The Onset of Tricarboxylic Acid Cycle Activity with Aging in Potato Slices

The rest period of the potato tuber was studied in relation to certain biochemical changes that are induced by gibberellic acid (GA3). The concentration of reducing sugars in excised plugs with buds treated with 10-M GA3 decreased in the first 4 hours after treatment and then rapidly increased up to 70 hours. The pattern in control buds was similar, but the changes occurred more slowly. The response to GAs is temperature-dependent and is not limited to any particular tissue of the tuber. The concentration of reducing sugars in excised buds increased proportionally to the log of the concentration of GA3 in a range from 10-8 to 10-4 M.At 10-3 M, GA3 slightly inhibited production of reducing (1,3,9,13,29,35,38,40). Application of gibberellic acid promotes sprouting of intact tubers during tuber development or after they are harvested as marketable (23,36,38 the level of enzymes associated with carbohydrate metabolism (4,19,25,32). There is mounting evidence that the hormone can induce synthesis of several hydrolytic enzymes (6,14,20,49,50). Working with Avena fatua, Simpson and Naylor (44) noted that the activity of maltase was higher in imbibed nondormant seeds than in imbibed dormant seeds. Gibberellin A3 caused an increase in maltase in dormant seeds, with a resultant increase in sugar production. Moreover, whereas excised nondormant embryos would grow on a sugar-amino acid medium, dormant embryos would grow on this medium only if GA3 was present (45). Thus in A. fatua, GA3 appears to have dual functions-to induce in the aleurone layers synthesis of enzymes that hydrolyze carbohydrate reserves and to induce in the embryo enzymes that utilize the resulting substrates. Development of cell wall invertase in tissue slices of Helianthus tuberosa in response to GA3 was observed by Edelman and Hall (10, 11) and Bacon, MacDonald, and Knight (2). Palmer (34) reported similar results with root slices of Beta vulgaris L.The expectation that GA3 would promote protein synthesis in potato buds was heightened by the observation that GA3 accelerates synthesis of RNA and DNA in excised buds from resting potatoes (39,41,49). We have shown (7) that reducing sugar content of potato buds increased shortly after excision, and the increase was accelerated by treatment with the hormone. It was therefore of interest to explore certain biochemical responses that occur in potato buds shortly after excision and treatment with GA3. MATERIALS AND METHODSPLANT MATERIALS White Rose potatoes were harvested 100 to 120 days after planting at which time they were in deep rest. The tubers were washed by hand and placed in the dark at 200. They were used within 3 days after harvest and were cooled to 00 hr before an experiment was begun; thereafter all procedures associated with preparation of plugs were at this temperature. In most experiments plugs with an apical bud (eye) were excised with a potato "deeyer" (internal diameter 0.8 cm) and cut to a length of 0.5 cm (35). In some experiments, 0.2 cm x 0.2 cm plugs with a bud were used. Such...

Section: Discussionmentioning

confidence: 53%

Regulation of Bud Rest in Tubers of Potato, Solanum tuberosum L

Clegg

Rappaport

1970

“…In an early study, fresh potato slices were found to lack full' tricarboxylic acid cycle activity in consequence of their inability to oxidize citrate to a-ketoglutarate (15). At the same time NADlinked isocitrate dehydrogenase was shown to exhibit positively cooperative kinetics (12,22), and accordingly, ICDH2 was proposed as a potential regulator ofthe tricarboxylic acid cycle subject to modulation and control by an array of cofactors and metabolic intermediates (1,6,8,9,12).…”

mentioning

confidence: 99%

Membrane-Associated NAD-Dependent Isocitrate Dehydrogenase in Potato Mitochondria

Laties

1983

Self Cite

The oxidation isotherms for citrate and isocitrate by potato (Solanm tuberosum var. Russet Burbank) mitochondria in the presence of NAD differ markedly. Citrate oxidation shows positively cooperative kinetics with a sigmoid isotherm, whereas isocitrate oxidation shows MichaelisMenten kinetics at concentrations up to 3 millimolar, and cooperative kinetics thereafter up to 30 millimolar. In the absence of exogenous NAD, the isocitrate isotherm is sigmoid throughout. The dual isotherm for isocitrate oxidation in the presence of exogenous NAD reflects the operation of two forms of isocitrate dehydrogenase, one in the matrix and one associated with the inner mitochondrial membrane. Whereas in intact mitochondria the activity of the membrane-bound enzyme is insensitive to rotenone, and to butylmalonate, an inhibitor of organic acid transport, isocitrate oxidation by the soluble matrix enzyme is inhibited by both. The membrane-bound isocitrate dehydrogenase does not operate through the NADH dehydrogenase on the outer face of the inner mitochondrial membrane, and is thus considered to face inward. The regulatory potential of isocitrate dehydrogenase in potato mitochondria may be realized by the apportionment of the enzyme between its soluble and bound forms.In an early study, fresh potato slices were found to lack full' tricarboxylic acid cycle activity in consequence of their inability to oxidize citrate to a-ketoglutarate (15). At the same time NADlinked isocitrate dehydrogenase was shown to exhibit positively cooperative kinetics (12,22), and accordingly, ICDH2 was proposed as a potential regulator ofthe tricarboxylic acid cycle subject to modulation and control by an array of cofactors and metabolic intermediates (1,6,8,9,12). Subsequently, Ribereau-Gayon and Laties (20,21) demonstrated the sigmoidicity of the isotherm for isocitrate oxidation in potato mitochondria together with the socalled activating effect of citrate, which both lowered the SO.5 for isocitrate and seemingly converted the isotherm from sigmoid to hyperbolic (see below). During this period, the details of di-and tricarboxylic acid transport across the inner mitochondrial membrane received exhaustive attention, and it was established that carrier-mediated tricarboxylic acid uptake into the mitochondrion was dependent upon concomitant outward transport of dicarboxylic acid-malate in particular-the latter, in turn, being taken up from the milieu in exchange for intramitochondrial phosphate (3

“…The quantitative and qualitative changes in the synthesis of fatty acids occur very early during the aging process, earlier than the changes in respiration described by Laties (10)(11)(12) in the same tissue tinder the same conditions of aging. This observation makes difficult a correlation of the sudden rise in metabolic activity with a relief from a negative feedback control of respiration, determined by the level of a volatile intermediate (11).…”

mentioning

confidence: 82%

Fat Metabolism in Higher Plants. XXXIV. Development of Fatty Acid Synthetase as a Function of Protein Synthesis in Aging Potato Tuber Slices

Willemot

Stumpf

1967

Summary. Experiments with inhibitors of protein synthesis (actinomycin D, puromycin, actidione) showed that the increase and the change in fatty acid synthetase activity, observed during the aging of potato disks, were accompanied by and related to a temporary risqe in the rate of protein and RNA synthesis. These results concur with the earlier stuggestion by Click and Hackett that the aging process involves a type of derepression. A possible course of events during aging, and possible derepression mechanisms are suggested and discuissed.