Physiological and Biochemical Studies of Chilling Injury in Bananas

The physiological changes in green bananas (cv. Sin-zun), which are very sensitive to chilling injury, were studied during and after exposure to low temperatures (4±1°C, 6±0.5°C) for various periods. While the fruits injured by chilling did not fail to produce CO₂ and ethylene, the pattern of both CO_2- and ethylene production in these chilled fruits (9 and 15 days at 6°C) after transfer to 20°C was not normal. The contents of acetaldehyde and ethanol in chilled fruits, both in peels and pulps, increased with the advance of chilling, injury. There was an accumulation of α-keto acids in the peels of chilled fruits. Only half the conversion of ¹⁴C (fed as succinic acid-1, 4-¹⁴C) to citric acid and isocitric acid was observed in chilled tissues as compared with healthy ones; the activity of citrate synthase in banana peels appears therefore to be inhibited by chilling injury. A histological study of the tissues showed that the browning substances (polyphenols) present in chilled fruits accumulate around the vascular tissues.     

Enzymic mechanism of starch breakdown in germinating rice seeds I. An analytical study

Time-sequence analyses of carbohydrate breakdown in germinating rice seeds shows that a rapid breakdown of starch reserve in endosperm starts after about 4 days of germination. Although the major soluble carbohydrate in the dry seed is sucrose, a marked increase in the production of glucose and maltooligosaccharides accompanies the breakdown of starch. Maltotriose was found to constitute the greatest portion of the oligosaccharides throughout the germination stage. α-Amylase activities were found to parallel the pattern of starch breakdown. Assays for phosphorylase activity showed that this enzyme may account for much smaller amounts of starch breakdown per grain, as compared to the amounts hydrolyzed by α-amylase. There was a transient decline in the content of sucrose in the initial 4 days of seed germination, followed by the gradual increase in later germination stages. During the entire germination stage, sucrose synthetase activity was not detected in the endosperm, although appreciable enzyme activity was present in the growing shoot tissues as well as in the frozen rice seeds harvested at the mid-milky stage. We propose the predominant formation of glucose from starch reserves in the endosperm by the action of α-amylase and accompanying hydrolytic enzyme(s) and that this sugar is eventually mobilized to the growing tissues, shoots or roots.     

A mutation causing reduced biological activity and stability of thyroxine-binding globulin probably as a result of abnormal glycosylation of the molecule

T4-binding globulin (TBG), a 54-kilodalton glycoprotein, is the major thyroid hormone transport protein in man. The exact nature of the mutations causing X chromosome-linked TBG deficiency, which affect about 1 in 2,500 newborn males, is unknown. Here we report the sequence of a unique variant TBG (TBG-Gary) encoding a protein with severely impaired T4 binding as well as decreased stability at 37 C, resulting in its rapid in vivo denaturation. A single nucleotide substitution in the codon for residue 96 of the mature protein replaces isoleucine with asparagine; this replacement creates an additional site for N-linked glycosylation. The anodal shift of TBG-Gary on isoelectric focusing gel electrophoresis suggests that this new site is likely glycosylated. Since glycosylated is required for TBG to assume its correct tertiary structure, but is not subsequently necessary for maintenance of the biological properties or stability of the molecule, we believe that the likely presence of additional carbohydrate probably affects a higher order structure of the molecule and is thus responsible for the reduced stability and hormone binding activity of TBG-Gary (TBGASN-96).     

The formation of flavonoids in cell suspension cultures ofPrunus x yedoensis matsum

Two lines of the red and pale yellow cell suspension cultures, prepared fromPrunus x yedoensis Matsum. callus induced by Murashige and Skoog's (1962) basal medium supplemented with 2, 4-dichlorophenoxyacetic acid (2, 4-D, 1.0 mg/l), kinetin (0.1 mg/l) and sucrose (30 g/l), were maintained on Schenk and Hildebrandt medium as modified by Mitchell and Gildow (1975). The red cell suspension culture produced cyanidin 3-monoglucoside, 5, 4′-dihydroxy-7-methoxyisoflavone 4′-glucoside (prunetrin), isoquercitrin, catechin, epicatechin, and procyanidin B-1, B-2, B-3 and B-4, while the pale yellow cells produced only a small amount of catechin and epicatechin as main flavonoids. These flavonoid compounds found in the red cell culture were present also in maturePrunus leaves. Maximum growth and maximum amount of total phenol and proanthocyanidin (procyanidins) were obtained with 0.3 mg/l of both 2,4-D and kinetin. Maximum concentration of anthocyanin was also obtained with 0.3 mg/l 2, 4-D regardless of kinetin concentration. Accumulation of proanthocyanidin was markedly stimulated by low concentrations of phosphate, which reduced growth by about half, and also by high concentrations of inorganic nitrogen. Production of both anthocyanin and proanthocyanidin was reduced by lowered nitrogen levels. Cell growth and production of all phenolics were inhibited when ammonium ion replaced nitrate in the medium.