Chapter III Inorganic Nutrients of Plants The main teaching content: The importance of water in the plant vital movement, water potential,water transport and distribution in plants, physiological significance and influence factors of transpiration. The absorption characteristics of plant cells and descending axis in water and mineral elements, as well as the similarities and difference in absorption water and mineral elements, assimilation of mineral elements in plant, the physiological basis of reasonable rrigation and indicator of reasonable fertilization. Focus and difficulties: the concept and components of water potential is difficult, with a focus on water-absorbing mode by water plant cells and the descending axis, the mechanism of stomatal movement, as well as water-saving agriculture; the absorption characteristics of descending axis in water and mineral elements, as well as the similarities and differences points of absorption. Teaching methods: 5 hours for classroom teaching, three hours for experimental. Teachers taught absorption of mineral elements and water using multimedia and animation. Section I water metabolism in plant First, absorbing water in plant roots (1) The exist form of soil moisture Soil moisture can be divided into three types by physical state: 1capillary water:which is water held against the force of gravity, in pores of the soil. 2Hygroscopic water is physically bound to the soil particles and is unavailable to plants. 3Gravitational water drains out of the pore spaces after a rain. If drainage is poor, it is this water that interferes with normal plant growth. In addition to water use or not by plants can be divided into available water and not available water. (2) The location of root absorbent water: mainly in the root tip of about 10 cm, the specific are the region of elongation and the region of maturation adjacent to. It can be said that is the root hair region. (3) mode of absorption water: active and passive water absorb active transport: The plants absorb and retain these solutes against adiffusion (or electrical) gradient through the expenditure of energy. This process is called descending axis metabolic activities cause ion uptake and transport, resulting in water potential difference of the internal and external, so that the water according to the decline in water potential gradient, from the environment through the epidermis, cortex to central cylinder catheter and upward transport. the roots life activity produce pressure upwarding the water from the roots. Note: Bleeding and guttation relate with the root metabolism, metabolism strong, robust growth, bleeding and guttation obviously r. (4) the water absorption mechanism: superior extremity motivity (passive absorption) -- transpiration pull;
Inferior extremity motivity (initiative absorption) - root pressure; Intermediate motivity - cohesive force and adhesive power between water molecules (5) The edaphic conditions impact on roots absorption 1, soil ventilation: good ventilation is conducive to root absorption; 2, soil temperature: in a suitable temperature range, the higher the soil temperature, the more roots absorb; 3, soil solution concentrations: water potential in root cell less than that in soil is conducive to water absorption. Second, the plant transpiration 1. Concept: transpiration (trans-puh-ray shun) loss of water in vapor form; most transpiration takes place through the stomata.the water loss from the plant into the atmosphere in the way of two kinds, one way by liquid to escape, such as guttation; another way to escape as gas, that is, transpiration, which is the main form of plant water loss. 2. Physiological significance of transpiration (1) Transpiration is a major driving force for water absorption and transportion; (2) Transpiration promotes the absorption and transport of minerals; (3) Transpiration reduced the temperature of plants and leaves; (4) The normal transpiration, stomata opening is conducive to fix CO2 for photosynthesis. 3. Transpiration organs: leaves (mainly), stems and other organs in up-ground part. 4. Transpiration ways: stomata transpiration (main), horny transpiration, lenticular transpiration. All parts of the plant have the potential to evaporate water. When the plants young surface exposed up-ground can all transpiration;after woody plants grow up, the lenticel in stem and shoot can transpiration, called lenticuler transpiration. But lenticular transpiration is only 0.1 percent of the full-transpiration. so most of transpiration of plant through the leaves. There are two means for leaf transpiration: (1) transpiration through corneum called cuticular transpiration, (2) transpiration through stomata called stomatal transpiration. Stomatal transpiration is the main form of plant leaf transpiration. 5. Stomatal movement Stomata is the main aisle for a plant leaf exchanging gas with the outside.the gas diffuse through the stomata are O2, CO2 and water vapor. In light, CO2 absorption for plant photosynthesis through stomata, so their stomata must open, but also opening stomata in transpiration inevitably, stomata can adjust its opening size according to environmental conditions so that plants can access to the most CO2 while losing least moisture. When stomatal transpiration strong leaves in water deficit or inadequate water supply by soil, stomata aperture reduce and eventually completely shut down when the supply is good, stomata opening, as a mechanism to regulate plant water loss in transpiration. (1) stomata structure characteristics: Cell wall thickening uneven; cell organs are different with epidermal cells, its
bulk smaller than epidermal cells, and without plasmodesmata with epidermal cells. (2) Mechanism of stomata opening and closing: The mechanisms of stomatal movement, mainly the three doctrines following. amylon and sugar translation theory In light, photosynthesis consumed CO2, thus guard cells cytoplasm ph increase to 7, starch phosphorylase catalysis positive reaction that hydrolysis starch to sugar, osmotic potential of guard cells decline, water potential is lower, and drawing moisture from the surrounding cells, guard cell enlargement, thus stomata opening. In the dark, guard cells stop photosynthesis but respiration are still on, CO2 accumulation then ph dropped to about 5, starch phosphorylase catalytic reverse reaction that translate sugar to starch, solute particles decreased in the number, then cells osmotic potential increased, water potential also increased,cell water loss, turgor pressure disappear, stomata closed. Potassium ions accumulation theory Malic acid metabolism theory 6, Metry of transpiration Quantitative indicators commonly used in transpiration are: Transpiration rate: in a certain period of time, the dissipation amount of water in unit area known as transpiration rate, also known as transpiration intensity. Transpiration ratio: by the consumption of 1 kg water produce the number of grams of dry matter, or that the dry matter cumulative amount in a certain period of time compare to the same period of the water consumed known as transpiration rate or transpiration efficiency. Transpiration coefficient: the consumption of water (g) when manufacture 1 g dry matter called transpiration coefficients (or water requirement), which is the reciprocal of transpiration rate. 7, external affecting factors of transpiration (1) Light: The light promote stomata opening, transpiration increase. (2) Water Status: adequate moisture make for stomatal opening, excessive moisture has made the stomata closed. (3) Temperature: opening of stomata increase with the temperature increasing, but high temperatures make increase water loss, stomatal closed. (4) Wind: breeze profit to transpiration, strong winds reduced transpiration. (5) CO2 concentration: lower CO2 concentration promote stomata opening, transpiration increase. (6) Transpiration indicators: transpiration intensity (transpiration rate), transpiration efficiency, transpiration coefficients 8, ways to reduce transpiration: (1) Reduce transpiration area; (2) improve the ecological environment of plants; Antitranspirant application. Third, the moisture transportation in plants 1. Transport (1) the channels of moisture from absorb to transpiration out:
Soil solution - the root - cortical parenchyma cells - catheter and tracheid of xylem - the stem or leaf of xylem - membrane end cell in leaves xylem- the cell wall of mesophyll cells near substomatic cavity - transpiration (2) Organization classification according to the appearance of plant protoplasts: apoplast, non-protoplast: the part without protoplasts; (3)Two ways of transporting water in the stem, leaf cells: Through dead cells: long-distance transport Through living cells: suitable for short distance transport 2, the momentum of water up-warding along catheter or tracheid (1) The momentum of water up-warding along catheter or tracheid: root pressure, transpiration pull (mainly power). (2) Cohesion theory: guarantee the water column in catheter continuous. When water evaporates from the mesophyll cells in a leaf and diffuses out of the stomata (transpires), the cells involved develop a lower water potential than the adjacent cells. Because the adjacent cells then have a correspondingly water potential, replacement water moves into the first cells by osmosis. This continues across rows of mesophyll cells until a small vein is reached. Each small vein is connected to a larger vein, and the larger veins are connected to the main xylem in the stem, and that, in turn, is connected to the xylem in the roots that receive water, via osmosis, from the soil. As transpiration takes place, it creates a pull, or tension, on water columns, drawing water from one molecule to another all the way through an entire span of xylem cells. The cohesion required to move water to the top of a tall tree is considerable, but the cohesive strength of the water columns is usually more than adequate. Fourth, the physiological basis of reasonable irrigation 1. Water needing regularity Plant seedlings demand less water, with plant growth, trophont augmentation, water demand increase, to the period vegetable growth transite to reproductive growth, the water demand get to maximum, which will gradually reduce. 2. Irrigation principles: timely, adequate amount, high quality, high efficiency 3. Irrigation optimum period: moisture critical period, the largest water demand amount period. 4. Irrigation indicators (1) Soil indicators: field capacity below 60% -80% to irrigation. (2) Morfhous indicators: young stems and leaves wilting; stems and leaves redden, plant growth rate decrease. (3) Physiological indicators: cell sap concentration, osmotic pressure of leaves, water potential of leaf and stomata openning, stomatal resistance. 5. Water requirement of irrigation: to estimates through transpiration coefficients and field evaporation amount. 6. Irrigation ways: broad irrigation and furrow irrigation, sprinkler irrigation, drip irrigation. 7. The reasons for irrigation increasing production: physiological effects, ecological effects.
Section II mineral nutrition in plant First, mineral elements which are needed by the plants and its role The process plant uptaking, transporting and assimilating of mineral elements is called as mineral nutrition. There are 17 kinds of elements which are recognized as essential to plant are: C, H, O, N, P, S, K, Ca, Mg, Cu, Zn, Mn, Fe, Mo, B, Cl, Ni. Macronutrients, which are used by plants in greater amounts and constitute from 0.5% to 3.0% of the dry weight of the plant; micronutrients, which are needed by the plant in very small amounts, often constituting only a few parts per million of the dry weight. These nutrients elements have three standards which defined by the International Plant Nutrition Institute as identified standard for necessary elements.essential elements have three physiological role in plants: 1 as components of plant structural material; 2 as regulator in plant life activities, participate in enzyme activities, affect plant metabolism; 3 take electrochemical action, participate osmotic adjustment, stabilize colloidal and neutralize charge, and others. The lack of essential elements interfere plant growth and development and affect agricultural production. To ensure agricultural production, accurate diagnosis and the right remedy is necessary. There are three ways to diagnosis elements lack, namely chemical analysis diagnostics, disease diagnostics and joined diagnostics. Some nutrients can move after enter in plant, can be recycle, so deficiency appears in the old leaves first, these elements are: N, P, K, Mg, Zn, and some nutrients can not move after enter in plant, can t be recycle, so deficiency appears in young leaves first, these elements are: Ca, B, Cu, Mn, Fe, S. Some elements directly or indirectly involved in the biosynthesis metabolism of chlorophyll, the lack of these elements chlorophyll biosynthesis will be blocked, cause chlorosis, these elements are: N, Mg, Mn, Fe, S, and so on. Second, uptake of mineral elements by plant Plant essential mineral elements in the soil exit as three forms: soil solution, adsorbed on the surface of soil colloids, soil insoluble salts. Plant roots can use all the three forms salt. Soil solution is the main mode for the use of plant roots. (A) uptake of mineral elements by plant cell The methods for plant cells absorbing mineral elements: active absorption, passive absorption and pinocytosis. Active absorption is the principal way to absorb mineral elements by plant cells. 1, passive absorption is the process that not consume metabolism energy and through diffusion or other physical process. O2, CO2, NH3, and other gas molecules can pass through the lipid bilayer membrane go into the cells in a simple diffusion. The power for diffusion is the difference of substances chemical potential on both sides of the membrane. And the passive absorption of charged ions is conduct along the electrochemical potential gradient, not consume metabolism energy. And through diffusion or others can not pass through the lipid bilayer membrane, the diffusion needs the help of transfer protein, so called assisting diffusion or facilitated diffusion, the diffusion power is electrochemical potential difference of both sides of the membrane.
2. Active absorption refers to the process using of metabolic energy opposite to concentration gradient absorb mineral elements. Active absorption need transfer protein participation. Transfer protein can be divided to channel protein and carrier protein. Carrier protein is divided into one-way carrier protein, syntropy carrier protein and anti-way carrier protein. Ions transport transmembrane through ion pump (proton pump and calcium pump). 3, Pinocytosis is the process to transfer minerals into the cell which adsorbing on the plasma membrane through the pack. Pinocytosis is the non-selective absorption, macromolecular material even virus go into the cell through pinocytosis. Pinocytosis in plant cells is not very common. (B), mineral elements absorption by descending axis (1) The relative absorption of mineral elements and moisture: The mechanism is different in absorption salt and water, absorbing amount is disproportionate. (2) Selective absorption of ions: that the absorption of certain ions is more, and ion absorption of some less or none absorption. (3) uni-salt poisoning and ion confrontation: the poisoning effect of cation is obvious; the poisoning effect of anionic is not obvious. In uni-salt solution adding a small amount of different metal ions with other prices, the salt poisoning phenomenon will reduce or disappear. Such interaction between ions called ion confrontation. Usually different grp metal ions in the periodic table of elements will have confrontation. Plant can grow in a certain concentration, a certain proportion of the variety salt mixture, this solution is balanced solution. This should be paid close attention to in fertilization. Absorption mineral elements by descending axis have to go through the following steps: (1) Ions are adsorbing on the surface of root cells. Cationic exchange with H + which on surface of root cells membrane, anion exchange with HCO 3 - which on surface of root cells membrane. (2) Ions go into the internal of root cells. Ions adsorbed on the surface of root cells can be absorbed through the plastid way into the xylem, or through apoplast channels diffuse into apoplast which in outside of the root endoderm. But because there are Casparian band in endoderm, ion must be transported into plastid in order to continue to go inward to the endoderm; (3) Ions go into the catheter. The ions through plastid way into the xylem, then by active or passive manner through parenchyma cells go into catheter. Third, the assimilation of mineral elements in plant Higher Plants can not fix N 2 in the air and soil NO 3 + and NH 4 is an important source of nitrogen. Inorganic nitrogen are mainly NO3 + in the soil, because NH4 + was usually oxidate into NO3 + bynitrite bacteria and nitrate bacterial, NO3 + is the main form absorb by root. Plant cells absorb ammonium salt from the soil, and then synthesis amino acids or amide. If plants absorption NO3 +, nitrate reductase catalytic nitrate reduction to ammonia, then can be used. it must be assimilation. The reduction of absorption NO3 + can happen,in the roots or in the ground part.
Fourth, transportation of mineral elements in plants The mineral elements absorpt by roots, and some were assimilation to the formation of organic compounds in roots then transport to up-ground, some still ions transport to the up-ground. The absorption of minerals by root is accompanied with transpiration stream, transporting to up-ground through xylem. The absorption of minerals by leaf is transported through phloem or xylem to the up-ground, or through phloem transport to the underground.