john_hewitson at breathe.com
Thu Dec 4 07:30:59 EST 2003
Like you, this experiment/demo used to work a treat 30 years ago, but
became more and more unreliable such that we dropped it.
Obviously, sterility is important as almost any bacteria will produce
amylase. We dipped the seed samples in diluted bleach, with a small
piece of matchstick as a control to demonstrate that the bleach itself
did not digest starch.
The main problem is that the plant breeders have spent the last 30
years selecting short straw varieties which are resistant to lodging
and can therefore respond to higher doses of N fertiliser with a
heavier head without falling over. These varieties are short straw
because they do not respond to GA in the normal way. They are
non-responsive to GA in the seed's response in amylase production as
well as in the stem's response in elongation growth.
We were able to get a small sample of long-straw barley seed and this
worked well for a few years, but the seed is not easy to get. Long
straw wheat and barley are still grown in UK for thatching straw, so I
guess the varieties are still commercially available.
I know this doesn't completely fit with the results you are reporting,
but it was a partial solution for us.
I'd be most interested in the responses you get to this topic.
Dr. John F. Hewitson
Science and Plants for Schools (SAPS)
Cambridge CB2 2PH UK
Tel: +44 (0)1223 507168
Fax: +44 (0)1223 215004
web site: http://www-saps.plantsci.cam.ac.uk
On Thursday, December 4, 2003, at 02:09 am, Bill Williams wrote:
> Dear Plant-Edders,
> For years now, we've been using a barley-seed amylase assay as part
> of our introductory-biology lab. The students cut barley seeds in
> half cross-sectionally, so one half contains the embryo and the other
> does not. We then incubate the seeds, cut-side down, on agar plates
> containing either plain starch or starch plates spiked with GA. The
> idea is that the halves with embryos, and also the halves without
> embryos but with exogenous GA, will synthesize amylase. The amylase
> will digest some of the starch in a ring around the seeds, and
> developing the plate with iodine will reveal these rings.
> Every time we do this, we get large rings around the GA-treated,
> embryo-free seed halves. Sometimes we get small rings around the
> embryo-containing seed halves and sometimes hardly any ring at all,
> even if the seed-halves have germinated. Last year, we got rings
> around *everything*!
> Any idea what we're doing wrong? For the rings around the non-GA
> seeds, could improper storage of the seeds (e.g., getting them damp)
> have caused enough GA synthesis that the embryo-free halves were
> already synthesizing amylase before we cut them open? And, can anyone
> suggest why we so consistently get tiny rings, if any rings at all,
> in the seed halve with embryos but without exogenous GA?
> William E. Williams <MailTo:WEWilliams at smcm.edu>
> Biology Department
> Saint Mary's College of Maryland
> 18952 E Fisher Road
> Saint Marys City, MD 20686-3001
> Voice: (240)895-4365
> FAX: (240)895-4996
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