Charcoal in Seed Medium....
 

Does anyone know the benefit and/or circumstance for using charcoal in seed media? i.e. Should it be used when sowing, during re-plate, both? Why? Just something I've been curious about, ever since I started shopping for media. Figured someone out there must know.... Thanks in advance!

I remember reading somewhere that it acts as an absorber of harmful substances that are released during culture (ie polyphenols, which can induce browning off of seedlings). I did a quick literature search and came up with the following article:

Article on charcoal and in vitro culture

So far, all the sowing I've done has been on media with activated charcoal :)

I think I got lost in there! I didn't find the actual article, but you're explanation sounds highly probable....thanks for the input.

Adsorbsion of 'bad stuff' and darkening of media seems to benefit the roots of some species.

It will adsorb the good with the bad - it can't tell.

Must be some sort of licensing thing - I can't access it from my home computer either, but I can on my laptop at the university.

Here's an excerpt with the main points:

"Activated charcoal is commonly used in tissue culture
media due to its structure, and its addition may
have either beneficial or harmful effects, especially
on organogenesis and embryogenesis. The effects of
activated charcoal could be attributed to (a) providing
a dark environment in the medium; (b) adsorption
of certain inhibitory substances in culture, produced
by either media or explants; (c) adsorption of plant
growth regulators and other organic compounds; and
(d) the release of substances naturally present in or
adsorbed by activated charcoal, which are beneficial
to growth of in vitro culture.
Use of charcoal in culture medium may either
promote or inhibit growth in vitro, depending on a
number of factors. Most publications have concentrated
on the promotive effects on tissue response in
vitro culture. Addition of activated charcoal in culture
medium may affect growth especially rooting, shoot
elongation and embryogenesis. Activated charcoal
can provide a dark environment and adsorb substances
presumed to be deleterious and/or inhibitory to in vitro
culture, but adsorption of growth regulators being
supplied to the tissue by activated charcoal could also
occur at the same time. The non-selective adsorption
effect of activated charcoal may result in negative
effects on cultured explants. Some researchers
noted that activated charcoal adsorbs thiamine, nicotinic
acid [80], pyridoxine, folic acid [32], growth
regulators, iron chelate [29, 32], and Zn. Both Fe
and Zn were only slightly adsorbed in the presence
of sucrose [47]. The adsorption of the plant regulators
may result in inhibitory effects on growth in
vitro."

Pan, M.J., Van Saden, J. The use of charcoal in in vitro culture – A review. 1998. Plant Growth Regulation. 26:155-163.

Thanks Calvin, that's what I was looking for!