An experiment in breeding apples

Ohne Zusammenfassung

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An experiment in breeding apples

     

Low temperature breakdown in apples

Low temperature breakdown in apples was increased by geraniol and a number of inhibitors of isoprenoid biosynthesis which were injected into the fruit after harvest. The addition of gibberellic acid reduced breakdown.     

Lipid metabolism of ripening apples

Little change was observed in the concentration of sitosterol, the principal free sterol of apple, during ripening of the fruit in air at 12°. Phospholipid increased by ca 10% during the first 15–18 days and thereafter showed little change. Phosphatidylcholine increased during ripening whilst phosphatidylethanolamine exhibited a transitory increase in the first 7–18 days. Incorporation of [¹⁴C]acetate into free sterol by apple cortical discs showed little change during ripening but incorporation into phospholipids increased substantially between days 1 and 15 with a 27-fold increase in incorporation into phosphatidylcholine and an 8-fold increase into phosphatidylethanolamine and phosphatidylinositol.     

Chilling-induced ethylene biosynthesis in Braeburn apples

We observed a chilling-induced ethylene biosynthesis in Braeburn apples.The stimulatory effect depended on the length of the cooling period. The longerthe period, the stronger the stimulation. Low temperature stimulated activityand gene expression of ACS, but only stimulated gene expression of ACO. Thestimulatory effect of low temperature on gene expression was stronger andearlier in ACS than in ACO. 1-MCP (1-methylcyclopropene), an inhibitor ofethylene action, inhibited ethylene biosynthesis in fruit stored at 20°C and 0 °C. This inhibitory effect can beslightly recovered in fruit stored at 0 °C, but not at 20°C. Expression of genes for ACS and ACO was weaker in1-MCP-treated fruit stored at 20 °C, than those at 0°C. Thus, it is possible that expression of genes for ACS andACO in fruit at low temperature was mainly, but not completely, regulated bytheethylene receptor.     

β-Galactosidase activity in ripening apples

β-Galactosidase activity has been identified in soluble and cell wall preparations from apple cortex tissue. The enzyme degrades pectin galactan and has a pH optimum of 4·0 with p-nitrophenyl-β, d-galactopyranoside as substrate. Soluble polygalacturonide increased as the applies softened with ripening and these changes were preceded by loss of galactose residues from the cell wall and an increase in β-galactosidase activity.     

An ethylene-related cDNA from ripening apples

We report the isolation of a ripening-related apple cDNA which is complementary to a mRNA which may be involved in ethylene production. Poly(A)⁺ RNA was extracted from cortical tissue of ripe apple fruit (Malus domestica Borkh cv. Golden Delicious) and a cDNA library constructed in the plasmid vector pSPORT. The library was screened with pTOM13, a tomato cDNA clone thought to code for ACC oxidase in that fruit. An apple cDNA clone (pAP4) was isolated and sequenced. The 1182 bp cDNA insert includes an open reading frame of 942 bp, and shows strong homology with reported tomato and avocado sequences, both at the nucleic acid and amino acid levels. The polypeptide has a calculated molecular mass of 35.4 kDa and a calculated pI of 5.15. In apple cortical tissue, expression of pAP4-complementary RNA increased with ethylene production by the fruit during ripening. Expression was also enhanced in both ethylene-treated and wounded fruit.     

The infection of apples by Phytophthora syringae

Contamination with infected soil has led to high wastage of apples in storage due to rotting by Phytophthora syringae. At 3-3 ^oC lesions formed 3–4 wk after inoculation with zoospores; the percentage infection fell if the suspensions dried after 48 h at this temperature and after 22 h at 15 ^oC. Infected soil rotted fruit only if kept moist; at 3-3 ^oC a 3-day period of wetness resulted in 37-5% rotting after 8 wk. Fruit dipped in soil slurry remained wet in some parts of a 4361(12 bushel) bin for at least 3 wk. There was a 10-fold increase in rotting by contact between sound and rotting fruit after 11 wk at 3-3 ^oC. Captan gave effective protection against rotting derived from zoospores or infected soil; it had no eradicant action.     

Some aspects of enzymatic browning in apples

The investigations outlined in ‘Browning reactions in fruits’, part of the special study of food science of the Nuffleld Advanced Chemistry course, are modified to make the material meaningful and relevant to pupils in the middle school. This article discusses a series of simple experiments on apple browning which were performed by third formers. A summary of the nature of the browning process and its control are included.     

Endosperm responses to irradiated pollen in apples

Summary The cytological effects of pollen -irradiation at 50 and 100 krad on both embryo and endosperm development were studied in Malus × domestica. Fruit and seed set were reduced by increasing doses of pollen irradiation, while embryo sacs resulting from the treatments differed in number and morphology of endosperm nuclei and in the presence or absence of an embryo. Nuclear abnormalities, distinguished from normal nuclear behaviour in embryo sacs derived from unirradiated pollen, included enhanced numbers of polyploid restitution nuclei, bridges between nuclei, excluded metaphase chromosome fragments and disrupted mitotic synchrony. Generally, a high dose of pollen irradiation (100 krad) generated an all-or-nothing response in the embryo sac, either creating highly abnormal embryos and/or endosperms which aborted, or showing relatively normal development. Callus produced from excised cellular endosperm differed in average genome size, that derived from 100 krad pollen being smaller than that from unirradiated pollen.