Why Ethylene Can Make A Fast Fruit Ripe?

To discuss how it works, we should mention that there are two types of fruit: climacteric and non-climacteric. Climacteric fruits continue ripening after being picked (which will be accelerated by ethylene gas). Climacteric fruits include: apples, apricots, avocados, bananas, cantaloupes, figs, guava, kiwis, mangoes, nectarines, peaches, pears, plums, and tomatoes. Non-climacteric fruits ripen only while still attached to the plant. Their shelf life is diminished if harvested at peak ripeness. Non-climacteric fruits include: cherries, grapes, limes, oranges, pineapples, and berries (blue-, black-, rasp-, straw-, etc.). Essentially all parts of higher plants produce ethylene (stems, roots, flowers, tubers, and seedlings). Ethylene production is induced at several key stages of the plant’s life. Notable for us, ethylene production is promoted during fruit ripening and abscission (dropping) of leaves. However, it is now known that ethylene production can be artificially increased by external factors: wounding of the fruit, environmental stress, and exposure to certain chemicals. The biosynthesis of ethylene starts with the amino acid methionine. The enzyme met adenosyltransferase converts methionine into S-adenosyl-L-methionine (SAM). The enzyme ACC synthase (ACS) converts SAM into 1-aminocyclopropane-1-carboxylate (ACC). The last step in ethylene biosynthesis involves molecular oxygen. The enzyme ACC-oxidase (ACO, which used to be called Ethylene Forming Enzyme, EFE) converts ACC into ethylene, as well as carbon dioxide, hydrogen cyanide, and water. Ethylene Biosynthesis Ethylene Biosynthesis The rate of ethylene production is regulated by ACC synthase converting SAM into ACC. Thus, regulation of this enzyme is key for the biosynthesis of ethylene. Manipulation of this enzyme by biotechnology delays fruit ripening. The Flavr Savr tomatoes used this biotechnology. On the other hand, in a sort of positive feedback loop, the biosynthesis of ethylene is upregulated by either endogenous or exogenous ethylene. Producing ethylene causes more ethylene to be produced. In 1993, the genes involved in the fruit ripening response were identified. The ETR1 and CTR1 genes are turned on until ethylene is produced. Then ETR1 and CTR1 turn off. This initiates a cascade ultimately turning other genes on. These other genes make the various enzymes mentioned earlier (amylases, hydrolases, kinases, and pectinases) needed to ripen the fruit. ince ethylene controls the ripening process, if we can control the ethylene, we can control the fruit. While ethylene is synthesized by plants, it is also prepared commercially. Ethylene is the most produced organic compound in the world (>107 million metric tons in 2005). The petrochemical industry produces ethylene through steam cracking of gaseous or light liquid hydrocarbons by heating to 750-950 °C. Compression and distillation purifies the ethylene. Ethylene is then used for a variety of applications, including the synthesis of PVC and polyethylene plastics. The picking of unripe fruit and artificial ripening later is not uncommon. In parts of Asia, a plastic cover is placed over unripe harvested mangoes. Calcium carbide is placed in open containers in strategic positions inside the bag. Moisture from the air converts the calcium carbide into acetylene which has the same fruit-ripening effect as ethylene. However, industrial-grade calcium carbide is sometimes contaminated with trace arsenic and phosphorous. The use of calcium carbide to stimulate fruit ripening is illegal in most countries. Catalytic Ethylene Generator An ethylene generator More commonly, however, catalytic generators are used to produce the ethylene gas necessary for fruit ripening. The generators allow for control of the overall ethylene concentration in the room. Typically, between 500-2000 ppm of ethylene is administered for 24-48 hours to successfully ripen the fruit. On the other side of the spectrum, after the unripe fruit is picked, we want it to remain unripe until after shipment. Scientists have researched ways to inhibit ethylene biosynthesis and inhibit ethylene perception. Aminoethoxyvinylglycine (AVG), aminooxyacetic acid (AOA), and silver ions inhibit ethylene synthesis, but this is not always effective because exogenous ethylene can still be perceived by the fruit and stimulate ripening. 1-methylcyclopropene 1-MCP