This study investigates the seasonal variation of three species of Leptospermum (Myrtaceae) grown in Brazil. The chemical composition of the volatile oils of L. flavescens and L. petersonii did not show any significant seasonal variation in the major components, while for Leptospermum madidum subsp. sativum the levels of major constituents of the volatile oils varied with the harvest season. Major fluctuations in the composition of L. madidum subsp. sativum oil included α-pinene (0-15.2%), β-pinene (0.3-18.5%), α-humulene (0.8-30%), 1,8-cineole (0.4-7.1%) and E-caryophyllene (0.4-11.9%). Levels of β-pinene (0.3-5.6%), terpinen-4-ol (4.7-7.2%) and nerolidol (55.1-67.6%) fluctuated seasonally in the L. flavescens oil. In L. petersonii, changes were noted for geranial (29.8-32.8%), citronellal (26.5-33.9%) and neral (22.7-23.5%). The activity of the volatile oils against the tested bacteria differed, depending on season the oils were obtained. In general, the volatile oils were more active against Gram-positive bacteria.

Recebido em 10/2/09; aceito em 24/6/09; publicado na web em 13/11/09The essential oils of seven Myrtaceae species were investigated for its chemical composition and antibacterial activity. The volatile oils were characterized by a high content of monoterpenoids of which 1,8-cineole (88.0, 65.0 and 77.0% for Melaleuca hypericifolia, Callistemon viminalis and Callistemon citrinus respectively), terpinen-4-ol (47.0 and 49.8% for Melaleuca thymifolia and Callistemon polandii respectively) and α-pinene (54.5% for Kunzea ericoides) were the major components. The oil from M. linariifolia was characterized by a high concentration of methyleugenol (87.2%). The oil from Melaleuca thymifolia was the most active, exhibiting high antimicrobial activity against all tested bacteria.

Colleters are secretory structures that occur in vegetative or reproductive shoot apices of many botanical families. However, in the order Myrtales, reports of colleters have considered only external morphology. We therefore evaluated apical meristems of 52 species belonging to 17 genera from seven tribes of subfamily Myrtoideae (Myrtaceae), so as to analyse the incidence and morphological types of colleters. The samples were fixed for light and scanning electron microscopy. Histochemical tests were carried out on fresh and methacrylate-embedded material. Proteins of the colleter secretions were analysed by SDS-PAGE. We have classified and described the following three new colleter types: petaloid, conic and euryform. None of the species contained all three colleter types. The petaloid colleters were present in three tribes (Syzygieae, Melaleuceae and Lophostemoneae). The conic colleters were observed in three tribes (Leptospermeae, Myrteae and Melaleuceae) and the euryform type occurred in five tribes (Leptospermeae, Syncarpieae, Myrteae, Syzygieae and Melaleuceae). In the tribe Eucalypteae, we found no evidence of colleters. The presence of mucilaginous secretion that defines colleters was confirmed by histochemical tests, and no proteins were found in the secretion. The colleters in Myrtoideae may help clarify the phylogenetic relationships of the Myrtaceae family.

RESUMO. O efeito de estresse hídrico sobre o teor, a composição química do óleo essencial e o crescimento de Melaleuca alternifolia Cheel (Myrtaceae) foi estudado. Cada tratamento constituiu-se de um regime hídrico: 1-irrigação em dias alternados com 0,5 L de água por vaso; 2-irrigação diária com 1 L de água por vaso; 3-lâmina de 1 cm de água (1 L) e 4-lâmina de 10 cm de água (12 L). A deficiência hídrica severa diminuiu o crescimento, a produção de biomassa fresca e seca das plantas e o teor de óleo essencial. Os principais constituintes do óleo essencial de M. alternifolia não diferiram significativamente entre os tratamentos, com 1,77 a 3,22% para o p-cimeno, 1,86 a 3,54% para o 1,8-cineol, 9,05 a 10,25% para o α-terpineol, 19,10 a 20,80% para o γ-terpineno e 37,89 a 39,37% para terpinen-4-ol.Palavras chave: Myrtaceae, terpenos, 1,8-cineol, efeitos ambientais, α-terpineol, tea tree.ABSTRACT. Effect of the water stress on the growth and the essential oil production of the Melaleuca alternifolia Cheel. The effect of water stress on the production, chemical composition of the essential oil and on the growth of Melaleuca alternifolia Cheel (Myrtaceae) was investigated. Each treatment consisted of a water regime (1-irrigation with 0,5 L of water per pot every two days; 2-irrigation with 1L of water per pot every day; 3-the pots were kept in a container with 1 cm of water (1L); 4-the pots were kept in a container with 10 cm of water (12L). The severe water deficiency resulted in a reduction in the plant growth, production of fresh and dry biomass and in the essential oil. The major constituents of the essential oil of M. alternifolia did not differ significantly among the treatments, with 1.77 to 3.22% for p-cymene, 1.86 to 3.54% for 1,8-cineol, 9.05 to 10.25% for α-terpineol, 19.10 to 20.80% to γ-terpinene and 37.89 to 39.37% for terpinen-4-ol.Key-words: Myrtaceae, terpenes, 1,8-cineol, environmental effects, α-terpineol, tea tree. IntroduçãoA adaptabilidade das plantas em condições de estresse é influenciada pela duração e magnitude do estresse, além da variabilidade genética. A concentração de princípios ativos nas plantas depende do controle genético e também das interações genótipo e ambiente, que podem ser desencadeadas em condições de estresse, ou seja, excesso ou deficiência de algum fator do meio ambiente, como água, luz, temperatura, nutrientes, dentre outros (Andrade e Casali, 1999).A água é essencial à vida e ao metabolismo das plantas, portanto, seria esperado que em ambientes mais úmidos a produção de princípios ativos fosse maior. No entanto, para algumas plantas medicinais a maior disponibilidade de água pode diminuir a produção de óleo essencial. Alguns estudos têm verificado que plantas com deficiência hídrica são mais vulneráveis a pragas e doenças, porém a resposta quanto as defesas químicas de muitas espécies ainda não está bem esclarecida (Andrade e Casali, 1999). Em condições de baixa disponibilidade de água no solo, vários processos metabólicos nas plantas podem ser influenciados, como o fec...

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