‘Passe-Crassane’ is a winter pear which requires a cold storage period to produce ethylene and properly ripen. In this study, the effects of 1-methylcyclopropene (1-MCP), an ethylene perception inhibitor, were studied during cold storage (30, 60, 90, and 135 days) and shelf life at 20 °C (30 days) of ‘Passe-Crassane’ pears. Ethylene accumulation was monitored and quality parameters were measured. Oxidative stress of fruit was estimated by measuring lipid peroxidation. The cell antioxidant status was assayed determining ascorbic acid (AsA) content and the activities of the enzymes ascorbate peroxidase (APX), monodehyroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), and glutathione reductase (GR) involved in its oxidation and recycling. AsA content was positively affected by higher temperature (20 °C) and by 1-MCP after 90 days of storage. This effect was more evident after shelf life. Thiobarbituric acid reactive substances (TBARS) increased in pears kept at 20 °C and in treated pears, starting from 60 days of cold storage and remained elevated after shelf life. Although during storage 1-MCP enhanced the activities of APX and DHAR only at 90 days, after shelf life the effect on APX, MDHAR, and DHAR activities was more pronounced and enzyme activities were higher in treated pears sampled after 60 and 90 days of storage. The results indicate that 1-MCP has a beneficial effect on the antioxidant potential of winter pears: it maintained high AsA levels throughout storage and shelf life and improved the enzymatic mechanisms of AsA recycling, especially after shelf life. The effect of 1-MCP on pear ripening may not be solely due to its action on ethylene but also to an increase in antioxidant defense. A stress response linked to lipid peroxidation is triggered by the interaction of cold temperatures and treatment as ‘Passe-Crassane’ pears acquires ripening competence. However, it may be compensated by the high AsA content.
Apple (Malus domestica Borkh.) trees are often affected by a severe June fruit drop, which is often correlated with competition phenomena involving fruit nutrition. This research was initiated to determine if June drop in `Gloster'/M.9 apple could be correlated with a diminished nutrient availability in developing seeds and fruit. During the test period [30 to 62 days after full bloom (AFB)], the fruit that abscised had a diameter similar to that reached by persisting fruit 13 days earlier. Biochemical parameters related to nutritional status of fruit were measured when an abscission peak occurred 38 days AFB. Persisting fruit (control) and abscised fruit were compared along with fruit that abscise 13 days later. The cortex tissue obtained from the two kinds of abscised fruit showed a higher level of soluble reducing sugars and sucrose and a lower content of K+, acid hydrolyzable polysaccharides, and protein compared to the control. Further, the Ca2+ content was higher in abscised fruit than in controls of the same age, whereas there was no difference when fruit of the same size were compared. Total amino acid level was similar in control and abscised fruit at the same age, but there was a lower amino acid level in abscised fruit of the same size. Histological analysis of cortex tissue indicated that abscised fruit have larger cells with less evident nuclei and thinner cell walls than controls. Compared to control fruit, abscised fruit showed the same average number of seeds and a severe inhibition of seed growth; seeds from both kinds of abscised fruit had the same or higher levels of the parameters measured. No positive correlations were observed between fruit abscission and nutrient content of seeds or fruit.
The delta absorbance (DA) meter is a handheld instrument which noninvasively measures the chlorophyll content in fruits. In the present work, it was used to monitor the ripening process linked to the climacteric phase in apple (Malus ×domestica). The results [index of absorbance difference (IAD)] were correlated to quality attributes at harvest and after commercial scale storage at different conditions. Two cultivars (Red Delicious, Golden Delicious) were analyzed in two different seasons, whereas Morgenduft and Gala were analyzed only in the first and second seasons, respectively. In general, a linear reduction of the IAD values was observed in all apple cultivars along with the progression of ripening and ethylene biosynthesis. When ethylene production was inhibited by 1-methylcyclopropene (1-MCP) treatment, the decrease of IAD values was markedly reduced. IAD threshold values for each cultivar were identified, delineating the central phase of the ethylene climacteric rise. Predictive models were built by correlating IAD index to the soluble solids concentration (SSC), titratable acidity (TA), and firmness measured at harvest and after removal from different storage regimes. The best model was developed for SSC prediction on ‘Red Delicious’ apple [ratio performance deviation (RPD) = 1.88] and for firmess evaluation in ‘Golden Delicious’ apple (RPD = 1.84). Moreover, IAD values were consistently associated with the differences in fruit quality as affected by optimal and suboptimal storage conditions. The IAD, due to its acceptable accuracy and speed of assessment, can be a promising tool for assisting in sorting apples before and after storage in warehouses or commercial packing lines. IAD cannot totally replace standard ripening indices, but can effectively supplement data for these parameters.
‘Big Top’ nectarine [Prunus persica (L.) Batsch] has appreciable keeping quality because it resembles, at ripening, the stony hard (SH) peach (P. persica) in firmness and crispness but melts at a slow speed at full ripening. We have characterized the postharvest behavior of ‘Big Top’ fruit, treated or not with ethylene for 5 days after harvest (DAH), and compared it with that of a SH peach (‘Ghiaccio’). Pp-ACS1 expression, ethylene evolution, endo-polygalacturonase (endo-PG) production, and softening were evaluated and compared with those of the physiologically ripe melting flesh (M) cultivar Bolero. Like ‘Bolero’, ‘Big Top’ fruit expressed Pp-ACS1 and evolved ethylene but with a 5-day delay. Pp-endo-PG expression, production of an active endo-PG, and fruit melting showed a parallel behavior; ethylene treatment enhanced all these features. In SH ‘Ghiaccio’ Pp-ACS1 expression, ethylene evolution, endo-PG production, and softening were absent during the first 5 DAH in air. ‘Ghiaccio’ neither expressed Pp-ACS1 nor evolved ethylene even after ethylene treatment but responded by accumulating Pp-endo-PG transcripts and an active endo-PG protein, with flesh melting. A ‘Big Top’ Pp-endo-PG clone showed several single nucleotide (SNP) and insertion-deletion (InDel) polymorphisms in comparison with the M Pp-endo-PG clone of ‘Bolero’ and substantial similarity with the Pp-endo-PG clone of ‘Ghiaccio’. In ‘Big Top’, we identified a peculiar SNP (bp 348) and InDels shared with ‘Ghiaccio’, possibly suitable for discriminating among different genotypes. Overall, the data confirm the pivotal role of ethylene in the regulation of endo-PG production and in the determination of peach flesh texture and support the evidence that ‘Big Top’ could be classified as a melting (slow-melting) phenotype.