Fruit Ripening Fruit Is an Integral Part

Fruit Ripening Fruit is an integral part of certain types of plants' ability to reproduce by providing a means to disperse it's seeds. The process of seed dispersal involves the activity of animals; which digest the fruit and disperse the seeds in its feces. But the fruit must appear and taste agreeable to the various animals which the plant depends upon to eat the fruit and disperse the seeds.

In order to accomplish this, the fruit undergoes a physiological change which allows the fruit to become softer and more edible, while simultaneously changing colors. "The cause of fruit ripening is a natural form of a chemical synthesized to make PCV (polyvinyl chloride) piping and plastic bags - namely, a gaseous hormone called ethylene." (Kendrick, 2009) It is the production of ethylene that will activate certain genes inside the fruit that will begin the ripening process.

Once the production of ethylene begins, a series of processes start that fundamentally alter the fruit. As a result of the ethylene signal, a number of "ethylene receptor" genes are affected which, in turn, instigate the production enzymes which catalyze the metabolic reactions which transform the fruit. (McManus, 2012, p.288) This process is called ripening. The presence of ethylene causes certain genes, for example the ETR-1 and CRT-1 genes, to de-activate which then turns on other genes and allows a series of genetic processes which produce the necessary enzymes for ripening.

The process of ripening causes the naturally occurring chlorophyll to be broken down which can lead to the production of new and different pigments. These new pigments allow the fruit to change color from green to red, yellow, or blue. While developing, the fruit maintains a high level of acids, which make the unripe fruit taste sour and unappetizing. But when the ethylene signal is activated, the enzymes produced will break down the acids in the fruit, changing the fruit's taste from sour to neutral.

But it is the degradation of starch by the enzyme amylase which will increase the level of sugar, called fructose when naturally occurring in fruits, to increase. The amylases produced "…accelerate hydrolysis of starch into sugar," making the fruit more palatable to animals. (Koning, 1994) How much amylases are produced will have a direct effect on how sweet, sour, or neutral a fruit will taste; the more amylase transforms starch into fructose, the sweeter the taste.

The ethylene signal also begins a process by which the fruit will become softer, and easier to eat and digest: the production of pectinase. Pectin is a naturally occurring molecule in fruit which is instrumental in the formation of cell walls and the structure of the fruit. In effect, pectin is the glue which holds the fruit's cells in place and allows it to form a structure.

Pectinase is the enzyme which breaks down the naturally occurring pectin in fruits, making them softer, juicier, and more easy for animals to digest.

In addition to these enzymes, there are others which specifically break down the larger molecules inside the fruit into smaller ones that "can be volatile (evaporate into the air) and we can detect as an aroma." (Koning, 1994) The overall process can be demonstrated with a common fruit such as a pear; which the activation of the ethylene signal causes the fruit to change color from green to yellow, alters the structure transforming the pear from green to yellow, makes the pear softer, and converts the taste from tart to sweet while producing an elegant aroma.

(Koning, 1994) In nature, once a fruit is ripe it is ready to be digested by an animal. The ripening process has turned the fruit into a delectable treat and great source of nutrition for the animal. But there is a reason behind this process, the animals who ingest the fruit also ingest the seeds which lie at the heart of the fruit. And when the animals excrete their waste products (their feces), the seeds, which have a very hard protective shell, are dispersed in different areas where the animals travels.

The seeds can then use the natural fructose and starch found in the fruit as a medium for its growth and development; giving rise to a new plant, thus completing the reproduction cycle of the plant. But unless the fruit ripens to a point where it can be eaten by the animal, the seeds inside the fruit.