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?
-W2
--
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
USA
Voice: (240)895-4365
FAX: (240)895-4996
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