Plant Physiology Short Notes PDF: Find below the important notes for the chapter, Plant Physiology as per the NEET Biology syllabus. This is helpful for aspirants of NEET and other exams during last-minute revision. Important notes for NEET Biology- Plant Physiology Short Notes PDF cover all the important topics and concepts useful for the exam.

Plant Physiology Short Notes PDF

Plant physiology deals with different plant structures and their functioning. It enables analysing processes in plants, namely – photosynthesis, mineral nutrition, respiration, transportation, and ultimately plant development and growth which are traits displayed by living entities. Plant physiology deals with all those events that are vital for the sustenance of a plant. Therefore, plant physiology is the applied field of plant anatomy and plant morphology.

Transport in Plants

Transportation is the process of movement of water and minerals to all parts of the plant body. Plants have a specialized system that enables them to distribute water and nutrients throughout their body. They use several processes such as translocation, absorption, storage and utilization of water. Transport in plants takes place through different mechanisms:

• Diffusion: Movement by diffusion is passive, and may be from one part of the cell to the other, or from cell to cell, or over short distances, say, from the intercellular spaces of the leaf to the outside. No energy expenditure takes place. In diffusion, molecules move in a random fashion, the net result being substances moving from regions of higher concentration to regions of lower concentration. Diffusion is a slow process and is not dependent on a ‘living system’. Diffusion is obvious in gases and liquids, but diffusion in solids rather than of solids is more likely. Diffusion is very important to plants since it is the only means for gaseous movement within the plant body. Diffusion rates are affected by the gradient of concentration, the permeability of the membrane separating them, temperature and pressure.
• Facilitated Diffusion: Facilitated diffusion is the passive movement of molecules along the concentration gradient. It is a selective process, i.e., the membrane allows only selective molecules and ions to pass through it. It, however, prevents other molecules from passing through the membrane. The electric charge and pH helps in the diffusion across the membrane. Examples of facilitated diffusion are Glucose Transporter, Aquaporins, Ion Channels.
• Active Transport: Active transport uses energy to pump molecules against a concentration gradient. Active transport is carried out by membrane-proteins. Hence different proteins in the membrane play a major role in both active as well as passive transport. Pumps are proteins that use energy to carry substances across the cell membrane. These pumps can transport substances from a low concentration to a high concentration (‘uphill’ transport). Transport rate reaches a maximum when all the protein transporters are being used or are saturated. Like enzymes the carrier protein is very specific in what it carries across the membrane. These proteins are sensitive to inhibitors that react with protein side chains.
• Water Potential: Water potential is used by the plants to transport water to the leaves that help in carrying out photosynthesis. Solute potential and pressure potential are the two main components of water potential. Solute potential is also known as osmotic potential and is negative in the plant cell. Pressure potential is positive in the plant cell. Higher the concentration of water in the system, greater will be the water potential.
• Osmosis: Osmosis is the movement of molecules from a region of higher concentration to a region of lower concentration across a semi-permeable membrane until an equilibrium is reached. The plant cell wall is freely permeable to substances in solution and water. Osmosis is of two types:
  • Endosmosis: This is the movement of water molecules enters into the cell when the cell is placed in a hypotonic solution.
  • Exosmosis: This is the movement of water molecules out of the cell when the cell is placed in a hypertonic solution.
• Plasmolysis: Plasmolysis occurs when water moves out of the cell and the cell membrane of a plant cell shrinks away from its cell wall. This occurs when the cell (or tissue) is placed in a solution that is hypertonic (has more solutes) to the protoplasm. It depends upon three types of solutions:
  • Isotonic: This refers to two solutions with the same osmotic pressure across the semi-permeable membrane.
  • Hypotonic: This is the solution which has a lower osmotic pressure than another solution.
  • Hypertonic: This is the solution with higher osmotic pressure than another solution.
• Imbibition: It is a special type of diffusion in which water is absorbed by solid particles (or colloids) of an object resulting in a dramatic increase in volume. For example, when dry wood is soaked in water, it swells and grows in volume.
  • Imbibition in plant cells means water exposure by hydrophilic-protoplasmic and cell wall elements.
  • It causes swelling of the seed which leads to the rupture of the seed coat or testa.
  • It forms the first step in seed germination.
  • It aids in the flow of water to the ovules, which mature into seeds.
  • It is required in the early stages of root water absorption.
• Transpiration: Transpiration is the removal of excess water from the aerial parts of the plants. It mainly occurs through the stomata of the leaves. It is influenced by light, temperature, wind and humidity. Xylem helps in the movement of water from roots to the leaf veins. The phloem helps in the movement of food prepared by the leaves to various parts of the plants. There are three different types of transpiration in plants:
  • Stomatal Transpiration: It is the evaporation of water from the stomata of the plants.
  • Lenticular Transpiration: Lenticels are minute openings in the bark of branches and twigs. Evaporation of water from the lenticels of the plants is known as lenticular transpiration.
  • Cuticular Transpiration: It is the evaporation of water from the cuticle of the plants.

The Process of  Transportation

In plants, there are pipe-like vessels through which water and minerals can enter the plants. These vessels are made up of elongated cells and thick walls. A group of cells forms a tissue that performs a specialized function within the organisms. These are conducting tissues. These conducting tissues are divided into two types which are xylem and phloem.

• Xylem: It is a vascular tissue that spreads from the top to bottom of the plant. For the transport of water molecules, it helps a lot. It also plays a vital role in the case of dissolved substances from the root hairs to aerial parts of the plant. It transfers water in one direction. Commonly, xylem occupies the central part of the vascular bundle. It mainly includes different types of cells such as tracheid, vessels, and xylem parenchyma and xylem fibers.
• Phloem: It is also vascular tissue. In a plant where the necessity of food molecules is there, the use of the phloem transportation process will take place. Some elements are there in the phloem such as sieve elements, phloem parenchyma, fibers, and companion cells.

Mineral Nutrition

Plant nutrition is an important aspect instrumental in the growth of plants. It gives an insight into the methods used to identify essential elements for the development of plants, the role of these elements, criteria to identify their essentiality, deficiency symptoms and mechanism of absorption of these elements. It also conveys the importance of nitrogen fixation.

Role of Nutrients

• Balancing Function: Some salts or minerals act against the harmful effects of the other nutrients hence balance the effect of each other.
• Maintenance of Osmotic Pressure: In few minerals the cell sap is present in organic or inorganic form, to control the organic pressure of the cell.
• Influencing The pH of The Cell Sap: Different anions and cations have different influences on the pH of the cell sap.
• Construction of The Plant Body: Some of the elements which help to construct the plant body are Carbon, Nitrogen and Oxygen. They help by entering the protoplasm and constitution of the wall.
• Catalysis of The Biochemical Reaction: Zinc, magnesium, calcium, and copper act as metallic catalysts in biochemical reactions.
• Effects of Toxicity: Under specific conditions, minerals like arsenic and copper have a toxic effect on the protoplasm.

Micronutrients

Macronutrients are generally present in plant tissues in large amounts (in excess of 10 mmole Kg –1 of dry matter). The macronutrients include carbon, hydrogen, oxygen, nitrogen, phosphorous, sulphur, potassium, calcium and magnesium. Of these, carbon, hydrogen and oxygen are mainly obtained from CO₂ and H₂O, while the others are absorbed from the soil as mineral nutrition.

Functions of Micronutrients:

• Copper:  It is responsible for activating the enzymes as a component of oxidase, cytochrome oxidase, phenolases, and ascorbic acid oxidase. It as well plays a vital role in photophosphorylation. Copper helps to balance carbohydrate-nitrogen regulation.
• Manganese: It is necessary for photosynthesis during the photolysis of water. The mineral is required for the synthesis of chlorophyll. It acts as an activator of nitrogen metabolism.
• Zinc:  It is essentially required for the synthesis of tryptophan, metabolism of carbohydrates, and phosphorus. Zinc is a constituent of enzymes like alcohol dehydrate-gas, carbonic anhydrase, lactic dehydrogenase, hexokinase, and carboxypeptidase.

Macronutrients

Macronutrients are the nutrients required by plants in larger proportions. These may include sulfur, nitrogen, carbon, phosphorus, calcium, potassium, and magnesium.

Functions of Macronutrients:

• Phosphorous: Phosphorous boosts fruit ripening and root growth in a healthy manner by helping translocation of carbohydrates. They are found abundantly in fruits and seeds. Deficiency of Phosphorus leads to premature fall of leaves and they turn purplish or dark green in color.
• Nitrogen: It is present in various coenzymes, hormones, and ATP etc. Nitrogen is a vital constituent of vitamins, nucleic acids, proteins and many others. Deficiency of nitrogen leads to the complete suppression of flowering and fruiting, impaired growth, and development of anthocyanin pigmentation in stems.
• Potassium: Potassium is the only monovalent cation that is necessary for plants which acts as an enzyme activator including DNA polymerase. The deficiency of potassium leads to Mottled chlorosis.

Sources of Essential Elements

Elements	Sources of the elements
Carbon	Taken as CO2 from the atmosphere (air)
Oxygen	Absorbed in the molecular form from air or from water. It is also generated within a green plant during photosynthesis.
Hydrogen	Released from water during photosynthesis in the green plant.
Nitrogen	Absorbed by the plants as nitrate ion (NO3–) or as ammonium ion (NH4+) from the soil. Some organisms like bacteria and cynobacteria can fix nitrogen from air directly.
Potassium, calcium, iron, phosphorus, sulphur, magnesium	Absorbed from the soil (are actually derived from the weathering of rocks. So they are called mineral elements). They are absorbed in the ionic forms.

Photosynthesis in Higher Plants

Photosynthesis is a physicochemical process by which green plants use light energy to synthesize organic compounds (sugar). In this process, oxygen is released into the atmosphere.

6CO₂ +12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂

Photosynthesis occurs in the chloroplast, found in the mesophyll cells of the leaves. There are 4 pigments involved in photosynthesis:

• Chlorophyll a
• Chlorophyll b
• Xanthophylls
• Carotenoids

• Photosynthesis occurs in mesophyll cell of the green leaves in a cell organelle called chloroplast.
• Within the chloroplast there is a membranous system consisting of grana, the stroma lamellae and the fluid stroma.
• The membrane system trap the light energy and synthesizes ATP and NADPH. This set of reaction reaction which depends on light is called light reaction.
• In stroma, enzymatic reactions incorporate CO2 into the plant leading to the synthesis of sugar which in turn forms starch. This set of reactions which are not directly dependent on light but are dependant on the products of light reactions. (ATP and NADPH) is called dark reaction.

Pigments Involved in Photosynthesis

• Chlorophyll a is the main pigment.
• Pigments like chlorophyll b, xanthophylls and carotenoids are called accessory pigments.
• Accessory pigments absorb light and transport the energy to chlorophyll a.

Processes of Photosynthesis in Higher Plants

Photosynthesis in higher plants involves the following processes:

Light Reaction (Photochemical Phase)

• Light reactions include light absorption, water splitting, oxygen release and the formation of high energy chemical intermediates, ATP and NADPH.
• The pigments are organized into two discrete photo chemical light harvesting complexes within the photosystem I (PS I) and photosystem II (PS II).
• In PS I the reaction centre chloroohyll a has an absorotion peak at 700 nm, hence is called P700 while the PS II has an absorption peak at 680 nm and is called P680.

Photophosphorylation: The formation of ATP in the presence of sunlight is called photophosphorylation. It is of two types:

• Non-cyclic photophosphorylation: PS-II absorbs light at a wavelength of 680 nm and causes excitation in the electrons. These excited electrons are accepted by an electron acceptor and transferred to the electron transport system. The electrons from the electron transport system are transferred to the PS-I. At the same time, the electrons at PS-I receive a wavelength of 700 nm and get excited. An electron from the electron acceptor is added to NADP+, which is then reduced to NADPH+ H+. The electrons lost by PS-II does not return to it and hence named non-cyclic photophosphorylation. In this, both the photosystems are involved.
• Cyclic photophosphorylation: In cyclic photophosphorylation, only PS-I is involved. The electrons circulate within the photosystem which results in a cyclic flow of electrons. This only forms ATP and not NADPH+ H+.

Splitting of water: The light-dependent splitting of water is called photolysis. This process is associated with PS-II in which manganese and chlorine play an important role. The electrons lost from P680 are replaced by the electrons formed in this process. A molecule of water splits to release oxygen upon the absorption of light by P680.

Dark Reaction (Biosynthetic Phase)

This process occurs in the absence of light in the stroma of the chloroplasts. The following cycles are involved in the process:

• Calvin Cycle (C3 Cycle): This cycle involves the following steps:
  • Carboxylation: Ribulose -1,5 bisphosphate combines with carbon dioxide to form 3-carbon compound 3 phosphoglyceric acid. The enzyme RuBisCO is involved in the process.
  • Reduction: Reduction is series of reaction that leads to formation of glucose. Two molecule of ATP and two molecules NADPH are required for reduction of one molecules of CO2. Six turn of this cycle are required for removal of one molecule of glucose from pathway.
  • Regeneration: Regeneration is the generation of RUBP molecules for the continuation of cycle. This process requires one molecule of ATP.

• C4 Cycle (Hatch and Slack Pathway): This cycle involves the following steps:
  • This pathway is operational in plants growing in dry tropical region like Maize, Sugarcane, Sorghum etc.
  • The first stable product is a 4-carbon compound Oxaloacetic acid (OAA).
  • The primary CO2 acceptor is 3C Phosphoenol pyruvate(PEP) present in mesophyll cell and enzyme involved is PEP carboxylase.
  • OAA is converted to Malic acid which is transported to bundle sheath cells.
  • In bundle sheath cell, it is broken into CO2 and a 3C molecule.
  • The 3C molecule is transported back to the mesophyll where is converted to PEP again, thus completing the cycle.
  • The CO2 released in the bundle sheath cells enters the Calvin cycle, where enzyme RuBisCO is present that forms sugar.

Photorespiration

Photorespiration is a process that lowers the efficiency of photosynthesis in C3 plants. In these plants, oxygen binds with RuBisCO during photosynthesis, which results in reduced carbon dioxide fixation. Additionally, this process does not result in the synthesis of sugars nor ATP or NADPH.

Factors affecting Photorespiration

• When the level of carbon dioxide is low and oxygen is high, the rate of photorespiration increases.
• Under water, stress conditions, the rate of photorespiration is higher.

Respiration in Plants

Respiration is the stepwise oxidation of complex organic molecules and release of energy as ATP for various cellular metabolic activities. It involves exchange of gases between the organism and the external environment. The green as well as non-green plants obtain oxygen from their environment and return carbon dioxide and water vapour into it.

Do Plants Breathe?

Yes, like animals and humans, plants also breathe. Plants do require oxygen to respire, the process in return gives out carbon dioxide. Unlike humans and animals, plants do not possess any specialized structures for exchange of gases, however, they do possess stomata (found in leaves) and lenticels (found in stems) actively involved in the gaseous exchange. Leaves, stems and plant roots respire at a low pace compared to humans and animals.

Types of Respiration

• Aerobic Respiration: The respiration that occurs in the presence of oxygen is named aerobic respiration due to ‘air’ which has oxygen. The aerobic respiration contains utilization of oxygen for the breaking of chemical bonds in glucose to liberate energy in high volumes. It is the central source of energy for plants. Animals and plants that use oxygen for respiration are aerobes. Aerobic respiration takes more energy because a complete breaking of glucose takes place during respiration with the use of oxygen.

C₆H₁₂O₆ + 6O₂ ⟶ 6CO₂ + 6H₂O + Energy

• Anaerobic Respiration: The respiration that occurs in the absence of oxygen is known as anaerobic respiration. In this process, the incomplete oxidation of food substance is being made by carbon dioxide CO₂ and alcohol (OH). Beside this other organic matter such as citric acid, oxalic acid, lactic acid, etc are also produced. This process is also called intramolecular respiration. The anaerobic respiration occurs in organisms like yeast, certain bacteria, and parasitic worms. All the organisms which gain energy by anaerobic respiration can exist without the oxygen.

Glucose ⟶ Alcohol + CO₂ + (Energy)

Respiration in Roots

In plants, respiration occurs with the help of roots. In soil oxygenated air is already present in spaces between soil particles. This oxygen is then absorbed into the roots with the help of root hair present on the roots. The hairs of the roots are in straight contact with them. In fact, a root hair is a lateral tubular outgrowth of the external epidermal cells of a root.

The oxygen present among the soil particles diffuses into the root hairs. From root hairs, oxygen is transported to all the parts of roots for respiration. During the respiration process, oxygen is transformed into carbon dioxide gas which is spread in the opposite direction i.e. out of the roots by the same root hairs which complete the respiration process of roots.

Respiration in Stems

The air in case of stem diffuses into the stomata and moves through different parts of the cell to respire. During this stage, the carbon dioxide liberated is also diffused through the stomata. Lenticels are known to perform gaseous exchange in woody or higher plants. 

Respiration in Leaves

The leaves of plants have tiny pores on their surface which are called stomata. The exchange of gases in the leaves during respiration takes place through stomata. Oxygen from the air enters into a leaf through stomata and reaches all the cells by the process of diffusion. This oxygen is used in respiration in cells of the leaf. The carbon dioxide produced during diffuses out from the leaf into the air through same stomata.

Plant Growth and Development

Plant growth could be defined as the increasing of plant volume and/or mass with or without formation of new structures such as organs, tissues, cells or cell organelles. Growth is usually associated with development (cell and tissue specialization) and reproduction (production of new individuals).

Plant Growth

• Growth is a quantitative parameter and refers to an irreversible increase in size or weight of a cell, tissue or organ. Plants are capable of growing throughout their life due to meristematic tissues present in certain parts.
• In plants growth is accomplished by cell division, increase in cell number and cell enlargement. So, growth is a quantitative phenomenon which can be measured in relation to time.
• Plant growth is generally indeterminate due to capacity of unlimited growth throughout the life. Meristem tissues are present at the certain locality of plant body.
• The plant growth in which new cells are always being added to plant body due to meristem is called open form of growth.
• Root apical meristem and shoot apical meristem are responsible for primary growth and elongation of plant body along the axis.

Phases of Plant Growth

There are three phases of growth:

• Meristematic (Formative phase): The phase of cell division or cell formation is called the formative phase. It takes place at the shoot apex, root apex, and other regions having meristematic tissue. The rate of respiration is very usually high in the cells undergoing mitosis division in the formative phase.
• Elongation (Enlargement phase): The newly formed cells produced in the formative phase will undergo enlargement. This enlargement leads to the development of vacuoles that further lead to an increase in cells’ volume.
• Maturation: It is characterized by cell wall thickening and lignification. Cells attain maturity and their maximal size and undergo protoplasmic modifications.

Measurement of Growth

Growth in plants being a quantitative phenomenon can be measured in relation to time. The growth rate may be different in nature. Growth can show either arithmetic or geometric progression.

Arithmetic Growth: In this type of nature, the rate of growth is constant, and an increase in growth follows an arithmetic progression- 2,4,6,…

L_t = L₀ + rt

L₀ is the initial length

L_t is the length after time ‘t’

r is the growth per unit time

Length at beginning + growth rate x time = Length after time

Geometric Growth: In this method, the initial Growth is gradual and then rapidly increases. Each cell divides. The daughter cells divide and grow, and further the granddaughter cells that lead to the exponential growth. It is common in a unicellular organism.

It can be represented by:

W_t = W₀ e^rt

W₀ is the initial size, it can be increased in the number of cells, weight or height.

W_t is the size after time ‘t’

r is the growth per unit time or also referred to as efficiency index.

e is the base of the natural logarithms (2.71828).

Most of the living organisms follow the sigmoid curve of growth, e.g. cells, tissue and organs of plants.

Condition of Growth

• Water is essential and also required for enzymatic activity. Turgidity helps in growth.
• Oxygen is required for respiration and metabolism of organic compounds to release energy required for growth.
• Macronutrients and micronutrients are required as an energy source and for the synthesis of protoplasm.

Differentiation, Dedifferentiation and Redifferentiation

Differentiation is when the cells have stopped dividing and are beginning to mature and perform special functions. For example, to form tracheids (elongated cells that carry water in the xylem), the cells lose their protoplasm. They also develop strong, elastic cell walls to carry water across long distances.

Dedifferentiation is the phenomenon where differentiated cells that have lost their ability to divide, regain the capacity to divide under specific conditions. Example – fully differentiated parenchyma cells can go back to their earlier meristem form and divide.

Redifferentiation is the phenomenon where dedifferentiated cells divide and once again produce cells that can no longer divide but mature to perform specific functions. Example – the meristems obtained after dedifferentiation (described above) can divide and again produce cells that stop dividing but go on to mature.

Plant Development

Development refers to growth as well as differentiation. The development includes all the phases of the lifecycle from seed germination to senescence. Development is controlled by:

• Intrinsic Factors: These include genetic as well as hormonal control.
• Extrinsic Factors: Environmental factors like oxygen, temperature, water, nutrients, etc.

Plant Growth Regulators

Growth regulators are chemical substances, other than naturally produced hormones, which promote, inhibit or modify growth and development in plants. They are chemical compounds and found naturally in plants. They are also synthesised commercially and used in agricultural practices. They are known as plant hormones or phytohormones. They are derivatives of adenine (kinetin), carotenoids (ABA), terpenes (GA3) and indole compounds (auxins). They are present in a very low concentration and act as chemical signals between cells.

Auxin

Auxin is a growth promoter, generally produced by the growing apex of stem and root of the plants. It helps in the elongation of shoot and root tips behind apical meristem. The naturally produced auxins is Indole-3-Acetic Acid (IAA). They are also produced by chemical synthesis, which show same physiological responses like Auxin. Some of the synthetic auxin are Indole-3-butyric acid (IBA), 2,4- Dichlorophenoxy Acetic Acid (2,4-D), and Naphthalene acetic acid (NAA).

Functions of Auxin are:

• It promotes cell elongation.
• It delays fall of leaves. (leaf abscission)
• Induce parthenocarpy, i.e. formation of seedless fruits, e.g. Tomatoes
• Promote flowering, e.g. Pineapples
• It suppresses the growth of lateral bud. If the tip of a plant is removed, the lateral branches begin to grow; In most of the plants apical bud suppresses the development of lateral buds. This is called apical dominance.
• NAA (Naphthalene acetic acid) is used for preventing fruit drop in apples before they are ripe.
• 2, 4-D (2, 4-dichlorophenoxy acetic acid) acts as a dicot weedicide.

Gibberellins

Gibberellins are the plant growth regulators involved in regulating the growth and influencing different developmental processes which include stem elongation, germination, flowering etc. They are denoted as GA1, GA2, GA3 and so on. Gibberellic Acid is the most common one.

Functions of Gibberellins are:

• It breaks dormancy of seeds and buds.
• It helps in elongation of stems in genetically dwarf plants.
• It induces parthenocarpy. (Formation of seedless fruits without fertilization)

Cytokinins

Cytokinins have specific effects on cytokinesis and were discovered as kinetin (a modified form of adenine, a purine) from the autoclaved herring sperm DNA. The most common forms are zeatin, kinetin, etc. They are mainly made in the roots.

Functions of Cytokinins are:

• Stimulates cell division, cell enlargement and cell differentiation.
• Prevent aging of plant parts.
• Inhibit apical dominance and help in growth of lateral buds into branches.

Ethylene

Ethylene is a gaseous hormone. It is found in ripening fruits, young flowers and young leaves.

Functions of Ethylene are:

• It induces ripening of fruits.
• It promotes senescence and abscission of leaf, and flowers.
• In cells it only increases the width not the length.

Abscisic Acid (ABA)

It is also referred to as stress hormone or dormin. It works like a general plant growth inhibitor. Abscisic acid is formed at the terminal buds of the top of the plant or in the roots of the plants.

Functions of Abscisic Acid are:

• It induces dormancy of buds and seeds as opposed to Gibberellin, which breaks dormancy.
• It promotes the senescence of leaf, i.e., fall of leaves happen due to abscissic acid.
• It inhibits seed germination and development.
• It causes closing of Stomata.

Photoperiodism

Photoperiodism is the effect of photoperiods or day duration of light hours on the plant’s growth and development, especially flowering. Flowering plants are classified into the following categories, based on their flowering pattern in response to light:

• Short day plants: Flowering is initiated on the exposure of light for a shorter duration
• Long day plants: Flowering is initiated on the exposure of light for a longer duration
• Day-neutral plants: Flowering does not depend on the duration of light exposure

Brassinosteroids

Brassinosteroids (BRs) are a class of polyhydroxylated steroidal phytohormones in plants with similar structures to animals’ steroid hormones. Brassinosteroids regulate a wide range of physiological processes including plant growth, development and immunity.

Vernalisation

It is the process of reducing the juvenile or vegetative phase and fastening the flowering procedure by cold treatment. Meristematic cells help in perceiving the stimulus of vernalization. It reduces the vegetative period of plants and leads to early flowering. It applies to temperate plants like Rice, Wheat, Millets, etc.

Seed Dormancy and Germination

Seed germination is the return of metabolic activities and growth by the seed tissue to give rise to a new plant by the development of the embryo.

Some seeds do not germinate immediately after dispersal even if suitable conditions of growth are provided. In this period growth of the seeds remains suspended and it is said to be in the rest or dormant stage. This phenomenon is called dormancy of seeds. Seed dormancy is caused by various factors:

• Hard and impermeable seed coat.
• Chemical inhibitors, e.g. ABA, para-ascorbic acids, phenolic acids, etc.
• Immature embryo.

 

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