PHOTOSYNTHETIC APPARATUS OF CUCUMBER AND PEA-PLANTS GROWN UNDER RED-LIGHT WITH DISCRETE OR CONTINUOUS SPECTRA

The effect of light sources with discrete or continuous spectra of red light (50 W/m(2), 600-700 nm) on the structural and functional charac teristics of chloroplasts were studied in leaves of cucumber (Cucumis sativum L.) plants, which die under strong red light, and pea (Pisum s ativum L.) plants, which tolerate red light under the same conditions. Leaf condition was assessed by measuring thermo- and photoinduced cha nges in the chlorophyll fluorescence yield and the photochemical and p hotophosphorylating activities of the chloroplasts. Different response s of the pigment apparatus of pea and cucumber plants to red light wit h continuous or line spectra were revealed. Pea plants responded to di screte-spectrum light by changing P-700 content, the ratio of antenna chlorophyll to P-700 and the position of the low-temperature peak of t he temperature-induced chlorophyll fluorescence yield. In cucumber pla nts, disturbances in the energy transfer from the short-wavelength pig ments to chlorophyll a were observed, In both plants, the effects of l ine spectrum light on the pigment apparatus were reversible; the ratio of cyclic to noncyclic photophosphorylation, photosynthetic control, and the extent of the coupling of photosynthetic electron transport to photophosphorylation did not change compared the control light. The n eed for examining the line spectra of light sources for growing plants under moderate intensities of artificial light (about 50 W/m(2) of ph otosynthetically active radiation) is discussed.