J. Plant Physiol. Vol. 140. pp. 527-530 {1992} Effect of Fe Deficiency on the Photosynthetic System of Maize SAMIR SHARMA and G. G. SANWAL Department of Biochemistry, Lucknow University, Lucknow - 226007, India Received March 12, 1992 . Accepted May 22, 1992 Summary We investigated the effect of Fe deficiency on the photosynthetic system of maize (lea mays var. Ganga 5). Chlorophyll content, PSI and PSII electron transport rates, P700, Q, cytochrome f, cytochrome b559 HP and CO 2 fixation by intact leaves show a decrease in Fe deficient plants. Maximum reduction is observed in the amount of cyt f, which may be the component that limits overall photosynthetic rates, in- stead of PSI, which has been described as the component most severely effected by Fe deficiency in other plants. Loss in carbon fixing ability is much greater than the loss of chlorophyll, but corresponds closely to the reduction in cytochrome content, further implicating cyt f as the limiting factor. Reaction centers of the photosystems were not reduced as much as other components, suggesting that in the case of Fe defi- ciency the plant shows selectivity when loss of electron transport components is imminent. Key words: lea mays, C02>fixation, eyt b559 HP , eytf, Fe deficieney, P700, PSI, PSII Abbreviations: Cyt b559 HP = Cytochrome b559(high potential); cyt f = cytochrome f; DCMU = Di- chlorophenyl dimethyl urea; FW = fresh weight; PC = plastocyanin; PSI = photosystem I; PSII photosystem II; Q = primary electron acceptor of PSII (QA)' Introduction Fe deficiency causes chlorosis in plants by inhibiting chlo- rophyll biosynthesis (Chen and Barak, 1982). Several steps in chlorophyll biosynthesis have been reported to be Fe de- pendent (Pushnik et aI., 1984) and chlorophyll biosynthesis is stopped at the b-Amino levulinic acid synthesis step (Miller et aI., 1982). Light saturated rates of photosynthetic electron transport are decreased due to Fe deficiency (Terry, 1980). However, the decrease in electron transport rates, in- vestigated predominantly in Beta vulgaris, has been reported to be maximum at the level of PSI. Fe deficiency has so far not been known to effect any enzyme involved in photo- synthetic carbon fixation (Terry and Abadia, 1986). The maximum rate of photosynthesis on a leaf area basis obtain- ed under conditions of light and CO 2 saturation has been found to decrease in proportion to chlorophyll content, which is regarded as a measure of photosynthetic electron transport capacity (Terry, 1980; Nishio and Terry, 1983). © 1992 by Gustav Fischer Verlag, Stuttgart Since enzymes involved in photosynthetic carbon fixation do not show a reduced capacity for CO 2 reduction, it has been suggested that it is the reduced electron transport capac- ity that results in a reduced availability of ATP and NADPH, which is responsible for the decrease in CO 2 as- similation (Terry, 1980). In the present work we determined the amounts of Q, P700, cyt f, cyt b559 HP , electron transport through PSI and PSII, and photosynthetic CO 2 fixation to find out the limiting factor in photosynthesis in a C crop plant (lea mays) under Fe deficiency conditions. Materials and Methods Growth conditions Maize (Zea mays var. Ganga 5) was grown on refined sand in a glass house during April-August, when PAR levels at noon ap- proached 1500 to 1700 Ilmol m- 2 s- 1 • The control plants were given a nutrient solution containing in mM: 4Ca(N0 3 )z, 2 MgS0 4 , 1.33