Ultrastructure of Eucalyptus grandis x Eucalyptus urophylla. I. Shoots cultivated in vitro in multiplication and elongation-rooting media

Structural changes of the leaf blade of Eucalyptus grandis x Eucalyptus uro phylla shoots from multiplication and elongation-rooting (E-R) steps of in vitro cultures were analyzed by electron microscopy and morphometry. Normal and hyperhydric shoots were produced in a multiplication medium, while onl y normal plants were transferred to an E-R medium. In both plant types, the wax deposit and cuticle layers were thin, indicating that they did not pla y the main role in avoiding water loss. In contrast to normal shoots, the h yperhydric types were characterized by a decline in the number of stomata o n the adaxial surface and an enlargement of palisade cells. At the ultrastr uctural level, the hyperhydric shoots showed chloroplasts with small grana, absence of starch grains, and a higher density of rough endoplasmic reticu lum, indicating that their metabolic activity is higher than in normal shoo ts. In E-R-medium-derived plants, the stomata were sometimes localized in p rotrusions and were unable to close. However, they were not ultrastructural ly altered. In palisade cells of E-R-medium-produced leaves, the peroxisome s increased in number and size; this increase was related to chloroplast en largement. These observations were thought to be involved in the higher pho tosynthetic capacity and the increase in metabolic activity required for le af expansion during root formation. The adaptation of E. grandis x E. uroph ylla to multiplication and E-R steps of in vitro cultures leads to ultrastr uctural changes, indicating that the metabolic activity of hyperhydric and rooted plants was higher than in normal plantlets produced in multiplicatio n medium.