Features of photosynthesis in Haloxylon species of Chenopodiaceae that are dominant plants in Central Asian deserts

Haloxylon aphyllum and H.persicum of Chenopodiaceae are dominant plants in the continental deserts of the Asian Irano-Turanian region. The photosynthetic organs, assimilating shoots and leaf-like cotyledons of these two species were studied to characterize their photosynthetic types. C-13/C-12 isotope ratios, the cellular anatomy of assimilating organs, primary photosynthetic products, and activities of carbon metabolism enzymes, RUBP carboxylase, PEP carboxylase, malic enzymes, and aspartate aminotransferase, indicate different pathways of CO2 fixation in the photosynthetic organs. Assimilating shoots had attributes of the C-4 photosynthesis entirely, while cotyledons lack Kranz-anatomy and incorporated CO2 via C-4 photosynthesis, Cotyledons and seeds had lower delta(13)C values compared to shoots, consistent with the contribution of C-3-like CO2 assimilation. Two pathways of carbon donation to the Cf cycle via decarboxylation of C-4 acids in bundle sheath cells are suggested to occur in shoots of Haloxylon, The primary photosynthetic product malate can be utilized through NADP(+)-malic enzyme which occurs in high activity. NAD(+)-malic enzyme may contribute to C-4 photosynthesis (some aspartate is formed as an initial product, the bundle sheath chloroplasts have some grana, and NAD(+)-malic enzyme is found in bundle sheath cells of shoots, all criteria for NAD(+)-malic enzyme type photosynthesis). We propose that organ diversity of CO2 fixation pathway in Haloxylon species is an important factor for their growth, survival and reproduction in continental climate deserts.