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Keywords:

  • Bienertia;
  • Borszczowia;
  • Chenopodiaceae;
  • C4 plants;
  • facultative C4/C3 plants;
  • C3/C4 intermediates;
  • Kranz anatomy;
  • carbon isotope ratio;
  • δ13C values

Abstract: Following up an earlier study on Borszczowia aralocaspica, a second C4 leaf type without Kranz tissues is described from Bienertia cycloptera Bunge ex Boiss. The species belongs also to tribe Suaedeae and grows in similar temporarily wet saline habitats in southwestern C Asia. Like Borszczowia, the species has the ability to perform C4 photosynthesis in single chlorenchyma cells but the cytological compartmentation differs. Evidence is cited from anatomy (cytoplasmic compartmentation, starch formation), from carbon isotope composition and from indirect sources. It is documented by micrographs and δ13C values (mean - 14.7 %). Variations of the δ13C values subsequently found in newly formed leaves of the same greenhouse plants (- 15.5 to - 21.1 %) support the hypothesis that Bienertia is a facultative C4/C3 species. The new described bienertioid leaf type differs from the leaves of C3 species in Suaeda by strict separation of the mesophyll into a central aqueous tissue without chloroplasts and a peripheral 1 - 3 layered chlorenchyma with elaborate cytoplasmic compartmentation. Each cell of the latter contains a peripheral cytoplasmic layer with scattered chloroplasts and a large globular cytoplasmic body located in the central vacuole which is densely packed with starch producing chloroplasts, and joined by the nucleus. Comparative studies on different leaves of the same individuals of ordinary C4 species demonstrated a remarkable range of variation, from 1.0 % in Salsola tragus up to 2.5 % in Petrosimonia sibirica. This corresponds well with the variance in data from different individuals and populations. For explaining the larger interspecific variation from about 23 other species of Salsoloideae, the hypothesis is developed that in species or groups of taxa specific leakages of their C4 systems do occur. By three characters unique in tribe Suaedeae and detected during the study, Bienertia is confirmed as well separated from Suaeda and as a monotypic genus.