Subject: Re: measuring pH of roots

From: [email-masked] (Vikram Prabhu)
Date: 14 Mar 1995 21:48:59 GMT

Amy J. Harris ([email-masked]) wrote:

: I am doing research on determining how much plants(grasses) change the pH 
: of the soil around their roots.  I am currently using a standard pH meter 
: and probe.  I am curious if anyone else has done anything like this.  I 
: have read in the literature about microelectrodes but I don't know 
: anything about them.  The hypothesis is that one grass that I 'm studying 
: can pump protons to acidify the surrounding soil so as to make it 
: "easier" to take up minerals such as phosphorous (PO4).  If you have any 
: information about this topic please send it to my e-mail address.

: Thank you,
: [email-masked]

Theres plenty of literature on this subject, especially see work by Horst 
Marschner and colleagues. Some very elegant pH experiments have been 
done. Also see the importance of proton pumps etc in Fe nutrition by the 
same group. Many grasses have been shown to excrete phytosiderophores as 
a response to Fe deficiency, which is related to the pH of the rhizosphere.

---

From: "Amy J. Harris" <[email-masked]>
Date: Tue, 14 Mar 1995 13:57:58 -0600

I am doing research on determining how much plants(grasses) change the pH 
of the soil around their roots.  I am currently using a standard pH meter 
and probe.  I am curious if anyone else has done anything like this.  I 
have read in the literature about microelectrodes but I don't know 
anything about them.  The hypothesis is that one grass that I 'm studying 
can pump protons to acidify the surrounding soil so as to make it 
"easier" to take up minerals such as phosphorous (PO4).  If you have any 
information about this topic please send it to my e-mail address.

Thank you,
[email-masked]

---

From: [email-masked] (b.morris)
Date: 16 Mar 1995 16:27:47 GMT

: Thank you,

We have done some work in this field in this laboratory. All plants
(measured to date) show some proton pumping at the elongation zone and at
mature root tissue.  Some plants expel protons at the tip others take them up
depending on a number of factors (soil pH, nitrogen status, age of 
root etc...). 
It is possible to use microelectrodes but it can be technically quite time
consuming and also requires specialized equipment.  As a general method try
using bromo-cresol purple in agar and grow up some seedlings from seeds.  The
change in pH can be monitored by a change in colour.This method has been used
successfully with a number of plants. 

In the meantime a few references :- 
Gow,N (1993) Nonchemical signals used for host location and invasion by 
fungal pathogens.  Trends in Microbiology Vol 1, No2, 45-50 
Miller, A.  et al (1988)Ion currents associated with...  Plant Cell 
& Environment 11, p21-25 
Miller A, Gow,N (1989) Correlation between profile of ion-current.....  
Physiologia Plantarum 75, p102-108 
Miller, L.  Gow, N (1989) Correlation between root generated ion-currents, 
pH fusicoccin....  Plant Physiology 89, p1198-1206

I hope this is a useful starting place.
Mike Morris ([email-masked])