The drought caused by global climate change has an increasing negative impact on agriculture; therefore, the importance of genotypes with drought stress resistance also increases in the future. The understanding of the stress response of varieties tolerant to water deprivation could contribute to the breeding of genotypes with have higher level of stress resistance. The aim of our work was to reveal the histological changes in the developing grain yield caused by drought stress which results in yield reduction used in the sexed processes of wheat. For this reason, we examined the impact of drought stress triggered by total water deprivation at the stages of meiosis, anthesis and the early grain development on the yield, fertility and grain yield morphology of the drought sensitive Cappelle Desprez winter wheat variety, as well s Plainsman V (Triticum aestivum L.) which is tolerant to water deprivation. We used histological methods to examine the changes affecting the morphology of the developing embryos, the starch endosperm cells and the maternal cell layers surrounding them. Also, we used stereological methods to determine the number of developing endosperm cells and the amount of reserve nutrients accumulating in them. We also determined the number of A and B type starch particles per cell, as well as the amount of protein bodies which play a protein storage role in the cells. As a result of the treatments used at the time of meiosis and anthesis, the fertility, grain filling and yield of both varieties decreased and their grain yield development slowed down. On the contrary, there was no detectable change in the number of cell constituents. As a result of the water deprivation used at the stage of early grain development, there was a reduction in the number of B type starch particles in the endosperm, while the development of aleurone cells and the degradation of the cell layers embracing the ovulum significantly sped up in the case of both genotypes. At the time of early grain development, water deprivation increased the pace of grain filling, reduced the ripening period and significantly decreased yield. The size of ripened embryos is significantly lower than the control in the case of the drought sensitive Cappelle Desprez variety, while the endosperm cells of the variety accumulated significantly less B type starch than those of the tolerant Plainsman V variety. The number of protein bodies in the treated grain yield of the tolerant genotpye significantly exceeded the typical value of the control. Considering the regeneration of the vegetative tissues, grain filling and yield, the stress reaction of the drought tolerant Plainsman V was significantly better than that of the sensitive genotype.

Keywords: embryo, endosperm, starch, winter wheat, drought stress