Diurnal changes in the malic acid content of vacuoles isolated from leaves of the crassulacean acid metabolism plant, <i>Sedum telephium</i>

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The reciprocal cycling between malic acid and starch in CAM plants constitutes a massive metabolic investment by these green tissues. It has been determined that between 15 to 20%o of the total organic matter in CAM leaves are involved in these daily interconversions (17). The transitions between light and dark, coupled with daily temperature differences, initiate dramatic reversible changes in metabolism which result in malic acid formation via PEP3 carboxylase each night and starch formation via the C3 cycle

Section: Resultssupporting

confidence: 79%

Diurnal Changes in Metabolite Levels and Crassulacean Acid Metabolism in Kalanchoë daigremontiana Leaves

Kenyon¹,

Holaday²,

Black³

1981

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“…Citrate has been shown to undergo relatively small daily changes compared to malate in the leaves of some species of CAM plants (10,15,20,25). Conversely, isocitrate, which is a major component of the leaves of Kalanchoe pinnatum and S. telephium, has been reported to undergo little diurnal fluctuation (3,15,24).…”

Section: Diurnal Changes In Sugars and Organic Acids Of Pineapplementioning

confidence: 99%

“…At night, carbon mobilized from the carbohydrate pool is oxidized via glycolysis to PEP,4 which then is carboxylated and reduced subsequently to form malate. The malate accumulates and is stored as malic acid in the vacuole (3). During the day, malate or oxaloacetate is decarboxylated in the cytoplasm to form CO2 for photosynthesis plus either pyruvate or PEP which is recycled via gluconeogenesis and accumulates as the storage carbohydrate pool.…”

mentioning

confidence: 99%

Maintenance Carbon Cycle in Crassulacean Acid Metabolism Plant Leaves

Kenyon

Severson²,

Black³

1985

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The reciprocal relationship between diurnal changes in organic acid and storage carbohydrate was examined in the leaves of three Crassulacean acid metabolism plants. between pools of malate at night and carbohydrate in the day (2,15,16).In all CAM species studied, malate is the predominant organic acid that accumulates in CAM leaf tissue at night and is depleted during the day. Nocturnal '4C02 assimilation profiles indicate that various metabolites are labeled, especially aspartate, alanine, and intermediates ofthe citric acid cycle (17, 23). The percentage of the label that accumulates in these components relative to malate, however, is low. In some species, citrate fluctuates diurnally but the amplitude is three orders of magnitude less than that exhibited by malate (10,15,20,25

“…Therefore, in some aspects, the function of plant vacuoles is similar to animal lysosomes. An example of the dynamic function of plant vacuoles is provided by the diurnal rhythmic fluctuation in the contents of vacuoles isolated from Sedum telephium and the role of these vacuoles in the organic acid metabolism of this CAM plant (10). Active transport of sugars into vacuoles has been demonstrated using sugarbeet (3,5), sugarcane (22), and rubber tree (2).…”

mentioning

confidence: 99%

Translocation of Photosynthates into Vacuoles in Spinach Leaf Protoplasts

Asami¹,

Hara‐Nishimura²,

Nishimura³

et al. 1985

A method was developed for the isolation of vacuoles from the mesophyll protoplasts of spinach leaf, employing the discontinuous Ficoll density gradient centrifugation technique. Isolated vacuole preparations were judged to be free from other organellar fractions based on the assays of marker enzyme activities of individual organelles.Using this isolation method, a time-dependent translocation of '4C-labeled photosynthates into vacuoles was determined. In contrast to a significant transport of 4C organic acids such as malate and citrate within 10 to 15 minutes '4C neutral sugars and amino acids were barely transported into vacuoles during 40 minutes incubation, in spite of the fact that a relatively large amount of these compounds are found in the vacuoles. It was also found that a majority of I"Cqsucrose remains in the cytosoL apparently not actively moving into the vacuoles. Overall results appear to suggest that vacuoles are not actively engaged in photosynthetic carbon metabolism in spinach leaf protoplasts.The isolation of central vacuoles from various higher plant tissues has been reported by numerous investigators who have shown that several solutes, e.g. salts, neutral sugars, amino acids, organic anions, and secondary metabolites, accumulate in vacuoles, and the mechanism(s) of transport of these substances across tonoplasts have been discussed (15). It has also been established that some lytic enzymes such as proteinase, DNase, phosphodiesterase, and a-mannosidase are localized in vacuoles (19) and that these enzymes are possibly involved in the hydrolytic breakdown of storage substances as well as cellular components (27). Therefore, in some aspects, the function of plant vacuoles is similar to animal lysosomes. An example of the dynamic function of plant vacuoles is provided by the diurnal rhythmic fluctuation in the contents of vacuoles isolated from Sedum telephium and the role of these vacuoles in the organic acid metabolism of this CAM plant (10). Active transport of sugars into vacuoles has been demonstrated using sugarbeet (3, 5), sugarcane (22), and rubber tree (2). The mechanism of ion transport into vacuoles is largely unknown, but experimental evidence is available showing the involvement of ATPase in the ion movement associated with vacuoles (11,17,24,25).In MATERIALS AND METHODSProtoplasts. Leaf of spinach (Spinacia oleracea cv Kyoho), freshly harvested in the field, was used throughout this investigation. Protoplasts were prepared according to the two-step enzymic digestion method described by Nishimura and Akazawa (18) after a slight modification; in the second step, 2% Driselase was added to 2% Cellulase Onozuka. Also, to avoid contamination with epidermal protoplasts, the final preparation of protoplasts obtained by the centrifugation at 100g for 3 min was washed twice with 0.7 M mannitol containing 3% Percoll. Epidermal protoplasts were not sedimented in 0.7 M mannitol containing 3% Percoll. The precipitate was suspended with 0.7 M mannitol and washed twice with 0.7 M mannit...