植物生理學

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(1)是一門探討植物從萌芽、生長、分化、成熟至死亡的生命週期以及植物對環境因子反應的科學，即研究植物生命功能特性的學科。利用已知的生物化學、生物物理、分子與遺傳之原理，闡釋植物各種生理現象的機制，探究植物生命現象的奧妙。 Text: Plant Physiology (2010) Taiz L, Zeiger E References: Introduction to Plant Physiology (2009) Hopkins WG., Huner NPA. 植物生理學 (2006) 審校者：王淑美；主編者：潘瑞熾 07-5919230 [email protected]. Part 1: Water and Plant cells ∗ 95~5% water content vegetative, storage tissues: 80~95% xylem: 35~50% seeds: 5~15%, mucilage. ∗ 500 g H2O / g organism of plant Less than 5% of the absorbed water is actually retained for growth and even less used in biochemical reactions. ∗ Absorb vs. lose water: Absorption (吸收): major via root (~97%), take up soil minerals Transpiration (蒸散): occur in leaf, dissipate the heat of sunlight Photosynthesis: occur in leaf, CO2 uptake — Even slightly imbalance…….. ∗ Water movement at cell level — chemical properties and physical forces. 1.

(2) § The polarity of water molecules ∗ An excellent solvent for ionic substances − hydration shells (水合層) formation. ∗ Transparency (透明) ∗ Hydrogen bond. − high specific heat: buffer temperature fluctuations. − high latent heat of vaporization: regulates plant’s temp. light absorb ca. 50% solar energy, 300 μm H2O ——→ 100 °C / min. ∗ Hydrogen bond cohesive and adhesive properties cohesion (內聚力): the mutual attraction between H2O molecules, to minimizes the surface area at air-water interface − most stable.. surface tension (表面張力): the energy required to increase the surface area of air-liquid interface. adhesion (附著力): the attraction of H2O to a solid phase. ⇒ cohesion, adhesion, surface tension → capillarity (毛細現象). 2.

(3) Θ: solid surface through the liquid to the gas-liquid interface in clean glass. (taro). Capillarity. wettable cohesion＜adhesion. cohesion＞adhesion. ∗ Hydrostatic (流體靜力) pressure − Positive hydrostatic pressure: push Negative hydrostatic pressure: pull tensile strength (tension，張力) The Max. force per unit area that to break the water column the tensile strength of water column: − 30 MPa. If have air bubble? / cavitation in xylem. 3.

(4) ∗ Osmosis (滲透): the diffusion of water Osmotic pressure (+). selective. Reverse osmosis (RO). 4.

(5) § Water potential (Ψw，水勢) − the free energy of water per unit of volume (J m-3) − a good overall indicator of plant health The water potential of solution is dissected into three components ∗ Osmotic potential (Ψs) ↔ osmotic pressure Ψs = − RTCs, Cs is osmolality (mole/L H2O) − independent of the nature of solutes − ionic solutes (dissociation) e.g., sucrose, NaCl. ∗ Hydrostatic pressure potential (Ψp). positive hydrostatic pressure: turgor negative hydrostatic pressure: tension pure water in standard state: Ψp=0 ∗ Gravity (Ψg) Ψg = ρwgh At the cell level: Ψw=Ψs+Ψp Plant in space. Water potential − evaluate the water status of a plant. ∗ Ψw of a typically well-watered leaves: − 0.2 ~ − 1.0MPa; the leaves of plants in arid climates: − 2 ~ − 5MPa.. 5.

(6) Cactus stem: outlayer: photosynthesis inner layer: water storage, larger size and thinner cell wall ⇒ more flexible walls. During drought: Inner cells: [soluble solutes] ↓, polymerization [nonsoluble starch granules] ↑ Ψs ↑ ⇒ Ψw ↑. ⇒ water enter into outlayer cells, maintain photosynthesis. 6.

(7) Part 2: Translocation (運移) in plants A: in xylem (木質部) Water → soil → plant → atmosphere. major driving forces. Ψs is minor, except salt soil. § Root pressure Root pressure: (+ 0.05 ~ 0.5 Mpa) − The stem of a young seedlings is cut off just above the soil… − Root absorb ions which are transported to xylem ⇒ ψs , ψw of xylem ↓ ⇒ root pressure ↑ occur when soils Ψw are high and transpiration rates are low. 1.

(8) § Water transport through xylem ∗ The longest, simplest and most low resistance pathway. ∗ Also transport dissolved minerals, and, on occasion, small organic molecules. ∗ Mature xylem is a grouped ‘dead’ cell, no membranes, no organelles, and remain the thick, lignified (木質化) cell wall, which form hollow tube C6-C3. ∗ Consists two types of tracheary elements: (a) tracheids (假導管) (b) vessel elements (導管). Long-distance water transport: Volume flow rate (m3/s)= (πr4/8η) (ΔΨp/Δx) the rate of transport ⇒ Jv (m s-1) = (r2/8η) (Δτp/Δx) Jv = 4×10-3 m s-1 r = 40 μm η = 10-3 Pa s water Δτp/Δx = 0.02 MPa/ m If 100 m huge tree: 100 × 0.02 + 100 × 0.05/5 = 3 MPa. 2.

(9) § The ascent of xylem water on huge trees * Root pressure: * Capillarity * Cohesive-tension theory Venation (脈紋) pattern: vein minor vein: 0.5 mm. Capillary rise (2πrcosα) γ = πr2hρg 20℃ γ=0.073 N/m ρ=998 kg/m3 g= 9.8 m/s2 If r= 40μm h= 0.75 m. Cohesive-Tension theory: the predominate driving force Ψp= -2T / r air-water interfaces. 3.

(10) § The physical challenges of water movement in the xylem * Air seeding * Cavitation (gas bubbles expansion) or embolism (gas-filled void，栓塞) gas bubbles expand under tensile forces, break the continuity of water column and prevent water transport Acoustic shock. § Plants minimize the consequence of xylem cavitation * Detour (繞道)around the embolized conduit * Dissolve gas into xylem solution at night, transpiration↓, solubility↑. * New xylem formation * Repair cavitation (?). § Water movement from the leaf to atmosphere ∗ Transpiration (蒸散): loss of water from plants occur through pores in the leaf * Transpiration rate :. difference in water vapor conc.. * rs: leaf stomatal resistance (biological factor). * rb: leaf boundary layer resistance (non-biological factor) wind velocity, anatomical and morphological aspects. 90~95 % stomatal transpiration. 4.

(11) Guard cells: a pair of specialized epidermal cells, which surround the stomatal pore. § Leaves must dissipate vast quantities of heat (Temp.) light. absorb ca. 50% solar energy, 300 μm H2O ——→ 100 °C / min. * long-wavelength radiation (1000 nm) * Sensible heat loss * Evaporative heat loss (latent) perspiration Bowen ratio: sensible / evaporative heat loss. Desert plants: 10 Tropic rain forests: 0.4. 5.

(12) § Mineral nutrition. Hoagland solution. MS/B5…. Transporters. 6.

(13) ∗ Plant via roots absorb mineral nutrients, primarily in the form of inorganic ions from the soil, act as a “miner (礦工)”. ∗ To recycle animal wastes and remove deleterious minerals from toxic-waste dumps – phytoremediation (植生復育). 植生復育的概念重金屬性植物(metallophytes): 向日葵、包心菜、芥菜及天竺葵等目的： 1. 清除重金屬汙染；2. 採礦. § Mycorrhiza(e) (根菌共生)– are not unusual. ∗ fungus (supply nutrients and water) and root (supply carbohydrates) ∗ in cabbage, spinach, macadamia nuts, aquatic plants ∗ Absent in very dry, saline, flooded soil or the fertility of soil is extreme, either high or low. ∗ To facilitate nutrient uptake ∗ Ectotrophic mycorrhizae (外生菌) Vesicular-arbuscular mycorrhizae (胞囊叢枝狀菌). − nitrogen-fixing bacteria − Herbicide (殺草劑). 7.

(14) Ectotrophic mycorrhizal fungi — A thick sheath (鞘) or mantle (外膜) of. fungal mycelium (菌絲體) around the roots, and some of the mycelium penetrates between the cortical (皮層的) cells.. Vesicular-arbuscular mycorrhizae — No mantle. The hyphae (菌絲) even. penetrate individual cells of the cortex and can form vesicles and arbuscule.. B: in phloem (韌皮部). * Root: anchor, absorb water and nutrients; absorption Leave: absorb light and exchange gas; assimilation (同化) efficiently exchange via long-distance transport. * The long-distance transport pathways: Xylem: transport water and nutrients from roots to aerial portions Phloem: mature leaves (sugars)→ growth and storage portions (Phalaenopsis) redistributes water and various compounds transmits signaling molecules such as hormones, proteins and RNA.. 8.

(15) Materials translocated in the phloem Water: the most abundant substance. Sugar-rich sap Carbohydrate Sucrose (0.3 to 0.9 M) Nitrogen Asx (Asp, Asn) Glx (Glu, Gln). − RNAs: mRNA, pathogenic RNA, small regulatory RNA − Plant hormones, including auxin, GAs, sytokinins, and ABA − Proteins (proteomics analysis, 2009). Phloem: ♣ living cells, nonlignified walls ♣ sieve element: directly involved in translocation sieve tube element (angiosperms) ♣ companion cells (伴細胞) functions: to supply energy, to transport the photosynthetic products, take over (接管) some of the critical metabolic functions, such as protein synthesis.. Lack: nuclei, Golgi bodies, ribosomes. Retained: mitochondria, plastids smooth ER. 9.

(16) § P-protein (slime): rich in phloem are synthesized in companion cells along the periphery of the sieve tube element, or evenly distribute in the lumen P-protein (body): the major function is in sealing off damaged sieve elements − short-term solution. § Callose deposition − long-term solution a β-1,3-glucan is synthesized during damage and other stresses, such as mechanical stimulation and high temperature and dormancy callose disappears when the damage is recovery or break dormancy. Callus (癒創，癒合組織). The translocation patterns of phloem. ¤ is not exclusively either an upward or downward direction irrespective to gravity. ¤ Source (供源): area of supply, an exporting organ mature leaves, storage root beet (Beta maritima). Sink (沉積): area of metabolism or storage, a receiving organ nonphotosynthetic organs, root and shoot apices, young tuber, developing fruits, immature leaves. ¤ Not all sources supply all sinks on a plant → certain sources preferentially supply specific sinks. plasticity. 10.

(17) The features of source-to-sink pathways a. proximity b. development: vegetative or reproductive stage c. vascular connections: orthostichy () d. modification of translocation pathways: wounding, pruning Sugar beet plant. Oncidium a sympodial (複莖的) and epiphytic (著生的) orchid. 11.

(18) 6 CO2 + 6 H2O ☼ → C6H12O6 + 6 O2. 光合作用是地球上最重要的化學反應，是自然界將太陽的光能轉變為化學能的主要途徑。能源危機的再現與環境惡化造成日益嚴重的溫室效應，使人類更加重視此無聲無息的高效能反應。. § Photosynthesis: the light reaction. fluorescence. Algae’s pigment. 1.

(19) Emerson: ♣ Enhancement effect. ♣ Red drop effect Far-red light alone is insufficient in driving photosynthesis Accessory pigments. ＞ 680 nm. ⇒ Two photochemical complexes. Z scheme: noncyclic electron transfer in photosynthetic organisms ∗ Consist of four major protein complexes: (1) PSⅡ; (2) cytochrome b6f complex; (3) PSΙ ; (4) ATP synthase. ∗ The primary source of electrons: the oxidation of H2O The final electron acceptor: NADP+. cyclic e- flow ATP synthesis, no NADPH formation. The major source of O2 in earth. 2.

(20) Z scheme Trends in Plant Science (02) 7: 183. 3ATP, 2 NADPH, O2 / 8 photons / 4 e-. Hill reaction (1937) ♣ an artificial electron acceptors in isolated chloroplast thylakoid No CO2 condition, still O2 production ☼ 3+ 2+. 4 Fe. + 2 H2O → 4 Fe. + O2 + 4 H+. ♣ CO2 + 2 H2S → (CH2O) + 2 S + H2O H218O + CO2 → (CH2O) + 18O2 (1) CO2 + 2 H2O → (CH2O) + O2 + H2O (2) CO2 + H2O → (CH2O) + O2. 3.

(21) O2 evolved. Late 1800s. Three light parameters: spectral quality, amount, and direction. ♣ Spectral quality − Light sources: sunlight, incandescent light, fluorescent light, light emitting diode − photoreceptors Phytochromes (光敏素) for red light Cryptochromes (隱色素), Phototropins (向光素), Carotenoid zeaxanthin (玉米黃素) for blue light. ♣ Spectral amount − Light compensation point (光補償點): the photon flux when photosynthetic CO2 assimilation equal to CO2 release by mitochondria respiration − Photoinhibition (光抑制): absorption of too much light. 4.

(22) ♣ Lux (流明) or foot-candles (呎燭光): − lumen (lm): the luminous flux on a unit surface, all points of which are at unit distance from a uniform point source of one candle. − intensity was expressed either as foot candles (lm ft-2) or lux (lm m-2) − based on the perception of light by the human eye, which is maximally sensitive to light within the green region of the spectrum, at 555 nm.. ♣ Photosynthetic photon flux density (PPFD) − Under direct sunlight 2000 μmole m-2s-1 − Photosynthetically active radiation (PAR): 400-700 nm. Instruments/calibration. Ecological functions. Red/far red. 5.

(23) § Photosynthesis: Carbon reactions ♣ dark reaction → carbon reactions of photosynthesis ♣ take place in stroma (基質). 40% CO2 fixation was derived from marine phytoplankton. Calvin-Benson cycle: 1961 Nobel Ribulose bisphosphate carboxylase/oxygenase (rubisco) C3 plant. Light regulation. 6.

(24) Photorespiration (光呼吸) − a wasteful process. C2 oxidative photosynthetic carbon cycle. 1×CO2+ 1×3C (¾ C). 2×2C. [gas] µM = Pgas × α × 106/ V0 In vitro vs. In vivo. Pgas: partial pressure; α: absorption coefficient Solubility of CO2 and O2 as a function of temperature. 9.11/21.92 (41%). 228.2/401.2(56.9%). T↑ ⇒ tilt toward the C2 oxidative photosynthetic cycle. 7.

(25) Photosynthesis rate (Max.) >> Photorespiration rate > normal respiration rate [chloroplast]. [C, M, peroxisome]. [mitochondria]. § The C4 photosynthetic carbon cycle − Kranz (wreath) cells: present mesophyll (葉肉) and bundle sheath (維管束鞘)cells spatial (空間的) − concentrating CO2, little phosphorespiration. 8.

(26) ♣ Single-celled C4 photosynthesis Borszczowia aralocaspica. 2 5 μ m. Bienertia cycloptera. 25μm. Importance!. § Crassulacean acid metabolism (CAM，景天酸代謝) Cacti, pineapple, vanilla, and agave.. Spatial and temporal Water use efficiency Nocturnal acidification. rubisco. 9.

(27) 蝴蝶蘭. 10.

(28) Part 4: Plant hormones have profound effects on development at vanishingly low concentration (< 1 mM). kinds: auxins, gibberellins, cytokinins, ethylene, abscisic acid, brassinosteroids, jasmonic acid, salicylic acid, polypeptide systemin, strigolactone (the later buds outgrowth), flavonids. Plant growth regulators: promoters and inhibitors. § Auxin: the first growth hormone to be discovered in plants Kinds: natural (天然的) vs. synthetic (合成的) auxins. Functions: Plant cell expansion, viability, stem elongation, apical dominance, root initiation, fruit development, oriented, tropic growth or phototropism. 1.

(29) § Gibberellins: Regulators of plant height. ¤ 1950s, the second groups of hormones (Auxin: discovery, 30 years; structural elucidation, 20 years). ¤ a disease of rice: “foolish seedling” or bakanae ¤ a chemical secreted by Gibberella fujikuroi, GA3 ¤ C19 or C20, defined by their chemical structure, more than 136 ¤ only a few are biologically active Functions: increase in plant stem and root growth, regulate the transition from juvenile to adult phases, floral initiation and sex determination, promote pollen development and (pollen) tube growth, promote fruit set and parthenocarpy (單性結果) (some fruits), promote seed germination. biosynthesis inhibitors. Stem elongation: GA. Auxin. Lag time: Auxin-induced wall acidification GA-promoted wall extension: xyloglucan endotransglycosylase/hydrolase (XTH). 2.

(30) § Cytokinins: a diffusible and water-soluble regulators of cell division. autoclaved herring sperm DNA. immature endosperm of corn. Auxin/cytokinin ratio: regulate morphogenesis in cultured tissues. § Ethylene: the gas hormone. 3.

(31) Inhibit ethylene production and action ♣ inhibitors of ethylene synthesis AVG, AOA, Co2+. ♣ inhibitors of ethylene action Silver ions (AgNO3 or Ag (S2O3)23-) carbon dioxide (5~10%) –antagonist, less efficient than silver ions. trans-cyclooctene 1-methylcyclopropene (MCP). ♣ remove ethylene alkaline potassium permanganate lysophospatidylethanolamine. EthylBloc. Effect of ethylene on defoliation birch 50 ppm C=C fumigated 3 days. ¤ supraoptimal auxin concentrations stimulate ethylene production and cause defoliation e.g., 2,4,5-T, during Vietnam War. 美國和越南首次就越戰期間，美軍化武「落葉劑」的遺害達成賠償金額協議，美方願賠3億美元。美軍在越戰期間，在越南叢林和農田上空，投下了數以千噸計的「橙劑」（落葉劑）。美國和越南的一個聯合小組周三表示，清理橙劑遺害以及治療受害者，約需3億美元。這是越戰結束近35年後，美國和越南的決策者和專家首次就賠償數字達成協議。不過，有關賠償還需要美國國會通過確認。(2010) 越南茶. 4.

(32) § Abscisic acid (ABA): ♣ a seed maturation dormin: a growth inhibitor was purified from sycamore leaves collected in early autumn, when the trees were entering dormancy ABA-deficient mutants: Vivipary (母體發芽) : precocious germination of seeds in the fruits. § Abscisic acid (ABA): ♣ antistress signal inhibit growth and stomatal opening, particularly when the plant is under environmental stress. Maize exposed to water stress. [ABA] in tissues are highly variable ~ 3000-fold increase. 5.

(33) § Brassinosteroids novel growth-promoting substances in pollen 1970 Mitchel et al the pollen of rape (油菜) plant (Brassica napus L.) in the organic solvent fraction. 1979 Grove et al 227 kg of bee-collected rape pollen ⇒ 4 mg bioactive brassin compound, X-ray analysis: a polyhydroxylated steroid, a steroidal lactone. Functions: involved shoot growth, root growth, vascular differentiation, pollen tube growth, and seed germination. BRs act locally near their sites of synthesis Reciprocal grafting. wild shoot. Endogenous BRs do not seem to undergo root-to-shoot (a longdistance) translocation. wild root. 6.

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