PARENT SESSION
Posters P3B Photosynthetic acclimation: Ecophysiology, diverse environments. Abstracts (479-522)

Photosynthesis and photochemical activity in mesophyll and bundle sheath chloroplasts of C4 types regulated by environmental factors. Elżbieta Romanowska^*,1, Anna Drożak¹, Eugeniusz Parys¹, Berenika Pokorska¹, Paulina Zwolińska¹, ¹ Department of Plant Physiology, 02 096 Warszawa, Poland

ABSTRACT- A chararacteristic feature of C4 plants is the differentiation of the photosynthetic tissues into the two distinct cell types, mesophyll (M) and bundle sheath cells (BS). C4 plants have been devided into three metabolic types:NADP-ME, NAD-ME and PCK. We attempted to compare the acclimation of photosynthetic apparatus in Zea mays (NADP-ME), Panicum miliaceum (NAD-ME) and Panicum maximum (PCK) plants during cultivation under defined light conditions (450, 80 and 20 E m^-2 s^-1). The lowest rate of photosynthesis (Pn) was noticed for P. maximum ; for Z. mays and P. miliaceum were higher by about 50 and 70%. The rate of Pn correlated with light intensity during its measurement, but not with the light intensity during the growth. The fluorescence parameters (NPQ,qP,PSII)of PSII measured in high- and low light intensities did not change significantly. The PSII and PSI activities as well as the polypeptide levels in M and BS chloroplasts of three C4 types was found to vary with respect to light intensity during growth and the age of plants. PSI activity in the old Z. mays plants was twice higher in BS than in M chloroplasts, but in the young plants were similar in both type of chloroplasts. PSII in BS chloroplasts of maize sustained a very limited electron transport activity. There was close correlation between Chl-P complexes composition and PSI and PSII activities in M and BS chloroplasts. Higher activity of PSI was accompanied with larger amount of PSI-LHCI in M and BS chloroplasts of P. miliaceum, and in BS chloroplasts of Z. mays. In both Panicum species PSII was more active in M than in BS chloroplasts, where higher amount of oligomeric form of light harvesting complex was noted. The highest PSI and PSII activities were observd for P. miliaceum seedlings. It was also a strong correlation between oxygen-evolution capacity and abundance of OEC polypeptides. When the plants were grown in high light CF1, cyt. f and b proteins markedly increased in M and BS chloroplasts. Our results suggest that intensity of light during growth can influence differently the organization and activity of both M and BS chloroplasts in examined C4 grasses. PSII in BS chloroplasts of maize has the ancillary function of preventing PSI over-oxidation. This work was supported by the Polish Committee for Scientific Research Grant 3 P04C 043 25.

KEY WORDS: light reaction, C4 types, chloroplasts, photosynthesis