WHAT IS HYDROTROPISM? MECHANISM AND IMPORTANCE - BIOLOGY - 2025

The hidrotropismo is a growth response of plants to water concentrations; the answer can be positive or negative. Roots, for example, are positively hydrotropic, as plant root growth occurs towards a higher relative humidity level. The plant is able to detect this at the root cap and then send signals to the elongated part of the root.

A positive hydrotropism is one in which the organism tends to grow towards humidity, while a negative hydrotropism is when the organism grows away from it.

Image recovered from slideshare.net.

Hydrotropism is a form of tropism (it is an orienting response of an organism to a stimulus) characterized by the growth or movement response of a cell or an organism to humidity or water.

Mechanism of hydrotropism

A class of plant hormones called auxins coordinate this root growth process.

Auxins play a key role in bending the roots of plants towards the water because they cause one side of the root to grow faster than the other and thus the bending of the root.

The hydrotropism process is initiated by the root cap capturing the water and sending a signal to the elongated part of the root.

Hydrotropism is difficult to observe in underground roots, since the roots are not easily observable.

Water moves easily in the soil and the water content of the soil is constantly changing, so any gradient in soil moisture is not stable.

Why is hydrotropism so important for plants?

The roots grow into the water

This ability to bend and grow the root towards a moisture gradient provided by hydrotropism is essential because plants need water to grow. Water, together with soluble mineral nutrients, is absorbed by the root hairs.

So in vascular plants, water and minerals are transported to all parts of a plant through a transport system called xylem.

The second transport system in vascular plants is called phloem. The phloem also carries water, not with soluble minerals, but mainly with soluble organic nutrients instead.

This is of biological importance, as hydrotropism helps increase the efficiency of the plant in its ecosystem.

Misconceptions about hydrotropism

Hydrotropism and root growth in humid areas

Greater root growth in moist soil areas than in dry soil areas is not usually the result of hydrotropism.

Hydrotropism requires a root to bend from a dryer to a moist area of ​​the soil. Roots require water to grow so roots that happen to be in moist soil will grow and branch much more than those in dry soil.

Water absorption

The roots cannot feel the water inside the intact pipes through hydrotropism and must break the pipes to get the water.

Distance required for water absorption

The roots cannot feel water several feet away through the hydrotropism and grow towards it.

At best, hydrotropism probably operates at distances of a couple of millimeters.

Hydrotropism studies

Research on hydrotropism has been primarily a laboratory phenomenon for roots grown in moist air rather than soil. Its ecological importance in the roots cultivated in the soil is not clear. The recent identification of a mutant plant lacking a hydrotropic response helped elucidate its role in nature.

Hydrotropism can be important for plants grown in space, where it can allow roots to orient themselves in a microgravity environment. In reality, this response to plant growth is not easy to study. The experiments, as mentioned, are performed in laboratories and not in the natural environment.

However, more and more is being learned about the complex nature of this plant growth process.

The most popular plants to study this effect are: pea plant (Pisum sativum), corn plant (Zea mays) and sour thale (Arabidopsis thaliana).

Alter direction of gravity vector

Another approach to studying hydrotropism is to use instruments to alter the direction of the gravity vector received by plants.

The direction of root growth is towards the water

Although it is not possible to eliminate the effect of gravity on the Earth, there are machines that rotate plants around an axis or, in some cases, in three dimensions in an attempt to neutralize the effects of gravity, which are called positioning machines. random.

In fact, the hydrotropism in the roots was most evident when the pea and cucumber plants were grown in one of these machines.

Microgravity

An even more interesting approach to study is to use the microgravity conditions present during space flight.

The idea is that, in the absence of significant gravitational forces, the predominant gravitropic responses of the roots are effectively negated, so that other root tropisms (such as hydrotropism) become more apparent, above gravitropism. This is a spinning or growing movement of a plant or fungus in response to gravity.

Other difficulties

Another obstacle to studying hydrotropism is the difficulty of establishing a system in which there is a reproducible moisture gradient.

Classic German botanists' methods, also used by the Darwins, included placing the seeds in a hanging cylinder of damp sawdust, which resulted in the roots first growing downward, but then growing back into the moist substrate.

It is noteworthy that one of the lesser known tropisms is hydrotropism, directed growth in response to gradients of water or moisture.

Although hydrotropism had been studied in plant roots by 19th century German botanists and by the Darwins, the existence of this tropism has been questioned until recent years.

These processes simply need to be studied further. Each scientific study will increase the understanding of these complex mechanisms.

References

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6. Takahashi, N., Yamazaki, Y., Kobayashi, A., Higashitani, A., and Takahashi, H. (2003). "Hydrotropism interacts with gravitropism by degrading amyloplasts in seedling roots of Arabidopsis and radish". Plant Physiol. 132 (2): 805–810.
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