Optional use of CAM photosynthesis in two C4 species, Portulaca cyclophylla and Portulaca digyna

Holtum, Joseph A.M., Hancock, Lillian P., Edwards, Erika J., and Winter, Klaus (2017) Optional use of CAM photosynthesis in two C4 species, Portulaca cyclophylla and Portulaca digyna. Journal of Plant Physiology, 214. pp. 91-96.

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Low levels of crassulacean acid metabolism (CAM) are demonstrated in two species with C4 photosynthesis, Portulaca cyclophylla and P. digyna. The expression of CAM in P. cyclophylla and P. digyna is facultative, i.e. optional. Well-watered plants did not accumulate acid at night and exhibited gas-exchange patterns consistent with C4 photosynthesis. CAM-type nocturnal acidification was reversible in that it was induced following drought and lost when droughted plants were rewatered. In P. cyclophylla, droughting was accompanied by a small but discernible net uptake of CO2 during the dark, whereas in P. digyna, net CO2 exchange at night approached the CO2 compensation point but did not transition beyond it. This report brings the number of known C4 species with a capacity for expressing CAM to six. All are species of Portulaca. The observation of CAM in P. cyclophylla and P. digyna is the first for species in the opposite-leaved (OL) Portulacelloid-anatomy lineage of Portulaca and for the Australian clade therein. The other four species are within the alternate-leaved (AL) lineage, in the Atriploid-anatomy Oleracea and the Pilosoid-anatomy Pilosa clades. Studies of the evolutionary origins of C4 and CAM in Portulaca will benefit from a more wide-range survey of CAM across its species, particularly in the C3-C4 intermediate-containing Cryptopetala clade.

Item ID: 50545
Item Type: Article (Research - C1)
ISSN: 1618-1328
Keywords: C4 photosynthesis; crassulacean acid metabolism; facultative CAM; gas-exchange; Portulaca; succulents
Funders: Australian Research Council (ARC), Smithsonian Tropical Research Institute (STRI), US National Science Foundation (NSF)
Projects and Grants: ARC grant DP160100098, NSF grant DEB-1252901
Date Deposited: 22 Sep 2017 04:50
FoR Codes: 31 BIOLOGICAL SCIENCES > 3108 Plant biology > 310806 Plant physiology @ 100%
SEO Codes: 97 EXPANDING KNOWLEDGE > 970106 Expanding Knowledge in the Biological Sciences @ 100%
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