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 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.     

Effects of Light Spectral Quality on Morphogenesis and Source–Sink Relations in Radish Plants

The accumulation of dry matter and the content of major phytohormones in the aboveground and underground plant parts, as well as light curves and the diurnal course of photosynthesis in the leaves were studied in radish (Raphanus sativusL.) plants of different ages that were grown under red (RL) or blue (BL) light. As seen from the rapid increase in plant biomass, the development of storage organs (hypocotyl or tap root) started on the 14th day after the emergence of seedling of the BL plants and on the 21st day for the RL plants. Conversely, RL stimulated biomass accumulation in the aboveground parts (petioles and stems) already in the early stages of plant development. Light spectral quality only slightly affected the activity and the diurnal course of photosynthesis. The GA content was ten times higher in the aboveground parts of the RL plants than those of the BL plants. The hypocotyl of the BL plants contained much higher amounts of cytokinins and IAA than that of the RL plants. The specific responses of the source–sink relations to the light quality were related to the distribution of various phytohormones between the aboveground and underground parts of the plants: RL increased the content of gibberellins (GA) in the aboveground parts of plants, thus increasing their sink activity, whereas BL stimulated the synthesis of cytokinins and IAA in the hypocotyl and enhanced its development. Light quality-specific morphogenetic responses were reversed when plants were treated with exogenous GA or paclobutrazol, an inhibitor of GA synthesis. The treatment of the BL plants with exogenous GA stimulated petiole and hypocotyl elongation and induced stem formation. The treatment of the BL plants with paclobutrazol led to shortened petioles, the flattening of the storage organ, and the disappearance of the stem.     

Involvement of Exported Photosynthetic Products in the CO2Exchange of the Skeletal Shoots of Pine

CO₂exchange in the leafy and skeletal parts of attached shoots of Pinus sylvestrisL. was measured with an infrared gas-analyzer in an open differential system during daylight hours. The ¹⁴CO₂assimilation rates in the leafy parts of shoots and ¹⁴CO₂evolution from current photosynthetic products in the lower skeletal part of shoots were measured in afternoons. Chlorophyll content was measured in the needles of the same shoot. The carbon of exported assimilates contributed only about 4% to CO₂exchange in the heterotrophic tree tissues. Only this component of CO₂evolution from the surface of the skeletal part of the tree was related to the losses of the net primary photosynthetic production (NPP) in the aboveground part of the pine stand during the current growth period.