DEVELOPMENTAL PATTERN OF ROOT AND SHOOT ORGANOGENESIS IN CULTURED LEAF EXPLANTS OF NICOTIANA-TABACUM CV XANTHI NC

Caulogenesis and rhizogenesis were studied in cultured leaf explants of Nicotiana tabacum cv. Xanthi nc. using both light and scanning electron microscopy. The timing of organ appearance was also recorded. The patterns of development seen were compared to each other and to that in explants grown on growth regulator-free medium. Shoots first appeared after 12 d in culture and roots after 7 d. In caulogenesis nodules appear at the explant edge and from these the shoots arise. The nodules are mainly derived from palisade mesophyll cells, along with some spongy mesophyll and bundle-sheath cells. The nodules form a continuous row along the edge of the explant and their initiation appears to be centred on veins. Shoots are produced indirectly. Roots are produced directly from bundle-sheath and vein parenchyma cells. Without plant growth regulators bundle-sheath cells still divide, although only a few divisions were seen.