Patterns of phosphoenolpyruvate carboxylase activity and cytosolic pH during light activation and dark deactivation in C3and C4plants

✍ Scribed by A. V. Rajagopalan; M. Tirumala Devi; A. S. Raghavendra

• Publisher: Springer
• Year: 1993
• Tongue: English
• Weight: 771 KB
• Volume: 38
• Category: Article
• ISSN: 0166-8595
• DOI: 10.1007/bf00015061

✦ Synopsis

The rate and extent of light activation of PEPC may be used as another criterion to distinguish C 3 and C 4 plants. Light stimulated phosphoenolypyruvate carboxylase (PEPC) in leaf discs of C4 plants, the activity being three times greater than that in the dark but stimulation of PEPC was limited about 30% over the dark-control in C 3 species. The light activation of PEPC in leaves of C 3 plants was complete within 10 min, while maximum activation in C 4 plants required illumination for more than 20 min, indicating that the relative pace of PEPC activation was slower in C 4 plants than in C 3 plants. Similarly, the dark-deactivation of the enzyme was also slower in leaves of C4 than in C3 species. The extent of PEPC stimulation in the alkaline pH range indicated that the dark-adapted form of the C a enzyme is very sensitive to changes in pH. The pH of cytosol-enriched cell sap extracted from illuminated leaves of C 4 plants was more alkaline than that of dark-adapted leaves. The extent of such light-dependent alkalization of cell sap was three times higher in C4 leaves than in C 3 plants. The course of light-induced alkalization and dark-acidification of cytosol-enriched cell sap was markedly similar to the pattern of light activation and dark-deactivation of PEPC in Alternanthera pungens, a C 4 plant. Our report provides preliminary evidence that the photoactivation of PEPC in C 4 plants may be mediated at least partially by the modulation of cytosolic pH.