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

Abstract

Changes in levels of phosphoenolpyruvate carboxylase (PEPC, EC 4.1.1.31, orthophosphate: oxaloacetate carboxy‐lyase, phosphorylating) were followed in leaves and stems of CAM‐expressing and non‐expressing Portulaca oleracea L. plants. CAM expression was induced by growing plants under an 8‐h photoperiod and water stress conditions (SD‐WS). Leaves and stems of these plants (designated CAM) expressed nocturnal acidification with an oscillation pattern and an amplitude characteristic of CAM plants. Generally, PEPC activity increased by ca 3‐fold during the period of CAM induction. Over the day/night cycle. PEPC activity oscillated in a pattern typical of CAM plants. Treatment of the other plant group (designated as non‐CAM) by growth under a 16‐h photoperiod and well‐watered conditions (LD‐WW) did not induce expression of the tested criteria of CAM in plants. In these plants, nocturnal acidification as well as changes in the magnitude of PEPC, activity and fluctuation pattern were undetectable. SDS‐PAGE of leaf extracts of the CAM‐expressing plants and the corresponding densitometric scans show progressive increase in the amount of PEPC subunit protein (ca 95 kDa) during the period of CAM induction. These results show that induction of CAM‐like characteristics in the C4 plant Portulaca oleracea is also accompanied by increased PEPC activity, which may be partly due to an increase in enzyme synthesis.

Evolutionary trajectories, accessibility and other metaphors: the case of C4 and CAM photosynthesis

“…It is quite common to find C 4 and CAM plants co‐occurring across many landscapes, albeit often presenting different life histories and growth strategies. From a functional point of view, it also is important to briefly mention Portulaca , a facultative CAM lineage that has likely evolved C 4 photosynthesis three times in parallel while maintaining a functional CAM cycle (Koch & Kennedy, ; Kraybill & Martin, ; Mazen, ; Guralnick et al ., ; Lara, ; Christin et al ., ; Holtum et al ., ; Winter et al ., ). Although C 4 and CAM evolutionary trajectories are largely presented here as distinct, Portulaca demonstrates that they also can overlap, and furthermore, that the two syndromes are even compatible at the organ level.…”

Ecophysiology of Crassulacean Acid Metabolism (CAM)

“…It appears, however, that there genuinely are some C 4 /CAM intermediate species, e.g. Peperomia camptotricha (Nishio and Ting, 1993), Portulaca oleracea Kennedy, 1980, 1982;Mazen, 1996) and Portulaca grandi¯ora Kennedy, 1980, 1982;Ku et al, 1981;Kraybill and Martin, 1996;Guralnick and Jackson, 2001;Guralnick et al, 2002). Only succulent C 4 dicotyledons are capable of diurnal¯uctuations of organic acids, where dark-respiratory CO 2 is trapped in bundle sheaths by PEPC and the water storage tissue in the succulent leaves may also participate in the ®xation of internally released CO 2 (Ku et al, 1981).…”

Ecophysiology of Wild Plants and Conservation Perspectives in the State of Qatar

“…3) [35]. The study of Mazen [36] on Portulaca oleracea (C4 plant) may show two different behaviors concerning CAM characteristics, these are CAM-expressing and non CAM-expressing, and the induction of CAM-like characteristics in this plant was accompanied by increased activity and synthesis of phosphoenolpyruvate carboxylase (PEPC). Mesembryanthemum nodiflorum, the slender ice plant, is a succulent annual that is native to southern Africa, and introduced to many parts of the world.…”