Some Biochemical Characteristics of Chloroplasts from Mineral-deficient Maize.

The effects of mineral deficiencies on plant growth have been studied for many years, but little use has been made of mineral deficiency as a tool for understanding the photosynthetic process. Hill reaction rates of chloroplasts from mineraldeficient plants were measured by Spencer and Possingham (1), who found lower rates per unit of chlorophyll in all deficiencies except iron. Kessler's (9) study of manganese-deficient plants indicate a role for this element in photosystem II, and this work has proved to be an important wedge into a difficult area of investigation (6). We have measured the activity of each of the two photosystems in mesophyll cell chloroplasts from maize deficient in macronutrient elements. The work of Hall et al. (7) shows that some mineral deficiencies cause a distortion in chloroplast morphology. The work described below is an attempt to relate changes induced in chloroplast structure by mineral deficiencies with alterations of the composition and function of the photosynthetic apparatus. Maize seed, Zea mays (H55 X C 103 Rf), was obtained from the Agriculture Alumni Seed Association, West Lafayette, Indiana. Diphenyl carbazide was purchased from Aldrich Chemicals, DCIP' from Eastman Organic Chemicals, and methyl viologen from K and K Laboratories. DCMU was a gift of the E. I. DuPont de Nemours and Co. Six major mineral deficiencies (S, Mg, Ca, N, P, and K) were induced by the methods of Hoagland and Arnon (8). The growth conditions have been described by Hall et al. (7). The pigment composition and gross morphological symptoms of these deficient plants have been described earlier by Barr et al. (3). The chloroplasts were isolated from normal and deficient leaves 8 weeks after transplanting. Growth on deficient media for 4 weeks did not cause any pronounced alterations in the biochemical parameters measured, as seen by photosynthetic reaction rates. Chloroplasts from 10 g of fresh leaves were prepared by briefly (45 sec-1 min) homogenizing the leaves in 0.4 M sucrose with 25 mm Tricine buffer, pH 7.5, in a Waring Blendor. This brief homogenization broke a minimum of bundle sheath cells (1). The leaf homogenate was passed through four layers of cheesecloth and centrifuged at 600g for 2 min. The supernatant was centrifuged at 1500g for 10 min. The pellet con-