Regulation of Salt Respiration in Carrot Root Slices

Abstract

In slices of carrot-phloem parenchyma washed for 7 days in water at 20 C, 50 mM KCI stimulates respiration by up to 100% of the ground respiration within 4 minutes of application. The The increase in rate of oxygen uptake usually occurring when washed slices of plant tissue are treated with salt solutions was described as "salt" respiration by Robertson (13). Although he initially believed that the extra respiration was essential for accumulation of salt, subsequently Robertson and Thorne (15) observed accumulation without salt respiration, and Atkinson and Polya (5) markedly inhibited respiration of carrot slices with ethionine without seriously inhibiting salt accumulation.In the experiments reported here, we measured the rate of oxygen uptake immediately after applying KCl to slices of carrot-phloem parenchyma and investigated the reactions regulating the rate of respiration while it was increasing.As in a previous paper (3), we identify the reactions of glycolysis concerned by applying the crossover theorem of Chance (7), as applied to the glycolytic sequence (10). A site of regulation is identified during a period of increasing influx of respiration as the irreversible reaction at which substrate is depleted and product increased during that period (3, 7 to be in quasi-equilibrium with TP3 (11) and the concentration of the latter used in detecting crossovers. ADP is a substrate for both PGK and PK and, although one of the two may be the regulator reaction, change in ADP must affect both; since the reactions of the glycolytic series between PGK and PK are reversible, accumulation of 3PGA when PGK is stimulated, or depletion of PEP when PK is stimulated, will tend to be reduced, thus masking crossovers which will then be shown only by depletion of substrate (PGK) or accumulation of product (PK). HK and PFK would be affected in the same way.The experiments reported here were carried out on slices from the same batches as those used in the previous reports on induced respiration (1, 2, 3). MATERIALS AND METHODSMethods used for preparing slices of carrot-phloem parenchyma, for measuring oxygen uptake, and concentrations of metabolites were as previously described (3). Slices were treated with KCl in the electrode flask either by adding concentrated KCl or by changing the liquid in the flask. Washed tissue (60 g) to be treated with KCl was placed in a bag of Fiberglas netting and held in distilled water to equilibrate for 30 min. Excess water was then removed by shaking, and the bag was transferred to 3 liters of 50 mm KCI for the required time, removed again, quickly shaken free of salt solution, and plunged into liquid N2 for 4 min. A series of extracts using HCIO, (3) was prepared from batches of treated, frozen tissue at 42, 73, and 166 hr (Fig. 1). Most extracts in each series were prepared within the 4 min period in which the respiratory flux changed, for only then does the crossover theorem apply (7,10). Extracts were also prepared from samples of tissue "treated" with distilled water for up to 5...

The Climacteric in Ripening Tomato Fruit

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Aspects of regulation of ketoglutarate dehydrogenase activity from ribbed mussel (Modiolus demissus) gills and cauliflower (Brassica oleracea)

“…The transport of salt also consumes ATP and releases ADP therefore stimulating respiration and activating glycolysis. This process promotes the production of sugars and other compatible solutes such as proline (Adams, 1970;Adams and Rowan, 1972). This new ionic environment might last for a short period after salt is removed (Poole, 1976) probably^due to the inhibition of membrane transporter proteins that release the osmolites from the cell.…”