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The rates of photosynthetic СО2 assimilation were determined in fully expanded second leaves of 21-day-old wheat (Triticum aestivum L.) seedlings grown on media supplied with nitrate or ammonia and on a nitrogen-free medium (NO3 –- or NH4 +-treatments and N-deficit treatment, respectively). The maximal quantum efficiency of photosynthesis was independent on conditions of nitrogen nutrition. When leaves were exposed to 0.03% СО2 and high-intensity light, the lowest photosynthetic rate was noted for N-deficit treatment and the highest rate was characteristic of NH4 + treatment. The elevation of the СО2 concentration in the gas phase to 0.1% stimulated photosynthesis at high-intensity light in all treatments. The rate of СО2 uptake by the leaf of N-deficient seedlings increased with СО2 concentration to a larger extent than in other treatments and approached the СО2 uptake rate characteristic of the NO3 – treatment. In plants grown on a nitrogen-free medium, the leaf accumulated lesser amounts of reduced nitrogen and higher amounts of starch, but the content of chloroplast protein corresponded to that of NO3 – treatment. In the leaf of NH4 +-treated seedlings, the rate of СО2 assimilation was higher than in the leaf of NO3 – treated plants, regardless of the composition of the gas mixture. The ammonium-type nutrition, as compared to the nitrate-type nutrition, elevated the amount of reduced nitrogen in the leaf and promoted accumulation of chlorophyll and protein, the chloroplast protein in particular. |
