Features of photosynthesis in Haloxylon species of Chenopodiaceae that aredominant 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 photosynthe tic organs, assimilating shoots and leaf-like cotyledons of these two speci es were studied to characterize their photosynthetic types. C-13/C-12 isoto pe ratios, the cellular anatomy of assimilating organs, primary photosynthe tic 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. Assimilati ng shoots had attributes of the C-4 photosynthesis entirely, while cotyledo ns lack Kranz-anatomy and incorporated CO2 via C-4 photosynthesis, Cotyledo ns and seeds had lower delta(13)C values compared to shoots, consistent wit h the contribution of C-3-like CO2 assimilation. Two pathways of carbon don ation to the Cf cycle via decarboxylation of C-4 acids in bundle sheath cel ls are suggested to occur in shoots of Haloxylon, The primary photosyntheti c 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 chloropl asts have some grana, and NAD(+)-malic enzyme is found in bundle sheath cel ls 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 conti nental climate deserts.