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Plant Growth Hormone Basics

Plant growth hormones are the chemical substances which govern all the factors of development and growth within plants. Some other names used to refer to it are phytohormones and plant growth regulators.

Phytohormones are organic compounds which are either synthesized in laboratories or produced naturally within the plants.  They profoundly control and modify the physiological processes like the growth, development, and movement of plants.

Based on their actions, plant growth regulators are broadly classified into two major groups:

  • Plant growth promoters
  • Plant growth inhibitors.

Auxins, Gibberellins, and Cytokinins are grouped into plant growth promoters while Abscisic acid and Ethylene are grouped into plant growth inhibitors.

Types of Plant Growth

Primary and Secondary Growth

The meristematic cells present at the root and shoot apices divide mitotically and increase the length of the plant body. This is known as primary growth. Secondary growth is referred to as the increase in the diameter of the plant body by the division of the secondary meristem.

Unlimited Growth

When the plant constantly grows from the germination stage to death, it is called unlimited growth.

Limited Growth

In this stage, the plant parts stop growing after attaining a certain size.

Vegetative Growth

It involves the production of stem, leaves, and branches, except the flowers.

Reproductive Growth

Flowering occurs at this type of growth stage.

Factors Affecting Plant Growth

There are four major factors that affect the growth of the plants. They are light, water, temperature and nutrition.

Light

Plants require light for manufacturing their food. Limited light or the absence of it greatly affects the growth of the plant.  Light also encourages flowering and fruiting. During winters when the days are short, the growth of the plants can be reduced depending on the plant type.

Water

Plants cannot survive without water. Around 90% of the plant body comprises water. Plants become stressed in the absence of water and die. Water present in the soil is absorbed by the plant, which absorbs and transports the nutrients through transpiration. High transpiration however may lead to reduced photosynthesis due to the inability of the plant to replace water fast enough causing the plant to shut down for short periods of time.

Temperature

Plant growth is greatly influenced by temperature. High temperatures speed up transpiration, photosynthesis, and germination processes. Too high of a temperature though, and plant growth can be slowed or even stop as a natural abiotic stress defense. Low temperatures, however, may also slow down the growth of the plants if they are below the ideal range for the particular plant to grow in.

Nutrition

Plants require proper nourishment for their growth and development. Nutrients are divided into macronutrients and micronutrients. Nitrogen, potassium, calcium, magnesium, sulfur, and phosphorus are the major macronutrients required by the plants. The micronutrients needed include iron, copper, manganese, magnesium, and others. Deficiency of just one nutrient in plants may result in stunted growth of the plant or poor physiological development during critical stages.

Check out our next blog entry to learn more about the characteristics of plant growth regulators!