metabolism by exposition in 1CO, and activities of enzyme of primary carbon fixation, ribulose-1,5-bisphosphate carboxylaseloxygenase (RuBPCO), in various wheat genotypes grown over a wide area in the field and contrasting in photosynthetic traits and productivity are presented in this paper. It was established that high productive wheat genotypes with the optimal architectonics (7-9 t ha possess higher rate of CO, assimilation during leaf ontogenesis. Along with the high rate of photosynthesis, high values of photorespiration are characteristic for high productive genotypes. There is a parallel increase in the rates of true photosynthesis and photorespiration in ontogenesis. Genotypes with moderate (45 t ha) and low
(3tha ) grain yield are characterized by relatively low rates of both C0, assimilation and  photorespiration. The ratio of true photosynthesis to photorespiration in genotypes with different productivity is equal on average to 3:1. A value of photorespiration constitutes 28-35% of photosynthetic rate in contrasting wheat gen otypes. The activities of RuBP carboxylase and RuBP oxygenase were changing in a similar way in the course of the flag leaf and ear elements development. RuBP exygenase activity was higher in high productive wheat than in low productive ones. The rates of sucrose (the main ransport metabolite in plants) biosynthesis and products of glycolate metabolism also correlate with the CO, assimilation rate and the activity of RuBP oxygenase. High productive genotypes are also characterized by a higher rate of biosynthesis and total value of glycine-serine and a
thetic rate. Pattern of changes in biosynthesis rate and total value of glycine-serine as well as ratio of photosyRuBP carboxylase to oxygenase activities and CO assimilation rate predisposes to parallel change in the rates of photosyathesis and photorespiration during leaf ontogenesis. High rates of photosy nthesis and photorespiration in conjunction with favourable photosynthetic traits, an
and the best architectonics define high productivity of wheat ception arisen during many ycars on wastefulness of photorespiration, taking into account the versazenotypes. Thereleal area index contrary to contile investigations on different aspects of  plhotorespiration it was proved that photorespiration is one of the evolutionary developed vital metabolic precesses in plants and the attempts to reduce this process with the purpose of increasing the crop productivity are incoasistent. Phosphogly colate phosphatase, a key enzyme of photorespiration was first homogeneously purified from cukaryotic greea algae Chle mydomonas reinhardtil with subsequent determination of conuplete aucleotide and deduced amia acid sequences (NCBI Nudeotide 1:AB052169) Since sctabolic processes of photorespiratioa ia the leaf ocCur in the light simultaneausly with piotosy atbesis, it is evideat that relcased caergy is used ia ceetain reactions of photosynthesis.