Corner of branches affected by gravity

(Researchers at Leeds University) have discovered how plants make corners of branches.

While other principle properties that manage the structure of plants, such as controlling the number of branches and the position of the main stem branches that have been well known by science, scientists have yet to find the answer. words to the question of how plants arrange and maintain the angle of their lateral branches in relation to gravity.

The mechanism is a basic principle to understand the shape of the plants around us: explain why, for example, a Lombardy birch produces the upper branches close to the tops while an oak spread more horizontally.

Dr. Stefan Kepinski, senior lecturer at Leeds University's Department of Biology and the lead author of an article in Current Biology magazine, touched the bottom of the mystery, saying: 'We are studying about This is after a train arrives in Leeds. Looking out the window, I was fascinated by the fact that the way we recognize plants and other plants from afar is based largely on the angle at which their branches grow. "

'These characteristic angles are around us and the same thing is happening underground; Many different things between species often have root system structures that are determined primarily by the angle of development of lateral roots , 'Kepinski said.

The puzzles seem simple about how a plant establishes and maintains these angles in its structure, determined by the fact that the angle of the roots and the main branches is not usually set to correlate with main root or stem from which they grow, but related to gravity. If a plant is placed on its face, these branches will begin a period of bending growth, called gravitropism , adjusting them back toward the angle Their heads develop according to gravity.

In the case of the main root or stem, the part grows on the ground, the mechanism is understandable: gravity sensor cells called statocytes find that the tree has been tilted, will promote an increase in the movement of a The hormone that regulates growth is called auxin to the lower side of the stem or root and promotes growth in the stem and root-driven growth. When the growth is vertically back, the statocyte stops sending extra auxin to one side than the other and growth curves stop.

Dr Kepinski said: 'We have found another growth component - ' anti-gravity reaction ' - against normal gravity growth in these lateral branches. The mechanism of preventing against the development on the other side of a branch from growth is sensitive to gravity and preventing the branch from moving towards the corner to create a vertical angle. This suggests that this antagonistic development is also controlled by auxin, the same hormone that causes the development of reactions to gravity on the lower side of the branch. '

The conundrum for researchers is that many branches and roots form the same angle as gravity, rather than being completely vertical. Scientists do not understand how plants can establish non-vertical development angles for their branches.

The growing branches near the main body have a weak anti-gravity reaction while in the growing branches exceeding small angles from the body, the anti-gravity reaction is really strong.

Dr. Kepinski added: "You can compare this to the way a tank or a sailboat is diverted. If you want to go straight, you increase the speed of the sprocket or sail on one side. straight up, you balance the speeds - or in our case the 'speed' of development on one side of the branch - in a non-vertical branch, the reaction against gravity is constant, while the development of gravity response increases in size, according to the distance from the stem to the main body, giving rise to a strong system that maintains a whole range of branches. "

The Leeds team has demonstrated the presence of counter-gravity reactions by using a clinostat that is used to counteract the effects of gravity on plants. , slowly turning a growing tree on its edge, thereby drawing a stable gravity reference and enabling researchers to track the compensating mechanism to respond to gravity. Under these conditions, the researchers observed that the stem and root branches exhibited a further bending development, far from the main and stem roots, which were often masked by interaction with sensitive development. feel with gravity.

Dr Kepinski said: "The branches' growth angle is an important adaptation especially because it determines the ability of plants to interact with light and nutrients on the ground. This may be beneficial for finding nutrients on the surface of the soil layer or deeper down Likewise, in the trunk, a tree can gain the advantage of having steep slopes to avoid The shadow from their neighborhood plants So far, no one has really understood the non-vertical development angles , related to gravity like this, have been established and maintained. '

He added: "These insights are very important for breeding and access to biotechnology for productivity improvement because farmers and companies provide desirable seeds, which can turn changing the structure of plants to obtain higher yield crops, for example, lateral root growth angles have been shown to be very important for increasing nutrient uptake in both broad-leaf species and The results of our research provide methods and approaches to help address these crop improvement challenges. '

The team used the flower plant Arabidopsis thaliana (thale cress tree), as well as peas, beans and rice plants in their experiments, observing the same results.

Kepinski hopes that the same mechanism will be observed in larger trees and seedlings. In older trees, the mechanisms that control the development of gravitational sensitivity in wood tissue are different from those in non-woody plants. However, Kepinski said similar general principles could be applied.