Hill-Activity and P700 Concentration of Chloroplasts Isolated from Radish Seedlings Treated with -Indoleacetic Acid, Kinetin or Gibberellic Acid

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Abstract
The Hill-activity (reduction of DCPIP [dichlorophenolindophenol] or methylviologen) and the concentration of P700 were studied in chloroplasts isolated from cotyledons of radish seedlings (Raphanus sativus L. Saxa Treib), which were grown with the addition of IAA, kinetin, or GA. The photosynthetic activity of young chloroplasts from 3 day old Raphanus seedlings is very high (about 180 .mu.mol O2/mol chlorophyll per h) and decreases continuously thereafter with increasing age. The steady state Hill-activity is reached after 8-10 days (values of 55-50 .mu.mol O2/mg chlorophyll per h). Chloroplasts from plants treated with IAA or kinetin exhibit higher plastoquinone levels1,2 and also a higher P700-content and a higher Hill-activity. The promotion effect is more pronounced with kinetin (+36-40%) than with IAA (+12-17%). GA has a different effect on composition and activity of chloroplasts. In younger seedlings the Hill-activity appears to be somewhat stimulated, without promotion effect on plastoquinone2 or P700 concentration. After 10 days GA3-treated plants show signs of chlorosis combined with a strong decrease in photosynthetic activity. The data demonstrate that the composition and activity of the photosynthetic apparatus are under phytohormone control. IAA and kinetin promote the light induced formation of pigment systems and electron transport chains. GA3 seems to block the rebuilding of the photosynthetic apparatus under steady state conditions.