Saichol Ketsa

Phenolics, lignin, peroxidase activity and increased firmness of damaged pericarp of mangosteen fruit after impact

Abstract Firmness, phenolics and lignin content, and peroxidase activity were studied in damaged pericarp of mangosteen ( Garcinia mangostana L.) fruits after impact. Firmness of damaged pericarp increased rapidly after impact in air. Under nitrogen however, damaged pericarp was less firm and had lower lignin contents, with more total phenolics than in air. Peroxidase activity in damaged pericarp was greater than that in undamaged pericarp after impact. Damaged pericarp infiltrated with cycloheximide was less firm and had lower lignin and higher total phenolic contents than those of damaged pericarp without cycloheximide. Total phenolics in undamaged and damaged pericarp separated by thin layer chromatography showed no difference in patterns of distribution in R f values. Five R f values (0.00, 0.03, 0.06, 0.30 and 0.46) of phenolics in damaged pericarp had lower absorbance at 190–400 nm, while three R f values (0.63, 0.77 and 0.88) did not change. These results suggest that impact enhances incorporation of phenolics into lignin and that there is involvement of peroxidase activity in increased firmness of damaged pericarp.

Ethylene synthesis in mango fruit following heat treatment

Mango fruits (Mangifera indica L. cv. Nam Dokmai) were held for 3 days at 38°C and then transferred to 20°C. Fruits placed directly at 25°C after harvest reached their peak ethylene production after 4 days, while the heated fruit took 9 days (6 days after the end of the heat treatment). The 1-aminocyclopropane-1-carboxylic acid (ACC) content paralleled that of ethylene production in unheated fruits, with highest content occurring on day 4. In heated fruit, ACC content continued to increase for 8 days following the heat treatment. The 1-aminocyclopropane-1-carboxylic acid synthase (ACS) activity in unheated fruit was also highest on day 4. In heated fruit the activity was undetectable following heat treatment, but recovered partially during the ripening period. Initial ethylene production from discs with peel was 6-fold higher in unheated fruit than heated, although afte r6ho fincubation the production from both was similar. Activity of 1-aminocyclopropane-carboxylic acid oxidase (ACO) in the discs also showed an 8-fold difference in initial activity in heated versus unheated discs with peel. This difference disappeared during incubation of the discs. In heated discs without peel, both ethylene and ACO activity remained lower than in discs with peel, and the differences between heated and unheated fruit discs were more pronounced. We conclude that the inhibition of ethylene production found during heat treatment is due to inhibition of both ACS and ACO. ACO recovers full activity following heat, while ACS activity recovers only partially, but enough to allow the heated fruit to achieve an ethylene peak.

Firmness, pectin components and cell wall hydrolases of mango fruit following low-temperature stress

SummaryMango (Mangifera indica L. cv. Nam Dokmai) fruits chilled for 21 d at 48C were firmer than non-chilled fruits during subsequent ripening at 258C. The cell wall contents of chilled fruit contained less water-soluble pectin, more ammonium oxalate-soluble pectin and less alkali-soluble pectin than non-chilled fruits. The increase in ammonium oxalate-soluble pectin was at the expense of the alkali-soluble pectin and correlated with high pectinesterase activity in the fruit from low-temperature storage. Polygalacturonase and b-galactosidase activities were inhibited in chilled fruits. The relationships between delay in loss of firmness, and differences between activity of cell wall enzymes and pectin content of chilled and non-chilled fruits are discussed.

PHYSIOLOGICAL CHANGES DURING POSTHARVEST RIPENING OF DURIAN FRUIT (DURIO ZIBETHINUS MURRAY)

SummaryPostharvest changes in ethylene production, respiration, soluble solids, total sugars, starch, firmness, pectic substances and activities of polygacturonase (PG), pectinesterase (PE), β-galactosidase (GAL) and cellulase in ‘Chanee’ durian fruits were followed at ambient conditions. The rise in ethylene production and respiratory climacteric coincided and simultaneously reached a maximum on the fourth day. Soluble solids and total sugars in the aril also increased concomitantly with the decrease in starch content. The rapid decrease in the aril firmness was accompanied by changes in pectic substances; an increase in the water-soluble fraction and a decrease in ammonium oxalate and alkali-soluble fractions. PG and PE activities increased rapidly, while GAL and cellulase activities increased slightly. The increase in PG activity appeared more significant than that of the PE, GAL and cellulase activities.

Ethylene production, senescence and ethylene sensitivity of Dendrobium 'Pompadour' flowers following pollination.

Summary Dendrobium ‘Pompadour’ flowers had a burst of ethylene production that peaked 9 h after pollination. Pollination increased 1-aminocyclopropane-1-carboxylic acid (ACC) content and ACC synthase activity. Ovary, lip and pedicel ACC levels and ACC synthase activity were many-fold greater than those of the petals and sepals following pollination. Aminooxyacetic acid (AOA) application to the stigma prior to pollination reduced ethylene production, ACC levels and ACC synthase activity. Ethylene production by pollinated orchid flowers, with ACC application, increased more rapidly than in nonpollinated orchid flowers with ACC application. Pollination induced a rise in ethylene production, and then premature senescence. The first sign of premature senescence was a downward curvature of orchid flowers accompanied by drooping of the petals and sepals. Both AOA and 2,5-norbornadiene (NBD) delayed premature senescence of pollinated orchid flowers, though AOA was the more effective. Exogenous ethylene induced premature senescence of orchid flowers similar to pollination and pollination increased the ethylene-sensitivity. AOA treatment did not alter ethylene sensitivity of pollinated orchid flowers.

Peel Enzymatic Activity and Colour Changes in Ripening Mango Fruit

Summary Mango cultivars that have yellow (cv. Nam Dokmai) and green (cv. Tongdum) peels when ripe were compared. Pigment content, the activities of chlorophyllase and peroxidase, and ethylene production were monitored in yellow and green ripening mango fruit. Ripe green mango fruit had three times more chlorophyll and slightly more β-carotene in the peel, and had higher rates of ethylene production than that of the ripe yellow fruit. The activities of chlorophyllase and peroxidase in the peel of the ripe green fruit were about half of the ripe yellow fruit. These results suggest that the changes in the peel of ripe green fruit were due to either or both a lower activity of chlorophyllase or peroxidase activity rather than low ethylene production.

Senescence of Dendrobium `Pompadour' flowers following pollination

SummaryFlowers of Dendrobium `Pompadour developed premature petal and sepal senescence following pollination. Pollination induced an ethylene climacteric accompanied by a small respiratory climacteric, epinasty and increased flower or inflorescence fresh weight and water uptake. Pollination did not alter petal and sepal anthocyanin content and ion leakage, and lip, petal and sepal fresh weight and dry weight. The fresh weight and dry weight of stigmas (columns) together with pedicels increased significantly after pollination. Ovary growth of pollinated orchid flowers with petals and sepals intact was greater than that of pollinated orchid flowers without petals and sepals, while their water uptake was not significantly different.

Softening of Durian Cultivars

Summary The activities of the enzymes polygalactosidase, pectinesterase, β-galactosidase and cellulase were assayed during aril softening of durian (Durio zibethinus Murray) cvs. Chanee and Monthong. The aril of both and durians softened continuously throughout the ripening period and coincided with a marked increase in water-soluble pectin, polygalacturonase and pectinesterase activities, while β-galactosidase and cellulase activities were relatively high at picking time and slightly increased during ripening. The aril of durian was firmer and contained less water-soluble pectin and pectinesterase activity than that of durian, while their polygalacturonase activities were comparable during ripening.

The role of ethylene in enhancing the initial ovary growth of Dendrobium ‘Pompadour’ following pollination

Summary Pollination stimulated ethylene production concomitant with the increase in ovary growth of Dendrobium ‘Pompadour’. Emasculation stimulated ethylene production but did not increase ovary growth. Emasculation synergistically increased ovary growth of pollinated orchid flowers. 1-Aminocyclopropane-1-carboxylic acid (ACC) and 1-naphthylacetic acid (NAA) treatments stimulated ethylene production of orchid flowers but only NAA fully substituted for pollination in enhancing ovary growth, while ACC application synergistically increased ovary growth of pollinated orchid flowers. Aminooxyacetic acid (AOA) treatment inhibited pollination- and NAA-induced ovary growth. ACC application restored the ovary growth response with added AOA prior to pollination. The results suggested that ethylene was required for initial growth of the ovary following pollination in Dendrobium ‘Pompadour’.