A.C. Hulme

Metabolic changes in excised fruit tissue—III. The development of ethylene biosynthesis during the ageing of disks of apple peel

Abstract The production of ethylene by disks of peel from pre-climacteric apples is induced by ageing the disks aerobically at 25°. The development of the ethylene-producing system is dependent upon protein synthesis. Ethylene evolution is stimulated by peroxidation products from linolenic acid, but not by methionine. The relationship between changes occurring during the ageing of pre-climacteric apple peel disks during the development of the climacteric in whole fruit is discussed. A rapid and sensitive method for the determination of ethylene is described.

Metabolic changes in excised fruit tissue-I. Factors affecting the development of a malate decarboxylation system during the ageing of disks of pre-climacteric apples

Abstract A system develops in peel from preclimacteric apples during ageing for periods up to 48 hr which rapidly decarboxylates added malate (the malate effect). This development is preceded by a peak of incorporation of 14C-valine into the protein of the tissue. During the period of increased 14C-valine incorporation the tissue develops the capacity to produce ethylene, and exogenous ethylene reduces the time taken to reach the full malate effect. Cycloheximide and other inhibitors of protein synthesis prevent the incorporation of 14C-valine and the development of the malate effect. Changes in uptake of the various substrates do not appear to be involved in these phenomena. It is suggested that ethylene, RNA and protein synthesis are all involved in the development of the malate effect.

The respiration climacteric in apple fruits: Some possible regulatory mechanisms

Abstract The inhibition of succinate and malate oxidation by added oxaloacetate (OAA) has been studied in mitochondria isolated from the peel of apple fruits at various stages in the development of the respiration climacteric in fruit either attached or detached from the tree. The rate of relief of inhibition increases as the climacteric peak is reached. It is suggested that this faster relief of inhibition is related to the development of a special enzyme system for metabolizing OAA rather than to an increase in the rate of turnover of the Krebs cycle. The effect of addition of glucose and hexokinase to mitochondria oxidizing succinate and malate results in an enhancement of the rate of oxidation, and again the effect is most pronounced at the climacteric peak; the effect on CO 2 -output is greater than an O 2 -uptake. The effect of glucose and hexokinase is probably to provide a continuous supply of phosphate acceptors, but this does not explain the greater effect on CO 2 -output.

The relationship between ethylene and the synthesis of RNA and protein in ripening apples

Abstract The stimulation by ethylene of the respiration of whole fruits and peel discs prepared from them is followed using Worcester Pearmain and Coxs Orange Pippin apples. RNA and protein synthesis in relation to ethylene stimulation is investigated in terms of incorporation of 14 C-uridine and 14 C-valine into RNA and protein fractions in the discs of peel. Application of ethylene (40–60 ppm) to the preclimacteric fruit induces increased ethylene production in the fruit; uridine incorporation into RNA rises to a peak followed by a peak in valine incorporation into protein, while a malate decarboxylating system develops in the ripening fruit.

Metabolic changes in excised fruit tissue—II. The development of a lipid synthesis system during the ageing of peel disks from pre-climacteric apples

Abstract Disks of peel from immature (pre-climacteric) apples develop a lipid synthesizing system when aged aerobically at 25°. Full development of the system is rapid, occurring within 2–4 hr ageing and is dependent upon protein synthesis, being reversibly inhibited by low concentrations of cycloheximide. The ability to oxidize fatty acids and acetate to CO 2 is also increased by ageing. The nature of the lipids formed from 14 C-1-acetate by fresh and aged disks of apple peel is described.

The effect of ethylene on the respiration, ethylene production, RNA and protein synthesis for apples stored in low oxygen and in air

Abstract A comparison is made between the respiration rate and ethylene production of the whole fruit and the respiration rate, ethylene production, incorporation of 14 C-uridine into an RNA fraction and of 14 C-valine into a protein fraction of peel disks prepared from the fruit from Bramleys Seedling apples stored at 12° in air and in 3% oxygen. Results show that the respiration and ethylene production of the whole fruit is closely reflected in the behaviour of the peel disks in air, in low O 2 and on transfer from low O 2 to air. Ethylene appears to be the key to the increased rate of respiration and the other parameters including the development in the disks of a malate decarboxylating system (the malate effect) which appears to be a coupled system involving malic enzyme, pyruvate decarboxylase and alcohol dehydrogenase (NADPH 2 -dependent). While oxygenous ethylene has a temporary stimulatory effect on the various systems investigated when applied in 3% O 2 , autostimulation of ethylene production with attendant physiological action does not appear possible in low O 2 . Both production and physiological action of ethylene appear to require relatively high concentration of O 2 for their full operation.