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Secrets of Stomata: How Plants Balance Water and CO2 · Hydroponics Daily

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  Hello there and welcome back to
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  Hydroponics Daily, your go-to podcast for everything soilless cultivation.
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  I'm your host, Dr. Russell Sharp, the founder of Eutrema Limited,
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  where we make interesting fertilisers, novel biostimulants and organic biopesticides.
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  However, before I was an entrepreneur making fertilisers and inventing new fertilisers
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  and things like this, I was an academic plant scientist, a plant physiologist to be precise.
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  And one of the things you do as a plant physiologist
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  certainly where in the area i was working in was study water deficits
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  and key to that is looking at stomata now
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  stomata are the pores on your leaves that allow gases to be exchanged with the
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  air simple as that now stomata are the holes they are not the structure so they're
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  just the hole just like the pupil of your eye although i am not an animal scientist
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  so I don't even know if it's true or not.
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  So basically a stomata is made of two guard cells and those guard cells are very clever.
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  They can fill with liquid and close or they can empty of liquid and open.
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  So it depends on their turga pressure how open or closed the stomata are and
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  when the stomata are closed the plant can limit the amount of water that it
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  loses and that's useful if they become stressed.
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  If there's a drought then they can close their stomata and limit the amount
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  of water they lose. The same at night.
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  They don't need to open their stem master at night, so they close them and limit the water.
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  They lose, apart from tomatoes, apparently. Sorry, potatoes.
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  Potatoes, apparently they keep their stomata open 24 hours a day,
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  probably because they're growing in, they need the calcium to get,
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  and the calcium is absorbed in the soil, so they just keep them open all night,
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  get that calcium in, and they're growing in soil that's got loads of water anyway,
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  so they don't bother closing them at night.
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  That's what I'm told anyway. I've never actually researched it or looked at
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  it, but that's what I'm told from the research.
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  Now, why even open them in the first place?
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  So the reason why they open them and they lose water is because they need to exchange gases.
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  CO2 needs to diffuse in. It doesn't suck in. It has to diffuse in and oxygen has to diffuse out.
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  And a byproduct of that is that water escapes at the same time.
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  Just like when you're breathing, You lose a lot of water in your breath You
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  can't help that If you're in the desert You can't help losing water in your
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  breath So a plant can't help losing water When it's exchanging gases So.
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  The inside of it, the leaf, is covered in liquid. All the cells are wet inside a leaf.
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  And that's because it aids CO2 and O2 diffusion back and forth into the air.
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  Just like your lungs are all wet. If you were to go inside your lungs,
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  it would be covered in moisture.
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  And that's to aid oxygen absorption and CO2 release.
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  So the same thing in your lungs as happens in a plant,
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  except the two gases the different gases are going
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  a different way obviously in your lungs you breathe
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  in you suck in but plants don't
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  do that so they have to rely on diffusion so the leaves
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  have to be have to be sorry the cells inside
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  the leaf have to be wet for that exchange to happen
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  so there's a bit of a balancing act between the amount of
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  water lost and the amount of co2 that's being absorbed now things like cacti
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  we've talked in the past they can absorb co2 at night so they open their stomata
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  at night and then close them during the day and that limits the amount of water
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  that's being lost but most plants they're opening during the day and the peak
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  around peak happens around.
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  12 o'clock, noon, midday, which in the summer is at 1 o'clock.
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  And the stomata regulates that. Very little diffusion occurs through anywhere
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  else in the plant, gas exchange.
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  And most of the stomata are positioned on the underside of the leaf.
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  So 90, 95% of all the stomata are on the underside of the leaf.
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  Most plants have next to no stomata on the top side.
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  The top side is normally waxy and you you take
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  a house plant and look at it you'll find the top is very waxy and a
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  different color to the underside that's because that's where the gas
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  is exchanged on the underside and the leaf is the light is
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  being absorbed at the top so if you look at the structure of
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  a leaf you'll find what's called the palisade cells it's called
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  the palisade cells because they look like a fence the
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  striped fence the cells are all lined up their job
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  is to capture sunlight and they're at
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  the top of the leaf and the ones at the bottom they're spongy they
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  look like the lungs the cells in your lungs and
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  they are there to exchange gases that's their job now some
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  plants that will have equal stomata
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  on both sides so maybe like certain grasses or things
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  like that but they are the exception and not the real so we
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  said the stomata are the holes and the aperture how wide they're open governs
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  how much they like how much they'll lose the amount of stomata can be an influence
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  on how much gas exchange occurs but it's really about how open they are because
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  the cells push together, the guard cells,
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  and tightly close and limit virtually any water loss.
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  Now, how open they are, how close they are, how much gaskets, how much.
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  Water gets lost in from the stomata
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  is measured using something called a parometer and
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  that measures the oh just got
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  called away there where was i i was measuring the stomatal
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  conductance how easily gases are exchanged
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  how open the stomata are and that's measured
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  using a parometer as i said and it's measured in
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  the units micromoles per meter squared per second
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  so how much gas can get through a square
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  meter per second and using the parameters
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  really quick and easy it's a lot less laborious than
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  putting leaves under microscopes and seeing how they
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  open they are measuring how open the aperture is
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  and also you've got to remember that as soon as you take a leaf
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  and put it under a microscope you're changing the conditions so you
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  might get a lot more stressed and not really being representative
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  so you can use stomatal conductance
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  as a measure of stress a measure of water stress particularly and
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  so when you dry a plant out or even when you flood it it will
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  close its stomata if you stress it in any way it'll probably
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  close its stomata so promises are really useful pieces of kit
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  and they'd be used in plant physiology for a while for measuring how open the
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  stomata are and how much gas is being exchanged unfortunately they're still
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  really expensive and not widely available and so you can't really integrate
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  them into a medium or small-scale hydroponic unit.
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  You might have one to experiment with if you're a large-scale hydroponic grower,
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  but parameters still are out of the realms of most growers, unfortunately,
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  because the technology's not really epic.
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  It's just nobody's decided to produce a low-
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  Cost option because not many people want
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  them so unfortunately that's that's the case however
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  there is an easy way of looking at your stomata and
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  seeing if they're open or closed and it's not to just put your leaf under a
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  microscope because if you do that i've told in the past about how dissecting
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  microscopes are really good you just throw a leaf or throw a mite or a spider
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  mite or an insect under there and you can look at it whereas the normal microscopes
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  the type you talk about using school or university,
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  they're compound microscopes, and for them you need a thin layer of.
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  To actually see anything because the water the light needs to travel through the cells,
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  and so you have to use something called a microtome to make
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  small slivers and then put them on
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  a on a microscope slide and put some water there and a cover slip and be very
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  careful so that's not really you can't really do that with stomata because by
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  the time you've done that the stomata are all closed what you can do and this
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  is my top tip and um definitely you should try this because you can get some wicked,
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  wicked images doing it,
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  is to take your leaf on your plant and then apply a very small layer of clear nail varnish to it.
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  So when I was a plant physiologist, I had a drawer full of clear nail varnish,
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  even though my nails are terrible.
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  And I used to do, you paint on nail varnish onto my leaves, and then after it's dried,
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  you peel off the nail very carefully otherwise you can
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  deform the image of the cells that
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  you get and you get an absolute mirror image of your cells and
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  anything else that's on the leaf surface say if it's
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  trichomes or unusual shaped epidermal cells veins xylem phloem veins then you
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  can picture all this with and you get a black and obviously a black and white
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  image of what it looks like on your leaf So you take the peel,
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  you put it on a microscope slide,
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  place it nice and flat, maybe we'll put a cover slip over it,
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  and then just look at it under a microscope,
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  times 10, times 40, and you can see all the stomata, and you can see if they're
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  open or closed, you can see how many there are, the density,
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  and in Planck physiology we use this method, the nail varnish technique,
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  mainly to look at density, to count how many stomata there are per person.
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  Square millimeter and that's really useful because if
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  you stress the plant for long enough the new leaves that produced may have
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  more or less stomata more or
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  fewer stomata and and so
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  that's a really good useful tool so although it's a easy and
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  almost a silly method it does have is
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  very useful it's one of the methods we use to look to
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  study stomata so i definitely recommend that
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  and if you're just curious about looking
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  at your stomata it's really good so hydroponic growers tend to.
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  Be very inquisitive tend to be into botany and
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  plant science and so even if you have no need to measure
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  your stomata and look at your stomata you'll probably
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  do this now you'll get some clear nail varnish and from
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  boots or super drug or i don't know where do
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  you get where do you get nail varnish in america cvs something like that
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  or from your girlfriend or your partner and your
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  wife if you're a man or yourself or your
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  mom or your sister or your daughter and you'll
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  be applying it to your plants all your different plants that you're growing your house plants your
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  crops and seeing what the stomata look like if you found anything
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  useful interesting then please do let me know
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  send me a message you've got other ways of
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  measuring stomata then let me know as well if you
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  found this podcast useful then please leave us an apple podcast review if you're
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  leaving if you're listening on apple if you're not listening on apple leaving
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  to spell utreema it's latin for wasabi so just google that thank you very much
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  for listening to hydroponics daily for today and i'll see you again tomorrow.