Photosynthetic Characteristics of Portulaca grandiflora, a Succulent C₄ Dicot

Abstract

The succulent, cylindrical leaves of the C4 dicot Portulaca grandflora possess three distinct green cell types: bundle sheath cells (BSC) Intracellular localization of enzymes was studied in organelles partitioned by differential centrifugation using mechanically ruptured mesophyll and bundle sheath protoplasts. Phosphoenolpyruvate carboxylase was a cytosolic enzyme in both cells; whereas, ribulose 1,5-bisphosphate carboxylase and NADP+-malic enzyme were exclusively compartmentalized in the bundle sheath chloroplasts. NADP+-malate dehydrogenase, pyruvate, Pi dikinase, aspartate aminotransferase, 3-phosphoglycerate kinase, and NADP+-triose-P dehydrogenase were predominantly localized in the chloroplasts while alanine aminotransferase and NAD'-malate dehydrogenase were mainly present in the cytosol of both cell types. Based on enzyme localization, a scheme of C4 photosynthesis in P. grandflora is proposed.Well confirm the suggestion made by Koch and Kennedy (Plant Physiol. 65: 193-197, 1980) that succulent C4 dicots can exhibit an acid metabolism similar to Crassulacean acid metabolism plants in certain environments.Plants possessing the C4-dicarboxylic acid metabolism of photosynthesis are characterized anatomically by having two photosynthetic cell types in the leaves, mesophyll cells and distinct bundle sheath cells (Kranz type leaf anatomy). The structure and biochemical function of these two types of leaf cells in C4 plants have been of much scientific interest over the past decade (3,17,20). Variations in leaf anatomy have been observed among C4 plants (17,19,21). The succulent dicot Portulaca grandiflora Hook has been reported as a C4 plant based on a measurement of 6 13C (24) and biochemical studies (7). Anatomically, the succulent cylindrical leaves of P. grandiflora, in addition to mesophyll and bundle sheath cells, have a third distinct type of green cell which is localized in the center of the leaves. These cells form the water tissue and contain scattered chloroplasts. There are many morphological and anatomical similarities between succulent C4 dicots and CAM plants. Recently, it has been reported that under certain environmental conditions, Portulaca oleracea, a succulent C4 dicot, is capable ofdeveloping an acid metabolism with many similarities to CAM (13,14). In this report, leaf anatomy and acid metabolism were studied in P. grandiflora. Protoplasts from the three cell types were isolated and key photosynthetic enzymes were located to determine their potential function in C4 photosynthesis. The results indicate that the succulent C4 dicot P. grandiflora has a slightly different Kranz leaf anatomy and enzyme compartmentation compared to other C4 plants and that it is also capable of an acid metabolism similar to that of CAM plants. MATERIALS AND METHODSPlant Materials. Plants of P. grandiflora Hook were grown from seeds in a greenhouse under a day/night temperature regime of 25 to 30/20 to 25 C and a light period of 15 h. Light was provided with Lucolux lamps (General Electric, Clevela...

Portulaca grandiflora Hook. and P. oleracea L.: Formation of Betalains and Unsaturated Fatty Acids

“…Both P. grandiflora and P. oleracea are annuals. Their C 4 -dicarboxylic acid metabolism was shown to be similar to crassulacean acid metabolism and to be associated with some micromorphological peculiarities (Koch and Kennedy 1980;Ku et al 1981). The sieveelement plastids represent the P: CF type in which the pro tein inclusion consists of a central crystalloid and surrounding filaments (Behnke et al 1975).…”

“…Cell clusters, slices of leaves, or sterns and petals were incubated with Cellulase (2%) and Pectinase (0.5 to 2%) for some hours. The digestion was followed by the separation and purification of released protoplasts (Konar 1978;Ku et al 1981;Adachi et a!. 1982).…”

C3-C4 Intermediate Species in Alternanthera (Amaranthaceae)

“…The homogenate was centrifuged at 10,000g for 10 min in a refrigerated centrifuge and the supernatant was assayed for enzyme activities. The extraction medium for RuBP carboxylase contained 50mm Hepes-NaOH ( (19). The extraction procedure for the assay of NAD-and NADP-malic enzyme was similar to that of Edwards et al (7).…”

Compensation Point and Isotopic Characteristics of C3/C4 Intermediates and Hybrids in Panicum

“…For example, several species of Peperomia as well as species in Codananthe, Pereskia, Cissus, and Sedum have characteristics both of CAM and C3 plants and are called CAM-cyclers (15,16,19,(24)(25)(26)(27). Species in the Portulaca genus have physiological/biochemical characteristics of C4 photosynthesis and Kranz anatomy, as well as succulence and acid flux typical of CAM plants (13,14). Species in Panicum, Flaveria, Mollugo, Moricandia, and Neurachne also have physiological, biochemical, or anatomical characteristics of both C3 and C4 plants (17).…”