The Story Ripens

Green to Red
Green to orange
Green 'n' Black to Yellow 'n' Black (essentially to yellow!)
Green to Yellow
Green to Light Green
Green to Brownish maroon
Green to Blue
Green to other shades whose names I know not
Green to so on and so forth.....

Now, what could be this unidirectional change of colour that happens around us, in nature?

I thought of this astounding, universal colour change, when -

(skip if you do not like flashbacks and stories)

"I went to the fruit shop to buy an Avocado/Butter fruit, and since I hadn't tasted one and had only seen a picture on Wiki, I asked the seller to hand me one. He handed me a dark green fruit, which looked way smaller than I imagined it to be. It seemed a little hard, and without any questions, I walked away to go home and eat it. On cutting the fruit, I found a seed, as promised. But, the pulp was too hard. And scooping it out was an impossibility. After efforts, the real taste was not there. A little disappointed, I went to the shop again, a day later and asked him for a ripe avocado, and he handed me another green looking butter fruit and asked me to wait for three days or so. I was a little annoyed at my haste and went home equipped with patience. And two days later,it had become pulpy and the green had changed to brownish maroon. I was pleasantly surprised at this colour. I never remotely thought that avocados were brownish when they ripened."

(resume reading if you skipped above portion)

And then, I realised that most fruits are green till they ripen to yellow, orange or red or blue (in case of blueberries). So, why should a fruit ripen? Ripeness, as humans know it, is a quality of the fruit that makes it edible. But, ripeness is what civilisation has come up with to serve its needs of nutrition. But, why would nature subscribe to ripening a fruit only to be left into human consumption?

Turns out, one of the main gases responsible for causing ripening, is Ethylene. It is an important plant hormone which brings about senescence and death. Ripening of fruits is a relaxation to defenses against premature consumption. Fruit consumption is important for the plant as it helps in seed dispersal. At the level of consumption, there are both vertebrate and invertebrate consumers, like insect larvae. In view of better developed locomotory skills, plants choose vertebrate frugivores than others. During the process of ripening, what are the kind of changes that occur?

We observe a change in the fruit texture, colour and taste (sweetness). Ethylene is known to bring about all these changes. It turns on a few genes and sets the transcriptional and translational machinery in action, and increases the quantity of some enzymes in the cell. And these include enzymes which make the fruit sweet, starch to sugar converters (amylase), making the fruit softer (pectinases), and enzymes which break green pigments (chlorophyll) which are replaced by other coloured pigments (chromophylls) - red, blue, yellow.etc. This coordinated colour conversion, may also be too attract vertebrates to these fruits and enable dispersal of seeds. Fully ripe fruits are prone to degradation by microbes and hence, they are competitors for vertebrates to get good food.

And, so I learnt from avocados. Avocados are the only fruits that ripen after being picked. Firm avocados take about three days to ripen.

Remember not to eat fruits right under the same tree, and assist in achieveing the evolutionary goal of dispersal.

Yours