BIOPL3420 - Plant Physiology - Lecture 1

so let's start off by making a list what are the things that we should be thinking about in a course that covers plant physiology what are some of the basic issues let's say that plants have to deal with in their day-to-day existence nutrients getting nutrients from the environment but not just that because those nutrients if we take up nitrogen from the soil it doesn't stay as nitrate or ammonia in the plant they also get assimilated right so we've got assimilation of the nutrients as well yes let me have their hand up here yeah yeah water water is a big thing what else homeostasis what do you mean by that plants place keep a constant temperature nope they don't keep constant temperature for sure do they keep a constant bathing fluid inside the plant in other words we have blood and lymph circulating around their body plants have something similar for that but they maintain this look as long as you own the answer if that's okay so yeah so there is some level of homeostasis it's basically maintaining the internal environment of the plant within certain constraints temperature largely doesn't happen in plants but for example osmotic characteristics ion composition is highly regulated plants yes spider like yeah like the big thing right we need to think about it both in terms of competition for light and how that light is actually utilized what else grow so what about growth well why do you say growth everything is going to grow in what context is this is there something unique about this implant there's aspects of growth that are completely unique to plants yeah mostly like the front okay really found the eating that they grow longer basically adding more water ah yes of cells divide quickly and then enlarge and specialize but that's actually something that's common too well enlargement is is much more in plant cells in general than it is an animal cells but that's fairly common I'm thinking about for example oh go ahead what you can say yeah so we have meristems New York's temps are basically post embryonic growth all new cells come from the meristems whether they're chute or route meristems or whether the lateral meristem some wheat plants okay that's a really different there's another aspect of plant growth it's different yeah he'll bright moon I'll learn your names so I get your picture say that again oh yeah so there's alternation of generations associated with let's put it down here in this related reproduction what I'm getting at you're being missing is the role of cell wall swing cell walls will constrain the way the plant grows but also dictate the way the plant process how big a cell gets what its shape is is determined by the enlargement of the cell wall it's not a random process very highly constrained and obviously quite different than what happens in the elbow cells where there's no so well constraints right okay what else yeah yeah defense so when the bear walks in through the door here we can jump out the windows right we can we can escape plate a to do that they're stationed there sedentary right and so they have developed the whole range of mechanisms of dealing with things to eat the plants things that want to take booties out of the plant cells parasites and things like that so a planet defense is a big component of this and when this basically represents as far as what plants do we refer to as secondary metabolism perhaps make a whole bunch of specific compounds that are related to defense related to preventing or limiting things from being the plants of the invading the plants and giving the plant diseases and things like that the secondary metabolites or secondary metabolism distinguishes it from the sort of thing the metabolism that's common to all organisms we should put that down here primary metabolism so photosynthesis produces sugars nutrient acquisition takes up phosphorus and nitrogen and stuff like that from the soil but those got to be converted into proteins and nucleic acids and lipids and all that sort of stuff that's the bait that's the stuff of primary metabolism okay so we had a pretty good list here if you compare this list with the chapters in the textbook or the list of lecture topics we pretty much got it covered right this is the sorts these are the sorts of things that we're going to be talking about I think the one thing that we don't have on the list is environmental response in a sense defense is a type of environmental response to biotic factors but we also need to include environmental response to abiotic factors changes in temperature changes in water availability nutrient availability and things like that okay so by the end of the course you should be able to talk about how the details that are available to you in the textbook relate to all these different things and use that information to say okay suppose I suggest that the plant is exposed to certain certain environmental conditions you should be able to tell me how the plants going to what the plant has available to it to help it respond to that okay all right so let's some spend a few minutes talking about some of the things that are unique to plant cells if we think about plant cells they got a lot in common with all eukaryotic organisms they got nucleus and they got cytoplasm and all that kind of stuff but there's some things that plant cells have that are unique that that put a whole new perspective on the way the plant cells do things and one of them is a plant cell wall so we'll have a whole lecture topic where we talk about plant cell walls and then we'll talk about and again in terms of the role that walls play in relation to development and growth because as I said the walls the enlargement of the wall is what dictates how the cell volume and the cell shape changes so plant cell walls put very important constraints on plant cells one plant cells can't move it's a big difference in development between plant and animal cells in animals cells when two cells divide there's nothing that says one of those two daughter cells can't migrate halfway across the body to become some new type of cell that doesn't happen in plants when to one of cell divides those two cells are locked in position relative to each other that puts a lot of constraints on development and we'll talk in detail about this when we talk about development in implants plant cells also play a huge role in water relations we cannot tolerate in our body changing the internal osmotic conditions of the fluid that bathes our cells right because animal cells don't have a rigid wall the fluid that surrounds them must be isotonic must have the same osmotic characteristics as the cytoplasm not true in plants the the thing that bathes the the cells in plants is basically dilute water solution right and the reason the plants can withstand that is because water wants to move in osmotically we'll talk about this in the next couple of lectures but the cell wall resists that right so cell walls play a very important role in distinguishing what plant cells are capable of doing compared to the average cell in a bacteria yeast or an animal plant cells contain plastids so we think about when we think about plastids we think primarily about chloroplasts but chloroplasts are just one of a group of organ related organelles called plastids so we have chloroplasts there's a group of plastics called leuco PLAs the most Jukka PLAs means they're not colored at all the most common type of Luca plastic is Anna Milla Plast you'll see that these are involved in starch metabolism and there are colored plastids that are involved in other things besides photosynthesis we call these chroma blasts you're familiar with these like tomatoes the red of tomatoes are chloroplasts that have turned red by accumulating the carotenoid lycopene in them right so these are also found in the petals of colors of petals and flowers and things like that so these are all developmentally related to each other from a precursor called pro plastids they can develop into any of these things depending upon the cellular conditions Pro classes are inherited through sexual reproduction usually only in the egg sometimes in the sperm so it means because we know that chloroplasts and actually all of these plastids are semi-autonomous organelles they contain genes that encode a small fraction of the proteins that function in chloroplasts that we have non-mendelian inheritance and of traits associated with with plastids because in many plants the Placid Tsar only inherited from the maternal parent through the egg sperm is too small to hold deport Pro plastids let's see the other interesting thing that we need to think about we've already mentioned the fact that cell division implants is limited to specific regions not true in animals in plants it's the meristems the shoot apical meristem s a.m. the root apical meristem in all plants accounts for growth lengthwise upwards and downwards in woody plants like trees there are also lateral meristems that account for increase in diameter of the plant but all plants and what we're going to focus on when we talk about them are the apical meristem set their chute tip and the root tip so in the embryo in the development of plant embryo lots of cells divide but once the embryo is formed once the seed dries down and the seed imbibes water and starts to grow again all that post embryonic growth every new cell is the result of cell division in one of those meristems so the meristems account for all post embryonic growth and development it's obviously quite important in determining what's going on in a plant okay so cell walls plastids and meristems those are the sort of key things that we're going to come back to many times over the course of the semester to think about unique aspects of what plants do okay let's sort of go back to the level of introductory biology for a little bit so here's a picture of a typical plant cell well maybe not such a typical plant cell but you should know about all the stuff that's in there so we talked about endoplasmic reticulum and nucleus and Golgi and chloroplasts and mitochondria you should know about all that stuff right if you don't you better go back and read some of it there's some information in the first chapter of the textbook but if you're missing basic cell biology then you need to bone up on it because it's going to turn out to be important in a lot of different circumstances so we know that cells are basically the fundamental unit of life so everything that a plant does is dependent upon processes at the cellular level that's true for all organisms but we think about it in in an animal for example in in humans we have a heart that mechanically pumps to circulate fluids through our body plants circulate fluids through their body as well but there's no mechanical pump everything that happens to drive long distance transport in plants is the result of osmotic processes at the cellular level okay so so we're going to spend a fair amount of time this semester talking about processes that are happening at the cellular level and understanding how those give rise to the things that we see at the whole plant level or even at the ecosystem level so cell biology is going to be important here so let's talk about some of the things in here that I expect you to know about so we talked already about the cell wall and we'll come back to that again at the at the very end of the lecture as we move in from the cell wall what's the next thing that we encounter cell membrane okay so what about what's what's important about the cell membrane why should we spend any time talking about it about you in the back with the green and black shirt yeah you yeah so it determines what goes in and out of the cell how does that happen what does the plasma membrane what characteristics of the plasma membrane have that make it we'd like to use the term selectively permeable some things can go in and some things can't what are the characteristics of the plasma membrane that allow that to happen how about you in the gray shirt right back here yep you what how does the plasma membrane what characteristics of the plasma membrane allow it to be selectively permeable yeah so proteins that that allow specific things to go across the membrane what else yeah the membrane itself right so the easy way to think about it not just for the plasma membrane but for any of the membranes in a shell is that the bilayer for the most part is the barrier there are relatively few things that can cross through a lipid bilayer small molecules like water and gases they can go through pretty easily but things like even simple sugars glucose can't pass through membrane by itself it needs to have a protein and those proteins basically the proteins that are in membranes that function and transport our enzymes their enzymes that are catalyzing the movement of a molecule across the membrane that wouldn't otherwise cross the membrane okay so when we think about the plasma membrane or we think about any of the other organelles one of the common themes that's going to be there is selective permeability so let's think for just a second about imagine a photosynthetic cell from the leaf of a plant let's compare that with a unicellular photosynthetic prokaryotic no chloroplasts no internal membranes what are the differences between what that prokaryote does to live and what the plant cell does to live there are any big differences mm it potentially can yeah but it's a photosynthetic prokaryotic cell it's getting most of its nutrition autotrophic li rot rather than heterotrophic li what you're saying is correct even most photosynthetic prokaryotic even most photosynthetic eukaryotic algae have the capability of either taking up organic compounds or even engulfing things by phagocytosis but that's that's a that's a sort of a separate issue what other are there big differences between what a prokaryotic cell does and what a eukaryotic cell does yeah okay that's true the prokaryotic cell can move yeah yeah so that's an important decision all the membrane requiring processes like photosynthetic electron transport very electron transport you know Proterra happen in the old membrane is there in the plasma membrane what I'm trying to get you to think about is in fact there are virtually no differences when we think about the breadth of things that cells do there are very few differences between what a prokaryote and eukaryotic but there's a lot of structural differences why all these organelles what did the presence of organelles do for eukaryotes that's not possible in prokaryotes I just told you that virtually everything they do is the same there's very few processes that a eukaryotic an do that a prokaryote can't do so why have organelles what does that what does that benefit does that give how yeah more efficient but how um prokaryotes can store stuff too they often sort those sort things yeah except for actually in propose synthetic prokaryotes what you find is the plasma membrane invaginate some folds in and all those membranes in the error for example of element photosynthesis so there can be a ton of membranes in prokaryotic cell one thing that has components that we can't this little number of English literature yeah yes oh let me give you an example that we just talked about in the prokaryotes the electron transport associated with respiration photosynthesis occur in the same membrane and eukaryotes they occur in separate organelles in prokaryotes the glycolysis associated respiration and the calvin cycle associated with photosynthesis occur in the cytoplasm of the cell there's a lot of common intermediates there that actually make it harder to regulate those processes so by the compartment ation it provides a much cleaner way to regulate processes independently of each other that can be done in eukaryotic cells so the difference between prokaryotes and eukaryotes in terms of the actual processes that are there are very small the difference is how those processes are regulated compartment ation gives a lot of opportunity for for regulation that doesn't happen in prokaryotes okay one aspect of this membrane mess that I want you to be thinking about there's an emphasis in it on the readings in the first chapter is related to the endomembrane system so what are the worgen ELLs that are associated with in or what are the membranes that are associated with the endomembrane system yup what else Golgi what else plasma membrane yep what else nuclear man whoa yep what else yeah lots of vesicles let's switch the question around we've named almost everything in there what isn't part of the endomembrane system well you have a cyclops it's not a membrane so we're not going to worry about that but you have two separate entities what other membrane containing organelles are not part of the endomembrane system that goes hard endomembrane system two mitochondria and chloroplasts yep why why are mitochondria and chloroplasts not hard the endomembrane system yeah how did they originate yeah so you've heard about the end of symbiotic hypothesis or endosymbiotic theory that chloroplasts and mitochondria were free-living prokaryotes that we're taken up by phagocytosis but not degraded the fact that chloroplasts and mitochondria contain their own DNA their own ribosomes tells you that they have a history of being a free living organism what actually done fair amount of work on organisms that were precursors to chloroplasts how that endosymbiotic event might have happened it's just a ton of really interesting stuff we could spend a whole semester talking about that so you're correct that the things in the endomembrane system are ultimately derived from invaginations of the plasma membrane invaginations that can form individual vesicles that confuse together to form we are Golgi nuclear envelopes all those sorts of things chloroplasts and mitochondria are separate they came in they were taken up in one of these vesicles and we're retained the seat will see that they lost most of their genetic material but they retain a little bit of it okay so why do I care about this why should we worry about the complexities of membrane movement associated with endomembrane system what is this important for in plant cells Thanks yeah that's pretty good let's say most things one of the things that we talked about already how does a plant make a cell wall much of the material that forms the cell wall is produced in the Golgi and is exported in little vesicles that when those vesicles fuse with the plasma membrane the contents of the vesicle are released basically everything but the cellulose microfibrils is exported from the cell via the endomembrane system how do you add or remove proteins from the plasma membrane so they may be transport proteins that are needed because the plant runs out of nitrate and so you have to put high high affinity nitrate transporters in the plasma membrane or developmentally how do you insert or remove specific receptors protein receptors from the plasma membrane it's through this system right so the flow of membrane and the proteins that are in enclose in the membrane are very important in all sorts of things that happens in plant physiology okay so having a basic understanding of what's going on here both in terms of the membrane and in terms of the proteins proteins that are going to be secreted are synthesized on ribosomes that are bound on the rough ER as opposed to free in the cytoplasm proteins that are going to end up in the membrane of the endomembrane system so in the in the nuclear envelope or in the vacuole envelope or in the plasma membrane proteins integral membrane proteins are made in the rough ER and exported through this system to get them out there okay all the lipids that make up those various membrane systems except the chloroplast and the mitochondria are produced in the ER and spread around the system so when plant cells grow and divide and differentiate all of this is dependent upon what's happening in the endomembrane system okay so make sure that that's something that you're comfortable with I already mentioned the fact that plant cell walls play an important role and this is just sort of an example of where two different aspects of the plant cell structure become important when a plant cell divides so here we have late telophase after the nuclear envelopes of the two daughter cells are starting to form the next thing that happens is formation of new plasma membrane and cell wall between these two cells and the way that happens is by this comes from vesicles that are derived from the golgi the vesicles that are derived from the golgi these little little blue things here represent vesicles that aggregate on the cytoskeleton at the plane of cell division when those vesicles fuse the membrane becomes the new plasma membrane of the two daughter cells and the contents of those vesicles is the glue that holds the cells together it's called the middle lamella we'll talk a lot more about this later on in the semester so the cytoskeleton directs these vesicles to the plane of cell division and those vesicles fuse forming simultaneously the two plasma membranes of the daughter cells and the cell wall the first layer of the cell wall that holds those few cells together okay so here's an example of where the endomembrane system and the cytoskeleton interact together to dictate this particular process okay somebody mentioned vacuoles macules are the role of vacuoles play in plant cells is has been understated for a long time when we look at this is a micrograph of a leaf mesophyll cell so we see a nucleus so we see some chloroplasts and it's pretty out of focus it doesn't really show up very well but here's the cell wall and all this volume here is a vacuole so in one sense vacuoles are important in plant cells because many cells they take up most of the volume one of the other thing that distinguishes plant cells and animal cells is that plant cells tend to be much larger than animal cells and the thing that takes up most of the volume of large plant cells are vacuoles why why would well if you're going to have a large cell why would it make sense to have most of the space in that cell taken up by a vacuole yeah yeah okay so that's that's actually one I hadn't thought of but that's a good answer whatever's in the vacuole is probably cheaper to produce than what's in the cytoplasm another thing what determines for any animal cell what determines the maximum size of the Sun what are the physical constraints that limit how big an animal cell can get no you can add more membranes in the cell would continue to get bigger diffusion in what sense okay so if you're talking about diffusion within the cell it'll start buddy or diffusion into the cell in what sense to either of those effect any processes why do we have to worry about the fusion surface area what about that grow larger the ratio between volume and surface area like there's less surface area volume plus space too I think selves need to have things going in and out yeah they have to exchange vasudev's you with their environment to be so circus the body ratios is a very important one if you have a big cell that's mostly vacuole the actual volume of the cytoplasm is this little tiny strand around the outside and some stuff up there the cytoplasm is quite small but it's got a large surface area right so plant cells can be structurally larger by enclosing most of the volume in a vacuum so does that mean that the macula stays empty space what's the vacuole do give me some examples of what that Google does stores what water okay there's what a lot of waters near the up what else other stuff yeah let's be more specific than other stuff yeah yeah so like it can store toxic things in there a good example epidermal cells store plant defense compounds things that when the cell gets broken open inhibit for example a grasshopper that's eating the leaf inhibit digestion of the grasshopper if those kind of house were floating around with a cytoplasm they interfere with processes in those cells by sucking them away in the vacuole the only time that he uses one of the cell mates program right so it can be used as storage for compounds that would otherwise higher than the normal function of the cell will see the backhoes it needs from all sorts of things so the general idea that the vacuole is a bag of water that takes up a lot of space which if you took plant physiology 30 years ago which what most people thought that goals are a lot more complicated than the things that they do they play a huge role in regulating the composition of the cytoplasm by transferring ions in sighs okay we'll talk a lot more detail about that we talked about classes already this is a chloroplast and we'll spend lots of time talking about photosynthetic gas aspects of this and we mentioned that chloroplasts are just one of the larger family of classes but here's a picture license microscope and the electron microscope of colorized electron microscope of classes showing some rather weird things that we don't typically see with plastic one of these long stringy things sticking off there these pictures were taken by putting green fluorescent protein GFP small soluble protein that fluorescence green in the stroma in the liquid and closed by the chloroplast envelope so that means the stroma has these long extensions what are these things you don't see about it in any textbook they're actually discovered by a postdoc in maureen Hanson's lab over in molecular biology and genetics these things are called stro mules they're long extensions of chloroplasts that actually join two other chloroplasts sometimes they even join two other organelles like mitochondria or peroxisomes what what they're doing we don't have a clue well we're starting to figure it out so this is an example of the idea that our knowledge and how plants work is continuously advancing what's going on with these stro mules we don't really know but clearly they're important we've demonstrated that you can exchange materials between chloroplasts between your chloroplasts or between a chloroplast and a peroxy so so there's something going on there that's probably important okay so here's a chloroplast and here's a picture that shows two peroxisomes peroxisomes are in this in this category called micro bodies people used to say that micro bodies were unique to plants we now know that they're not there are peroxisomes or things that are involved in dealing with reactive oxygen species species things like hydrogen peroxide in all eukaryotes they're just more prevalent in plants so it's another category of membrane-bound organelles that we need to be thinking about let's see um cytoskeleton we're going to spend a lot of time talking about various aspects of the cytoskeleton so here's a picture of these are palisade cells in the upper layer the photosynthetic cells in the upper layer of a leaf they're very long gated and the this has got green fluorescent protein that's labeling the microfilaments that underlie the plasma membrane so you're seeing a network of microfilaments that we'll see play all sorts of roles in determining cell shape cell size cell growth and things like that okay so cytoskeleton one of the interesting aspects of cytoskeleton that we'll we'll talk about then it's important that you keep in mind is it's highly dynamic it can take itself apart and rebuild itself in other ways to accomplish specific processes one of them you're already familiar with mitosis right the microtubules that are involved in the mitotic spindle are they there throughout the cell cycle no there's microtubules throughout the cell but when mitosis is ready to happen those microtubules separate they break down into their individual parts reform the mitotic spindle play the role in separating the chromosomes and then that mitotic spindle disintegrates and the microtubules reform in other places in the cell it's a highly dynamic set of things in the cell that are involved in in moving things around in the cell moving organelles around shaping the cell dictating how the cell wall is laid down we'll see lots and lots of examples of this ok I want to finish with just one thing we talked about cell walls one of the unique aspects of plant cell walls that we're going to spend a fair amount of time talking about in a lot of different contexts are plasmodesmata plasma Desman are basically cytoplasmic connections between two adjacent cells ok so there's in the here's the cell wall here's the cytoplasm of one cell here's the other here's the plasmid ESMA there is a aligning membrane lining so the plasma membrane of this cell is continuous with the plasma membrane of this cell through the plasmid ESMA there's also a piece of ER it's called the desmotubule that goes through the plasma desmond from one cell to the other and there's literally cytoplasmic space between the in the plasma desmond will see that plasma desmond play hugely important roles in communication between cells whether it's communication involving metabolic intermediates in different pathways so for example in c4 photosynthesis we'll see various organic acids and an ATP being exchanged between cells there's chemical signaling that goes between cells through the plasmid ESMA and one thing that for anybody is a plant pathologist in here knows that the other thing that can go through here is viruses viruses have figured out a way to hijack the machinery that normally functions to transport small rnas from one cell to the other that's a that's associated with normal plant function to hijack that machinery to allow nucleic acids to move from one cell to the other to allow the viruses to replicate okay so we've had a reasonable introduction to the sorts of things that I want you to be thinking about as far as plant cell biology in this course this is going to be reinforced in almost every lecture because in almost every lecture we're going to talk about stuff at the cellular level and how that dictate what's happened what happens at a higher level of organization okay so for Thursday you are going to read the assigned readings are in Appendix 1 of the textbook it's about energy I also put a document in on the website associated with the lecture topic - that's called thermodynamics it's basically my restatement in a way that I think is easier to understand than the textbook of the thermodynamic principles that I want you to understand you need to understand free energy you need to understand equilibrium you need to understand how energy changes dictate the direction that reactions will go and how cells might manipulate that okay so read through the readings please answer the question that says what are you having the most trouble with because that will help me shape what we talked about next Thursday when we cover this topic okay thank you

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Length: 40min 35sec (2435 seconds)

Published: Thu Jan 17 2013