Biochemical properties and ultrastructure of mesophyll and bundle sheath thylakoids from maize (Zea mays) chloroplasts.

A characteristic feature of C4 plants is the differentiation of the photosynthetic leaf tissues into two distinct cell types: mesophyll (M) and bundle sheath (BS) cells. We have investigated several biochemical parameters, including pigment composition, polypeptide patterns, fluorescence at 77K, the activity of photosystems and ultrastructure of mesophyll and bundle sheath chloroplasts of maize (Zea mays L.) plants. It is shown that the BS chloroplasts have ~2-fold higher chlorophyll a/b ratio than M chloroplasts, 6.15 and 3.12 respectively. The PSI apoprotein (68 kDa) was more abundant in BS than in M thylakoids. Polypeptides belonging to PSII core antenna, are in similar amounts in both types of membranes, but the 45kDa band is more intensive in M thylakoids. Polypeptides in the region of 28-24 kDa of the light-harvesting complex of PSII (LHCII) are also present in both types of chloroplasts, though their amounts are reduced in BS thylakoids. The chlorophyll fluorescence emission spectra in M cells showed the presence of three bands at 686, 695 and 735 nm characteristics of LHCII, PSII core and PSI complexes, respectively. However, in the fluorescence spectrum of agranal plastids, there are almost traces of the band at 695 nm, which belongs to the PSII core complex. The research results revealed that the photochemical activity of PSII in BS chloroplasts is ~5 times less than in the chloroplasts of M cells. The highest PSI activity was found in maize BS chloroplasts.

Drought-induced changes in photosynthetic apparatus and antioxidant components of wheat (Triticum durum Desf.) varieties.

Water deficit is a key factor influencing the yield and quality of crops. In the present study, the photosynthetic responses by means of chlorophyll fluorescence of chloroplasts, thylakoid membrane proteins, and antioxidant components were analyzed in wheat (Triticum durum Desf.) plants differing in their tolerance to drought. Two durum winter wheat varieties, Barakatli 95 (drought tolerant) and Garagylchyg 2 (drought sensitive) were grown under field well-watered and drought conditions. It was found that contents of the PS I core (CPI) with Mr of 123 kD and apoprotein P700 with Mr of 63 kD were relatively higher in Barakatli 95 variety under drought stress compared with the control plants. Synthesis of α- and ß-subunits of CF1 ATP-synthase complex with Mr of 55 and 53.5 kD also slightly increased in the tolerant Barakatli 95 and decreased in the drought sensitive variety Garagylchyg 2. A decrease in the intensity of 30 kD band and a significant increase were found in the content of the 25-16 kD region in Garagylchyg 2 variety. The synthesis of 60 kD and content of low molecular mass polypeptides (21.5 and 12 kD) were increased in the tolerant genotype Barakatli 95. The intensity of peaks at 687, 695, and 742 nm considerably increases in the fluorescence spectra (77 K) of chloroplasts isolated from the sensitive variety Garagylchyg 2, and there is a stimulation of the ratio of fluorescence band intensity F687/F740. At the same time, higher level of glycine betaine was found in the drought tolerant variety compared with the control one throughout the different periods of growth.

Structural-functional state of thylakoid membranes of wheat genotypes under water stress.

Plants were grown in field conditions in the wide area under normal water supply and severe water deficit. Two wheat (Triticum aestivum L.) genotypes contrasting by architectonics and differing in drought-resistance were used: Giymatli-2/17, short stature, with broad and drooping leaves, drought-sensitive, and Azamatli-95, short stature, with vertically oriented small leaves, drought-tolerant). It was found out that Giymatli-2/17 was characterized by relatively low content of Chl a-protein of PS I (CP I) and beta-subunit of ATP-synthase complex, the high content of proteins in the 33-30.5 kDa region and LHC polypeptides (28-24.5 kDa), the intensive fluorescence at 740 nm and more high photochemical activity of PS II under normal irrigation compared with Azamatli-95. However, the content of CP I (M(r) 115 kDa) and apoprotein of P700 with M(r) 63 kDa insignificantly increases in the drought-resistant genotype Azamatli-95 under extreme water supply condition while their content decreases in drought-sensitive cv Giymatli-2/17. Intensity of synthesis alpha- and beta-subunits of CF(1) (55 and 53.5 kDa) also decreases in Giymatli-2/17. The levels of the core antenna polypeptides of FS II with M(r) 46 and 44.5 kDa (CP47 and CP43) remains stable both in normal, and stressful conditions. At the same time the significant reduction is observed in the content of polypeptides in the 33-30.5 kDa region in the more sensitive genotype Giymatli-2/17. There is an increase in the LHC II polypeptides level in tolerant genotype Azamatli-95 in contrast to Giymatli-2/17 (where the content of these subunits is observed decreasing). The intensity of short wavelength peaks at 687 and 695 nm sharply increases in the fluorescence spectra (77 K) of chloroplasts from sensitive genotype Giymatli-2/17 under water deficiency and there is a stimulation of the ratio of fluorescence band intensity F687/F740. After exposure to drought, cv Giymatli-2/17 shows a larger reduction in the actual PS II photochemical efficiency of chloroplasts than cv Azamatli-95.