Blue, red and blue plus red light control of chlorophyll content and CO₂ gas exchange in barley leaves: Quantitative description of the effects of light quality and fluence rate

The dependence of the Chl content and the rate of CO 2 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.