Internal Coordination in Plants

Plants, like animals, require some form of internal coordination for their growth and development to proceed in an orderly fashion and to respond appropriately to their environment. Unlike animals, plants lack a nervous system and rely entirely on chemical coordination. As a result, their responses are slower and often involve growth. Plant hormones control all activities of plants, from growth to fruit production and ripening.

 

Plant Movements

While plants do not exhibit locomotion (movement of the entire organism), individual plant organs can move in response to external stimuli. These movements can be classified into two types:

1. Turgor Movement

2. Growth Movement

 

Biological Clock and Circadian Rhythms

Many behavioral activities in plants occur at regular intervals and are known as biological rhythms or biorhythms. The internal mechanism maintaining these rhythms in the absence of environmental stimuli is called the biological clock. A biological rhythm with a 24-hour cycle is known as a circadian rhythm (from Latin *circum*, about, and *dies*, day) or diurnal rhythm. If the biological rhythm spans less than or about 365 days, it is referred to as a circannual rhythm.

 

Examples of Circadian Rhythms

1. Prayer Plant: The sleep cycle of the prayer plant changes to a 24-hour cycle.

2. Stomata and Flowers: Certain flowers and stomata usually open in the morning and close at night.

Nectar Secretion: Some plants secrete nectar at the same time each day or night.

Rhythms involving an internal clock are known as endogenous rhythms, while those controlled by external factors are called exogenous rhythms. The synchronization mechanism may be a combination of both types of rhythms. These rhythms are influenced by both genetic factors and the environment.

 

Additional Information on Plant Hormones

Plant hormones, also known as phytohormones, play a crucial role in regulating various aspects of plant growth and development. The major classes of plant hormones include:

Auxins: Promote cell elongation, root formation, and bud growth.

Gibberellins: Stimulate stem elongation, seed germination, and flowering.

Cytokinins: Promote cell division and delay leaf senescence.

Ethylene: Regulates fruit ripening and leaf abscission.

Abscisic Acid: Inhibits growth and promotes seed dormancy and stress responses.

Understanding the roles and interactions of these hormones helps in managing agricultural practices and improving crop yields.