华南师范大学：《植物生理学》课程教学资源（英文教案）Chapter One Water Metabolism of Plant

Chapter OneWaterMetabolismofPlant.Problem: what is the water metabolism?.Concept:@Howtothewatermoveintheroot?The contentof②Howtothewatertransportupward.plant watermetabolismHowtothe water transpiration in plant.IAbsorptionofwaterbyplantcells1.Water transport processes (pathway)in the membrane.WatercancrossplantcellmembranesBydiffusionof individual watermoleculesthroughthemembranebilayerTwopathways②By microscopic bulk flow of watermolecules through awater selective poreformedbyintegralmembranepotential suchasaquaporinsOUTSIDEOFCELLWatermolecules80Water-selectivepore(aquaporin)MembranebilayerCYTOPLASMFIGURE1.1Watercancrossplantmembranesbydiffusionof individual watermolecules through the membranebilayer,as shownontheleft,andbymicroscopicbulkflowofwatermoleculesthrougha water-selectiveporeformedbyintegralmembraneproteinssuchasaquaporins.2.ThedrivenforceofwatercrossmembrcmeOsmosis

Chapter One Water Metabolism of Plant ·Problem: what is the water metabolism? ·Concept: I Absorption of water by plant cells. 1．Water transport processes (pathway)in the membrane. ·Water can cross plant cell membranes. · 2.The driven force of water cross membrcme—Osmosis The content of plant water metabolism ①How to the water move in the root ? ②How to the water transport upward. ③How to the water transpiration in plant. Two pathways ①By diffusion of in dividual water molecules through the membrane bilayer ②By microscopic bulk flow of water molecules through a water selective pore formed by integral membrane potential such as aquaporins

@Osmossis concept:The movement of water across a selectivelypermeable membranetoward theregionofmore negative waterpotential,(lower concentration ofwater)②Waterpotential(y)· Chemial potential =free energy(KJ) · mol-' substance: The chemical potential ofwater represents the freeenergy status of water.V,=s_w_AmVwVwN·m-mol-!Chemical Potential of waterVw=Partialmolarvolumeof waterm'.mol-!= N.m-- PaUnit:1bar=0.987atm=10'Pa=0.1MPayeYw pure water =OMPaw other solutions<OMPaY w sea water--2.6MPaw 1mol.- sucrose solution=-2.5MPa?Waterpotentialofcells.Whatarethecomponentsofcellwaterpotential?: A typical cell, its water potential components: Three major factors contribute to cell waterpotential.W.=.(w,)+W,+Vg,(y,):The term y.(y,)called the solute potential or the osmotic potential, representsthe effect of dissolved solutes on water potential。 Solutes reduce the free energy of water bydiluting the water.V, =-CiRTC= concentration of the solution in moles per literR=the gas constant (0.00831kg · MPa mol-1 · K-')T=absolute temperature(K) =degrees C+273i-isotonic coefficientVp:Pressure potential The term Vp is the hydrostatic pressure of the solution Positive

①Osmossis concept : The movement of water across a selectively permeable membrane toward the region of more negative water potential,  w (lower concentration of water). ②Water potential (  w ) ·Chemial potential =free energy(KJ)·mol-1 substance ·The chemical potential of water represents the free energy status of water. w W w W W w V V     − − −  = = 1 w 3 1 Chemical Potential of water N m mol Partial molar volume of water m mol  − − = = 2 N m Pa − = = · w Unit: 1 bar=0.987 atm =105Pa =0.1MPa  w pure water =OMPa  w other solutions<OMPa  w sea water=-2.6MPa  w 1mol·L -1 sucrose solution=-2.5MPa ③ Water potential of cells ·What are the components of cell water potential ? ·A typical cell, its water potential components: Three major factors contribute to cell water potential. ( )      w s p g = + +  ( )   s :The term ( )   s called the solute potential or the osmotic potential, represents the effect of dissolved solutes on water potential。Solutes reduce the free energy of water by diluting the water.  s = −CiRT C concentration of the solution in moles per lit = er R=the gas constant (0.00831kg·MPa mol-1·K-1 ) T=absolute temperature(K) =degrees C+273 i=isotonic coefficient  p ：Pressure potential The term  p is the hydrostatic pressure of the solution. Positive

pressure of the solution raise the water potential; p is called pressure potential=OMPappure water and solutionGravity potential. Gravity to move downward unless the force of gravity is opposedWg:by an equal and opposite force. The term g depends on the height (h) of the water above thereference-state water, the density of water (Pw )and acceleration due to gravity (g). In symbols, wewrite the followingVg=PughWhere P.g has a value of 0.01 MPa m-1Thus a vertical distance of 10m translates into a0.1MPa changeinwaterpotential.When dealing with water transport at the cell level the gravitational component (g )isgenerally omitted because it is neglible compared to the osmotic potential and the hydrostaticpressure。Thus, in these cases Equation can be simplified as follows.yw=y.+VpWater enters the cell along a water potential gradient@ Water the cell along a water potential gradientWatermovement between cell and cell.For example :A cellBcell,=-1.0 MPa元=-0.8 MPa,=+0.8 MPap=+0.4 MPa=-0.2 MPa=-0.4 MPaYw:A>BWaterFlow.A(High,)B(low w)Forexample?Unit: MPaABcDFEndP EndV,=-1.0Vw= 0.2V,= 0.6V=-0.8

pressure of the solution raise the water potential;  p is called pressure potential.  p pure water and solution =OMPa  g : Gravity potential. Gravity to move downward unless the force of gravity is opposed by an equal and opposite force. The term  g depends on the height (h) of the water above the reference-state water, the density of water ( PW )and acceleration due to gravity (g). In symbols, we write the following  g w = P gh Where Pgw has a value of 0.01 MPa m-1 Thus a vertical distance of 10m translates into a 0.1 MPa change in water potential. When dealing with water transport at the cell level the gravitational component (  g )is generally omitted because it is neglible compared to the osmotic potential and the hydrostatic pressure。 Thus, in these cases Equation can be simplified as follows.    w s p = + Water enters the cell along a water potential gradient ④ Water the cell along a water potential gradient Water movement between cell and cell. For example ①: A cell Bcell  w : A>B Water Flow: A(High  w )→B(low  w ) For example②: Unit: MPa F End A 0.2  w = − B 0.6  w = − C 0.8  w = − D 1.0  w = − P End  =-1.0 MPa  p =+0.8 MPa  w =-0.2 MPa  =-0.8 MPa  p =+0.4 MPa  w =-0.4 MPa

:A>B>C>DWaterflow: F_H.o>PWater potential in the Plantwsowsemwlagwar

 w : A>B>C>D Water flow: H O2 F P ⎯⎯⎯→ ⑤Water potential in the Plant w soil  > w stem  > w leaf  > w air 