Plant Physiology - Module 2

Module 2 Plant Physiology Chandrashekhar Azad Vishwakarma, PhD Assistant Professor Department of Natural and Applied Sciences, TERI School of Advanced Studies  Contents Plant-water relations Mechanism of stomatal movement Water and nutrient uptake Transpi...

Module 2 Plant Physiology Chandrashekhar Azad Vishwakarma, PhD Assistant Professor Department of Natural and Applied Sciences, TERI School of Advanced Studies  Contents Plant-water relations Mechanism of stomatal movement Water and nutrient uptake Transpiration Photosynthesis: mechanism and environmental influences Respiration in plants Nitrogen metabolism Biological nitrogen fixation Ammonia assimilation Plant growth regulator Physiology of flowering  Contents Plant-water relations – Water Potential – Diffusion Pressure Deficit (DPD) – Permeability – Osmosis – Turgor pressure – Wall pressure – Plasmolysis – Deplasmolysis – Imbibition – Ascent of Sap Plant-water relations Plant-water relations  Available soil water Gravitational water: fills in micropores and drain quickly. Capillary water: fills the micropores and Source: https://www.toppr.com/ask/question/water-tightly-held-to-soil-particles-is/ drains slowly. Available to plants Hygroscopic water: water that forms a thin film around individual particles. Not available to plants Source: https://www.toppr.com/ask/en-af/question/amount-of-water-soil-can-hold-against-the-pull-of/ Available soil water  Plant classification Well-developed vascular system Oldest vascular plants Source: https://letstalkscience.ca/educational-resources/backgrounders/plant-taxonomy  Plant Tissues The collection of cells performing a specific function is called tissue. Plant tissue can be grouped into plant tissue systems and each performing specialized functions. The tissue system is a functional unit connecting all organs of a plant. Based on the function, various tissues grouped together. Source: https://www.slideshare.net/mrtangextrahelp/05-plant-cells-tissues-and-organs  Plant Tissues Plant tissues Meristematic Permanent tissue tissue Apical Lateral Intercalary meristems meristems meristems Source: https://www.sciencefacts.net/plant-tissue.html  Permanent Tissues When the meristematic cells differentiate and specialize and lose their ability to divide and form nonmeristematic or permanent tissue. The Meristematic tissues transform into three types of special permanent tissue: Dermal tissue: form the outer covering of the plant (roots, stems and leaves). Functions are: Transpiration Gas exchange Defense Source: Coelho, L. R. T. (2018). Vascularization: plant decellularization and electrospinning techniques for the development of small and medium caliber blood vessels (Doctoral dissertation).  Permanent Tissues Fig: Openings called stomata (singular: stoma) allow a plant to take up carbon dioxide and release oxygen and water vapor. The (a) colorized scanning-electron micrograph shows a closed stoma of a eudicot. Each stoma is flanked by two guard cells that regulate its (b) opening and closing. The guard cells are more curved when the stoma is open compared to when it is closed. The (c) guard cells sit within the layer of epidermal cells (Source: https://bio.libretexts.org/ )  Permanent Tissues Ground tissue: comprises much of the interior of the plant and help in metabolism, storage and support. There are three types of ground tissue: Parenchyma: It is a main component of young plant organs. The basic functions of parenchyma are photosynthesis and storage. Collenchyma: Its main function is the mechanical support of young stems and leaves via turgor. Sclerenchyma: Unlike other ground tissues, sclerenchyma has secondary cell walls composed of lignin. Provide structural support to the plant. Source: https://www.britannica.com/plant/angiosperm/Ground-tissue  Vascular Tissues Vascular bundles are the component of the vascular tissue system in plants. It is also called as ‘fascicle’ They are the part of the Transport system in plants. Vascular bundle consist of two main parts: Xylem: the water and mineral conducting tissue from roots through shoots to all part of the plant. They are dead cells and have thick cell walls and also support the plant body. Phloem: transporting sugar from leaf to Source: https://www.sciencefacts.net/vascular-tissue-in-plants.html the rest of the plant. It also carry various harmones and chemicals necessary for the growth and defense of the plant. Xylem + Phloem = Vascular bundle in stems Xylem + Phloem = vascular stele in roots  Plant-Water Relations Water absorption Passive Active absorption absorption Osmotic theory Non-osmotic theory Factors affecting the water absorption: Availability of soil water Source: Modern ABC Biology Soil temperature Soil solutes Aeration of soil Transpiration  Plant-Water Relations Difference between Active and Passive absorption Character Active water absorption Passive water absorption Energy Required Not required Pressure on xylem Positive Negative Season In season when rate of transpiration is low Takes place in all seasons Transpiration Plays no role Essential Living cells Required Not required Metabolic inhibitors Stop the process Show no effect  Plant-Water Relations Over short distances, substances move by diffusion whereas water and food move over long distance through xylem and phloem called as translocation. Diffusion The movement of the molecules of gases, liquids and solutes from the region of higher concentration to the region of lower concentration is known as diffusion. Or, it is the movement of molecules from high diffusion pressure to low diffusion pressure. Diffusion pressure Source: https://www.sciencefacts.net/diffusion.html It may defined as a tendency of different particles (ions or molecules) to diffuse. Greater the concentration of diffusing particles, greater is the their diffusion pressure and vice- versa. The diffusion pressure of pure solvent is maximum as compared to the same solvent in solution. Diffusion play very important role in gaseous exchange during photosynthesis and respiration.  Plant-Water Relations Permeability It is the degree of diffusion of gases, liquids and dissolved substances through a membrane. Membranes are of the following three types: Permeable: allow free movement of water and solutes into interior and exterior of the cell. Eg. Cell walls in plant cells. Impermeable: prevent diffusion of water and solutes into the protoplasm of cell. Eg. Cuticle layer of leaf. Semipermeable: membranes are very much alive and selective in nature. Allow solvent on one side to move freely but at the same time restrict the movement of solutes. Source: https://www.labxchange.org/library/items/lb:LabXch It is also called differentially permeable or ange:536819f8:lx_image:1 selectively permeable. Eg. Fish and animal bladders, egg membrane, plasma membrane of cell.  Plant-Water Relations Osmosis Osmosis is a special type of diffusion of a liquid. It is a migration of solvent from hypotonic solution (lower concentration) to hypertonic solution (higher concentration) through a semipermeable membrane to keep the concentration equal. Types of Osmosis: Exosmosis: water moves out of the cell due Source: https://www.sciencefacts.net/osmosis.html to hypertonic solution (higher concentration) Endosmosis: water enters the cell due to hypotonic solution (lower concentration) Three types of solution: Hypertonic solution Isotonic solution Hypotonic solution Source: https://brainly.in/question/31166240  Plant-Water Relations Osmotic pressure Osmotic pressure of a solution is the pressure which must be applied to it in order to prevent the passage of solvent due to osmosis. Or Osmotic pressure is that equivalent of maximum hydrostatic pressure which is produced in the solution, when this solution is separated from its pure solvent by a semipermeable membrane. The osmotic pressure (π) or osmotic potential (ΨS) or solute potential are numerically equal but opposite forces. Ψs = - π The hydrostatic pressure developed Source: inside the cell on the cell wall due to https://www.labxchange.org/library/ite ms/lb:LabXchange:fb8910d2:lx_image:1 endosmosis is called turgor pressure.  Plant-Water Relations Diffusion Pressure Deficit (DPD) Or Suction Pressure Diffusion pressure and Diffusion pressure deficit term was coined by B.S. Meyer in 1938. DPD was described by the term suction pressure by Renner (1915). Pressure exerted by diffusing particles is called diffusion pressure. When the solute particles are added, the diffusion pressure of the solution gets lowered. The amount by which the diffusion Fig: Change takes place during the uptake of water (Source: Modern ABC Biology) pressure of a solution is lower than that of its pure solvent is known as diffusion pressure deficit.  Plant-Water Relations Interrelationship of DPD, OP and TP (WP) Water enter into the cell TP of cell is increased Cell wall exert equal and opposite WP against TP Fig: Change takes place during the uptake of water (Source: Modern ABC Biology) Pressure responsible for entry of water = OP-TP (As WP=TP) DPD = OP-WP  Plant-Water Relations Interrelationship of DPD, OP and TP (WP): Example Suppose plant cell with OP = 10 atm, immersed in pure water In the beginning, TP inside cell is zero means, DPD = OP = 10 atm Water enter into the cell, TP increases, cell wall develop equal and opposite WP Fig: Change takes place during the uptake of water (Source: Modern ABC Biology) At equilibrium, TP = 10 atm and DPD = zero DPD = OP – TP = 10 – 0 = 10 (when flacid) = 10 – 10 = 0 (when turgid)  Plant-Water Relations Interrelationship of DPD, OP and TP (WP) Two aqueous solution with different OP, separated by semi-permeable membrane, then DPD tend to equate. Cell to cell movement of water depends upon the DPD not on OP and TP Example: OP of Cell A and B are same but DPD in cell B > cell A then water moves from A to B Example 2: TP is same for cell C and D Fig: Cell with different OP, TP and DPD (Source: Modern ABC Biology) but DPD of C > D then water will move from D to C. If DPD will become same in both the cell, there will be no further movement.  Plant-Water Relations Importance of Turgor pressure and Osmosis Plants live and grow normally due to turgidity in cells and turgidity in plants which depends upon osmosis. The rigidity of plant organs is maintained by turgidity caused due to endosmosis. Turgor pressure leads to cell enlargement in meristematic cells. Leaves remain erect and expanded due to turgidity and do not wilt. Turgidity provides mechanical strength to non—woody tissues of plants like Zea mays (maize), Saccharum oficinarurrm (sugarcane) and Musa paradisiaca (banana). Opening and closure of stomata occurs due to osmosis. Cell to cell movement of water occurs due to osmosis. Water is absorbed by the process of osmosis in roots.  Plant-Water Relations Water Potential The potential energy of water is called water potential. The measurement unit of water potential is pascal, Pa (1 mega pascal, Mpa = 10 bars). It is represented by Greek letter, Psi (Ψ). The chemical potential is the free energy per mole of any substance in a chemical system. Water potential (Ψw) is the difference between chemical potential of water at any Source: https://plantlet.org/concept-of-water-potential/ point in a system (µω) and that of pure water under standard conditions (µωo) can be calculated as: Where R is gas constant, T is absolute temperature (K), e is the vapor pressure of solution in the system at temp T and eo is the vapor pressure of pure water at the same temp.  Plant-Water Relations Water Potential Example: Sugar dissolved in pure water, resulting solution has lower OP (negative) than pure water. Increase in solute will produce more negative OP and hence more negative water potential too. Amount of solute, external pressure and gravity are the three factors that affect water potential. For solution, such as content of cell, water potential (Ψw) can be calculated as: Source: https://plantlet.org/concept-of-water-potential/ (Ψw) = Ψg + Ψs + Ψp Gravity potential = Ψg Solute potential = Ψs Pressure potential = Ψp  Plant-Water Relations Wilting Loss of water (transpiration) > rate of absorption = Plant wilts Incipient wilting: partial loss of turgidity does not cause visible wilting Permanent wilting: fail to regain their original state due to general loss of turgor. Temporary wilting: during Source: https://soilmoisture.wordpress.com/2019/08/16/soil-water-status-saturation- summer, the herbaceous field-capacity-and-wilting-point/ plants wilt during hot days and regain their turgidity and freshness during night, this type of wilting is called as temporary wilting.  Plant-Water Relations Plasmolysis When Plant cells kept in hypertonic solution, protoplast contract and leave a gap between cell wall and plasma membrane, this shrinkage of protoplasm from cell wall is known as Plasmolysis. And again when cell is place in hypotonic Source: https://www.sciencefacts.net/plasmolysis.html solution, protoplasm regains its original form and the process is called as deplasmolysis.  Plant-Water Relations Significance of plasmolysis It is practiced to know living nature of cell. It proves the permeability of the cell wall and the semipermeable nature of the protoplasm. Plasmolysis is a vital process as it explains the phenomenon of osmosis. It is used to preserve meat, jelly etc. as their salting kills bacteria by plasmolysis. Source: https://www.sciencefacts.net/plasmolysis.html It is used to determine the osmotic pressure of the cell.  Plant-Water Relations Imbibition Imbibition is the phenomenon of absorption of water or any other liquid without forming a solution. Plant cell contain many hydrophilic colloids (imbibants) such as protein, cellulose, starch etc. Material like seeds and wood when contact with water, imbibe and swell up. The liquid (usually water) which is imbibed is called as imbibate. During imbibition, water molecules get tightly adsorbed and become immobilized. Source: https://www.aquaportail.com/dictionnaire/definition/13131/i They lose most of their kinetic energy in the mbibition form of heat. It is called as heat of wetting or heat of hydration.  Plant-Water Relations Long-distance transport of water Diffusion is a very slow process and it takes 2.5s to cross 50 µm cell. So, with this process, it can take 32 years to move over 1m distance. So long-distance transport cannot be possible through diffusion alone. So in large multicellular complex organisms materials usually move by mass or bulk flow system due to pressure difference at two points. Such type of movement is called as translocation. Plants absorb water through its entire surface i.e. roots, stem and leaves but mainly through roots. Root hairs are delicate structures and last not more than two days. They are extensions of the epidermal cells. Fig: Area of root involved in absorption and translocation of water  Plant-Water Relations Long-distance transport of water Pathways of water movement in root I. Apoplast pathway: water moves exclusively through the cell wall. II. Symplast pathway: water moves from one cell to another cell through plasmodesmata. III. Transmembrane pathway: Water passes through cortex and crosses at least two membranes from each cell in its path. Water may also enter through tonoplast surrounding the vacuole i.e. also called as vacuolar pathway. Fig:  Plant-Water Relations Water Movement up a Plant (Ascent of Sap) The upward movement of water from the root towards the top of the plant is called ascent of sap. Path of Ascent of Sap Fig: Eosine test (a) The upward movement of water takes place through xylem. It can be proved by following two experiment: a. Movement of dyes b. Ringing experiment Fig: Ringing experiment (b)