Response of Photosynthetic Apparatus and Antioxidant Defense Systems in Triticum aestivum L. Genotypes Subjected to Drought Stress

Two wheat (Triticum aestivum L.) genotypes contrasting in architectonics and differing in drought-
resistance, Azamatli-95 (short-stemmed, with vertically oriented small leaves, drought-tolerant) and
Giymatli-2/17 (short-stemmed, with broad and drooping leaves, drought-sensitive) were grown in field
conditions in a wide area under normal water supply and severe water deficit. It was found out that
the content of CPI (M, 115 kDa), apoprotein of P700 with M, 63 kDa and LHCII polypeptides insignifi-
cantly increases in the drought-resistant Azamatli-95 under extreme water supply condition while
their content decreases in drought-sensitive Giymatli-2/17. The intensity of synthesis of a- and -
subunits of CF, (55 and 53.5 kDa) and 33-30.5 kDa proteins also decreases in sensitive genotype. The
intensity of short wavelength peaks at 687 and 695 nm sharply increases in the fluorescence spectra
(77K) of chloroplasts from Giymatli-2/17 under water deficiency and there is a stimulation of the ratio
of fluorescence band intensity F687/F740. After exposure to drought Giymatli-2/17 shows a larger re-
duction in the actual PSII photochemical efficiency of chloroplasts than Azamatli-95. The activitites of
antioxidant enzymes such as catalase, peroxidase, glutathione reductase and superoxide dismutase dif-
ferently change in wheat genotypes during ontogenesis.