In this work, we have compared photosynthetic performance and expression of the PsbS and Lhcb1 proteins in two contrast ecotypes of Tradescantia species, T. fluminensis (shade-tolerant) and T. sillamontana (light-resistant), grown at two intensities of light: 50-125 μmol photons m s (low light, LL) and 875-1000 μmol photons m s (high light, HL). Using the EPR method for measuring the P content, we have found that LL-grown plants of both species have higher (by a factor of ≈1.7-1.8) contents of PSI per fresh weight unit as compared to HL-grown plants. Acclimation of plants to LL or HL irradiation also influences the Chl(a + b) level and expression of the PsbS and Lhcb1 proteins. Immunoblotting analysis showed that acclimation to HL stimulates (by a factor of ≈1.7-1.8) the level of PsbS related to the total number of P centers. In light-resistant species T. sillamontana, the ratio PsbS/P is about 2-times higher than in shade-tolerant species T. fluminensis grown under the same conditions. This should enhance the capacity of their leaves for protection against the light stress. In agreement with these observations, the capacity of leaves for NPQ induction was enhanced during plant acclimation to HL. Kinetic studies of P photooxidation and light-induced changes in the yield of Chl a fluorescence also revealed that the short-term regulation of electron transport processes in chloroplasts, which manifested themselves in the kinetics of [Formula: see text] induction and the rate of Chl a fluorescence quenching, occurred more rapidly in HL-grown plants than in LL-grown plants. Thus, both factors, enhanced expression of PsbS and more rapid response of the photosynthetic electron transport chain to dark-to-light transitions should increase the capacity of HL-grown plants for their resistance to rapid fluctuations of solar light.

Agr family includes three groups of genes, Ag1, Agr2 and Agr3, which encode the thioredoxin domain-containing secreted proteins and have been shown recently to participate in regeneration of the amputated body appendages in amphibians. By contrast, higher vertebrates have only Agr2 and Agr3, but lack Ag1, and have low ability to regenerate the body appendages. Thus, one may hypothesize that loss of Ag1 in evolution could be an important event that led to a decline of the regenerative capacity in higher vertebrates. To test this, we have studied now the expression and role of Ag1 in the regeneration of fins of a representative of another large group of lower vertebrates, the fish Danio rerio. As a result, we have demonstrated that amputation of the Danio fins, like amputation of the body appendages in amphibians, elicits an increase of Ag1 expression in cells of the stump. Furthermore, down-regulation of DAg1 by injections of Vivo-morpholino antisense oligonucleotides resulted in a retardation of the fin regeneration. These data are in a good agreement with the assumption that the loss of Ag1 in higher vertebrates ancestors could lead to the reduction of the regenerative capacity in their modern descendants.

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