September 23, 2009, 4:09 pm
Why does pruning help plants grow bushy?
Gardeners know that cutting the top branch of plants can help them become more bushy, but how and why does this happen?
What was discovered?
The main shoot dominates the growth of the whole plant - leading it upwards towards the sunlight to be able to get more light for photosynthesis... this has been known for many years.
But scientists have now shown that it is because the main shoot was simply the FIRST shoot, rather than the fact that it is at the top of the plant, which gives it the power to direct growth upwards by inhibiting (slowing down) growth of lower branches.
The molecules that inhibit growth are known as plant hormones, the most "famous" is called auxin.
The new research explains that the auxin must travel in the stem down to the lower branches... and that this can occur from any tip... but if the stem already has lots of auxin, the lower branches cannot pour their auxin into the stem: they were beaten to it by the first tip - the one at the top!
So a kind of competition is set up where the different branches are trying to pour their auxin into the stem first to reduce the growth in the others.
Cutting the top branch, or indeed any other of the branches of the plant will give lower branches a chance to pour their auxin into the stem... and the plant becomes bushy as they grow!
The work also showed how the newly discovered hormone strigolactone works - read the article to find out!
How was it discovered?
Combining techniques of molecular genetics that enabled the effects of mutations on the way in which auxin is produced and used in plants, with computational mathematics to model different ideas to explain the data.
Why is it important?
Understanding plant growth is vitally important in growing crops for maximizing food production - if different pruning techniques could increase yield, that would certainly be good!
Do you have a favourite plant which is looking a bit tall and straggly? Try cutting the tip out of the top of the tallest brach, and maybe a few others too, to encourage growth of the lower branches...
in a few weeks you should have a "new" bushy plant!