Date: Wed, 6 Aug 1997 08:45:42 +0200 (MET DST) From: Guy Van Der Kinderen <Guy.VanDerKinderen@rug.ac.be> To: cp@opus.hpl.hp.com Message-Id: <aabcdefg2971$foo@default> Subject: Ping seed germination
Dear Laurent (Legendre), Loyd, and others,
Have been reading the information-exchange on Ping seed
germination with great interest, and also thank Loyd for his valuable
information. I was very surprised (and then again, maybe not) about the
similarities between my experiences with temperate orchids and data
concerning Pings. Dormancy in seeds of temperate plant species is not
uncommon, and even the small seeds of orchids may show biochemical (ABA)
or mechanical dormancy. I published some papers about experiments on this
matter, in which a correlation could be shown between ABA content and
germination behaviour. Further experiments showed that ABA, as in most
other plants, is present in the integuments, and may be leached out with
water. The 'seed-shell' or carapax itself, may impose mechanical dormancy,
witch cannot be released simply by water: scarification as in Drosophyllum
may help in this case. Both dormancies may however be released by
treatment with hypochlorite solutions. And this may be an alternative for
seeds in which even the more convenient method of Loyd does not work. The
technique has already been mentioned indeed in Rick Walkers' 'Tissue
culture in the Home Kitchen', by private correspondance with Jan Schlauer
(Hello Jan). The method involves carefull observation of the
affection/desinfection process of the seed coats with a hypochlorite
solution (I prefer the clear supernatant of a saturated basic
calciumhypochlorite solution with a few drops of Tween 80). The process
ends when seed coats change color: black seeds may turn brownish, brown
ones straw-colored, as described by Jan. Seeds are subsequently washed
with (sterile) water and sown.
Regarding ABA released by Ping leaves in vitro, I have some
comments. Although I do not know the details of this problem, I'm not sure
it concerns ABA (or only ABA) in this case. Some years ago, somebody (I
think Miloslav Studnicka) discussed this problem with me, and also
mentioned a brown coloration of the medium, which may be caused by
polyphenolics, again as in orchid culture. They inhibit further growth of
plantlets, unless special additives are put in the growing medium (or use
the Studnicka method). Mostly active carbon is added to adsorb these
compounds. I've seen it being used here by a commercial grower, in cloning
media for Sarr., Darl., Ping., Genlisea, Drosera, Byblis, Cephal., Heliam.
and Utrics.
As far as I know, dormancy-release by exogenous gibberellins is
rather uncommon, but it clearly does occur. As I recall, ABA and GA's have
the same precursor (mevalonic acid) and the balance towards one of them
may be triggered in several ways, such as cold stratification, but also
cytokinins. For thos who like some experimenting, one may try another
orchid-derived receipe: the addition of coconut-milk to the germination
medium.
Thats all from me now; have to work a little bit.
Friendly regards,
Guy VdK
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