Functionality of photosystem II in barley leaves under different supply with Mn2+

Estimation of parameters of chlorophyll a fluorescence measurements were carried out on six barley ( Hordeum vulgareL.) cultivars at 14 days after treatment with 0 mmol, 0.5 mmol, 1.0 mmol, 1.5 mmol manganese to investigate changes in some parameters of OJIP-test and reveal similarities or dissimilarities between cultivars in this respect. It is revealed that the sensitivity of different parts of the PSII units varies, and this response is the different for different Mn concentration and is cultivar-dependent. At the same time, none of the varieties, in any of the manganese exposure variant showed deviations of the maximum photochemical efficiency PSII from the physiological norm-the minimum value was noted in 1.0 mM Mn in the cv. Boyarin and amounted to 0.783 units. It was assumed that the change in the integral index of effective photosynthesis occurs in different cultivars due to different functional changes, while the level of stress factor also plays an important role. This indicates, firstly, the need for targeted breeding (to a specific level of the acting factor); secondly, the possibility of pyramidizing the integral level of resistance to stress by selecting parents differing in the level of change in individual functional reactions of photosynthesis.