(4) Chapter 37

1. (4) Chapter 37 Plant Nutrition 植物營養 CO2 O2 Light H2O Sugar phloem xylem O2 H2O CO2 Minerals

2. Key Concepts • Concept 37.1: Plants require certain chemical elements to complete their life cycle • Concept 37.2:Soil quality is a major determinant of plant distribution and growth • Concept 37.3:Nitrogen(N) is often the mineral that has the greatest effect on plant growth • Concept 37.4: Plant nutritional adaptations(營養適應) often involve relationships with other organisms

3. A Nutritional Network (營養網路) • Every organism is an open system connected to its environment by a continuous exchange of energy and materials. • In the energy flow and chemical cycling that keep an ecosystem alive, plants and other photosynthetic autotrophs perform the key step of transforming inorganic compounds into organic ones. • Plants need sunlight as the energy source for photosynthesis. And to synthesize organic matter, plants also require raw materials in the form of inorganic substances: carbon dioxide (CO2), water (H2O), and a variety of minerals present as inorganic ions in the soil. • With its ramifying root system and shoot system, a plant is extensively networked with its environment----the soil and air, which are the reservoirs of the plants inorganic nutrients. • For a typical plant water and minerals come from the soil, while carbon dioxide(CO2) comes from the air. CO2 O2 Light H2O Sugar xylem phloem O2 H2O CO2 Minerals

4. Root and shoot systems of a pea seedling Figure 37.1 • The branching root system and shoot system of a vascular plant • Ensure extensive networking with both reservoirs of inorganic nutrients (無機營養) CO2 CO2 mineral H2O

5. Concept 37.1: Plants require certain chemical elements to complete their life cycle • Plants derive most of their organic mass from the CO2 of air, but they also depend on soil nutrients such as water and minerals • Mineral nutrients H2O CO2 O2 CO2, the source of carbon for photosynthesis, diffuses into leaves from the air through stomata. Through stomata, leaves expel H2O and O2. Roots take in O2 and expel CO2. The plant uses O2 for cellular respiration but is a net O2 producer. Minerals O2 CO2 Roots absorb H2O and minerals from the soil. H2O Figure 37.2

6. Functions of water in plants • Solvent in the cell • Photosynthetic reactant • Metabolic reactant or product • Respiration • Vacuolar content for cell elongation and extension • Turgor pressure (膨壓) • Others

7. Macronutrients and Micronutrients巨量營養素與微量營養素 • More than 50 chemical elements • Have been identified among the inorganic substances in plants, but not all of these are essential (必需的/必要的) • Essential elements (必需元素) • A chemical element is considered essentialIf it is required for a plant to complete a life cycle

8. Hydroponic culture and essential elements(水耕法與必需元素) • Researchers use hydroponic culture(水耕法) to determine which chemicals elements are essential APPLICATION In hydroponic culture, plants are grown in mineral solutions without soil. One use of hydroponic culture is to identify essential elements in plants. TECHNIQUE Plant roots are bathed in aerated solutions of known mineral composition. Aerating the water provides the roots with oxygen for cellular respiration. A particular mineral, such as potassium, can be omitted to test whether it is essential. Experimental:Solution without potassium (K+) Control: Solution containing all minerals Figure 37.3 RESULTS If the omitted mineral is essential, mineral deficiency symptoms occur, such as stunted growth and discolored leaves. Deficiencies of different elements may have different symptoms, which can aid in diagnosing mineral deficiencies in soil.

9. 17 essential elements=9 macro- and 8 micrnutrients • Nine of the essential elements are called macronutrients (巨量營養素), because plants require them in relatively large amounts • C, O, H, N, S, P, K, Ca • The remaining eight essential elements are known as micronutrients (微量營養素) • Because plants need them in very small amounts • Cl, Fe, B, Mn, Zn, Cu, Mo, Ni

10.   Table 37.1 • Essential elements in plants

11. Symptoms of Mineral Deficiency (礦物質缺乏的症狀) • The symptoms of mineral deficiency • Depend partly on the nutrient’s function • Depend on the mobility of a nutrient within the plant • Chlorosis (黃化現象) • Deficiency of a mobile nutrient (移動力強的元素) • Mg • Usually affects older organs more than young ones • Drawing power (汲取力) is stronger in young organs • Deficiency of a less mobile nutrient (移動力弱的元素) • Fe • Usually affects younger organs more than older ones

12. Healthy/normal Phosphate-deficient Potassium-deficient Nitrogen-deficient • The most common deficiencies • Are those of nitrogen (N), potassium (K), and phosphorus (P) 磷缺乏 鉀缺乏 氮缺乏 Figure 37.4

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14. Concept 37.2: Soil quality (土壤質地) is a major determinant of plant distribution and growth • Along with climate (氣候) • The major factors determining whether particular plants can grow well in a certain location are the texture and composition of the soil (土壤質地與組成) • Texture (質地) • Is the soil’s general structure • Composition (組成) • Refers to the soil’s organic and inorganic chemical components

15. Texture and Composition of Soils(土壤質地與組成) • Various sizes of particles derived from the breakdown of rock (岩石) are found in soil • Along with organic material (humus腐植質) in various stages of decomposition (分解) • The eventual result of this activity is topsoil (頂層土壤) • A mixture of particles of rock and organic material

16. The A horizon is the topsoil, a mixture of broken-down rock of various textures, living organisms, and decaying organic matter. A B The B horizon contains much less organic matter than the A horizon and is less weathered (風化程度). C The C horizon, composed mainly of partially broken-down rock, serves as the “parent” material for the upper layers of soil. Figure 37.5. Soil layers or horizons (土壤分層) • The topsoil(表土/頂層土壤) and other distinct soil layers or horizons (土壤分層) • Are often visible in vertical profile(垂直剖面/斷面) where there is a road cut or deep hole

17. The availability (可利用性) of soil water and minerals • After a heavy rainfall, water drains away from the larger spaces of soil. But smaller spaces retain water because of its attraction to surfaces of clay and other particles • The film of loosely bound water is usually available to plants (與土壤結合不緊密的薄水層的水才能被根吸收) Soil particle surrounded by film of water 親水性 土壤粒子 Root hair (a) Soil water. A plant cannot extract all the water in the soil because some of it is tightly held by hydrophilic soil particles. Water bound less tightly to soil particles can be absorbed by the root. Water available to plant 土壤結合 不緊密 Air space 土壤結合不緊密 親水性土壤粒子 Figure 37.6a

18. Cation exchange in oil (土壤中的陽離子交換) • Acids (???) derived from roots contribute to a plant’s uptake of minerals when H+displaces (排擠/取代) mineral cations from clay particles (粘土粒子) 土壤粒子表面帶負電 Soil particle – – K+ K+ (b) Cation exchange in soil. Hydrogen ions (H+) help make nutrients available by displacing positively charged minerals (cations such as Ca2+) that were bound tightly to the surface of negatively charged soil particles. Plants contribute H+ by (1) secreting it from root hairs and also by (2) cellular respiration, which releases CO2 into the soil solution, where it reacts with H2O to form carbonic acid (H2CO3). Dissociation of this acid adds H+ to the soil solution. – – – – – – – Ca2+ Mg2+ Cu2+ K+ H+ H2O + CO2 HCO3– + H2CO3 H+ 1 2 Root hair Figure 37.6b

19. Soil Conservation and Sustainable Agriculture土壤保育與永續(可持續)農業 • In contrast tonatural ecosystems(自然生態系統), agriculture • (1) depletes the mineral content of the soil, • (2) taxes water reserves, and • (3) encourages erosion • The goal of soil conservation strategies (土壤保育策略的目標) • Is to minimize this damage

20. Fertilizers (肥料) • Commercially produced fertilizers • Contain minerals that are either mined or prepared by industrial processes • “Organic” fertilizers (有機肥料) • Are composed of manure (糞便), fishmeal (魚肉), or compost (堆肥)

21. No phosphorus deficiency Well-developed phosphorus deficiency Beginning phosphorus deficiency Deficiency warnings from “smart” plants • Agricultural researchers are developing ways to maintain crop yields while reducing fertilizer use • Genetically engineered “smart” plants (遺傳工程智慧植物) inform the grower when a nutrient deficiency is imminent (急迫性營養缺失) Figure 37.7

22. Irrigation (灌溉) • Irrigation, which is a huge drain on water resources when used for farming in arid regions (乾旱地區) • Can change the chemical makeup of soil • Topsoil from thousands of acres of farmland • Is lost to water andwind erosion(水與風的侵蝕) each year in the United States

23. Figure 37.8 等高線耕地 • Certain precautions (預警) • Can prevent the loss of topsoil

24. The goal of soil management (土壤管理的目標) • Is sustainable agriculture (永續農業), a commitment embracing (using) a variety of farming methods that are conservation-minded (保育理念)

25. Soil Reclamation (土壤復育) • Some areas are unfit for agriculture • Because of contamination of soil or groundwater with toxic pollutants • A new method known as phytoremediation(植物復育) • Is a biological, nondestructive (非破壞性) technology that seeks to reclaim contaminated areas • A part of bioremediation (生物復育)

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27. G A U C T • Concept 37.3: Nitrogen (N) is often the mineral that has the greatest effect on plant growth • Plants require nitrogen (N) as a component of • Proteins • nucleic acids • chlorophyll • other organic molecules

28. Atmosphere Atmosphere N2 N2 Nitrate and nitrogenousorganiccompoundsexported inxylem toshoot system 1.固氮細菌 Soil 4.脫氮細菌 Nitrogen-fixingbacteria N2 Denitrifyingbacteria H+ (From soil) 銨鹽 離子 NH4+ NH3 (ammonia) 氨 Soil NO3– (nitrate) NH4+ (ammonium) Nitrifyingbacteria 硝酸鹽 離子 Ammonifyingbacteria 3.硝化細菌 Root Organic material (humus) 2.氨化細菌 有機物質(腐質土) Soil Bacteria and Nitrogen Availability (氮的利用) • Nitrogen-fixing bacteria (固氮細菌) convert atmospheric N2to nitrogenous minerals that plants can absorb as a nitrogen source for organic synthesis • N2+8e-+8H++16ATP 2NH3+H2+16ADP+16Pi nitrogenase Figure 37.9. The role of soil bacteria in the nitrogen nutrition of plants.

29. Improving the Protein Yield of Crops • Agriculture research in plant breeding • Has resulted in new varieties of maize, wheat, and rice that are enriched in protein • Such research • Addresses the most widespread form of human malnutrition (營養不良): protein deficiency (蛋白質缺乏)

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31. Concept 37.4: Plant nutritional adaptations often involve relationships with other organisms 植物營養適應通常包括其與其它微生物的關係 • Two types of relationships plants have with other organisms are mutualistic (相互的) • Symbiotic nitrogen fixation (共生的固氮作用) • Mycorrhizae(菌根)

32. The Role of Bacteria in Symbiotic Nitrogen Fixation (共生固氮作用細菌的角色) • Symbiotic relationships with nitrogen-fixing bacteria (固氮細菌) by coevolution (共同演化) • Provide some plant species with a built-in source of fixed nitrogen • From an agricultural standpoint • The most important and efficient symbioses (共生) between plants and nitrogen-fixing bacteria occur in the legume family (peas, beans, and other similar plants)

33. Along a legumes possessive roots are swellings(膨脹物/隆起物) called nodules (根瘤), plant cells • Composed of plant cells that have been “infected” by nitrogen-fixing Rhizobium bacteria 根瘤 Nodules Roots (a) Pea plant root. The bumps (腫塊) on this pea plant root are nodules containing Rhizobium bacteria. The bacteria fix nitrogen and obtain photosynthetic products supplied by the plant. Figure 37.10a

34. Inside the nodule(根瘤), which a plant cell • Rhizobium bacteria assume a form called bacteroids (類菌體), which are contained within vesicles (囊泡) formed by the root cell 5 m Bacteroids within vesicle 囊泡中的類菌體 Infected root cell of nodule vesicle Uninfected cell of root 大豆根瘤中的類菌體 (b) Bacteroids in a soybean root nodule. In this TEM, a cell from a root nodule of soybean is filled with bacteroids in vesicles. The cells on the left are uninfected. Figure 37.10b

35. The bacteria of a nodule (根瘤中的細菌) • Obtain sugar from the plant and supply the plant with fixed nitrogen • Each legume (豆科) • Is associated with a particular strain (菌株) of Rhizobium

36. Development of a soybean root nodule (大豆根瘤的發育) Rhizobiumbacteria 根瘤菌 (2) The bacteria penetrate the cortex within the Infection thread. Cells of the cortex and pericycle begin dividing, and vesicles containing the bacteria bud into cortical cells from the branching infection thread. This process results in the formation of bacteroids (1) Roots emit chemical signals that attract Rhizobium bacteria. The bacteria then emit signals that stimulate root hairs to elongate and to form an infection thread by an invagination of the plasma membrane. Dividing cellsin root cortex Infectionthread 感染絲 類菌體 Bacteroid Dividing cells in pericycle 1 2. Infectedroothair 2 發育中 的根瘤 Developingroot nodule 3 Bacteroid 類菌體 4 (4)The nodule develops vascular tissue that supplies nutrients to the nodule and carries nitrogenous compounds into the vascular cylinder for distribution throughout the plant. (3) Growth continues in the affected regions of the cortex and pericycle, and these two masses of dividing cells fuse (融合), forming the nodule (根瘤). 4 3 Nodulevasculartissue 類菌體 Bacteroid 根瘤的 維管組織 Figure 37.11

37. Activation of Nod box by activated Nod D Expression of Nod gene Synthesis of Nod factor Activation of factor Nod D by flavonoid Chemical Signal between root and Rhizobium Flavonoid released by root as signal Nod factor trigger development by the root of the infection thread and nodule Activation of early nodule genes, leading to formation of infection thread and proliferation of cortical cells 此圖見第六版 The Molecular Biology of Root Nodule Formation • The development of a nitrogen-fixing root nodule depends on chemical dialogue(化學對話) between Rhizobium bacteria and root cells of their specific plant hosts

38. Symbiotic Nitrogen Fixation and Agriculture共生的固氮作用與農業 • The agriculture benefits of symbiotic nitrogen fixation • Underlie crop rotation (作物輪作/輪耕) • In this practice • A non-legume such as maize is planted one year, and the following year a legume is planted to restore the concentration of nitrogen in the soil (恢復土壤氮濃度)

39. Mycorrhizae and Plant Nutrition (菌根與植物營養) • Mycorrhizae (菌根), may be an evolutionary adaptation • Are modified roots (變形根) consisting of mutualistic (相互的) associations of fungi and roots • The fungus (真菌) • Benefits from a steady supply of sugar donated by the host plant (寄主植物穩定地供給糖類給真菌) • In return, the fungus • Increases the surface area of water uptake and mineral absorption and supplies water and minerals to the host plant (真菌回報以增加寄主植物根的表面績，以增加水份與礦物質的吸收) • Produce growth factor and antibiotics for host plants

40. Mantle(fungalsheath) 外套膜 Cortex Epidermis 100 m Endodermis Fungalhyphaebetweencorticalcells Mantle(fungalsheath) 外套膜 (colorized SEM) The Two Main Types of Mycorrhizae (菌根) • In ectomycorrhizae (外根菌), no formation of root hair • The mycelium (菌絲體) of the fungus forms a dense sheath (濃密的鞘) over the surface of the root 皮層 表皮 內皮 a (a) Ectomycorrhizae.The mantle of the fungal mycelium ensheathes the root. Fungal hyphae extend from the mantle into the soil, absorbing water and minerals, especially phosphate (P). Hyphae also extend into the extracellular spaces of the root cortex, providing extensive surface area for nutrient exchange between the fungus and its host plant. Figure 37.12a

41. The Two Main Types of Mycorrhizae (菌根) • In endomycorrhizae (內根菌), formation of root hair • Microscopic fungal hyphae extend into the root 表皮 皮層 Cortical cells Epidermis Cortex 10 m 內皮 2 Endodermis Fungal hyphae 菌絲 Vesicle Casparianstrip Root hair Arbuscules 枝狀瘤 (LM, stained specimen) (b) Endomycorrhizae.No mantle forms around the root, but microscopic fungal hyphae extend into the root. Within the root cortex, the fungus makes extensive contact with the plant through branching of hyphae that form arbuscules, providing an enormous surface area for nutrient swapping. The hyphae penetrate the cell walls, but not the plasma membranes, of cells within the cortex. Figure 37.12b

42. Agricultural Importance of Mycorrhizae (菌根在農業上的重要性) • Farmers and foresters • Often inoculate (接種) seeds with spores of mycorrhizal fungi to promote the formation of mycorrhizae • Green manure and crop rotation (綠肥與輪作)

43. Epiphytes, Parasitic Plants, and Carnivorous Plants • Some plants have nutritional adaptations(營養適應) that use other organisms in nonmutualistic ways(非互利共生) • Epiphytes (附生植物) • Parasitic Plants (寄生植物) • Carnivorous Plants (食蟲植物)

44. 附生植物 Exploring unusual nutritional adaptations in plants EPIPHYTES Staghorn fern, an epiphyte 寄生植物 PARASITIC PLANTS Host’s phloem Dodder Haustoria Mistletoe, a photosynthetic parasite Dodder, a nonphotosynthetic parasite (菟絲子) Indian pipe, a Nonphotosynthetic parasite (水晶蘭) 食蟲植物 CARNIVOROUS PLANTS Venus’ flytrap Sundews Pitcher plants Figure 37.13

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46. The Molecular Biology of Root Nodule Formation