Message in a pollen

 

 

Here is a tricky problem that we plants face: for us to make seeds and baby plants, a pollen grain from the anther of one plant has to find its way to the stigma of another plant and so meet the ovule. But how can this happen when we can’t move? The answer is that we use other things that move! We sometimes use wind and water, other times take the help of birds, insects and bats; and provide them a reward, or sometimes even trick them. Recently, humans found pollen on an insect in amber, fossilised from 100 million years ago! Over long periods of time, our flowers have been constantly adapting to better suit our pollinators. Here’s what I mean.

Bee-pollinated flowers are brightly-coloured and may feature landing-pads and flower marks directing the bee to its reward: nectar. While the bee visits the flower, the tiny pollen attach themselves to the bee to be carried to another flower. Bee-pollinated plants include grapes, oranges, lemons, chillis, coconuts, and strawberries. While bees and butterflies do the day-job of pollinating, moths and bats take over the night-shift. Night flowers often have a pleasant odour to invite their pollinators and are usually dull-coloured to reflect little available light. Did you know that the banana plant is bat-pollinated?

Mutually beneficial

The relationship between yucca moth and yucca plant in the Americas is so interlinked that each kind of plant is pollinated by a specific kind of moth. The female moth rolls up the pollen into a ball, deposits her eggs and packs the pollen into the stigma. The flower then develops into a fruit while the eggs of the yucca moth produce babies. Some of the fruit-seeds are eaten by the young caterpillars, while the rest are dispersed to germinate into more yucca plants.

Tricksters

Sometimes, we have to trick our pollinator friends! The bee orchids found in Europe are great mimics : they not only look like bees but also emit odours that attract male bees. The bees visit the flowers and in trying to mate with them, pollinate the flowers. A type of South African orchid attracts female fleshflies by smelling of dead animals. The fleshflies lay their eggs on the flower, and while doing this pollinate the flower. Clever, no?

Plants that live in water have interesting adaptations too. In one such plant, male and female flowers are enclosed within the leaf sheath which surrounds the flowers. When an air bubble is formed within the leaf sheath when it is submerged in water, the male anthers release their pollen and some of these pollen are deposited on the stigma and they germinate within a record 30 minutes!

Number is their strength

Some flowers need not collaborate with insect pollinators; instead, their strength lies in numbers. They release billions of pollen grains into the air, and these travel far with wind, some eventually settling on feathery stigmas. Many common plants are wind-pollinated: rice, wheat, corn and barley, among others. Next time you sneeze because of our pollen, remember that it was sent out in the air for another plant of our kind. Also, when you see a flower, try and guess who or what pollinates it, you may unfold an interesting story!

 


In flowering plants or ‘angiosperms’ which evolved about 130 million years ago, fertilization and reproduction occurs through pollination.

Pollination is the process in which the pollen from the male part of the flower, the anthers, are transferred to the female part of the flower, the stigma.

A pollinator is an animal that helps in pollination.

Insect pollination is of great worth, and estimated to have an annual economic value of over 170 million pounds in the United Kingdom; and over 14 billion dollars in the United States.

Pollinators have seen declining populations across the world; possible causes are the usage of pesticides in crops, loss of the pollinators’ habitats, air pollution and global warming, among other causes.

Although crops like rice, corn and wheat are wind-pollinated, scientists have shown that three essential nutrients: vitamin A, iron and folate are from insect-pollinated crops which makes insect pollination important for human nutrition and health.

 

This article appeared in the Hindu in School on 1 April 2015.

Picture: Reward-driven – While the bee is busy feeding on nectar, the pollen grains have attached themselves to the bee to be transported to another flower.
Credit: Karen Yadav Tewari