Occurrence of C-3 and C-4 photosynthesis in cotyledons and leaves of Salsola species (Chenopodiaceae)

Most species of the genus Salsola (Chenopodiaceae) that have been examined exhibit C-4 photosynthesis in leaves. Four Salsola species from Central Asi a were investigated in this study to determine the structural and functiona l relationships in photosynthesis of cotyledons compared to leaves, using a natomical (Kranz versus non-Kranz anatomy, chloroplast ultrastructure) and biochemical (activities of photosynthetic enzymes of the C-3 and C-4 pathwa ys, C-14 labeling of primary photosynthesis products and C-13/C-12 carbon i sotope fractionation) criteria. The species included S. paulsenii from sect ion Salsola, S. richteri from section Coccosalsola, S. laricina from sectio n Caroxylon, and S. gemmascens from section Malpigipila. The results show t hat all four species have a C-4 type of photosynthesis in leaves with a Sal soloid type Kranz anatomy, whereas both C-3 and C-4 types of photosynthesis were found in cotyledons. S. paulsenii and S. richteri have NADP- (NADP-ME ) C-4 type biochemistry with Salsoloid Kranz anatomy in both leaves and cot yledons. In S. laricina, both cotyledons and leaves have NAD-malic enzyme ( NAD-ME) C-4 type photosynthesis; however, while the leaves have Salsoloid t ype Kranz anatomy, cotyledons have Atriplicoid type Kranz anatomy. In S. ge mmascens, cotyledons exhibit C-3 type photosynthesis, while leaves perform NAD-ME type photosynthesis. Since the four species studied belong to differ ent Salsola sections, this suggests that differences in photosynthetic type s of leaves and cotyledons may be used as a basis or studies of the origin and evolution of C-4 photosynthesis in the family Chenopodiaceae.