Section 4 - Root physiology and plant structure (original) (raw)

Biol. Plant. 34 (Suppl.): 523, 1992 Explants from single trees of Abies concolor (Gord. et Glend) Lindl. • Abies grandis (mature embryo), Quercus robur L. (embryonic axis, young stem segments), Quercus rubra L. (young stem segments) and Castanea sativa L. (embryonic axis of mature embryo) were cultured on a callusinducing medium with NAb, or IBA (in Castanea) and BAP. Differentiation of tracheids tn both callus and explant tissues was preceeded by formation of cambium-like cells forming wound procambium zones of different shape. These zones produced tracheidal cells either on their convex side (cambium near to callus surface) or concave side (virtually wound cambium zones), where tracheid nests were produced. These were composed of irregulary arranged short or long and wound tracbeids surrounded by cells of the wound cambium. Tracheid nests originated in callus produced on hypocotyl-radicula region ofAbies explants were composed of nodal tracheids irregular in shape surrounded by the layer of the meristematic cells isodiametric in shape, capable of differentiation into tracheid cells. These tracheids as well as others differentiated in Abies explants had thickened secondary side walls with large circular bordered pits and sometimes, in addition, wound helical thickenings. On the other hand, in tracheids differentiated in callus of Quercus sp. and Castanea small circular or oval non-bordered pits or step-like thickening of secondary wail prevailed.