Carotenoid accumulation in durian (Durio zibethinus) fruit is affected by ethylene via modulation of carotenoid pathway gene expression.

Carotenoid content in durian (Durio zibethinus) fruit is an important aspect of fruit quality, with different cultivars distinguished by differing pigmentation. We have studied the dependence of carotenogenesis on ethylene. Fruit of the cultivar 'Chanee' harvested at the mature stage were either left untreated (controls), treated with 1-methylcyclopropene (1-MCP) for 12 h, or treated with application of an aqueous ethephon solution to the stem end, or treated for 12 h with 1-MCP followed by ethephon application. Fruit were then stored for 9 d at 25 °C. Pulp color of durian became steadily yellowish as a result of accumulation of carotenoids, which were mainly beta-carotene, and alpha-carotene, with a minor amount of zeaxanthin and lutein. 1-MCP delayed the increase in the accumulation of beta-carotene, alpha-carotene, and zeaxanthin, but not lutein. In contrast, ethephon had no significant effect on carotenoid accumulation. The expression of zeta-carotene desaturase (ZDS), lycopene beta-cyclase (LCYB), chromoplast specific lycopene beta-cyclase (CYCB) and beta-carotene hydroxylase (BCH) genes was highly correlated with carotenoid content and pulp color.1-MCP resulted in significant down-regulation of ZDS, LCYB, CYCB and BCH expression. The accumulation of beta-carotene and alpha-carotene appears to be controlled by the level of expression of LCYB gene, whose function was tested in bacteria to show conversion of lycopene and delta-carotene to beta-carotene and alpha-carotene, respectively. These results suggest that ripening-induced carotenoid accumulation is regulated by endogenous ethylene controlling the expression of key genes such as LCYB.

Carotenoids in durian fruit pulp during growth and postharvest ripening.

Durian (Durio zibethinus) cvs. Chanee and Monthong fruit were severed from the tree during 14 day intervals, from 10 weeks after anthesis until commercial maturity. We determined the pulp (i.e. aril; fruit flesh) carotenoid composition, together with pulp firmness, color and total soluble solids (TSS) and postharvest quality. In ripe cv. Chanee fruit the main carotenoids were ß-carotene (about 80%), and α-carotene (20%), with minor levels of lutein and zeaxanthin. In ripe fruit total carotenoid concentration (expressed per gram FW) was about 9-fold higher in cv. Chanee than in cv. Monthong. Large differences between the cultivars were also found in ß-carotene levels (about 11 times more in cv. Chanee), and even larger ones in those of α-carotene. Differences in lutein and zeaxanthin concentrations were small. Pulp color was deeper yellow in cv. Chanee than in cv. Monthong, which was correlated with α-carotene and ß-carotene concentrations. Durian contains a high fat percentage, which is conducive to carotenoid uptake. It is concluded that it is advisable to consume cv. Chanee rather than cv. Monthong if intake of carotenoids is considered important.

Lack of visible post-pollination effects in pollen grains of two Dendrobium cultivars: relationship with pollinia ACC, pollen germination, and pollen tube growth.

Dendrobium flowers, pollinated with pollinia from individuals of the same cultivar or other cultivars, usually show rapid post-pollination effects such as floral epinasty, a change in flower colour and early perianth senescence. However, pollination with the pollinia of cv. Karen or cv. Kenny flowers did not produce these effects. We compared these two cultivars with cvv. Pompadour, Willie and Sakura, and tested the hypotheses that the differences were related to levels of 1-aminocyclopropane-1-carboxylic acid (ACC) in the pollinia, ethylene production by the pollinated flower, pollen germination, or pollen tube growth. The pollinia of cvv. Karen and Kenny contained as much ACC as the pollinia of cv. Pompadour, but less than the pollinia of cvv. Willie and Sakura. Ethylene production after pollination with cvv. Karen and Kenny pollinia was much lower than after pollination with pollinia from the other cultivars tested. The pollen grains showed normal germination, but cvv. Karen and Kenny pollen grains exhibited much less tube growth than those of the other cultivars. Pollen tube growth in cv. Pompadour was positively affected by ethylene. Ethylene was required and sufficient for the induction of epinasty, rapid perianth colour changes and early perianth senescence, very similar to the changes after pollination. The absence of these effects after pollination with cvv. Kenny and Karen seems to be due to the low ethylene production induced by the pollinia of these cultivars. This low ethylene production could not be accounted for by the ACC content in the pollinia of cvv. Kenny and Karen.

Auxin is required for pollination-induced ovary growth in Dendrobium orchids.

In Dendrobium and other orchids the ovule becomes mature long after pollination, whereas the ovary starts growing within two days of pollination. The signalling pathway that induces rapid ovary growth after pollination has remained elusive. We placed the auxin antagonist α-(p-chlorophenoxy) isobutyric acid (PCIB) or the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) on the stigma, before pollination. Both treatments nullified pollination-induced ovary growth. The ovaries also did not grow after similar stigma treatment with 1-methylcyclopropene (1-MCP), AgNO3 (both inhibitors of ethylene action), aminooxyacetic acid (AOA) or CoCl2 (which both inhibit ethylene synthesis), before pollination. Pollination could be replaced by placement of the auxin naphthylacetic acid (NAA) on the stigma. All mentioned inhibitors nullified the effect of NAA, indicating that if auxin is the initiator of ovary growth, it acts through ethylene. The results suggest that the pollination effect on ovary growth requires auxin (at least auxin transport and maybe also auxin signalling), and both ethylene synthesis and ethylene action.

Corrigendum to: Auxin is required for pollination-induced ovary growth in Dendrobium orchids.

In Dendrobium and other orchids the ovule becomes mature long after pollination, whereas the ovary starts growing within two days of pollination. The signalling pathway that induces rapid ovary growth after pollination has remained elusive. We placed the auxin antagonist ±-(p-chlorophenoxy) isobutyric acid (PCIB) or the auxin transport inhibitor 2,3,5-triiodobenzoic acid (TIBA) on the stigma, before pollination. Both treatments nullified pollination-induced ovary growth. The ovaries also did not grow after similar stigma treatment with 1-methylcyclopropene (1-MCP), AgNO3 (both inhibitors of ethylene action), aminooxyacetic acid (AOA) or CoCl2 (which both inhibit ethylene synthesis), before pollination. Pollination could be replaced by placement of the auxin naphthylacetic acid (NAA) on the stigma. All mentioned inhibitors nullified the effect of NAA, indicating that if auxin is the initiator of ovary growth, it acts through ethylene. The results suggest that the pollination effect on ovary growth requires auxin (at least auxin transport and maybe also auxin signalling), and both ethylene synthesis and ethylene action.