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The analysis of the carbon isotopic data available from the literature evidences in favor of the significant effect of salinity on plant and photosynthesizing alga biomass. The nature of this effect is explained in terms of oscillation model of carbon isotope fractionation in photosynthesis. The data interpretation and conclusions are compared with those obtained from commonly adopted steadystate model of carbon isotope fractionation in photosynthesis. It is shown that the first model gives a new explanation and substantiation on the causes of different response of carbon isotope ratio of glycophyte (salt-sensitive plants) and halophyte (salt tolerant) plant biomass to salinity change. A new explanation for inversion of carbon isotope effect sign in C 4-plants in response to salt stress is given. Under salt stress due to the increase of CO 2 leakage from bundle sheath back to mesophyll cells the isotope fractionation in C 4-plants becomes similar to that in C 3-plants, i.e. the contribution of isotope fractionation in RuBP carboxylation grows up and results in 12 C-enrichment of biomass and inversion of isotope effect sign as well.

The optimization of plant-specific LED lighting protocols for indoor plant growing systems needs both basic and applied research. Experiments with lettuce, Lactuca sativa L., plants using artificial lighting based on narrow-band LEDs were carried out in a controlled environment. We investigated plant responses to the exclusion of certain spectral ranges of light in the region of photosynthetically active radiation (PAR); in comparison, the responses to quasimonochromatic radiation in the red and blue regions were studied separately. The data on plant phenotyping, photosynthetic activity determination, and PAM fluorometry, indicating plant functional activity and stress responses to anomalous light environments, are presented. The study on carbon isotopic composition of photoassimilates in the diel cycle made it possible to characterize the balance of carboxylation and photorespiration processes in the leaves, using a previously developed oscillatory model of photosynthesis. Thus, the share of plant photorespiration (related to plant biomass enrichment with 13C) increased in response to red-light action, while blue light accelerated carboxylation (related to 12C enrichment). Blue light also reduced water use efficiency. These data are supported by the observations from the light environments missing distinct PAR spectrum regions. The fact that light of different wavelengths affects the isotopic composition of total carbon allowed us to elucidate the nature of its action on the organization of plant metabolism.

Fractionation of carbon isotopes (13C/12C) by glycine decarboxylase (GDC) was investigated in mitochondrial preparations isolated from photosynthetic tissues of different plants (Pisum, Medicago, Triticum, Hordeum, Spinacia, Brassica, Wolffia). 20 mM glycine was supplied to mitochondria, and the CO2 formed was absorbed and analyzed for isotopic content.CO2 evolved by mitochondria of Pisum was enriched up to 8 %o in 12C compared to the carboxylic atom of glycine. CO2 evolved by mitochondria of the other plants investigated was enriched by 5-16 %o in 13C. Carbon isotope effects were sensitive to reaction conditions (pH and the presence of GDC cofactors). Theoretical treatment of the reaction mechanism enabled us to conclude that the value and even the sign of the carbon isotope effect in glycine decarboxylation depend on the contribution of the enzymesubstrate binding step and of the decarboxylation step itself to the overall reaction rate. Therefore, the fractionation of carbon isotopes in GDC reaction was revealed which provides essential isotopic effects in plants in addition to the well-known effect of carbon isotope fractionation by the central photosynthetic enzyme, ribulose-l,5-biphosphate carboxylase.