Plant Movements and classification of plants movements

 Plant Movements

Plant movements are usually too slow for the direct observation but the results are easily noticed e.g. the closing and opening of flowers,unfolding ofbuds, bending towards light,twining of tendrils, locomotion of Chlamydomonas and the gametes of algae, bryophytes and pteridophytes etc. dual natuce ye plant oc aswell

Classification of Plant Movements 

Generally movement of plant parts can be classified according to the mechanism involved. Plants movements are classified into two major types;turgor movements and growth movements, rest of the classification of plantmovements is as under.

(A)Turgor Movement

Turgor movements are due to the differential changes in turgor and size of the cells as a result of the gain or loss of water and are easily And reversible. The effective cells are often different from ordinary cells and may be concentrated in certain areas.

Petiole leaflets in normal position Petioledrooping Leaflets folded Pulvini at bases of leaflets. The rolling of leaves of many grasses in dry weather is caused by loss of water from the bulli-form cells, which form longitudinal rows in epidermis. The dropping folding up in some plants at night are caused by turgor changes in the cells of the pulvinus which are present at the base of the bubble shape structure and sent leaf or leaflet.The pulvinus is composed of parenchyma cells with large intercellular spaces and a central strand of vascular tissue. The water passes into or out of these cells more freely on one side of the pulvinus than on the other side. This unequal movement of water causes unequal enlargement or shrinkage (turgor response) and a consequent movement of the petiole and leaf blade. 

Turgor movement may be 

(a) rapid movements

 (b) sleep movements.

a. Rapid Movement

When the leaves of Mimosa or"touch me not" are touched, the lower cells of the pulvinus loose their turgidity. The leaves bend downward.After some time the leaves regain their turgidity and thus become erect.

Response of Mimosa pudico to

b. Sleep Movements

shock. Left (before) and right(after)

Some plants of family leguminoceae such as bcan plants lower their leaves in the evening and raise them in the morning. These are called sleep movements. The sleep movements are due to daily changes in the turgor pressure in the pulvinus. When the turgor pressure on the lower side of the

pulvinus increases, the leaves rise and when decreases, the leaves lower.This is called sleep movement.

(B) Growth Movements

Growth movements may be self controlled or induced by the plant

organs by external stimuli. They are irreversible movements, caused due to

unequal growth on both sides of the plant organs like roots, stems, buds and

tendrils. On this basis the growth movements are classified into:

1. Autonomic 

2. Paratonic

1. Autonomic Movements

Movement in which the whole plant shifts from one place to another is called Tocomotion. These are spontaneous movements or self control

movements e.g. certain algae such as Chlamydomonas and volvox move

through water. Also the zoospores and motile gametes of lower plants show

locomotion. These move in response to stimuli i.e sweet fluids etc. The

around vacuole. protoplasm of the living cells of many plants shows streaming movements in uppec part of leaves is fast in low

Types of Autonomic Movements

Following are the types of the autonomic movements.

(a) Epinasty

(b) Hyponasty (c) Nutation

(a) Epinasty-> 

when the growth It is seen in the petals and leaves especially in the bud condition. The upper

surface of the leaf shows more growth in the bud condition than the lower

surface, which results in the opening of the buds.

(b)Hyponasty

It is also shown by petals and leaves in bud condition, the lower surface of

the leave shows more growth than the upper surface which keeps the bud

closed.

(C) Nutation

The growing tip of the young stem

moves in zig zag manner due to alternate

change in growth on opposite side of the

apex.

2. Paratonic Movements

These movements are induced by the

external stimuli. Paratonic movements may

be:

(a) Tropic movements

 (b) Nastic movement

(C) Tactic movements

Tropic Movements

These are induced movement of curvature shown by the plant organ(shoot or root), which are capable of turning in any direction. The direction of movements is determined by the direction of stimulus (light, water,gravity etc) Tropism or tropic movements are classified 

(1):Geotropism

Geotropism occurs in radially symmetrical organs like root and stem. The orientation of stem and roots in response to the force of gravity is called geotropism. The roots grows towards the force of gravity and are said

and is there fore called negatively geotropic.

to be positively geotropic, the stem grows away from the force of gravity and is there fore called negatively geotropic. 

(2): Phototropism

The tropic movement of curvature induced in plants organs in response to the unilateral effect of light is called phototropism

Young stems are positive phototropic, turn towards light. The curvature is

due to the greater growth on the shaded side then on the side on which the

light acts. Roots are usually indifferent to stimulus of light, their orientation

being determined chiefly by the gravity.

(iii) Hydrotropism

This is the movement of the plant organs in response to the stimulusof moisture. The primary roots, secondary roots of higher plants, rhizoid of

liverwort and hyphae of certain fungi exhibit growth movement in response

to variation in the amount of moisture. Roots are sensitive to variations in

the amount of moisture in the soil.

(iv) Thigmotropism

These movements of the plant organs is in response to the stimulus

of touch, contact or friction e.g. the plants, which climb by means of

tendrils, are sensitive to the stimulus of contact. The tendrils are found in a

number of plants e.g. in Passiflora, Lathyrus, Smilax etc.

Thigomotropic responses are also met

within the roots. If the tip of the young root

comes in contact with a solid object such as

small stone, the root bends away from it. This

negative curvature helps the root to avoid

obstacle in the soil. The stamens of certain

plants are sensitive to touch and their

dehiscence takes place only when the body of

an insect rubs them.

(V) Chemotropism

 Passiflora species have tendrils

that allow them to crawl all over everything,

This is the movement of a part of the plant in response to a chemical stimulus. The plant organ may grow either towards the chemical stimulus or away from it e.g, the pollen tube grows towards the egg in the angiosperms

due to the disintegration of the synergid cells, which produced chemicals.

Similarly the tentacles of Drosera (or sundew) show positive chemotropism.

The chemicals like the proteins, phosphates and the salts of ammonia cause

the tentacles to bend. In the same way the hyphae of many fungi shows

show negative chemotropism towards acids and alkalis. positive chemotropism towards sugar, peptones. The hyphea of the fungi

(b) Nastic Movements

The movements brought about by the stimuli which are non directional but diffuse are called nastic movements. It is the variation in the Photonasty intensity of some external factor rather than its direction, which acts as a stimulus. The direction of the movement is here determined by the structure

of the plant organs like the leaves and the petals of flowers, which can bend only in one direction. Nastic movements may be the result of growth changes or they may be the movements of variation.

(i)Nastic movements may be:

(ii) Thermonasty 

(111) Seismonasty

Photonasty 

This nastic movement is induced by variation in the intensity of light.Many leaves, which keep their surfaces fully exposed during the daytime, drop at night. The dropping of the leaves is brought about by changes in the turgidity of parenchymatous cells of the pulvini i.e. Many flowers such as oxalis close up at night or when the light is diminished on a cloudy day and open during the daytime in sunshine.

Thermonasty

This is due to variation in the degree of temperature. Many flowers

open when illuminated and close up when it is dark e.g. crocus, tulips etc.

(ii)Seismonasty

This nastic movement is induced by mechanical stimuli such as touch

or friction etc e.g. when the leaf of Mimosa pudica is touched the leaflets close and the whole leaf drops. This shock movement of Mimosa pudica is called seismonastic movement. These movements are caused by the differential loss and support of turgor on the two sides of the pulvinus.

(c) Tactic Movements 

These are the movements of the entire organism or of motile organs and are

induced by the external stimuli, which influence their direction. The stimuli

can be light, temperature or chemicals.

(1)::Phototactic

It is the locomotary movement of free swimming organisms or their organs

in response to one-sided illumination e.g. Chlamydomonas, Volvox and the

zoospores of Ulothrix and many other algae when illuminated by weak light

move towards the light, thus showing positive phototaxis. When illumination is too intense, they move away from light, showing negative phototaxis. Similar movements are also exhibited by the chloroplast in the

pallisade cells of the green leaves

(2)::Thermotactic

This is the movement of free organism in response to the stimulus of

temperature. When there is difference in temperature, the unicellular algae

are seen to move toward the warmer side.

(3)::Chemotactic

This is the movement of free organism or their gametes in response to

chemical stimuli. The spermatozoids of bryophytes and pteridophytes move

towards the chemical substances like sugar and proteins secreted by the

archegonia