Plants have a tightly regulated growth mechanism that prevents them from overgrowing. This mechanism is regulated by various hormones, including auxin, which affects cell division in the meristem. The video below introduces the basic principles of plant growth, as well as other recent developments.
The video presents plant growth at three different levels: physiological, cellular and molecular. On the physiological level, we can see that there are specialized areas of the plant called meristems in which undifferentiated cells divide very frequently. As we examine cells further away from the meristem, we find more differentiated cells, into specific tissues such as phloem, xylem, parenchyma etc. The cell division and differentiation processes are regulated by different hormones secreted from the meristem. The lower the hormone concentration (i.e. the further away a cell is from the meristem), the more it tends to differentiate, and conversely, the higher the hormone concentration (i.e. the closer it is to the meristem), the more it tends to divide.
In plants, as opposed to animals, cells can easily revert to undifferentiated states and re-differentiate. That is why roots can develop from branches in a process called cutting.
On the cellular level, certain hormones prevent cell division or encourage it. Thus, different concentrations of hormones, based on the cell's distance from the meristem, determine the cell's fate. The video also shows this process, called mitosis, which you can read about elsewhere on this website.
On the molecular level, certain hormones affect processes in the cell through changing gene transcription patterns. For example, a hormone could cause a certain transcription inhibitor to be destroyed, allowing for the transcription of a set of genes whose products drive the cell towards mitosis.
Erez S. Garty, Ph.D.
Editor in Chief, Davidson Online
Davidson Institute of Science Education
Weizmann Institute of Science
Article translated from Hebrew by Aviv J. Sharon, M.Sc. student at the Weizmann Institute of Science.
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