Optional use of CAM photosynthesis in two C 4 species, Portulaca cyclophylla and Portulaca digyna

Low levels of crassulacean acid metabolism (CAM) are demonstrated in two species with C 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-exc...

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Bibliographic Details
Published inJournal of plant physiology Vol. 214; p. 91
Main Authors Holtum, Joseph A M, Hancock, Lillian P, Edwards, Erika J, Winter, Klaus
Format Journal Article
LanguageEnglish
Published Germany 01.07.2017
Subjects
Carbon Cycle - physiology
Carbon Dioxide - metabolism
Droughts
Photosynthesis - genetics
Photosynthesis - physiology
Portulaca - metabolism
Portulaca - physiology
Portulaca
Crassulacean acid metabolism
Facultative CAM
Gas-exchange
Succulents
C photosynthesis
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Summary:Low levels of crassulacean acid metabolism (CAM) are demonstrated in two species with C 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 C 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 CO during the dark, whereas in P. digyna, net CO exchange at night approached the CO compensation point but did not transition beyond it. This report brings the number of known C 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 C and CAM in Portulaca will benefit from a more wide-range survey of CAM across its species, particularly in the C -C intermediate-containing Cryptopetala clade.
ISSN:1618-1328