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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Abstract. Levels of ATP and ADP were studied in primary leaves of barley (Hordeum vulgare L. cv. Viner) seedlings grown under blue (BL) or red light (RL) of various irradiances. In mature leaf segments, BL stimulated a greater accumulation of adenylates than RL. Transfer of barley seedlings from RL to BL for 48 h caused about a twofold increase in the content of adenylates, probably due to de-novo synthesis of adenine nucleotides. Weak BL was found to stimulate an increase in the adenylate content and a higher irradiance enhanced the stimulatory effect. The adenylate content increased markedly from the base towards the tip of barley leaves grown under BL but not in those grown under RL. However, the adenylate content was higher in the basalmost segment of barley leaves grown under RL, indicating that the action of RL on adenylate content proceeded more rapidly than that of BL. The same conclusion could be drawn from the results of experiments with de-etiolated leaves. A linear relationship was established between the maximum rate of CO 2 fixation and the ATP or ADP content in mature segments of primary barley leaves. The possible involvement of two photoreceptors, phytochrome and cryptochrome, in the long-term light regulation of the total content of adenylates in primary barley leaves is discussed.