There are various factors that control plant growth. In addition to physical factors such as temperature, light, and humidity from the external environment, various regulatory factors within the plant body have also been studied. In the field of plant biotechnology, the technique of “tissue culture” is essential, primarily inducing callus formation and redifferentiation through the concentration and composition of “plant hormones.”
The technology of tissue culture is indispensable not only in research but also in fields such as aseptic seedling production. The identity of plant hormones includes chemicals collectively referred to as auxins and cytokinins. Even looking at auxins alone, there are various types, such as indole-3-acetic acid (IAA), naphthaleneacetic acid (NAA), and indole-3-butyric acid (IBA), with different plants having different sensitivities. The differences in these compounds also lie in whether they are “natural” or “synthetic,” and personally, I feel that synthetics work with a smaller amount, although it greatly depends on the plant species. Because they work in small amounts, on the contrary, a large amount of plant hormones can disrupt plant growth, to the extent that they are used as herbicides.
However, these plant hormones are not something that can be simply spread over fields to increase yield. The balance of plant hormones is exquisite, and plants grow in a miraculous balance. Nevertheless, the addition of a small amount of plant hormones can affect the yield and quality of crops, so moderate use is considered desirable. Especially if it’s the “necessary amount of natural” plant hormones, it may allow for sustainable use with less disruption to the ecosystem.
So, where do these plant hormones come from? One source is “microorganisms.” It has been known for quite some time that plant hormones themselves are involved in the interaction between plants and microorganisms, but recently, it has been discovered that bacteria have the synthesis pathways for plant hormones or genes essential for synthesis. These genes are expressed in interaction with plants and help the growth of both plants and bacteria, but under the right conditions, bacteria can provide plant hormones to plants to aid their growth.
Microorganisms that live in symbiosis with plants exist either as soil microorganisms in the rhizosphere or as endophytic fungi within the plant. By controlling the types and activity of these microorganisms, it might be possible to aid plant growth. Such technologies are considered suitable for sustainable agriculture with less environmental impact. Moreover, if they are soil bacteria, they can remain in the soil after one crop cycle and may help the growth of the next crop. While this might be overly optimistic, in an agricultural sector where labor-saving and sustainability are demanded, this is a field worth investing research effort into.
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