Light Induced Stress: A Boon in Disguise vis-a-vis Colour Development in Fruits

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Have you ever happened to visit an apple orchard? Have you ever noticed that some fruits, especially, those borne on outer canopy are deeper in colour than those borne inside the canopy? You perhaps have noticed that even those apples, which are sold in market, have intense red colour on a particular side, while the opposite side has less intense red or yellowish/greenish peel colour. Ever thought about the reason behind this discrepancy in colour intensity of fruit peel?

It has been observed that fruits exposed to sun light develop better colour than those that grow inside the canopy. Likewise, apples grown on higher hills develop attractive red colour than those grown at mid or lower hills.

The red colour of fruits is chiefly due to the presence of flavonoids (mainly anthocyanins). The sun light comprises seven per cent of ultraviolet (UV) range (200-400 nm) radiations. UV radiation acts as an abiotic physical elicitor of resistance mechanisms, and thus leads to a rapid increase of stress-response compounds. High influence of UV radiation causes cellular damage by generating photoproducts in DNA.

The most effective protection mechanism stimulated  under  such  a light  regime  is  the  biosynthesis  of  flavonoids  and  other UV-absorbing  phenolic  components (https://books.google.co.in/books?).

This in turn results in the production of more anthocyanins and hence, improved colour in exposed fruits. Anthocyanins are strong antioxidants, which protects our body cells from being damaged by free radicals (which in turn are generated as a result of either regular metabolic processes in the human body or from external sources such as exposure to X-rays, ozone, cigarette smoking, air pollutants, and industrial chemicals).

Author: Dr Hare Krishna, Principal Scientist (Horticulture), I.C.A.R.- Central Institute for Arid Horticulture, 
Beechwal, Bikaner, Rajasthan.

Posted By : ScienceIndia Administrator