A COMPARATIVE ANATOMICAL AND BIOCHEMICAL-ANALYSIS IN SALSOLA (CHENOPODIACEAE) SPECIES WITH AND WITHOUT A KRANZ-TYPE LEAF ANATOMY - A POSSIBLE REVERSION OF C-4 TO C-3 PHOTOSYNTHESIS

Leaf anatomy was studied by light and electron microscopy and the leaf activities of RUBP carboxylase, PEP carboxylase, and malic enzyme wer e assayed in: Salsola australis and S. oreophila grown on the West Pam irs at 1800 m altitude; in S. australis grown on the East Pamirs at 38 60 m; and in S. arbusculiformis grown in the Kisil-Kum desert in Middl e Asia near 500 m. Carbon isotope fractionation ratio values also were measured on whole leaf tissue for 18 Salsola species field collected in these and other regions of the former USSR. S. australis leaves are cylindrical and in cross section exhibit a peripheral ring of mesophy ll and then an inner ring of bundle sheath type cells; and its biochem ical characteristics and delta(13)C values are typical of a C-4 specie s of the NADP-malic enzyme malate-forming group. These traits were exp ressed independent of the plant growth altitude up to 4000 m. C-4 type delta(13)C values were obtained in 14 of the Salsola species. Anatomi cal, structural, and biochemical features typical of the C-4 syndrome were absent in S. oreophila and S. arbusculiformis. Four Salsola speci es, including these two, had C-3-type delta(13)C values. Their cylindr ical leaves in cross section exhibited two to three peripheral rings a s layers of palisade parenchyma. Although their vascular bundles were surrounded by green bundle sheath cells, their organelle numbers were comparable to those in mesophyll cells. Neither bundle sheath cell wal l thickenings nor dimorphic chloroplasts in two leaf cell types were o bserved. In S. oreophila, there was a high activity of RuBP carboxylas e, but a low activity of C-4 cycle enzymes. Interpretation of these da ta lends evidence to the hypothesis that a small group of C-3 Salsola species, including S. oreophila, S. arbusculiformis, S. montana, and S . pachyphylla, arose as the result of it reversion of a C-4 to a C-3 t ype of photosynthetic CO2 fixation in the cooler climates of Middle As ia.