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Effects of naphthaleneacetic acid (NAA), aminoethoxyvinylglycine (AVG), and sprayable 1-methylcyclopropene (1-MCP) alone or in combination on fruit ethylene production, preharvest fruit drop, fruit quality, and fruit maturation were examined in ‘Delicious’ apples (Malus ×domestica Borkh.). 1-MCP and AVG + NAA, when applied 15 days before anticipated harvest (DBAH) for untreated control trees, more effectively delayed preharvest fruit drop than AVG or NAA used alone. However, there was no significant difference in ethylene production between fruit treated with 1-MCP or AVG + NAA and those treated by AVG. Two applications of NAA increased fruit ethylene production and fruit softening, whereas AVG inhibited NAA-enhanced fruit ethylene production and fruit softening. There was no significant difference in fruit ethylene production, fruit firmness, and fruit drop control between one and two applications of 1-MCP. The concentrations of 1-MCP did not affect the efficacy of 1-MCP when applied 15 DBAH, but high concentration of 1-MCP more effectively delayed preharvest fruit drop than low concentration of 1-MCP when applied 7 DBAH. Both AVG and 1-MCP suppressed expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase gene MdACS1, ACC oxidase gene MdACO1, and polygalacturonase gene MdPG1 in fruit. Expression of ACS5A and MdACO1 but not MdACS1 in fruit abscission zones was decreased by AVG and 1-MCP. 1-MCP more effectively suppressed expression of MdPG2 in fruit abscission zones than AVG alone.
The expression of genes for ethylene biosynthesis, ethylene perception, and cell wall degradation in the fruit cortex and fruit abscission zone (FAZ) was examined in relation to preharvest fruit abscission (PFA) and fruit ripening in ‘Golden Delicious’ and ‘Fuji’ apple (Malus ×domestica Borkh.). PFA, fruit ethylene production, and fruit softening increased rapidly during fruit ripening in ‘Golden Delicious’ apples, whereas no PFA, little fruit ethylene, and gradual fruit softening were recorded in ‘Fuji’ apples. The transcript levels of 1-aminocyclopropane-1-carboxylate (ACC) synthase genes, MdACS1, MdACS3, and MdACS5A, increased rapidly in the fruit cortex of ‘Golden Delicious’ apples during ripening, but not in ‘Fuji’ apples. However, only the level of MdACS5A mRNA was up-regulated in the FAZ of ‘Golden Delicious’ apples. The transcript level of ACC oxidase gene, MdACO1, increased in the fruit cortex for both cultivars but increased only in the FAZ of ‘Golden Delicious’ apples. Expression of the ethylene receptor genes, MdETR1, MdETR2, MdERS1, and MdERS2, increased in the fruit cortex for both cultivars, but only MdETR2 and MdERS2 increased in the FAZ of ‘Golden Delicious’ apples. The transcript levels of MdPG2, a polygalacturonase gene (PG), and MdEG1, a β-1,4-glucanase gene, markedly increased only in the FAZ of ‘Golden Delicious’ apples, whereas only MdPG1 rapidly increased in the fruit cortex of ‘Golden Delicious’ apples. Our results suggested that MdACS5A, MdACO1, MdPG2, and MdEG1 in the FAZ might be related to the difference in PFA between these two cultivars, whereas MdACS1 and MdPG1 were associated with fruit softening.
To understand the relationship between fruit cracking and gene expression patterns, we identified two expansin genes from litchi (Litchi chinensis Sonn.) fruit and then examined their expression profiles in pericarp and aril at different stages of fruit development, using the cracking-resistant cultivar Huaizhi and the cracking-susceptible cultivar Nuomici. Two full-length cDNAs of 1087 and 1010 base pairs encoding expansin, named LcExp1 and LcExp2, were isolated from expanding fruit using RT-PCR and RACE-PCR (rapid amplification of cDNA ends) methods. LcExp1 mRNA could be detected from the early stage of fruit rapid growth (59 days after anthesis). The LcExp1 mRNA increased and reached to the highest level at the end of growth phase (80 days after anthesis) in pericarp of `Huaizhi', while the mRNA could be detected at the stage of rapid fruit growth, then increased slightly and finally kept remained almost constant in the pericarp of `Nuomici'. Similar accumulation of LcExp2 mRNA was observed in fruit aril of `Nuomici' and `Huaizhi', whereas LcExp2 accumulated only in pericarp of `Huaizhi' but did not appear in pericarp of `Nuomici'. The results indicate that expression of two expansin genes in litchi pericarp are closely associated with fruit growth and cracking.