Plant Physiology PDF

Plant Physiology For. Joy Hilel C. Pantalone Plant Physiology  It is a science that deals and study about the different physiological processes and functions in plants. Plant Functions 1.Capture energy and assimilate carbon 2.Distribute nutrients and water 3.Grow and develop...

Plant Physiology For. Joy Hilel C. Pantalone Plant Physiology  It is a science that deals and study about the different physiological processes and functions in plants. Plant Functions 1.Capture energy and assimilate carbon 2.Distribute nutrients and water 3.Grow and develop 4.Respond to the environment 5.Reproduce Tree growth  Is the increase in size and numbers of the vegetative structures. Vegetative Structures  Leaves  Stems  Roots Reproductive Structures  Flowers/Cones  Fruits  Seeds  Where does growth occur?  Growth occurs in meristems.  A meristem – is a tissue containing cells that have the capacity to divide to make new cells.  In general, during growth, CELLS DIVIDE, CELLS ELONGATE, and CELLS Differentiate into structures such as roots and shoots.  Meristems can also produce new meristems called PRIMORDIA SHOOT GROWTH  Shoots elongate or grow in height at the tips of the branches  Apical meristems are located in the terminal buds at the tips of the branches.  Cells at the apical meristem divide, elongate and differentiate in distinctly visible steps: 1. The bud at the tip of the branch opens, 2. Leaves emerge and enlarge, and, 3. The area between the leaves expands (i.e., the stem grows). Lateral (side) buds grow in the same way but often these are dormant and do not grow until they are released after such activities as pruning. Leaf growth  On the surface of the apical meristem in the bud, a new meristem is formed, known as :  LEAF PRIMORDIUM – where cells divide and grow into a leaf.  Then a new bud primordium is formed at the base of each leaf stem, known as AUXIALIARY BUD has the capacity to become a branch, but may lie dormant for many years.  Diameter growth  Between the wood and bark is a thin layer of dividing meristematic cells called the vascular cambium.  The cambium divides producing new wood towards the inside and bark on the outside. Two types of new growth will occur:  a) Xylem - carry water and minerals up from the roots to the leaves. The old wood in the middle is the heartwood - while dead, it supports the weight of the tree.  b) Phloem - carry sugars and other materials to the growth and storage locations of the tree.  c) New layers of wood are added each year between the bark and the previous year’s wood. These are called growth or annual rings and may be used to age a tree.  d) Annual rings vary in size and thickness according to the season that they are formed.  e) Cells that are produced in the spring are larger with thinner cell walls. These are the light-colored rings, and the wood is called “early” or “spring” wood  f) Cells produced in the summer are smaller, and this “late” or “summer” wood has a higher density and darker color.  g) All woody trees have an outer bark that constantly renews itself and protects the tree from pest attacks and environmental impacts such as fire and mechanical injury.  h) The bark thickens as the tree aged and is influenced by the activity of the cork cambium PROCESSES: ABSORPTION (Soil – Roots) Adsorption  is the process in which atoms, ions or molecules from a substance (it could be gas, liquid or dissolved solid) adhere to a surface of the adsorbent ABSORPTION is the process in which a fluid is dissolved by a liquid or a solid (absorbent).  ABSORPTION  Plants take up water and essential minerals via their roots and thus need a maximal surface area in order to optimize this uptake  The monocotyledon root has a fibrous, highly branching structure which increases surface area for maximal absorption  The dicotyledon root has a main tap root which can penetrate deeply into the soil to access deeper reservoirs of water and minerals, as well as lateral branches to maximize surface area  The root epidermis may have extensions called root hairs which further increase surface area for mineral and water absorption  These root hairs have carrier proteins and ion pumps in their plasma membrane, and many mitochondria within the cytoplasm, to aid active transport. Pathways By Which Minerals Move From The Soil To Roots  Diffusion: Movement of minerals along a concentration gradient  Mass Flow: Uptake of mineral ions by means of a hydrostatic pressure gradient  – Water being taken into roots via osmosis creates a negative hydrostatic pressure in the soil  – Minerals form hydrogen bonds with water molecules and are dragged to the root, concentrating them for absorption  Fungal Hyphae: Absorb minerals from the soil and exchange with sugars from the plant (mutualism)  Process of Mineral Absorption  Minerals enter the root by active transport.  Minerals that need to be taken up from the soil include K+, Na+, Ca2+, NH4+, P4O3- and NO3-  Fertile soil invariably contains negatively charged clay particles to which positively charged minerals may attach  Root cells contain proton pumps that actively pump H+ ions into the surrounding soil, which displaces the positively charged minerals allowing for their absorption (the negatively charged minerals may bind to the H+ ions and be reabsorbed with the proton)  Mechanism of Transport  a. Active transport – involves symplast movement where the solutes enter first the cell sap and then passes from one cell to another.  b. Passive transport – involves apoplastic movement where the solutes move through the free spaces of the root. CONDUCTION : Roots - Leaves  From the root hairs, solutes are moved to the vascular cylinder via active transport.  Solutes from the vascular cylinder are then conducted via the Xylem as can be explained by the following theories:  Capillarity Theory. According to this theory, water is translocated because water molecules adhere to the surfaces of small, or capillary, tubes. This adhesion causes water to somewhat “creep” upward along the sides of xylem elements.  Atmospheric Pressure Theory. This is based on the observation that normal atmospheric pressure is able to push water in a tube upward up to about 10.4 meters. This is demonstrated by first filling with water a long tube with one end closed. This tube is then placed with its open end down in a tub of water. The force of gravity will tend to pull the water in the tube downward, but atmospheric pressure exerted on the water surface in the tub will push it up. These opposing pressures equilibriate when the height of the water column in the tube is 10.4 m  Cohesion-Tension or Transpiration-Cohesion Theory. This explains that the upward movement of water is mainly due to the creation of a negative force or tension attributed to the continuous evaporation of water at the surfaces of leaves in the process of transpiration. As molecule after molecule of water evaporates through the stomata, it creates a pulling action on the next molecules of water in the transpiration stream. This pulling force, otherwise called transpiration pull, is strong enough to overcome the force of gravity which is responsible for the tendency of water to move  TRANSPIRATION – is the process by which moisture is carried through plants from roots to small pores on the underside of leaves, where it changes to vapor and is released to the atmosphere.  PROCESSES: Photosynthesis  Photosynthesis - is the process of converting light energy to chemical energy and storing it in the bonds of sugar.  Plants are autotrophs – which means they can manufacture their own food (sugar).  Plants need only the following materials to manufacture sugar:  light energy  Carbon dioxide  water  The overall chemical reaction involved in photosynthesis is:  6CO2 + 6H2O (+ light energy) → C6H12O6 + 6O2.  Photosynthesis takes place in the chloroplast, specifically using chlorophyll - the green pigment that captures light through the stomata (stomates) of the leaves.  The chloroplast is located in the mesophyll cells of the leaves.  Structure of the Chloroplast  the outer and inner membrane  Inter membrane space  Stroma  thylakoids, stacked in grana  STAGES OF PHOTOSYNTHESIS A. Light Reaction-  happens in the thylakoid membrane and converts light energy to chemical energy.  Chlorophyll and several other pigments such as beta-carotene are organized in clusters in the thylakoid membrane and are involved in the light reaction.  Each of these differently-colored pigments can absorb a slightly different color of light and pass its energy to the central chlorphyll molecule to do photosynthesis.  Two Forms of Energy Produced 1. Adenosine Triphosphate ( ATP) 2. Nicotinamide Adenine Dinucleotide Phosphate ( NADPH) B. DARK REACTION  takes place in the stroma within the chloroplast, and converts CO2 to sugar, utilizing the energy formed from light reaction.  involves a cycle called the Calvin cycle in which CO2 and energy from ATP are used to form sugar.  glyceraldehyde 3-phosphate - first product of photosynthesis, a three-carbon compound.  C3 plants – all plants that directly process sugar into a Calvin cycle.  During hot weather, the amount of water that evaporates from the plant increases.  To counter act this process, plants have to close their stomates which lead to low absorption of carbon dioxide, hence Photosynthesis rate decreases.  If the plants continue to attempt fixing CO2 while its level in the leaf becomes low ( 50 ppm), Photorespiration occurs.  To prevent photorespiration, two specialized biochemical additions have been evolved in the plant world:  a.C4 plants- have a special enzyme that can work better, even at very low CO2 levels, to grab CO2 and turn it first into oxaloacetate, which contains 4 carbons and put it into the Calvin cycle. Ex. crab grass, corn, sugar cane  b. CAM plants (crassulacean acid metabolism). These are plants from CRASSULACEAE, ex. Cacti and pineapple. Their stomata are closed during day time. At night when they can open their stomates and take in CO2, these plants incorporate the CO2 into various organic compounds to store it. In the daytime, when the light reaction is occurring and ATP is available (but the stomates must remain closed), they take the CO2 from these organic compounds and put it into the Calvin cycle.  Factors Affecting Photosynthesis  1.Light  2.Mutual shading of leaves - the more number of leaves shading each other the slower is the rate of photosynthesis.  3.Photoperiod - Trees will accumulate more total photosynthate if exposed to a long day than if exposed to short one.  4.Temperature  5.Carbon dioxide - the higher the concentration of carbon dioxide, the greater is the rate of photosynthesis.  6.Soil fertility - Nitrogen and magnesium are components of chlorophyll molecule, and a deficiency of either inhibits photosynthesis.  7. Age of leaves – young leaves have low photosynthesis due to small leaf area. Photosynthesis increase with age up to a critical level of maturity and then declines with age.  8. Stomatal distribution and behavior - the more dense the stomata in the leaf, the higher the intake of carbon dioxide, thus increase photosynthetic rate.  9. Chlorophyll content - photosynthesis in leaves with an abnormally light green color usually is less than that in leaves with a -end-