Photosynthetic apparatus of chilling-sensitive plants. IX. The involvement of alpha-tocopherol in the electron transport chain and the anti-oxidizing system in chloroplasts of tomato leaves.

1. The role of tocopherols in tomato chloroplasts from fresh, cold and dark-stored as well as stored and illuminated leaves was studied. 2. The cold and dark storage of leaves results in a loss of chloroplast alpha- and gamma-tocopherols of about 30-40% accompanied by an increase in chloroplast delta-tocopherol of about 40%. On illumination of stored leaves, an elevation of alpha- and gamma-tocopherol level to about 110 and 95% of the control, respectively, occurs, whilst delta-tocopherol content is not affected. 3. Experiments performed with 2,2-diphenyl-1-picrylhydrazyl-treated chloroplasts show that only about 70% of total alpha-tocopherol is functionally active in the electron transport of Photosystem II between the diphenylcarbazide (DPC) donation site and the inhibition site of DBMIB. 4. A small amount of alpha-tocopherol quinone (about 10% of alpha-tocopherol content) is found in chloroplasts from fresh, fresh and illuminated as well as cold and dark-stored tomato leaves, whereas the illumination of the latter increases the chloroplast alpha-tocopherol quinone content 3-fold. Moreover, following the illumination of chloroplasts from cold and dark-stored as well as stored and illuminated leaves, the oxidation of exogenous alpha-tocopherol to alpha-tocopherol quinone is 2-fold faster then in chloroplasts from fresh leaves. 5. The primary product ('alpha-tocopheroxide') formed during the alpha-tocopherol oxidation by illuminated chloroplasts was identified as 8a-hydroxy-alpha-tocopheron. 6. Exogenous alpha-tocopherol inhibits the lipid photoperoxidation by about 40-50% in chloroplasts from all three kinds of tomato leaf. 7. The results seem to suggest that chloroplast alpha-tocopherol is involved in both electron transport of PS II and antioxidizing system of chloroplasts.