Hill-acitivity and P700 concentration of chloroplasts isolated from radish seedlings treated with-indoleacetic acid, kinetin of gibberellic acid.

The Hill-activity (reduction of DCPIP or methylviolgen) and the concentration of P700 were studied in chloroplasts isolated from cotyledons of radish seedlings (Raphanus sativus L. saxa Treib), which had been grown with the addition of beta-indoleacetic acid (IAA), kinetin, or gibberellic acid. 1) The photosynthetic activity of young chloroplasts from 3 day old Raphanus seedlings is very high (c. 180 micron mol O2/mol chlorophyll X h) and decreases continuously thereafter with increasing age. The steady state Hill-activity is reached after 8 to 10 days (values of 55 to 50 micron mol O2/mg chlorophyll X h). 2) Chloroplasts from plants treated with IAA or kinetin not only exhibit higher plastoquinone levels 1,2, but also a higher P700-content and a higher Hill-activity. The promotion effect is more pronounced with kinetin (+36 tb 40%) than with IAA (+12 to 17%). 3) Gibberellic acid 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 plastoquinone 2 or P700 concentration. After 10 days GA3-treated plants show signs of chlorosis combined with a strong decrease in photosynthetic activity. 4) The data clearly demonstrate that the composition and activity of the photosynthetic apparatus are under phytohormone control. IAA and even better kinetin promote the light induced formation of pigment systems and electrontransport chains. GA3 seems to block the rebuilding of the photosynthetic apparatus under steady state conditions.