Ripening

[3] At the molecular level, a variety of different plant hormones and proteins are used to create a negative feedback cycle which keeps the production of ethylene in balance as the fruit develops.

When calcium carbide comes in contact with moisture, it produces acetylene gas, which is similar in its effects to the natural ripening agent, ethylene.

For example, a drop of iodine on a slightly rotten part (not the skin) of an apple will stay yellow or orange, since starch is no longer present.

If the iodine is applied and takes 2–3 seconds to turn dark blue or black, then the process of ripening has begun but is not yet complete.

If the iodine becomes black immediately, then most of the starch is still present at high concentrations in the sample, and hence the fruit has not fully started to ripen.

Specifically, this process activates ethylene production and the expression of ethylene-response genes affiliated with the phenotypic changes seen during ripening.

[18] Ripening can be induced by abscisic acid, specifically the process of sucrose accumulation as well as color acquisition and firmness.

Studies found that the addition of exogenous ethylene induces secondary ripening processes in strawberries, stimulating respiration.

[20] They suggested that this process involves ethylene receptors, a type of gasoreceptor, that may vary between climacteric and non-climacteric fruits.

Studies showed that the expression of genes involved in various pathways in ripening was increased with the addition of methyl jasmonate.

[17] This study found that methyl jasmonate led to an increase in red coloration and the accumulation of lignin and anthocyanins, which can be used as ripening indicators.

The genes they analyzed include those involved in anthocyanin accumulation, cell wall modification, and ethylene synthesis; all of which promote fruit ripening.

This occurs because ABA acts as a regulator of ethylene production, increasing synthesis similarly to climacteric fruits.