Malic acid cam plants5/16/2023 ![]() ![]() A diurnal oscillation in pHcyt and a quantitatively similar cytoplasmic malic acid is predicted from an established mathematical model which allows simulation of the CAM dynamics. With this value, an acid load of the cytoplasm by about 10 mM malic acid can be estimated as the cause of the observed drop in pHcyt. From monitoring delta pHcyt in response to loading the cytoplasm with the weak acid salt K-acetate a cytoplasmic H(+)-buffer capacity in the order of 65 mM H+ per pH unit was estimated at a pHcyt of about 7.5. Due to its pH sensitivity, phosphoenolpyruvate carboxylase appears as a likely target enzyme. In the physiological context the variation in pHcyt may be a component of CAM regulation. It dropped during midday by about 0.3 pH units before recovering again in the late-day-to-early-dark phase. At the beginning of the light phase, pHcyt was slightly alkaline (about 7.5). The corresponding changes of the cytoplasmic pH (pHcyt) were monitored in mesophyll protoplasts from the CAM plant Kalanchoe daigremontiana Hamet et Perrier by ratiometric fluorimetry with the fluorescent dye 2',7'-bis-(2-carboxyethyl)-5-(and-6-)carboxyfluorescein as a pHcyt indicator. “Although time-consuming, expensive and requiring specialized equipment and techniques not usually available in most laboratories, it should help elucidate the relationship between mesophyll succulence and CAM mode.In crassulacean acid metabolism (CAM) large amounts of malic acid are redistributed between vacuole and cytoplasm in the course of night-to-day transitions. ![]() C 3 plants would be highly desirable,” Herrera writes. “A systematic, quantitative comparison of vacuole area in CAM vs. As Herrera puts it, “it should be accepted that there are no ‘typical CAM’ values of traits.” Associations held within some families: for example, a strong correlation between leaf thickness and δ 13C in some Crassulaceae species, as well as one between leaf thickness and nighttime malic acid accumulation in some species of the Bromeliaceae that carry out obligate CAM, but nothing could be generalized across distantly related plants. Herrera found that neither leaf thickness nor various measures of mesophyll structure were predictive of CAM mode or degree of expression across all taxa. Herrera’s analysis covered 81 species in 15 relatively phylogenetically distant families across nine orders. She compared published values of the carbon isotopic ratio (δ 13C), an indicator of CAM mode, to measurements of leaf thickness, cell area and density, the proportion of intercellular space in the mesophyll, and the length of cell wall facing the intercellular air spaces. ![]() In a study recently published in Annals of Botany, Ana Herrera set out to test these assumptions. To date, however, no study has evaluated the link between these features and obligate or inducible CAM mode. Conventional botanical wisdom tells us that plants using CAM have a standard set of accompanying anatomical features, including thick leaves with large mesophyll cells, which contain large vacuoles for the containment of malic acid produced during the night. Malic acid accumulates through the night and is decarboxylated during the day. In CAM plants, carbon dioxide is taken up during the night and converted to malate. Crassulacean acid metabolism (CAM) is a common feature of plants growing in arid, saline, or drought-prone environments, and can be either obligate or inducible when used in concert with C 3 or C 4 photosynthesis. ![]()
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