Influence of cytokinins on the formation of photosynthetic enzymes in rye seedlings

Abstract

1. Factors were investigated which control the formation of photosynthetic enzymes during germination. Enzymes of the reductive pentose phosphate cycle like carboxydismutase (EC 4.1.1.39) and NADP-dependent glyceraldehydephosphate dehydrogenase (EC 1.2.1.9.) are formed in the primary leaves of dark-grown rye seedlings. The rate of their synthesis is determined by the level of cytokinins. This rate can be increased by treatment of normal seedlings with kinetin. After application of kinetin to dark-grown seedlings, the investigated enzymes finally reach the same activity as they do in untreated light-grown plants. The formation of these photosynthetic enzymes can be strongly reduced by excision of the roots early in the development, a treatment which is known to lower the supply of cytokinins. A high rate of enzyme formation can be restored by feeding kinetin to rootless seedlings. Neither adenosine nor gibberellic acid have this effect on enzyme formation. 2. Changes in the content of cytokinins preferentially influence the formation of the investigated photosynthetic enzymes. Some cytoplasmic enzymes are not affected by the decrease of the cytokinin level which is achieved by excision of the roots. At the beginning of germination only cytoplasmic enzymes are promoted by application of kinetin, whereas in later stages, after 96 hours of germination, only the formation of photosynthetic enzymes is increased. The formation of photosynthetic and cytoplasmic enzymes seem to differ in their cytokinin requirements. 3. Cytokinins seem to be necessary for the formation of enzymes of the reductive pentose phosphate cycle. However, the cytokinins do not alter the time of appearance of these enzymes. Also the suppressing action which is exerted on the formation of photosynthetic enzymes by low temperature cannot be prevented by the application of kinetin. The action of cytokinins probably does not induce the derepression of the genes, but the level of cytokinins determines the extent of the manifestation of the genes. 4. The formation of the photosynthetic enzymes is also promoted by phytochrome. Phytochrome and cytokinin act as independent factors in a multiplicative system. The rate of synthesis of these enzymes in the dark, which corresponds to the cytokinin level of the seedlings (rootless, normal or treated with kinetin) can be increased by a constant factor via the phytochrome system by continuous irradiation with far-red light. In the case of carboxydismutase this factor is nearly 2. 5. After excision of the roots carboxydismutase and NADP-dependent glyceraldehydephosphate dehydrogenase reach higher activity in red and blue light than in far-red light, under which no chlorophyll is formed. In this case formation of carboxydismutase in red and blue light seems to proceed in close correlation with chlorophyll synthesis.