Water loss and anatomical modifications in leaves of micropropagated banana plants during acclimatization/Perda de agua e modificacoes anatomicas em folhas de plantas de bananeiras micropropagadas durante a aclimatizacao

Studies concerning factors involved in the adaptation of micropropagated plants to ex vitro conditions are indispensable to define which procedures should be used during the acclimatization phase. The objective of this research was to evaluate the presence of stomata and epicuticular wax on water loss control in micropropagated banana plants. For 24 days axillary buds were rooted in MS medium supplemented with NAA (1mg [L.sup.-1]) and agar (6g [L.sup.-1]), and afterwards the plantlets were acclimatized for 120 days. The treatments consisted of the evaluation of in vitro leaves and at different acclimatization stages, as follows: T1--leaves of plants at the end of the in vitro rooting phase T2--persistent leaves of plants after 30 days of acclimatization; T3--new leaves from plants after 30 days of acclimatization (transition leaves); T4--transition leaves from plants after 60 days of acclimatization; T5 and T6--new leaves from plants after 60 and 120 days of acclimatization, respectively. Data regarding stomatal density, relative water content and presence of epicuticular wax were also evaluated. It was verified that new leaves from plants rooted in vitro under mixotrophic condition presented hight stomatal density and hence a reduced control of water loss. The reduced transpiration of leaves formed during the acclimatization phase can be attributed to the small number of stomata per unit of leaf area associated to the largest capacity of these in restricting water loss, and the presence of epicuticular wax. Key words: Musa spp., stomata, leaf transpiration, epicuticular wax. Estudos sobre os fatores envolvidos na adaptacao das plantas micropropagadas ao ambiente ex vitro sao imprescindiveis para definir quais os procedimentos devem ser utilizados durante a fase de aclimatizacao. O objetivo deste trabalho foi avaliar a contribuicao da densidade estomatica e da presenca de cera epicuticular no controle da perda de agua, em folhas de bananeiras micropropagadas. Para tanto, brotacoes axilares oriundas da etapa de multiplicacao in vitro foram enraizadas por 24 dias, em meio MS, contendo 1mg [L.sup.-1] de acido naftalenoacetico (ANA) e 6g [L.sup.-1] de agar e, posteriormente, foram aclimatizadas por 120 dias. Os tratamentos consistiram de folhas formadas in vitro e em diferentes estadios de aclimatizacao, tais como: T1--folhas de plantas ao final da fase de enraizamento in vitro; T2--folhas persistentes de plantas aos 30 dias de aclimatizacao; T3--novas folhas