Do you know what geotropism is? This is a reaction of plants that makes them grow and develop as they do; that is, generally with the roots down and the stem up.
It is also called gravitropism, since gravity exerts a great influence on plants (and in reality on everything: living beings, inanimate objects, … everything). But, What does this tropism really consist of?
What is geotropism or gravitropism?
Said in simple words, geotropism is what allows roots and stems to know where to grow. Thus, the former will normally grow downwards, that is, towards the center of the Earth, and the stem upwards, that is, towards the Sun.
It is for this reason that it is especially important during the germination of seeds, since to start life well the seed has to be in the correct position; in this way, the seedling will be able to develop correctly.
Type
There are two types:
- Negative geotropism: it is the one that the stems present, since they are those that grow in an opposite direction towards gravity.
- Positive geotropism: this is presented by the roots, which are those that grow towards the center of gravity.
How do plants detect gravity?
To answer this question we have to talk about the vegetables cells. In them it is known that there is a part, probably the amyloplasts, that detects the acceleration of gravity and that, therefore, is what makes the cells work in the right direction. But what are amyloplasts?
These are plastos that do not have chlorophyll, therefore they do not have photosynthetic capacity nor, therefore, they can contribute to the production of food, but they do have very dense starch granules. These granules are believed to be used as statolithsthat is, as organelles that move within the cytoplasm in response to gravity (the cytoplasm is a gelatinous liquid composed of water and salts that surrounds the nucleus of the cell).
Gene involvement
Genes are information codes that make us who we are: humans, plants, cats, dogs, etc .; but they also indicate our life expectancy, if we are prone to having any disease, and much, much more. Genetics is a world as exciting as it is complicated; in fact, to give you an idea, it took four years and more than 100 scientists to sequence the genome of the Virginia black poplar (populus trichocarpa) according to the portal CORDIS.
Therefore, if we want to know more about how gravity affects plants, it is a good idea to investigate genes. And that is just what is being done. Up to now, it has been shown that the synthesis of messenger RNAs (These are the ones in charge of transferring the genetic code of the DNA from the cell nucleus to the ribosome found in the cytoplasm), also called SAURs (acronyms that come from small auxin up-regulated RNAs), is stimulated when auxins are added (plant hormones that regulate growth)with the geotropism that occurs in the hypocotyls of soybeans.
Related article:
Hypocotyl
When the bean sprouts grow normally, that is, vertically, the SAUR genes are distributed symmetrically, but when the sprouts are placed horizontally, this distribution changes rapidly, concentrating on the lower half of the hypocotyl. Thus, the stem grows forming a curvature with which it grows back vertically (here! you have the study, in case you want to read it; Yes, it is in English).
Examples of geotropism
We can find examples just by leaving the house: trees and palm trees are some types of plants in which we will see it well. The trunk, called a stipe if it is a palm tree, grows more or less straight up, in search of sunlight; the roots on the other hand we do not see them with the naked eye since they are buried when developing downwards.
We can even do experiments ourselves. If we sow lentils, for example, in a small pot, 5,5 centimeters in diameter, we wait for the seedling to root well (that is, until we see its roots poking out of the drainage holes) and then we lay the pot down, After very little we will see how the plant bends upwards.
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