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Anatomical, ultrastructural and enzymic studies of leaves of Moricandia arvensis, a C3-C4 intermediate species

1981; Elsevier BV; Volume: 637; Issue: 2 Linguagem: Inglês

10.1016/0005-2728(81)90172-9

1879-2650

A. Scott Holaday, Yuh-Jang Shieh, Kit W. Lee, Raymond Chollet,

Plant Stress Responses and Tolerance

The possibility that reduced photorespiration in the crucifer Moricandia arvensis is due to a limited C4-photosynthesis system similar to that in the C3-C4 intermediate Panicum milioides (Rathnam, C.K.M. and Chollet, R. (1979) Biochim. Biophys. Acta 548, 500−519) was investigated. The anatomical, physiological and biochemical features of this crucifer which are similar to those of P. milioides are: (a) the presence of prominent leaf vascular bundle sheaths which contain numerous, centripetally arranged chloroplasts and mitochondria; (b) a CO2 compensation concentration of 16 ± 3 μl/l at 21% O2 and 25°C; (c) a C3-type phosphoenolpyruvate carboxylase exhibiting a maximal velocity which is 2–3-times that of the enzyme from C3 plants; and (d) aspartate and alanine aminotransferase activities which are 2–3-fold higher than in a representative C3 species. However, M. arvensis differs from the C3-C4 intermediate Panicum species in that the activities of the three known C4 acid decarboxylating enzymes present in leaves of C4 plants (NAD- and NADP-malic enzymes and phosphoenolpyruvate carboxykinase) and pyruvate, orthophosphate dikinase (a key C4-related enzyme) are low or undetectable. From these comparative results we conclude that the mechanism by which photorespiration is reduced in M. arvensis is qualitatively different from the limited C4-like CO2-concentrating system operating in P. milioides.