Sheheda I. The physiological basis of winter wheat grain protein content formation, depending on the conditions of nitrogen nutrition.

In pot and field experiments there were used 6 varieties of bread winter wheat (Triticum aestivum L.). In pot experiments, the plants were grown on two mineral nutrition backgrounds – optimal (N160P160K160 mg/kg soil) and low (N32P32K32 mg/kg). For the first time it was established that with a lack of nitrogen in the soil, in the leaves of wheat plants the content of hydrogen peroxide increase, indicating that they are under stress. Foliar treatment with carbamide (5 % solution) at the end of flowering (BBCH 69) helps to maintain the functional state of the leaves, in particular, stimulates the work of antioxidant enzymes, and helps to maintain the assimilation activity of the leaves at a higher level relative to the untreated plants during grain filling. Intervarietal differences were revealed in the efficiency of nitrogen remobilization from various organs into grain, as well as the contribution of remobilized nitrogen to the formation of its total pool in the grain, which is due to the different plants' ability to absorb this element from the soil after flowering. On the low background of mineral nutrition, the efficiency of nitrogen remobilization from leaves and stems was lower, and among the elements of the ear – higher, than on high background. The ability to additional absorption of nitrogen from the soil after flowering is a positive factor in the realization of the genetic potential of grain protein content. It is proved that foliar nutrition with carbamide increases the amount of nitrogen carried out with the grain, and the increase compared with untreated plants is significantly greater than the amount of nitrogen per shoot during treatment. This is due to the increased efficiency of nitrogen remobilization from the vegetative parts of the shoot, as well as the enhancement of its additional absorption from the soil during the grain filling due to the stimulation of leaf assimilation by foliar top dressing. It was shown that nitrogen content in the leaves during the flowering period positively correlated with the protein content in the grain, while the decrease in the mass of the stem during the period of ripening correlated with the grain productivity, and the increase in the level of mineral nutrition increases the correlation tightness. These indices can be used in the complex as physiological markers to optimize the wheat production process in breeding programs in order to increase the protein removal with the grain due to the increase in yield without reducing the protein content. Calculations of the increase in nitrogen carryover with grain for the treatment of plants at the end of flowering in field experiments showed that it was significantly higher than the dose introduced with foliar feeding (N7 kg/ha). However, it should be noted that this difference was smaller than that obtained under the conditions of pot experiment, apparently due to the impact of more uncontrolled factors, first of all – moisture supply. It is proved that to increase the collection of protein with the harvest, foliar top dressing of wheat with carbamide at the end of the flowering phase (BBCH 69) is advisable. This event stimulates the functional activity of plants, improves the use of nitrogen by increasing the efficiency of its remobilization and additional absorption.