Crassulacean Acid Metabolism in Three Species of the C₄Genus Portulaca

Abstract

The putative existence of Crassulacean acid metabolism was investigated in three succulent species of the C 4 genus Portulaca: P. grandiflora (a widely cultivated species), P. oleracea (a cosmopolitan weed), and P. mundula (found on rock outcrops throughout the southwestern United States). Patterns of diurnal conductance and C0 2 exchange, as well as diurnal tissue malic acid fluctuations, were measured in plants under well-watered and drought-stressed conditions. Net C0 2 uptake in both treatments occurred only during the day, although small amounts of nighttime C0 2 uptake occurred in a few individuals. Stomatal conductances in well-watered and drought-stressed P. mundula and droughtstressed P. oleracea were higher during the night than during the day, though these higher conductances were generally not accompanied by net CO, assimilation. No significant diurnal malic acid fluctuations occurred under well-watered conditions in any species; however, under drought stress, significant diurnal malic acid fluctuations occurred in the three species. The primary source of carbon for nocturnal malic acid production is presumed to be respiratory C0 2 , as occurs in C 3 plants that undergo CAM-cycling. This study confirms past reports of CAM acid fluctuations in P. grandiflora and P. oleracea and marks the first report of CAM activity in P. mundula.

Deciphering the mechanisms involved in Portulaca oleracea (C4) response to drought: metabolic changes including crassulacean acid‐like metabolism induction and reversal upon re‐watering

“…The induction of CAM‐like metabolism in P . oleracea has been also reported under natural environmental conditions (Koch and Kennedy , , Kraybill and Martin ). The species belonging to Portulaca constitute a line in the Portulacaceae family that has evolved from CAM ancestors (Guralnick and Jackson ).…”

“…Under different stress conditions P . oleracea exhibited diurnal acid fluctuation, accounted by malic acid, accompanied by low nocturnal leaf resistance and net dark CO 2 uptake and day time CO 2 release, typical of CAM plants (Koch and Kennedy , Kraybill and Martin , Lara and Andreo ). After 23 days of drought the induction of a CAM‐like metabolism was also observed.…”

A phylogenetic view of low‐level CAM in Pelargonium (Geraniaceae)

“…Nighttime acid accumulation became more pronounced under water stress in P. reniforme, P. carnosum, and P. tetragonum, suggesting a physiology such as CAM idling may be occurring during water stress. Crassulacean acid metabolism idling has been described in CAM species when water stress induces continuous closure of stomata and nocturnal cycling of low levels of organic acids through the CAM pathway (e.g., Holthe, Sternberg, and Ting, 1987;Ting et al, 1993;Kraybill and Martin, 1996). Considered to be a modification of CAM, CAM idling may be a mechanism for maintaining the plant in a physiologically ''poised'' state during the period of stress, preventing photodamage as well as recapturing respiratory CO 2 (Ting, 1985).…”

Changes in levels of phosphoenolpyruvate carboxylase with induction of Crassulacean acid metabolism (CAM)‐like behavior in the C4 plant Portulaca oleracea

“…Total soluble protein in erude extract, g P' 1,6(0,07) 2.3(0,11) 24 (0,07) 2.1 (0,14) 2,5(0,14) 2,7(0, Shift to CAM or combination of C4-CAM is a rare phenomenon among Ci species (Koch and Kennedy 1980, Ku etal, 1981, Guralnick .and Jackson 1993, Kraybill and Martin 1996 compared to C3 species. Understanding the ecological significance of these cases of shifts must be based on a full understanding of the biochemical regulation.…”