Morphophysiological Indices of the Source Leaf in Wheat Plants Acclimated to Conditions of Nitrogen Nutrition

Growth, leaf and cell morphology, and the chemical composition of the second leaf were studied in wheat (Triticum aestivumL., cv. Inna) plants grown on the medium containing nitrate, ammonium, or no nitrogen at all. Independent of the nitrogen nutrition, the second leaf of the 21-day-old plants matures and functions as a source of assimilates. Both ammonium nutrition and nitrogen deficiency decreased the fresh weight, area, and cell size in the leaf; however, the conditions of nitrogen nutrition did not affect the dry weight of the leaf. Nitrogen starvation increased and ammonium nutrition decreased the relative content of the cell walls in the dry weight. In the nitrate-fed plants, the leaf content of sucrose increased, and the contents of reduced nitrogen (Nred) and protein were lower than in the ammonium treatment. Reciprocally, the contents of reduced nitrogen and protein were highest in the ammonium treatment, the content of sucrose was lowest, with starch practically absent from the leaf. The nitrogen-starved leaf accumulated a large amount of starch, the Nredcontent was two times lower than in the ammonium-fed plants, and the protein content was similar to that in the nitrate-fed plants. Thus, leaf and cell morphology and the content of Nred, protein, and carbohydrate changes in different ways during wheat acclimation to the condition of nitrogen nutrition. By assessing the cell wall weight, the authors established that, depending on nitrogen nutrition, this cell compartment accepts a variable flow of carbon.