Is it possible to extract tissue-culture material from a seed?
Yes. It's quite common, to the degree that it's done by some hobbyist plant breeders. See en.wikipedia.org/wiki/Embryo_rescue  However, AFAIK (I'm not an expert), it wouldn't be done for raising multitudes of plants, like tissue culture.  

Rather, it's used in hybridization, where you hope to produce hybrids from plants that don't readily hybridize.  You would typically rescue a number of embryos, grow them on until mature, then perhaps use tissue culture to mass-propagate the ones that have interesting characteristics.