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Effect of metal salts on freshly lysed chloroplasts.
ION T R A N S P L A N T
569
1008
EFFECT OF METAL SALTS ON FRESHLY LYSED CHLOROPLASTS. S.E. Castillo-Bluma , J.L. Mendoza-Arizmendib, B. Kingb , X. P6rezMartfnezb , N. Barba-Behrensa and B. Lotina-Hennsenb.
aDepartamento de Quhnica lnorgdnica, bDepartamento de. Bioqu[mica, Divisidn de Estudios de PosglzMo, Facultad de Qu[mica, Universidad Nacional Autdnoma de Mdxico, Coyoacdn, M#xico, D. F. (04510), Mdxico. The toxicity of transition metal ions in plants is partly attributable to the binding of the metals to enzymes, inhibiting their catalytic activities. Some reports about their specific site of action on thylakoid redox enzymes remain controversial (concentration range of the salts 0-100/~M) where it is informed that they act as Hill's reaction inhibitors [1,2]. The effect of metal salts (MX2; M = Co, Ni, Cu, Zn, Cd; X = C1, NO 3, CH3COO) was studied on photosynthetic activities within the concentration range 0-300 /~M on freshly lysed pea (Pisum sativum) chloroplasts. Copper salts, cadmium chloride, cadmium nitrate and zinc acetate behave as energy transfer inhibitors (binding H -ATPase), while cadmium acetate acts as Hill's reaction inhibitor. Nickel salts, zinc chloride and zinc nitrate show no effect on photosynthesis; cobalt chloride acts as an uncoupler on phot0Phosphorylation. It is important to point out that salt concentration required for activity is higher when experiments are carried out with intact chloroplasts. Our results are different to those published by other authors maybe due to the fact that we used intact organelles instedad of washed thylakoids, where the chloroplast components present in the stroma (such as nucleic acids, enzymes, ribosomes, etc.) are removed. While the experiments reported by us were carried out on freshly lysed intact chloroplasts, where the metal salts may interact with the different components of the stroma and lead to a different pattern of behaviour. This means that the tested salts can be partitioned among the stroma components and consequently only a small amount of the tested salt reaches the target thylakoid membranes. It is known that the confgrmation of the H -ATPase and the response to inhibitors are different in tile intact organelles from those found in washed thylakoids. The active conformation of the enzyme, present in freshly lysed chloroplasts, may allow the metal salts to interact with it, consequently behaving as energy transfer inhibitors. I.
2.
D. P. Singh and S. P. Singh, Phmt Physiol., 83, (1987) 12. F. Van Assche and H. Clilsters, Plant Physiol., 66 (1986) 717.
569
1008
EFFECT OF METAL SALTS ON FRESHLY LYSED CHLOROPLASTS. S.E. Castillo-Bluma , J.L. Mendoza-Arizmendib, B. Kingb , X. P6rezMartfnezb , N. Barba-Behrensa and B. Lotina-Hennsenb.
aDepartamento de Quhnica lnorgdnica, bDepartamento de. Bioqu[mica, Divisidn de Estudios de PosglzMo, Facultad de Qu[mica, Universidad Nacional Autdnoma de Mdxico, Coyoacdn, M#xico, D. F. (04510), Mdxico. The toxicity of transition metal ions in plants is partly attributable to the binding of the metals to enzymes, inhibiting their catalytic activities. Some reports about their specific site of action on thylakoid redox enzymes remain controversial (concentration range of the salts 0-100/~M) where it is informed that they act as Hill's reaction inhibitors [1,2]. The effect of metal salts (MX2; M = Co, Ni, Cu, Zn, Cd; X = C1, NO 3, CH3COO) was studied on photosynthetic activities within the concentration range 0-300 /~M on freshly lysed pea (Pisum sativum) chloroplasts. Copper salts, cadmium chloride, cadmium nitrate and zinc acetate behave as energy transfer inhibitors (binding H -ATPase), while cadmium acetate acts as Hill's reaction inhibitor. Nickel salts, zinc chloride and zinc nitrate show no effect on photosynthesis; cobalt chloride acts as an uncoupler on phot0Phosphorylation. It is important to point out that salt concentration required for activity is higher when experiments are carried out with intact chloroplasts. Our results are different to those published by other authors maybe due to the fact that we used intact organelles instedad of washed thylakoids, where the chloroplast components present in the stroma (such as nucleic acids, enzymes, ribosomes, etc.) are removed. While the experiments reported by us were carried out on freshly lysed intact chloroplasts, where the metal salts may interact with the different components of the stroma and lead to a different pattern of behaviour. This means that the tested salts can be partitioned among the stroma components and consequently only a small amount of the tested salt reaches the target thylakoid membranes. It is known that the confgrmation of the H -ATPase and the response to inhibitors are different in tile intact organelles from those found in washed thylakoids. The active conformation of the enzyme, present in freshly lysed chloroplasts, may allow the metal salts to interact with it, consequently behaving as energy transfer inhibitors. I.
2.
D. P. Singh and S. P. Singh, Phmt Physiol., 83, (1987) 12. F. Van Assche and H. Clilsters, Plant Physiol., 66 (1986) 717.