COORDINATION IN PLANTS
BOTANY

COORDINATION IN PLANTS | PLANT MOVEMENTS & HORMONES


What is Coordination in Plants? Plants behave but their behaviour is fundamentally different from that of animals. The difference is due to two ways of life sessile on one hand and motile on the other.

  1.      Passive, complex and dynamic: Plants, compared to animals are far from being passive, and are a complex dynamic organism that grows, change, react to external/internal stimuli, and show a response.
  2.      Movement: Much of the behaviour of plants depends on variations in growth rates, or changes in the turgidity of cells when they show movement. Animals-have evolved tissues like muscles, specialized for the production of rapid movements.
  3.      Slow speed of response: The most obvious difference is, in the slow speed of response shown by plants.
  4.    Control systems: There are different ways employed by plants and animals to respond and have evolved different control systems accordingly. In plants, the control is solely by the plant hormones. In animals much more variety of hormones and the nervous control, make them respond with greater speed to specific stimuli:

Hormonal control in plants: Hormonal control in plants is relatively a slow process. Even when a hormone is transported, there is a delay between the release, its arrival at the target cells, and its action in the body. So, response to a stimulus that induced the secretion of hormone is usually not immediate. But keeping in view the slowness of the mechanism of plant movement, the delay involved in hormonal control is insignificant. All the activities of plants from growth to fruit production and ripening are under the control of plant hormones.

Plants, therefore, respond to the stimuli by:

1.        Regulating their growth and development in appropriate ways.

2.     Controlling their body functions through plant hormones or growth hormones.

PLANT MOVEMENTS  | COORDINATION IN PLANTS

Many plants do not show locomotion (movement of the whole organism). However, movements of plant organs are possible and are modified according to the nature and intensity of external stimuli. There are two kinds of movements in plants i.e. turgor movements and growth movements.

RESPONSES TO ENVIRONMENTAL STRESSES IN PLANTS

All plants need water, light, carbon dioxide and a variety of nutrients from their environment for optimal development and growth. The absence or short supply of any of these factors in the environment may exert environmental stresses on plants comprising their health and survival. If plants are grown without light, they become extremely long and they fail to form chlorophyll. They are said to be etiolated.

Many plants take on a yellowish hue (dye) when they fail to form chlorophyll in sufficient amounts. This condition is known as chlorosis usually arises from short supplies of mineral nutrients in the soil. Iron shortage is a major cause of chlorosis.

DEFENSE AGAINST PATHOGENS IN PLANTS

Diseases of plants may arise from infections by viruses, bacteria or fungi or lichens/mycorrhizae in most cases.

Developmental abnormalities in plants

Plants may also show developmental abnormalities,

i) Calluses: If plants are wounded, they often develop masses of amorphous (formless or shapeless) material with very poor differentiate on known as calluses.

ii) Plant tumors and cancers: Plant tumors and even plant cancers may arise and spread through the plant as an amorphous (shapeless) Invasion of surrounding well-differentiated tissues.

iii) Galls are growths on a plant that are induced by parasites and usually, highly organized growth galls are tumors induced by bacteria. They are usually less differentiated than other types of galls.

BIOLOGICAL CLOCKS AND CIRCADIAN RHYTHMS

 Diurnal rhythms

In living things the behavioural activities occur at regular intervals which are called biorhythms or biological rhythms. Biorhythms may occur showing a periodicity of about 24-hours. These are called circadian (Latin circa -about, dies -day) which means about one day, so they are also called diurnal rhythms.

Circannual

If the biorhythms are less than or about 365 days, these rhythms in activity are called circannual. The organisms confront (meet, face) environmental changes that are cyclical. in nature such as days, tides, and seasons etc. Many organisms maintain internal rhythm or clock, to predict the onset of the periodic changes and to keep them prepared for these changes.

Reasons for Biorhythms

 Biorhythms may be the result of the following:

1. There may be a direct response to various changes in the external (exogenous) stimuli.

2. There may be an internal (endogenous) rhythm that progresses the organism’s behaviour in synchronizing with the exogenous temporal period, particularly a 24 hour or a 365 day period.

3. The synchronization mechanism may be a combination of 1 and 2.

The rhythms are in one’s genes but the environment influences the rhythms to some extent. Thus the timing of behaviour results from a combination of effects .of rhythmical internal processes and timed events of the environment. Basic period of the clock is innate. Thus, Ervin Bunning of the University of Tubingen, Germany has shown that exposure of fruit fly Drosophila to constant conditions for 15 consecutive generations fail to eliminate the essentially 24 hr rhythm of this insect.