visualizing potato plasmolysis

Han Asard hanasard at RUCA.UA.AC.BE
Wed Jan 31 05:40:41 EST 1996



On 31 Jan 1996, John Hewitson wrote:

> We have done a similar practical for many years, but our solution has been to
> use Rhubarb petiole epidermis (some of the cells contain pigment), or more
> recently, Onion bulb scales' epidermis (which being 1 cell thick, is easy tissue
> in which to observe plasmolysis).
> 
> It is possible to estimate Water Potential using Chardakov's Method and Osmotic
> Potential by Incipient Plasmolysis.
> 
> There are some "tricks of the trade":-  Strip the epidermis and plunge it
> straight into sucrose (else it dries very quickly). Immerse the epidermis in
> only a small amount of sucrose solution (to get sufficient change in the density
> of the sucrose to respond to Chardakov's in only 15 mins).
> 
> What puzzled my students and me was that the Pressure Potential which we
> calculated from the above gave us a figure of about 10 atmos - which seemed
> incredibly high - about the pressure of a lorry tyre!! Can this be true?
> 
> It is a good experiment to do anyway - gets students thinking and juggling all
> three terms and equations.
> 

We have done the same experiment with students for several years now. 
Like John wrote, onion epidermis peels are quite useful in particular 
when one uses 'red onion'. The discrimination between cell wall and 
protoplast becomes very easy with this material. It is also highly 
instructive to starting plant biology students. 

There is one more trick that I would strongly recommend: when epidermal
strips in sucrose solutions are brought under vacuum (for about 10 min)
the plasmolysis is even faster and much more reproducible. Also more
samples can be processed yielding reasonable averages. I found it a good
question to students asking why vacuum speeds up this process. It also
illustrates the use of 'unexpected' techniques in plant physiology
experiments. 

Good luck.
Han Asard

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