The dependence of the Chl content and the rate of CO2 gas exchange (RGE) on both blue and red quanta fluence rates have been studied in primary leaves of barley (Hordeum vulgare L. cv. Viner). Empirical equations connecting the two photosynthetic indices with fluence rates of blue or red light were developed. These equations consist of 3 (Chl content) or 2 (RGE) terms, each reflecting the involvement of a specific reaction in the long‐term light control of the development of the photosynthetic apparatus. On the basis of the equations the effects of mixed blue plus red light on both the Chl content and RGE were calculated. An additive mode of the co‐action of blue and red light in the range of high PFDs (10–170 μmol m−2 s−1) becomes evident from the comparison of the experimental results and calculated data. The results indicate the involvement of phytochrome, cryptochrome and chlorophyll in the long‐term regulation of the Chl content and RGE.

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The activity of NADP and 02 photoreduction by water is essentially higher in chloroplasts isolated from pea seedlings (Pisum sativum L.) grown under blue light as compared with that from plants grown under red light. In contrast, the photoreduction of NADP and 02 with photosystem I only is practically the same or even lower in chloroplasts isolated from plants grown under blue light. The data reported are interpreted in terms of differential rates of electron transport from water in the two chloroplast preparations.It is becoming increasingly evident that in green plants, light not only excites the energy-dependent reactions of photosynthesis, but it also serves in a regulatory capacity and controls essential mechanisms participating in the endogenous regulation of the vital activity of plants. The various pigments that function in this regulation may, obviously, either be involved directly in the reactions of photosynthesis or they may influence the process via other reactions which affect the metabolic and energetic state of the cell and chloroplast (15,24,25).It is possible to ascertain the specific regulatory role in photosynthesis of the pigments excited by blue light only (most probably carotenoids, flavins, porphyrins, and quinones) by comparing the effectiveness of blue and red light on photosynthesis. In comparing the effects of blue and red light on photosynthesis, it is necessary to provide equal light quanta for the energy-dependent reactions of the primary photochemical stage of photosynthesis (25). A comparative study of the fast, easily reversible effects of red and blue light on photosynthesis of white lightgrown plants gave evidence for the different influence of red and blue light on both gas exchange and carbon metabolism (12,18,24,25).Thus far, there is not a great deal known about the action of prolonged blue light on the formation of the photosynthetic apparatus of chloroplasts. A great deal of attention was paid to the role of red light in light-dependent macromolecular biosynthesis of chloroplasts (21). At the same time, it is apparent that blue light also affects the formation of the photosynthetic apparatus of chlorop!asts. Supporting evidence comes from the fact that the C02-gas exchange in plants grown under red and blue light is different and is essentially higher in blue light-grown plants (27) at all intensities of light. This is true both for C3 and C4 plants (19,28). The acceleration of C02-gas exchange in plants grown under blue light is correlated with increased activity of the carbon metabolism enzymes (19,28).As to the prolonged action of red or blue light on the photochemical activity of photosynthesis, it has been found only that blue light affects more efficiently the photoreduction of TPIP,' DPIP (1 1), and FeCN (1 1, 27) by water. To elucidate the events underlying this phenomenon, we undertook a study of the specific features of the electron transport chain organization in plants grown under blue light as compared to those grown under red light. MATERIALS AND ME...