The relationship between lipoxygenase (LOX) pathway-derived volatiles and LOX gene expression was evaluated in kiwifruit [Actinidia deliciosa (A. Chev.) C.F. Liang et A.R. Ferguson var. deliciosa cv. Bruno] during postharvest ripening at 20 °C. The C6 aldehydes n-hexanal and (E)-2-hexenal were abundant in peel compared with flesh tissue and declined as kiwifruit ripened. Esters such as ethyl butanoate and methyl butanoate were lower in the peel than flesh and accumulated when the fruit underwent a climacteric rise in ethylene production. Total LOX activity was higher in the peel than in the flesh and increased as kiwifruit ripened. Expression of AdLox2, AdLox3, AdLox4 and AdLox6 was high in the peel, whereas AdLox1 and AdLox5 showed similar levels in the peel and flesh at the ethylene climacteric. AdLox1 and AdLox5 transcript levels increased and AdLox2, AdLox3, AdLox4 and AdLox6 levels decreased during postharvest fruit ripening. Principal component analysis showed that n-hexanal and (E)-2-hexenal were grouped with LOX genes that were downregulated as kiwifruit ripened. The possible roles of LOX genes in relation to kiwifruit volatile formation during fruit ripening are discussed.
Bo Zhang, Xue-Ren Yin, Ji-Yuan Shen, Kun-Song Chen, and Ian B. Ferguson
Allan B. Woolf, Christopher B. Watkins, Judith H. Bowen, Michael Lay-Yee, John H. Maindonald, and Ian B. Ferguson
`Hass' avocados (Persea americana Mill.) were heated in air at 25 to 46C for 0.5 to 24 hours and stored at 0, 2, or 6C. After storage, fruit were ripened at 20C and their quality was evaluated. In unheated fruit, external chilling injury occurred in fruit stored at 0 or 2C, hut not 6C. Chilling injury was also evident after storage at 2C in fruit heated at 34C, and to a lesser extent in fruit heated at 36C. A heat treatment (HT) of 38C for 3, 6, or 10 hours and 40C for 0.5 hour further reduced external chilling injury induced by storage at 2C. These HTs did not reduce internal fruit quality and resulted in more marketable fruit than unheated fruit stored at 6C. Low-temperature storage and HT slowed avocado ripening, resulting in longer shelf life after storage. In flesh tissue sampled directly after selected HTs, the levels of mRNA homologous to cDNA probes for two plant heat-shock protein (HSP) genes (HSP17 and HSP70) increased to a maximum at 40C and declined at higher temperatures. These increases in gene expression coincided with the extent to which HTs prevented chilling injury. Hot-air HTs confer significant protection against low-temperature damage to avocados.