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(American Journal of Botany. 2007;94:1344-1351.)
© 2007 Botanical Society of America, Inc.

Physiology and Biochemistry

Crassulacean acid metabolism photosynthesis in columnar cactus seedlings during ontogeny: the effect of light on nocturnal acidity accumulation and chlorophyll fluorescence1

Olivia Hernández-González and Oscar Briones Villarreal2

Departamento de Biología Evolutiva, Instituto de Ecología, A. C., Apartado 63, 91000, Xalapa, Veracruz, Mexico

ABSTRACT

Columnar cacti have been traditionally classified as crassulacean acid metabolism (CAM) plants, though recent research indicates some cactus seedlings employ the C3 pathway. To verify this last result, we measured acidity fluctuations for five columnar and one globular cactus species in seedlings from 1 to 48 d old after experimental exposure to 60% and 30% full sunlight, and in adult plants in the field. Using light-response curves of chlorophyll fluorescence, we determined photosynthetic efficiency ({Delta}F/Fm'), maximum electron transport rate (ETRmax) and saturating photosynthetically active photon flux density (PPFDsat). All seedlings used the CAM pathway from their first day of development, and increases in nocturnal acidity depended on species, light treatment, and age. The CAM pathway was also found in adult plants. Cactus seedlings were able to acclimatize to light conditions by making photochemical adjustments, mainly by modifying the level of light at which photosystem II is saturated (PPFDsat). The presence of CAM in the seedlings of columnar cacti increases water-use efficiency and reduces the risk of photoinhibition. This could favor survival in the highly variable light levels characteristic of the desert environments of columnar cacti.

Key Words: Cactaceae • cactus seedlings • chlorophyll fluorescence • crassulacean acid metabolism • fluctuation in acidity • instant light-response curves • Tehuacán, Mexico




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K. Winter, M. Garcia, and J. A. M. Holtum
On the nature of facultative and constitutive CAM: environmental and developmental control of CAM expression during early growth of Clusia, Kalanchoe, and Opuntia
J. Exp. Bot., May 1, 2008; 59(7): 1829 - 1840.
[Abstract] [Full Text] [PDF]


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