Plant hormone

Plants use tiny signals to grow.

These signals are called hormones. They tell the plant how to change. They help make roots and stems.

Some signals help seeds stay asleep. This keeps them safe in winter. Other signals help leaves grow big. They also help plants fight off germs. Every part of a plant can make them. These signals help every plant live well.

Plants use tiny signals to grow and stay healthy. These signals are called phytohormones, or plant hormones.

Unlike animals, every cell in a plant can make them. These chemicals tell the plant how to change. They control how big parts grow and how seeds develop.

One type is abscisic acid. This hormone helps seeds and buds stay asleep. This is called dormancy. It keeps them safe during cold winters. If they grew too early, the frost might kill them.

Another type is auxin. Auxins help cells grow longer. They also help a plant make new roots. They can even help a flower turn into a fruit.

There are also brassinosteroids. These are special signals that help cells divide. They also help plants handle stress. Plants move these signals through tubes. Some tubes move water, and others move sugar. This helps the signals reach every part of the plant.

Plants use tiny signal molecules to manage their entire lives. These signals are called phytohormones, or plant hormones.

They control everything from how big an organ grows to how a plant defends itself. Unlike animals, which use special glands, every single plant cell can make these hormones. They are not nutrients, but they influence how cells grow and change.

Because they work in such tiny amounts, they are hard to study. Scientists only began to truly understand them in the late 1970s.

These hormones move through the plant in a few specific ways. Some move locally through a process called cytoplasmic streaming inside cells. Others move slowly between cells through diffusion.

For long trips, plants use vascular tissues. The phloem moves sugars from leaves to roots and flowers. The xylem moves water and minerals from roots to the foliage. This allows the signal to reach the parts of the plant that need it most.

Humans have studied these signals for a long time. The earliest scientific observations began way back in the 1880s. It took about 70 years to identify many of them.

In 1937, Went and Thimann used the term "phytohormone" in their book. Later, researchers found different classes of these chemicals. For example, Mitchell and others identified brassinosteroids in 1979. They found them by looking at pollen from rapeseed plants.

There are many different types of plant hormones. Auxins are the first class that scientists discovered.

They help cells get longer and help roots grow. Abscisic acid is another important type that acts as an inhibitor. It helps seeds and buds stay dormant during the winter. This prevents them from growing when it is too cold.

Other major types include gibberellins, cytokinins, and ethylene. Scientists also study brassinosteroids, jasmonates, and salicylic acid.

Understanding hormones helps us work with the world around us. Farmers use plant growth regulators to manage crops and weeds. Some synthetic auxins are even used as herbicides to control weeds. Other types of auxins help people grow roots when taking plant cuttings. This shows how these tiny signals can have a huge impact. Even the way a plant handles thirst depends on these chemicals. When a plant lacks water, abscisic acid helps close the small pores in leaves.

Plant hormones, also known as phytohormones, are essential signal molecules produced within plants. These chemicals regulate almost every aspect of a plant's life cycle. They control embryogenesis, which is the development of an embryo. They also regulate organ size, defense against pathogens, and stress tolerance. Unlike animals, which rely on specialized glands to produce hormones, every plant cell is capable of producing them.

These molecules are not nutrients. Instead, they function in extremely low concentrations to influence how cells grow and differentiate. This means they tell cells what to become and how to behave.

Because plants lack a cardiovascular or lymphatic system, they move hormones differently than animals do. They use four main types of movement to transport these signals. For local movement, they use cytoplasmic streaming within cells. They also use the slow diffusion of ions and molecules between cells.

For long-distance transport, plants utilize vascular tissues. The phloem moves sugars from leaves to roots and flowers. The xylem moves water and mineral solutes from the roots to the foliage. This allows hormones to reach distant parts of the plant body.

Plants must carefully manage their internal hormone levels to survive. They can regulate the amount of chemicals used to make new hormones. They can also store hormones in cells for later release. To stop a signal, plants can inactivate hormones or break them down chemically. They can even "cannibalize" hormones by attaching them to carbohydrates, amino acids, or peptides.

This process is called catabolism. Plants also use movement to dilute hormone concentrations. This precise control ensures that growth happens only at the right time and place.

Scientific understanding of these molecules has evolved significantly over time. The earliest observations began in the 1880s. However, it took about 70 years to identify many of these substances. In 1937, Went and Thimann coined the term "phytohormone" in their book. Because hormones work at such low concentrations, specifically $10^{-6}$ to $10^{-5}$ mol/L, they were difficult to study. It was not until the late 1970s that scientists began to fully understand their complex relationships.

Much of this progress came from studying genetically deficient plants or tissue-cultured plants grown in vitro.

There are several major classes of plant hormones. Auxins were the first to be discovered, described by Dutch biologist Frits Warmolt Went. They promote cell enlargement, bud formation, and root initiation.

Abscisic acid, or ABA, is a major growth inhibitor. It helps seeds and buds remain dormant during winter so they do not freeze.

Other major classes include gibberellins, cytokinins, and ethylene. Modern research has also identified brassinosteroids, jasminates, salicylic acid, and strigolactones. Some hormones even work through synergism. This occurs when two hormones, like auxins and cytokinins, work together to create an effect greater than their individual parts.

Brassinosteroids are a unique class of steroid-based hormones. They were first identified by Mitchell and his team in 1979. They discovered them by extracting components from the pollen of rapeseed plants.

The main active component they found was Brassinolide. These hormones control cell division, stress resistance, and gravitropism, which is how plants respond to gravity. They also help with xylem differentiation and can inhibit root growth or leaf abscission. This discovery added a whole new layer to our understanding of plant physiology.

Human technology often utilizes these natural processes through plant growth regulators (PGRs). Farmers use synthetic compounds to manage the growth of cultivated crops and weeds. For example, some synthetic auxins act as herbicides to control weeds by causing defoliation. Other specific auxins, like NAA and IBA, are used to stimulate root growth in plant cuttings. Even the way a plant survives drought involves hormones. When roots sense a lack of water, a signal triggers the production of ABA precursors in the leaves. This eventually causes the stomata, or small pores, to close and conserve water.