Ultrastructure of<i>Eucalyptus grandis</i>×<i>Eucalyptus urophylla</i>. I. Shoots Cultivated<i>in Vitro</i>in Multiplication and Elongation‐Rooting Media

Abstract

Structural changes of the leaf blade of Eucalyptus grandis × Eucalyptus urophylla 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 only 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 play the main role in avoiding water loss. In contrast to normal shoots, the hyperhydric types were characterized by a decline in the number of stomata on the adaxial surface and an enlargement of palisade cells. At the ultrastructural level, the hyperhydric shoots showed chloroplasts with small grana, absence of starch grains, and a higher density of rough endoplasmic reticulum, indicating that their metabolic activity is higher than in normal shoots. In E‐R‐medium‐derived plants, the stomata were sometimes localized in protrusions and were unable to close. However, they were not ultrastructurally altered. In palisade cells of E‐R‐medium‐produced leaves, the peroxisomes increased in number and size; this increase was related to chloroplast enlargement. These observations were thought to be involved in the higher photosynthetic capacity and the increase in metabolic activity required for leaf expansion during root formation. The adaptation of E. $$grandis\times E$$. urophylla to multiplication and E‐R steps of in vitro cultures leads to ultrastructural changes, indicating that the metabolic activity of hyperhydric and rooted plants was higher than in normal plantlets produced in multiplication medium.