Boron controls suspensor development in embryogenic cultures of Larix decidua

Suspensor formation in somatic embryos of Larix decidua Mill. was studied in relation to its dependence on nutritional factors of the culture medium. Protoplasts exhibiting embryogenic competence were prepared from an embryogenic suspension culture, immobilized in Ca-alginate and cultured in liquid media. Developmental patterns showed qualitative differences in the two basic media used. In one medium, containing 100 mu M boric acid, compact colonies developed, most of which displayed formation of polar suspensors after 3 to 4 weeks. In contrast, suspensor development never occurred in the other medium, containing 10 mu M berate, yet colonies of loosely connected cytoplasmically dense cells were regenerated without loss of embryogenic competence. Detailed examination of the constituents of the two media led to the conclusion that suspensor development is dependent on boron concentration: below 35 mu M boron, suspensor formation is blocked completely, whereas with an increase up to 1 mM boron there is a progressively faster development of suspensor-bearing embryos.