โ Scribed by J. Feierabend
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The action of eytokinin on the formation of photosynthetic enzymes in rye seedlings, which was described earlier, is further characterized by studying the interactions of kinetin with specific inhibitors of protein synthesis and with auxins. The combined action of eytokinin and auxin simultaneously affects enzymes of the oxidative pentose phosphate cycle which show a definite relationship to the appearance of the photesynthetic apparatus.
The formation of the photosynthetic enzyme carboxydismutase (EC 4.1.1.39) in rye seedlings can be almost completely prevented by chloramphenicol, but is also strongly inhibited by cycloheximide. These effects of chloramphenicol and cycloheximide cannot be overcome by the application of kinetin.
Plastid growth as well as the formation of photosynthetic enzymes (carboxydismutase; l~ADP-dependent glyeeraldehydephosphate dehydrogenase, EC 1.2.1.9) are selectively curtailed in dark-or light-grown rye seedlings by treatment with relatively high concentrations of auxins like 3-indoleacetic acid, ~-naphthaleneacetic acid (NAA) or 2,4-diehlorophenoxyacetie acid.
The inhibition of plastid growth and enzyme formation can be overcome to an increasing extent by applying increasing amounts of kinetin to young seedlings simultaneously with the ~qAA. Conversely, the promoting effect of kinetin on the formation of photosynthetic enzymes can be lowered by simultaneous application of NAA. In older seedlings the effect of N_A_A is no longer reversed by kinetin. An interpretation of the particularly high eytokinin requirement for the synthesis of photosynthetic enzymes in the seedlings is proposed.
The appearance of the photosynthetic enzymes in the dark and in the light is accompanied by a decline in the rate of accumulation of key enzymes of the oxidative pentese phosphate cycle, especially glueose-6-phosphate dehydrogenase (EC 1.1.1.49). This effect is not due to a simple insufficiency of nutrients. Moreover, applications of glucose-6-phosphate or 6-phosphogluconate did not suggest an inducing effect of these substrates on their corresponding enzymes. 1~o further increase of glueose-6-phosphate dehydrogenase can be achieved by application of either kinetin or NAA alone. But the formation of this enzyme continues at a high rate and reaches nearly twice the maximal activity of the controls when high concentrations of kinetin and I~AA are applied simultaneously. It is concluded * This paper is dedicated to Professor Dr. Andr6 Ph'son on the occasion of his 60th birthday with gratitude for his never failing, critical advice.
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