Module 4: Physiological Processes Affecting Crop Production PDF

LO 4. Module 4: Physiological Processes Affecting Crop Production CROP SCI 1 Principles of Crop Science WENDELL L. ULTRA, MSc., L.Agr. Instructor III (For instructional and educational purposes only. No copyright infringement intended. Republic Act No. 8293 Sec. 185.1) Concepts of Growth and Develo...

LO 4. Module 4: Physiological Processes Affecting Crop Production CROP SCI 1 Principles of Crop Science WENDELL L. ULTRA, MSc., L.Agr. Instructor III (For instructional and educational purposes only. No copyright infringement intended. Republic Act No. 8293 Sec. 185.1) Concepts of Growth and Development Plant growth is a process characterized by the irreversible change in the size of cells and organs that is a result of cell division and enlargement. Plant development is the process of progression from seed germination to maturation. Concepts of Growth and Development (cont.) Determinate: growth is called determinate when an organ or a part of or the whole of the organism stops growing after reaching a certain size, e.g., plant leaves and flowers mostly show determinate growth. Indeterminate: growth is said to be indeterminate when the cells of the organ, part, or organism continue to divide indefinitely. Plants as a whole have indeterminate growth. Concepts of Growth and Development (cont.) Growth Curve of plants (Sigmoid curve) Concepts of Growth and Development (cont.) Differentiation: the process by which undifferentiated cells transform into cells with specialized functions and distinct morphological and physiological characteristics. All cells in the plant body have the same genetic makeup. The only thing separating the cells of different parts or organs from each other in morphology and physiology is the way the cells undergo differentiation. Concepts of Growth and Development (cont.) Dedifferentiation: the exact opposite of differentiation. In this process, the mature and differentiated cells of the plant are stimulated under specific conditions to divide and become undifferentiated and lose all the specific characteristics they acquired previously. These dedifferentiated cells again differentiate. This is noted when the plant tissues undergo damage. Concepts of Growth and Development (cont.) Unlike animals, plants show indeterminate growth. As animals grow, when they turn into fully matured animals they stop growing. When they are growing the different parts of the animal grow until they reach a size that is determined by their genetic make-up. Plants on the other hand never stop growing. They continue to grow all through their lifespan. As young plants grow older, the growth gets Callus formation in trees restricted to their meristematic tissues. Phases of Plant Growth and Development Senescence - the condition or process of deterioration with age. Plant Movements/Crop Adaptation 1. Tropisms – the direction of the environmental stimulus determines the direction of the movement. Plant Movements/Crop Adaptation Tropisms Examples: o Phototropism (movement in response to light) o Geotropism (movement in response to gravity) o Heliotropism or Solar tracking; flat blade of the leaf is always at nearly right angle to the sun throughout the day Plant Movements/Crop Adaptation Geotropism Plant Movements/Crop Adaptation Nastic movement – triggered by an external stimulus but the stimulus direction does not determine the direction of movement Examples: oHyponasty (bending up) oEpinasty (bending down) oNyctinastic (folding of leaves in response to night) oHydronasty (folding of leaves in response to water stress) oThigmotropism (response to touch or mechanical stress) oSeismotropism (response to shaking without contact with the plant) Plant Movements/Crop Adaptation Crop Adaptation The capacity of plants to adapt to their environment enables them to survive under a wide range of changing environmental conditions: Plant Movements/Crop Adaptation 1. Morphological adaptations – presences of: Pneumatophores (breathing organs) or modified roots of certain trees growing on marshes. Modified petiole of water hyacinth as float. Plant Movements/Crop Adaptation 2. Physiological adaptations Closing of stomates Abscission of leaves in deciduous plants to reduce evaporative surface area. Abscission of some trees' branches to reduce photosynthate competition in forested areas where light penetration is limited. Cactus close their stomates during the daytime, then open at nighttime, to preserve water Plant Movements/Crop Adaptation 3. Biochemical adaptations Mutation of the target gene of glyphosate-resistant weeds. Increase heat-shock proteins when plants are subjected to sudden sub- or supra-optimal temperatures. Azolla plant with extremely reduced roots, root hairs are absent, to flow easily in the water The Law of Minimum The Law of Optima and Limiting Factors (Blackman) The law of limiting factors is the modification of Law of Minimum by Liebig The law states that, when a process is conditioned to its rapidity by several factors, then rate of the process is limited by the pace of the slowest factor (CO2, light, chlorophyll, water, temp.) The Law of Diminishing Returns A theory in economics (mostly universally applicable) that predicts that after some optimal level of capacity is reached, adding an additional factor of production will actually result in smaller increases in output. Plant Life Process Photosynthesis (PS) – is the process by which plants use the energy from sunlight to produce sugar, which cellular respiration converts into ATP, the “fuel” used by all living things. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll.  But first… What is ENERGY? a fundamental entity of nature that is transferred between parts of a system in the production of physical change within the system and usually regarded as the capacity for doing work.  But first… What is THE FIRST LAW OF THERMODYNAMICS? Energy cannot be created or destroyed, but it can change from one form to another  But first… What is THE SECOND LAW OF THERMODYNAMICS? Heat flows spontaneously from hot to cold, and entropy (disorder) increases  But first… What is light? A form of energy and electromagnetic radiation that can be perceived by the human eye. In physics, the term "light" may refer more broadly to electromagnetic radiation of any wavelength, whether visible or not. In this sense, gamma rays, X-rays, microwaves and radio waves are also light.  Plant Life Process: Photosynthesis – is the process by which plants use the energy from sunlight to produce sugar, which cellular respiration converts into ATP, the “fuel” used by all living things. The conversion of unusable sunlight energy into usable chemical energy, is associated with the actions of the green pigment chlorophyll. Photosynthesis rely on the Visible light, the Sun also produces Ultraviolet light Plant Life Process (PS) PS can be written in an overall reaction as: 6CO2 + 12H2O +light→ C16H12O6 + 6O2 + 6H2O No. of molecules of the compound Carbon dioxide + water → Glucose (sugar) + Oxygen + water Plant Life Process (PS) Leaves and Leaf Structure Plants are the only photosynthetic organisms to have leave. A leaf may be viewed as a solar collector crammed full of photosynthetic cells. The raw materials of photosynthesis, water, and carbon dioxide, enter the cells of the leaf, and the products of photosynthesis, sugar, and oxygen, leave the leaf. Think of the leaf as a solar panel. Collecting sunlight for energy. Relevant principles apply. Plant Life Process (PS) Why leaves as the main organ of PS? Typically expanded Usually held at a right angle to the incident light Has extensive internal surface and provided with an efficient vascular system for channeling the various reactants and end products of PS Provided with pigments for the absorption of light energy. Plant Life Process (PS) Cross section of a leaf, showing the anatomical features important to the study of photosynthesis: stoma, guard cell, mesophyll cells, and vein. Plant Life Process (PS) Plant Life Process (PS) 1. Diffusion Transport of CO2 from the air to the reaction site in the chloroplasts. The rate depends on the CO2 concentration in the air and in the leaf and resistance to the diffusion pathway. Plant Life Process (PS) 2. Photochemical process has an absolute requirement for light. Light Dependent Process (Light Reactions), requires the direct energy of light to make energy carrier molecules that are used in the second process. Plant Life Process (PS) Structure of a chloroplast Plant Life Process (PS) Light reactions Photosystems are arrangements of chlorophyll and other pigments packed into thylakoids Photophosphorylation is the process of utilizing light energy from photosynthesis to convert ADP to ATP. ADP – Adenosine diphosphate ATP – Adenosine triphosphate Plant Life Process (PS) Light reactions Non-cyclic photophosphorylation under light reaction Plant Life Process (PS) Light reactions Cyclic photophosphorylation under light reaction Plant Life Process (PS) Light reactions The action of a photosystem Plant Life Process (PS) Biochemical reaction (Dark reactions / Calvin cycle) o C3 pathway (Calvin – Benson cycle) o C4 pathway (Hatch – Slack) o CAM pathway (Crassulacean acid metabolism) Plant Life Process (RS) Respiration (RS) Enzyme-mediated process whereby food is broken down into CO2 and H2O with the release of energy. Source of energy for metabolic reaction Provide carbon skeleton for synthesis of other compounds Glucose is completely converted into CO2 Yield = 38 ATPs Plant Life Process (RS) 1. Glycolysis Anaerobic series of reaction Takes place in the cytoplasm where hexose sugar is cleaved and oxidized to pyruvic acid C6H12O6 → 2C3H4O3+4H glucose pyruvate Pyruvate is a three-carbon acid that is naturally formed during glycolysis, the process in which the body breaks down sugar (glucose). Plant Life Process (RS) Glycolysis Processes 1. Phosphorylation – addition of phosphate group to an organic molecule 2. Sugar cleavage – splitting of two molecules into 2 fragments 3. Pyruvic acid formation – oxidation of the fragments Plant Life Process (RS) 2. Kreb cycle – citric acid Citric acid or Tricarboxylic acid cycle Aerobic series of reactions takes place in the mitochondria. Two acetyl-CoA molecules are produced from each glucose ATP yield = 2 ATPs Plant Life Process (RS) 3. Electron Transport Chain Oxidative phosphorylation Series of enzymes found embedded in the intermediate of the mitochondria Electrons are passed along electron acceptors giving off energy in the form of ATPs Yield: o10 NADH (1 NADH = 3 ATPs) o2 FADH2 (1 FADH2 = 2 ATPs) Plant Life Process (RS) Factors Affecting Respiration 1. Age – young tissue respires stronger than old one. Tissues undergoing metabolic activities respire more than resting tissues. Plant Life Process (Transpiration) Definition Loss of water vapor from the aerial parts of the plants through the stomata. Loss of water from plant leaves by evaporation oWater is lost in a gaseous state or water vapor Plant Life Process (Transpiration) Types 1. Lenticular transpiration Loss of water through the lenticels Percentage loss = 0.1% Substantial loss during winter In fruits, this type is also significant Plant Life Process (Transpiration) Types 2. Cuticular transpiration Loss of water through the cuticle/cutins Percentage loss = ~3-10% 3. Stomatal transpiration Loss of water through the stomata Percentage loss = ~90% Plant Life Process (Transpiration) Data on daily water loss Tropical palm = 500 liters/day Corn plant = 3-4 liters/day o 99% of the water absorbed by a corn plant during its life cycle is lost through transpiration Tree size dessert cactus = 25 ml/day Plant Life Process (Transpiration) If the plant needs water for photosynthesis, why is water coming out of the stoma? Importance 1. Has a cooling effect Counters the heat effect of the sun on the whole shoot system Can lower the temperature of a leaf compared with the surrounding air o Can cool a crop canopy 4-8OC below ambient temperature Prevent the leaf from reaching temperatures that could denature various enzymes Plant Life Process (Transpiration) Importance 2. Transpiration stream draws nutrients up the plant from the root zone to the shoot Plant Life Process (Transpiration) Phenomena that drive transpiration 1. There is a continuum of water that goes all the way from the roots, through the vascular system (xylem) of the plant to the stomata Because water is polar, it adheres (adhesion) to the xylem and hydrogen bonds keep the molecules held together (cohesion) in a continuum Plant Life Process (Transpiration) Phenomena that drive transpiration 2. The stomata naturally allows water to evaporate What controls the closing and opening of the stomates (Stomatal Mechanism)? Opening and closing of the stomate is facilitated by the unique shape and uneven thickening of the guard cells due to changes in turgor pressure. Turgor pressure causes the guard cells to expand or contract and thereby causes the stomates to open and close The turgor pressure is primarily controlled by salt uptake and extrusion Plant Life Process (Transpiration) Phenomena that drive transpiration 3. The driving force of transpiration that moves the water from the ground to the leaves out to the atmosphere Water Potential Gradient or Vapor Pressure Gradient o This is the difference in vapor pressure between the internal spaces in the leaf and the atmosphere around the leaf Plant Life Process (Transpiration) Environmental factors that affect the Rate of Transpiration 1. Light Plants transpire more rapidly in the light than in the dark. o Because light stimulates the opening of the stomata, o Light also speeds up transpiration by warming the leaf 2. Temperature Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises. 3. Humidity When the surrounding air is dry, diffusion of water out of the leaf goes in more rapidly. Plant Life Process (Transpiration) Environmental factors that affect the Rate of Transpiration 4. Wind When a breeze is present, the humid air is carried away and replaced by drier air. 5. Soil water A plant cannot continue to transpire rapidly if its water loss is not made up by replacement from the soil, When absorption of water by the roots fails to keep up with the rate of transpiration, loss of turgor occurs, and the stomata close. This immediately reduces the rate of transpiration, if the loss of turgor extend to the rest of the leaf and stem, the plant wilts. Plant Life Process (Transpiration) Plant factors that affect the Rate Transpiration 1. Stomatal number and size More and bigger means faster or higher transpiration rate 2. Leaf surface area Greater surfaces have higher transpiration rate 3. Leaf rolling or folding Rolled/folded leaf has a lesser transpiration rate 4. Resistance in the pathway (xylem vessels) Plant Life Process (Translocation, Assimilates) Translocation and Partitioning of Assimilates What is translocation and assimilates? oTransport of assimilates from sources to sinks in plants is called as translocation. oThe products of photosynthesis that are moved around are called assimilates. Plant Life Process (Translocation, Assimilates) The location where the assimilates are produced is called the source. Sources are the area in a plant where sugars are produced or stored and the starting point of translocation. During translocation, the assimilates are moved to a location called the sink. Sinks are the areas in a plant where sugars are transported to be used or stored and the destination points of translocation. Plant Life Process (Translocation, Assimilates) Translocation occurs in the phloem tissue which consist of tube-like structure called phloem vessels. These vessels are responsible for transporting dissolved organic solutes such as sucrose and amino acids from the source to the sinks. Plant Life Process (Translocation, Assimilates) Translocation o The transport of photosynthesis (from the source to the sink), water, and inorganic elements within the plant system. Transpirational stream o Upward movement of solution from the roots through the xylem in the stem to the uppermost leaves. When are nutrients considered ESSENTIAL? 1. Element is needed for the completion of the vegetative and reproductive stages of the plant. 2. The deficiency or absence of element can be corrected only by the addition of the element in question; no other element can substitute. 3. When the element is directly involve in the nutrition of the plant and performs a specific function. Nutrient Deficiency Symptoms Nitrogen o Require in greatest amount o Constituent in cell component, including amino acids and nucleic acids o Chlorosis – yellowing of the leaves: starts from the older leaves; younger leaves may not show symptoms initially because nitrogen is mobilized from older leaves Nutrient Deficiency Symptoms Phosphorus o Integral component of important compounds of plants cells, including sugar phosphates intermediates of respiration and photosynthesis and phospholipids that make up plant membranes; component of nucleotides in DNA and RNA o Dark green coloration of the leaves o Necrotic spots o Stunted growth o Delay maturation Nutrient Deficiency Symptoms Phosphorus o Regulates osmotic potential of plant cells o Activates many enzymes involve in respiration and photosynthesis o First observable characteristics: Mottled or marginal chlorosis followed by necrosis (brown like appearance or dead tissues) at the leaf tips, margins and veins. o Curl and wrinkled leaves o Slender and weak stem o Leaf symptoms appear initially on the older leaves Nutrient Deficiency Symptoms Sulfur o Many symptoms are similar to nitrogen deficiency since nitrogen deficiency since nitrogen and sulfur are constituents of proteins. o Chlorosis starts at the younger leaves rather than mature leaves because sulfur is not easily remobilized. Many plant species occur simultaneously in all leaves. Nutrient Deficiency Symptoms Magnesium o Specific roles in the activation or enzymes in photosynthesis and respiration and synthesis of DNA and RNA. o Is also a part of the ring structure of chlorophyll molecule o Chlorosis between leaf veins occurring on the older leaves. Nutrient Deficiency Symptoms Calcium o Synthesis of new cell walls; mitotic spindle during cell division o Messenger for various plant response both environmental and hormonal signal o Necrosis of young meristem regions such as root tips, young leaves where cell division are rapid o Deformation of young leaves o Brownish and short root system o Severe stunting o Cracking and deformation of fruit and flowers Nutrient Deficiency Symptoms Iron o Component of enzymes involved in the transfer of electrons such as cytochromes o Intervenous chlorosis same as magnesium deficiency but symptoms appear on the younger leaves cause iron is not readily mobilized from older leaves  Element Soluble forms in soil Nitrogen NH4+ ; NO3- (Ammonium; Nitrate) Phosphorus H2PO4 ; HPO4 (Hydrogen phosphate) Potassium K+ Sulfur SO4- Calcium Ca2+ Magnesium Mg2+ Iron Fe2+ or Fe3+ Boron H2BO3- Manganese Mn2+ Zinc Zn2+ Copper Cu2+ Molybdenum MoO4 Chlorine Cl- Reasons for Soil Fertility Decline 1. Crop removal 2. Soil erosion 3. Conversion of nutrient to unavailable forms such as: a. Combination with other elements forming insoluble forms b. Microbial mediated transformation c. Volatilization d. Leaching Plant Reproduction Sexual – uses seeds Asexual – uses other parts of the crop except for seeds Plant Reproduction Why are seeds sexual? Seeds could contain varying genetic material from plants if cross-pollination occurs (heterozygous). Seeds underwent meiosis, which only occurs during fertilization, were sperm and egg meet Plant Reproduction Asexual parts These plant parts regenerate new roots due to adaptation to stress, hormones, external stimuli, and human interventions. These are “true-to-type”, which means the progeny (offspring) will be an exact copy of the mother plant (source).