Plant Growth and Movement

Plant growth may be defined as a permanent & irreversible change in the Size of a cell, organ or whole organism usually accompanied by an increase in dry weight.

• There are three phases of growth - cell division, cell enlargement & cell maturation. Maximum elongation occurs immediately behind the apex.
• Growth as phenomenon has two aspects ie quantitative & qualitative.
• Quantitative includes increase in length, breadth, Size, volume, body mass or dry wt whereas qualitative is all about development by differentiate.
• The time course of growth of an entire plant or plant organ plotted on a graph paper shows s-shaped or sigmoid curve.
• So Growth in plants can be measured in terms of:
  1. increase in the length or girth
  2. Increase in fresh or dry weight.
  3. Increase in area or volume (fruits + leaves).
  4. Increase in the number of cells produced.
• So: development is the Series of change which an Organism goes through during its life cycle. is usually always associated with morphogenesis differentiation.
• There are three distinct phase of plant development.
  1. Phase of seed germination & Vegetative growth
  2. Phase of seed reproduction (or Flowering)
  3. Senescence & death.

Seed Germination

• Germination is a process by which the embryo in the seed becomes activated & begins to grow into a new seedling.
• Seed germination may be defined as the fundamental process by which different plant species grow from a single seed into a plant this process influence both crop yield & quality.
• The quiescent embryo utilises the reserve stored food in cotyledons under suitable physiological & environmental condition results in emergence of small plant ie the seedlings.

Process of Seed Germination

• During the begining stage of the germination, the seeds takes up water rapidly & results in swelling & softening of the seed's coat at an optimum tempreature called imbibition. Hence growth occurs due to activation of enzymes.
• The internal physiology of seed activates & it start to respire produces protein & metabolizes the stored food so this is the lag phase.
• By rupturing of seed coat, radicle emerges & forms primary root. It starts absorbing underground water thus plumule shoot starts growing upward. Thus the cells of the seeds become metabolically active, elongate & divide to give rise to seedlings.

Epicotyl : The upper portion of the axis of the seedling above the cotyledons.
Hypocotyl : The lower portion of the axis below the cotyledons.

Types of Germination

There are two types of Germination:

1. Epigeal germination: In this type of germination the hypocotyl elongates rapidly & comes upward pulling the cotyledons which move above the soil. Ex: Beans, Cotton, papaya, onion germination. Ex: dicot plants.
2. Hypogeal Germination: In this types of germination, the epicotyl elongates & the cotyledons remains below the soil. Ex Pea, mango, maize, rice germination. Ex: monocot plants.

Factor Affecting Seed Germination

Seed Germination is directly affected by external & internal factor they are:

1) External factors

1. Water: water activates the enzymes which digest the complex reserve food of the seed so it affects seed germination.
2. Temperature: Seeds fails to germinate at low temp & high temp. the opt temp is 25°C to 35°C.
3. Oxygen: Germination seeds respire vigorously & release the energy required for growth so it is necessary.
4. Light: Plant requires exposure to low intensity of red light in order to germinate.
5. Soil: Soil is the natural habitat of plant & which hold all the requirement necessary for growth.

2) Internal Factors

1. Maturity of embryo: Immature seed doesn't germinate.
2. Viability: Seeds germinate only within the periods of viability.
3. Seed dormancy: This is the condition in which seed are prevented from germinating even under favourable condition.

Seed Dormancy

A resting peroid in the life of plant during which growth slows or appear to stop is called dormancy.
So Seed dormancy is defined as "state or condition in which seed are prevented from germinating even under favourable environmental condition".

Factors responsible for seed dormancy:

1. Seed coat: The presence of thick & hard seed coat is responsible for causing seed dormancy in many plants.
2. Immature embryo: The embryo in some seed are undeveloped so such seed do not germinate untill their complete maturation.
3. Germination inhibitory: There are many growth substance that inhibit germination such as Ammonia etc.
4. Specific light requirement: Seeds of many plant species have a light requirement for germination.

Types of Seed Dormancy

The seed dormancy is Following:

1. Innate dormancy: It is the condition of seeds which is incapable of germination even if Condition are suitable radling growth. Such as immature embryo. Ex:
   1. Enforced dormancy: Some seeds are incapable to germinate due to enviromental factors such as adequate amount of moisture, O2, light & temp. Ex:- Peach, cherry.
   2. Induced dormancy: It is the dormancy when the seed imbibes water but it is placed under extremly unfavourable condition the seed fails to germinate Ex:- walnut, stone fruit.

Method of breaking dormancy

1. Scarification: Mechanical & Chemical treatment like cutting of hard tough seed. By the use of organic solve, waxy layer of compound are removed & process called scarification.
2. Impaction: In some seeds water & oxygen are unable to penetrate into micropyle due to blockage by cork cells. Such seeds are vigorously shaker to remove the plug and the process is called impaction.
3. Stratification: Some seed will not germinate until these have been exposed to well aerated, moist condition under low temperature ie 0°C to 10°C for weeks to months. so such treatment is called Stratification.
4. Alternating temp: An alternation of low & high temp improves the germination of seeds.
5. Light: Such type of dormancy can be broken by exposing them to red light.

Photoperiodism

Plants responds to variation in day length & produce flowers in a particular reasons only. At the equator day length is about 12 hrs & is almost constant.
In temperature region the day length varies from 9-15 hours. As summer has long & warmer day & winter has shorter & colder days. All these changes influence the flowering in plants. So Requirement of specific day leaves for flowering is called photoperiodism.
- Photoperiodism is the response of an organism to changing relative length of the day & night.
Photoperiod: It refers to the length of the day or the light Period.
The role of photoperiodism was demostrated for the first time in 1920 by Garner & H.A Allard.

• Flowering plant have been divided into three groups on the basis of their response to photoperiod.

1. Short-day plants:

• They required short day & long nights.
• They flower only when the days become shorter than
• They need an uninterrupted long night for flowering & so called long-night plants.
• They do not flower if given short days & long night are interrupted by flashes of light though the flash is of one minute duration only.
• If short day are interrupted but not the long night they show flowering.
• The plant flower during autumn & winter when the night becomes longer & days are shorter.
• Ex:- Tobacco, soyabean, chrysanthemum, Rice.

2. Long-day plants:

• They require long day & short nights.
• They flower only when light period exceeds a certain length of the day.
• Short night is more essential than the length of the day so called short-night plants.
• They flowers even when the short night is interrupted by flashes of light.
• They show flowering even when a long day is interrupted by brief periods dark.
• The long day plants flowers during summer season winter days are longer than the night.
• Ex:- Spinach, radish, sugarbeet, wheat, barley.

3. Day-neutral plants:

• These plant do not require specific photo periods to flower such plant flower in almost all the photo periods ranging for a few hours to 24 hours of uninterrupted light periods. The day neutral plant are also known as photoneutral or interminate plants.
• Ex:- Cucumis sativus (cucumber), Zea mays (maize), tomato, cotton, Sunflower etc. Potato, Rhododendron.

Importance of Photoperiodism

• It determins the season in which a particular plant shall come to flower.
• A plant can be made to flower throughout the year under green house condition if a favourable photoperiod is provided to it.
• Helped the plant breeders in effecting cross-breeding in plants.
• So the knowledge of photoperiodic effect is useful in keping some plants in vegetative stage to obtain higher yield of tubers, rhizome etc or keep the plant in reproductive stage to obtain fruits & flowers.

Vernalisation

Vernalisation is the exposure to low temp for initiation of early flowering. It can also be said as the method of inducing early flowering by Pre-treatment of seeds with a certain low temperature.
- The actual site of cold stimulus in most of the plants is meristematic cells in the bud, apex of embryo, developing leaves etc.

* Critical day length: It is the duration of long Period required to induce flowering must not exceed. Ex: Xanthium a short day plant requires a critical day length of 15.5 hrs (15.5 hrs light / 8.5 hrs dark). If this plant get less than 8.5 hrs dark It fails to flower.

Senescence

Senescence is the gradual decline in smooth functioning of the organism ultimately leading to death.

• Senescence is a period between complete maturity & final death of an organ or organism.
• There is decrease in the functional capacity.
• The cellulose break down increase hence there is accumulation of toxic substances.
• The degeneration of cells increases.
• Senescence is controlled by some growth hormones.

Types of Plant Senescence

1. Whole plant senescence: The whole plant including stem, root & leaves undergo senescence at the same time & ultimately the plant dies after the seed production. Ex Beans, tomato, cereals, gram, mustard.
2. Progressive or sequential senescence: When the senescence gradual & follows a certain sequence is called Sequential senescence. Such in perennial plants first the older leaves than the lateral organs, branches & last main shoot undergoes senescence.
3. Shoot senescence: In certain plants, only the part above the ground dies every year & underground part survive & produces new plant under favourable condition. Ex Banana.

Advantage of Senescence & death

1. It allows a number of old & inefficient organs lies leaves buds, flowers & fruits are replaced by new young ones.
2. During senescence more nutrient are directed toward the developing growing parts.
3. Senescence during unfavourable peroids leads to bud dormancy and leaf fall that helps them to survive in cold winter.
4. leaf fall indirectly bring about the recycling of nutrients to maintain growth & development.

Plant Movement

Plants also show movement but not like animals they show movement of location. They are fixed to a place and only a part of them moved. It is of three types.

1. Movement of Locomotion

In this movement the whole plant body is moved from one place to another place. It is of two types.

a) Autonomic (Spontaneous) movement
This movement is infuenced by any external stimuli. It is of:

1. Temporary movement: It takes place due to presence cilia and flagella. Ex Volvox, Chlamydomonas, Antherozoids of fern etc.
2. Amoeboid movement: It is exhibited by the organism that produces pseudopodia Ex. Plasmodium.
3. Cyclosis: Movement of cytoplasm round vacuoles including cell organelles.

b) Paratonic (induced) movement of locomotion
This types of movement is exhibit by plant due to certain external stimuli. It is also called Tactic movement or taxic. It is of:

1. Phototaxis: It is the plant show movement in response to stimuli of light it is called phototaxis eg: volvox.
2. Chemotaxis: The plant movement occur in response to stimuli of chemical is called chemotaxis. Ex: Archegonia produces chemical towards which antherozoid are attracted and fertilization takes place.
3. Thigmotaxis: If the plant movement occur in response to heat is called Thigmotaxis.

2) Movement of curvature:

Higher plant are fixed and cannot show movement of locomotion, they only show the movement by bending the certain part of their body.
This type of movement is of two types:

(a) Movement of Variation (Turgor movement):
The plant parts bend in various direction and again arises in initial position which is due to turgor changes into plant parts.

• It is temporary.
• It is due to change is osmotic potential in the living cells of base of plant organ like petiole, stalk of flower & calyx etc. It again of two types.

1. Spontaneous movement of Variation: It is not stimulated by any external factors. Ex:- telegraph plant here two lateral leaflet move up and down periodically in every 2 min.
2. Induced (paratonic) movement of Variation: This movement occurs in response to the diffused stimulus which is not unidirectional. It can be of following types:
   • Hyponastic and Epinastic movement: It is due to due to the differential growth on the two side of these organs.
   • If more growth occurs in lower side of the organ the plant curved upward which is called hyponastic movement.
   • If more growth takes place in appear part of the leaves or sepals or petals curve downwards and this is called epinastic movement.
   • Examples:- The flower opens due to hyponasty and closed due to epinastic movement. In ferns hyponasty is observed in young condition so leaves are coiled and epinasty so observed in mature.
3. Nutational Movement: Sometimes the growth of the stem apices occurs in zig-zag manner due to the growth of two side of apex alternately so called nutational movement.
4. Circumnutational movement: It is due to maximum growth around the growing apex and occurs in rotational way is called Circumnutational movement.
5. Nyctinastic Movement: The leaves or flower of various plant exhibit different position in day and night is called nyctinastic movement or sleep movement.
   Ex: Oxalis the movement is due to presence or absence of light. It changes is due to temp is called thermonastic.
   Ex: Crocus as flower open at high temp & close at lower temp.
6. Seismonastic movement: This kind of movement is stimulated by the sensation of touch or shock. Ex:- Mimosa pudica.
7. Thigmonastic Movement (Haptonastic movement): This type of movement is stimulated by the touch in insect. The leaves closes at the insect touches them. Ex: Drosera (Sundew), Dionaea (Venus fly trap).

Movement of Growth

Here the growth of the plant parts in a particular manner directs them to curve in a particular direction. It is also of two types.

1. Autonomic movement of Growth

This growth movement is not directed by any stimulus.

2) Paratonic movement of Growth

When the growth in response to external stimuli and unidirectional called tropical movement and phenomenon is called tropism. It is of following types.

• Geotropism
• Phototropism: The movement that occurs in response to light.
• Chemotropism: The movement that occurs in response to chemical stimuli Ex pollen tube.
• Thigmotropism: The movement that occurs in response to touch or contact stimuli.
• Hydrotropism: The movement that occurs in response to water.
• Thermotropism: In response to temp.

3) Hygroscopic movement:

The movement is only seen in dead part of the plant which are hydroscopic in nature. This movement occurs either due to loss or gain of water.
Eg: elaters in bryophytes etc.