"Harvey Brenneise" <[EMAIL PROTECTED]> queried thusly: > Does anyone out there know of any work done with orchid seed viability, > particularly long-term and/or of seeds stored at very low temps?
There are a few papers out there; they're all referenced in my first book, and I can fetch those up if you really want to go back to the literature. About 99% of what we store is refrigerated at 4C, maintained over doubled calcium chloride (individual containers have calcium chloride slurry, and refrigeration units are dried with calcium chloride) to provide the right moisture balance. Although some are surprisingly short-lived, we've had good experiences with seeds that have been stored for years- even labile genera, like Stanhopea. Just had one accession that was 3-4 years old come up quite nicely, although that is an exception. We do maintain stores of seeds in liquid nitrogen for research purposes. The great thing about this kind of work is that the data tend to get better with age (even if it is a sort of binary response, making it tough to say precisely WHEN a given accession is flat-out nongerminable due to age), making it perfect for procrastinators like myself. Orchid seeds can be stored in liquid nitrogen and maintain their germinability; of the very few we've tested, it compares well with seeds that were never placed into cryogenic storage. However, there may be a difference between LN2 (at -196C) and deep refrigeration (at -70 or -80), and there's certainly a difference between these and domestic freezers (at -20); orchid seeds don't really freeze at -20. Instead, the liquid components turn into a biological glass. This is important as freeze-fracturing is what normally kills plant cells- the expansion of water as it freezes, shattering membranes and so forth. With orchid seeds, the endotherm (as gauged by differential scanning calorimetry- Pritchard and Seaton's work, although I did a very little bit of it back when I was an explosives chemist and had access to a DSC) is rather lower. I'd have to look up the values to be certain. Anyway- it's well below -20C, meaning that frozen storage (in domestic freezers) may be more effective than 4C while more convenient than -70 (or lower) without any additional damage. There are concerns with cycling, however, and this gets into some pretty deep issues in physical chemistry and why seeds die; there are also handling issues, and problems with moisture cycling (wet/dry from condensation)- even just on the packaging, which later translates to the seeds. If Dr. Norman Deno is correct, then moisture may play a much larger role in telomere degradation than is generally thought and casually cycling seeds through temperatures (as in pulling the box out to retrieve seeds, then replacing it) may have a greater role in shortening seed life than has been previously thought. This is one of the nice things about LN2- as the temperature of the boiling liquid nitrogen (as it is stored in a Dewar) is very nearly a constant, there is no cycling at all. The nitrogen itself is chemically inert, and may interact less with the seeds than wonderfully corrosive atmospheric oxygen. Best of all, a Dewar and a fill of LN2 is far less expensive than a -70 or -80 freezer, and the operating costs (about $10/month for adding more LN2) is probably less than the cost of keeping a freezer plugged in. Of course, the space is smaller- but if there's one kind thing afforded by orchid seeds, it's their space requirements. At least I'm not the coconut seedbank. Cheers, -AJHicks The Orchid Seedbank Chandler, AZ _______________________________________________ the OrchidGuide Digest (OGD) orchids@orchidguide.com http://orchidguide.com/mailman/listinfo/orchids_orchidguide.com
