Formation of C-4 syndrome in leaves and cotyledons of Kochia scoparia and Salsola collina (Chenopodiaceae)

The formation of photosynthetic structures in true and cotyledonary leaves was comparatively analyzed during leaf development in C-4 species of the fa mily Chenopodiaceae: Kochia scoparia (subfamily Chenopodioideae) and Salsol a collina (subfamily Salsoloideae). The operation of C-4 photosynthesis in cotyledons of both species was revealed, This was evidenced by the Kranz an atomy of mesophyll, high activity of phosphoenolpyruvate carboxylase, predo minance of dicarboxylic acids among the photosynthetic intermediates, and t he low level of the CO2 compensation point. K. scoparia and S, collina feat ured a common biochemical type of CO2 fixation in cotyledons and leaves (NA DP-malic enzyme type), but differed in the mesophyll structure. In K. scopa ria, the Kranz anatomy in leaves represented the evolutionary advanced type (kochioid type), whereas the Kranz anatomy in cotyledons resembled the atr iplecoid type. In both species, the ratio of bundle sheath cells to mesophy ll cells was 1 : 4 in fully expanded leaves, and only 1 : 2 In mature cotyl edons, In both species, the number of chloroplasts and phototrophic cells, as calculated per unit leaf area and the area of intraleaf assimilatory sur face, was 2-3 times lower in cotyledons than in leaves. Thus, the biochemic al traits of cooperative photosynthesis in the family of Chenopodiaceae are more conservative than the structural traits. The level of chlorenchyma de velopment was higher in leaves than in cotyledons; this was evidenced by th e formation of a more progressive type of Kranz anatomy and more elaborated structure for the operation of cooperative photosynthesis. The dissimilari ty of structural characteristics implies the possibility of independent and parallel evolution of photosynthesis types in the leaves and cotyledons of Chenopodiaceae.