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Coordination in Plants

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Tropic Movement in Plants: An Introduction

Tropic movement in plants is a biological phenomenon that denotes growth or bending movements in plants due to environmental influences. Tropism is a three-step procedure that entails sensing the stimulus, signal transduction or response to the stimulus and the directional movement of plants. In plants, there are five tropism types: geotropism, chemotropism, phototropism, hydrotropism and thigmotropism. These will be discussed in detail later. Keep reading to learn more about tropic movement and coordination in plants and types of plant hormones.

Types of Tropism

  • Phototropism: Phototropism occurs in plants in response to sunlight, and the plants are reported to grow in the direction of light. The movement can be either towards or away from the sunlight.

  • What is Geotropism?

Positive geotropism is when a plant moves in the direction of gravity, causing its roots to grow downward. Similar to this, the process can be described as negative geotropism if its shoots continue to grow upward. The directional growth in plants occurs due to the uneven distribution of plant hormone auxin.

  • Chemotropism: In addition to environmental influences, there are also chemical elements that affect the tropic movements. Chemotropism example includes movement of pollen tube in the direction of the ovule. The transport of pollen grains to the female gamete releases certain chemicals which help in movement in seed plants.

  • Hydrotropism: Response of plant roots towards water is called hydrotropism. This phenomenon helps in the growth of roots in water.

  • Thigmotropism: The movement in plants that takes place in response to touch is called thigmotropism. An example includes the tropism that occurs in the touch me not plant.

Chemical Control and Coordination

All forms of life respond to environmental stimuli. Certain chemical reactions are reported to occur in plant cells in response to environmental stimuli. The capacity to use many plant components harmoniously and effectively is known as coordination. A plant chemical mechanism produces coordination, which is assisted by hormones and phytohormones.

Plant hormones, also known as phytohormones, are in charge of controlling and coordinating the chemical processes in plants. Cells are stimulated to produce these hormones that later diffuse throughout the plant. Plant hormones are involved in processes like fruit development, leaf drop, fruit ripening, plant ageing, cell division, cell enlargement, cell differentiation, and fruit ripening.

Plants display two types of movements: Growth-dependent movements/directional or Tropic Movements, and non-growth dependent/non-directional movements, also called the Nastic Movements.

Tropic movements are classified into 5 types. Phototropism (in response to light), Geotropism (in response to gravity), Hydrotropism (towards the water), Chemotropic movement (in response to chemicals), and Thigmotropism (in response to touch).

Nastic movements in plants are non-directional movements and are independent of stimulus. The example includes the leaves of Mimosa pudica, which immediately fold themselves when touched. These sorts of changes occur due to the alteration in the water content in the leaves. The leaves either swell up or shrink depending on the quantity of water. These changes are acquired in the opposite direction to the stimulus.

Types of Plant Hormones

The development and growth of the plant are affected by different hormones, namely, auxins, gibberellins, cytokinins, and abscisic acid.

  • Auxin is made at the stem's tip and aids in plant growth by lengthening cells. Auxins play a significant role in cell division, differentiation, development of embryos, roots, apical dominance, and flowering.

  • Gibberellin participates in flowering, seed germination, stem growth, and flowering. The environmental conditions must be favourable to initiate this process. The important environmental factors that need to be optimum for the processes to take place are the amount of water, oxygen, soil depth, and temperature. The fundamental process of seed germination is how various species of plants develop from a single seed into a young plant. The seed germination stages are water imbibition, root and shoot growth and formation of seedlings.

Seed Germination Diagram

Seed Germination Diagram

  • In fruits and seeds, cytokinins are found where cells divide. It is primarily responsible for cytokinesis, but it also aids in the stomata opening, apical dominance, leaf senescence, and axillary bud growth.

  • Abscisic acid is in charge of stomata closing and limits the growth of several components, eventually inhibiting the plant's growth. Hence, the hormone is reported to encourage dormancy in seeds and buds. Plant hormones, also called phytohormones, are reported to regulate the directional or non-directional growth of plants.

Interesting Facts

  • Auxin was the first phytohormone to be identified, and it was found by biologist Charles Darwin.

  • Plant hormones are naturally occurring substances that impact a plant's growth and development.

  • Tropism in plants performs a protective role. They aid in creating an immediate reaction to a stimulus or change.

Key Features of Coordination in Plants

  • Plant hormones function as chemical messengers.

  • Plant hormones are reported to regulate all aspects of growth and development in plants. It also helps in the interaction that occurs between beneficial microbes and the plant.

  • Tropism promotes the development of pollen tubes that lead to ovules.

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FAQs on Coordination in Plants

1. What are chemical messengers?

A chemical messenger is a compound that helps in the transmission of messages. Examples include hormones and neurotransmitters. 

2. What is germination?

The process of formation of a fully developed plant from a spore or seed is termed germination. It occurs after a period of dormancy.

3. What are epicotyl and hypocotyl?

The epicotyl terminates with a plumule, while a hypocotyl terminates with a radical and pulls the seed above the ground during germination.

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