Studies of Delta-Aminolevulinic Acid Dehydrase from Skeletonema costatum , a Marine Plankton Diatom

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455

180

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confidence: 83%

Light—Shade Adaptation

Falkowski¹,

Owens²

1980

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455

180

“…S. costatum (Grev.) Cleve, Woods Hole clone SKEL, was grown on a 14:10 light-dark cycle at 15 C as previously described (10). The cultures were continuously mixed by stirring, and gently bubbled with sterile air by negative pressure.…”

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confidence: 99%

Chlorophyll Turnover in Skeletonema costatum, a Marine Plankton Diatom

Riper¹,

Owens²,

Falkowski³

1979

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13H1-and 8-14CIAminolevulinic acids were incorporated into the chlorophylls of Skektonema costatwn, a marine plankton diatom. In the stationary phase of growth, the tetrapyrrole-based pigments reached steadystate labeling after 10 hours. Under conditions of exponential cell division and chlorophyll accumulation, 3H was rapidly lost from the labeled chlorophylls and was replaced with 14C derived from acid. The kinetics of isotope dilution suggests recycling of tetrapyrrole precursors and/or two pigment pools, containing both chlorophyll a and chlorophyllide c, one which turns over rapidly (10 hours) and another which turns over more slowly (100 hours). Calculation of turnover times varied from 3 to 10 hours for chlorophyll a and from 7 to 26 hours for chlorophyllide c. The data suggest the dynamics of chlorophyll metabolism in S. costatum and explain the diatom's ability to undergo light-shade adaptation within a generation time.Light available for photosynthesis is highly variable in aquatic environments. As a result of mixing, wave action, scattering, and heterogeneous extinction, unicellular planktonic algae are potentially exposed to changes in light intensity of one or two orders of magnitude within a period of hours. These algae have evolved diverse and complex light-harvesting pigment systems, some of which are capable of adapting to variations in incident light. Changes in intracellular photosynthetic pigments, such as Chl a (light-shade adaptation), or carotenoids (chromatic adaptation) are often observed within a short time after exposure to a new light regime (5, 15). Such rapid and reversible responses in pigmentation suggest that the metabolism of Chl and accessory pigments is highly dynamic, and imply that pigments may turn over rapidly in vivo.In batch cultures, cell constituents are diluted as a consequence ofgrowth, and the significance of turnover as a means of regulating the steady-state level of many metabolites has been overlooked. We have attempted to examine the turnover of Chl a and chlide c in a common neritic diatom, Skeletonema costatum, as a means of understanding the regulation of light-shade adaptation.The [3,194 mCi/mmol) were purchased from New England Nuclear.Culture Conditions. S. costatum (Grev.) Cleve, Woods Hole clone SKEL, was grown on a 14:10 light-dark cycle at 15 C as previously described (10). The cultures were continuously mixed by stirring, and gently bubbled with sterile air by negative pressure. After 4 to 5 days of growth (cell density of about 2.5 x 106 cells/ml) a 500-ml aliquot was inoculated into 3 liters of fresh media containing 0.5 to 0.6 fLM [3,5-3H]ALA. The reinoculation resulted in a shift-up (12) in the permeability of the cell to ALA, allowing for enhanced uptake of ALA (see under "Results"). Following ALA uptake in isotope dilution and dual label experiments the cultures were continuously centrifuged at 12,000 g at 15 C with a flow rate of about 200 ml/min. The packed cells were washed with filtered seawater and resuspended in fresh media c...

“…Konis et al (15) have shown that LA prevents the synthesis of CPII, a pigment-protein complex associated with PSII activity, in greening maize leaves. LA is also reported to inhibit respiration in Scenedesmus (21), to stimulate paramylum breakdown in Euglena (23), and to retard cell division in Skeletonema (22). In a preliminary study, Duggan et al (5) afflicted with hereditary tyrosinemia (16).…”

mentioning

confidence: 99%

The Effects of Levulinic Acid and 4,6-Dioxoheptanoic Acid on the Metabolism of Etiolated and Greening Barley Leaves

Meller

Gassman²

1981

Application of levulinic acid (LA), a competitive inhibitor of 8-aminolevulinic acid (ALA) dehydratase, to greening plant tissues causes ALA to accumulate at the expense of chlorophyll. 4,6-Dioxoheptanoic acid (DA), which has been reported to be an effective inhibitor of this enzyme in animal systems, has a similar but more powerful effect on Byron, Minn., were germinated in vermiculite in darkness at 22 C.All manipulations of plant material were carried out under a dim green safelight (7). The apical 5-cm portion of 7-day-old leaves was excised in the dark and divided into 1-cm segments. One g lots were placed into 125-ml Erlenmeyer flasks containing 1 to 5 ,uCi of "4C-labeled compound, plus any additions, in 1.0 ml of 50 mm K-phosphate buffer, pH 5.0, and incubated for up to 4 h in the dark or in the light. Incubations with 32Pi were carried out in 50 mm citrate buffer, pH 5.0.Irradiations. Irradiations were carried out at 22 C for the indicated time under GE Cool-White fluorescent lamps at an irradiance of 1.5 x 104 ergs/cm2. s.Assay of ALA Dehydratase. ALA dehydratase (EC 4.3.1.24) was assayed by a modification of the method of Nandi and Waygood (20). Ten g of etiolated leaves, irradiated for I h, were ground in a mortar and pestle at 4 C in 20 ml of 50 mm Tris-HCl, pH 7.6, containing 10 mm cysteine. After filtration through four layers of cheese cloth, the extract was centrifuged at 18,000g for 15 min, and the supernatant used as a source of enzyme. Incubations were carried out at 30 C, with or without LA or DA, as indicated. The reaction mixture contained: ALA, 7.5 .tmol; 98 ,umol; MgCl2, 9.9 ,umol; GSH, 30,umol; and protein, 1.25 mg, in a final volume of 3.0 ml. The reaction was stopped by addition of 1.0 ml of 20% trichloroacetic acid, and porphobilinogen was determined by the method of Mauzerall and Granick (17).Determination of ALA Accumulation in Vivo. ALA, which accumulated in irradiated barley leaves treated with LA or DA, was determined as described previously (12