| Fruit senescence is a considerable hurdle to the horticultural industry as large losses are incurred annually worldwide due to the effects of ethylene on plant senescence. Because ethylene plays a key role in the ripening process, it is a potential target for controlling fruit ripening. By manipulating ethylene action in fruit at different stages of ripening, we can control the ripening process of the fruit. If we can slow down the rate of fruit ripening, higher maturity, therefore higher quality fruit can be harvested with less subsequent loss due to spoilage. As a result, control of ethylene biosynthesis and action remains a priority in modern day postharvest physiology and technology research.Several compounds have been shown to block the ethylene - binding site, causing an inhibition of ethylene effects. Synthetic cyclopropenes are capable of blocking ethylene receptors and preventing ethylene effects in plant tissue for long periods; and can therefore extend postharvest life of horticultural products. 1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor that has been found to block ethylene responses in plants and has the advantage that it can be applied as a gas, has low or no mammalian toxicity, and low or no negative environmental impact. 1-MCP therefore, may represent an ideal alternative to existing ethylene action inhibitors such as silver.The cultivated tomato (Lycopersicon esculentum Mill.) is well characterized physiologically and genetically, and has emerged as an intensively researched model system of fruit maturation. It is therefore an appropriate model for studying fruit ripening.This study investigated the effects of 1 -MCP on the ripening processes, fruit quality and cell wall degrading enzymes (cellulase and pectinase) of cherry tomato {Lycopersicon esculentum Mill. var. cerasiforme) fruit. In addition, the effects of 1-MCP on the ethylene biosynthetic system and ethylene receptors (LeETR 15) were assessed. Cherry tomato fruit at mature green (MG), breaker (BR), 2 days post breaker (BR + 2) and 4 days post breaker (BR + 4) and low 1-MCP concentrations (0.035, 0.07 0.11, 1 and 5 μl.l-1) were used in this study.At 1-MCP concentrations of 0.070.11 μl.l-1, the ethylene climacteric peaks were delayed. Although 1-MCP suppressed fruit softening, the initiation of softening was not delayed. Fruit softening was suppressed by 1 -MCP in a dose response manner. On thebasis of fruit firmness, 0.11 ul.l"1 1-MCP extended the storage life of MG and BR fruit by about 7 days. Higher concentration of 1-MCP delayed color development; especially in MG fruit, whereby treated fruit failed to reach the control fruit level. 0.1 luXl'1 1-MCP delayed color initiation in MG fruit by up to 6 days. Chlorophyll degradation, initiation and accumulation of lycopene were also delayed. However, though the accumulation of carotenoids was suppressed by 1-MCP its initiation was not affected. Titratable acidity (TA) was better maintained, especially in MG and BR fruit. The favorable dose -responses observed suggest the necessity for ethylene perception for chlorophyll as well as lycopene and carotenoids metabolisms. The efficacy of 1-MCP in regulating cherry tomato ripening is concentration-dependent; and 0.11 jj.1.1"1 seems to be quite close to the saturation concentration for MG cherry tomato fruit, this is much lower than most of reported concentrations in other species. Treatment at ripening stages later than BR may delay some of the ripening processes (including softening) but to a lesser extent compared to MG and BR stages.Although 1-MCP seems most effective at prolonging storage life when applied at MG ripening stage, there's the risk of fruit failing to develop suitable color intensity. It is advisable to treat BR fruit rather than MG fruit when fruit color becomes an important quality consideration. Our results thus identified the necessity to differentiate between the ripening stages for 1-MCP application in order to achieve different post harvest objectives.To determine ACO and ACS activities, fruit at different ripening stages were treated with a 1 ul.l"1 concentration of 1-MCP. The effects of 1-MCP on both ACS and ACO activities were not statistically significant. However, 1-MCP treatment appeared to suppress ACO activity in BR + 4 fruit.Fruit at BR stage of ripening were treated with 1-MCP at a concentration of 5u.l.l"' in order to determine the effect of 1-MCP on the ethylene receptors. 1-MCP differentially affected members of the ethylene receptor family. The expressions of LeETRl and LeETR2 were suppressed by 1-MCP within 1 minute, indicating a very swift regulating mechanism on the expression of these receptors. There was no observable effect of 1-MCP on LeETR3, 4 and 5 in this experiment. Given the fact that LeETRl and LeETR2 usually exhibit a constitutive expression pattern, while LeETR35 exhibits regulated patterns of expression, the phenomena that 1-MCP exerts more effect on constitutivelyexpressed receptors deserves more research attention. If our finding were verified, it would suggest that the constitutively expressed LeETRl and LeETR2 may also posses certain attributes or components which are responsive to ethylene.To determine 1-MCP effect on cell wall degrading enzymes, fruit were treated with a 5uir" concentration of 1-MCP and stored for 16 days. The cellulase and pectinase activities were determined viscometrically. Cellulase and pectinase activities (especially cellulase) were suppressed by 1 -MCP; more so when applied to MG and BR fruit. Peak cellulase activity was delayed by at least 3 and 6 days in MG and BR fruit respectively. In MG fruit, 1-MCP delayed pectinase activity initiation by 3 days compared to corresponding untreated fruit. In BR fruit, activity was suppressed but initiation was not delayed. In post-breaker fruit, although 1-MCP suppressed pectinase activity, at no stage was the difference significant. 1-MCP appears to be more pronounced in suppressing cellulase activity compared to pectinase activity.
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