RESUMO -As características morfogênicas e estruturais da gramínea Panicum maximum cv. Mombaça foram estudadas em função de diferentes níveis de suprimento de nitrogênio e alturas de corte. O estudo foi conduzido em casa de vegetação, sendo avaliadas quatro doses de nitrogênio (0, 50, 100 e 200 mg/dm 3 ) e três alturas de corte (5, 10 e 20 cm). As avaliações morfogênicas englobaram as taxas de aparecimento e alongamento de folhas, filocrono e duração de vida da folha. As estruturais avaliaram o número de folhas, o número de perfilhos e o comprimento final da lâmina foliar. Foi bastante expressiva a resposta da gramínea quanto às suas características morfogênicas em relação ao suprimento de nitrogênio na rebrotação, caracterizando o importante papel do nitrogênio como ferramenta para manipular a estrutura da planta. Todas as variáveis no estudo responderam positivamente ao suprimento de nitrogênio, com exceção do filocrono, que foi reduzido pelo efeito nutricional. As diferenças nas alturas de corte foram significativas para caracterização da duração de vida da folha, assim como para o comprimento de folhas e número de folhas verdes por perfilho. As taxas de alongamento e aparecimento de folhas foram incrementadas em até 133 e 104%, respectivamente, pelo aumento na disponibilidade de nitrogênio. A relação entre ambas as variáveis foi determinante na caracterização das principais mudanças vegetativas observadas. A grande resposta nas características morfogênicas do cultivar estudado constitui eficiente meio para manipular a estrutura do dossel, possibilitando melhor alocação dos recursos produtivos no processo de crescimento e desenvolvimento da planta.Palavras-chave: adubação, altura de corte, estrutura, folhas, morfogênese, perfilhos Morphogenetic and Structural Responses of Panicum maximum cv. Mombaça on Different Levels of Nitrogen Fertilization and Cutting RegimesABSTRACT -The morphogenetic and structural characteristics of Panicum maximum cv. Mombaça were evaluated in response to different levels of nitrogen supply and cutting regimes. The study was conducted in a glasshouse with natural conditions of light and temperature. Treatments corresponded to four levels of nitrogen supply (0, 50, 100 and 200 mg/dm 3 ) and three cutting heights (5, 10 and 20 cm). The morphogenetic evaluations included leaf appearance and elongation rate, phyllochron and leaf lifespan. The structural measurements were: number of leaves, number of tillers and leaf lamina length of fully expanded leaves. The morphogenetic responses were affected by nitrogen supply during regrowth, highlighting the importance of that nutrient for manipulating sward structure. All variables responded positively to nitrogen supply, except phyllochron. Cutting height had a significant effect on leaf lifespan, leaf lamina length of fully expanded leaves and number of green leaves per tiller. Leaf appearance and elongation rate per tiller were increased in 133 and 104%, respectively, by nitrogen supply. The relationship between both group of variables was dete...

RESUMO -Um experimento foi disposto no delineamento em blocos casualizados, sob o esquema fatorial 3x8, três dose de N (0, 20 e 40 mg dm -3 semana -1 de N) e oito tempos de rebrotação (0, 2, 4, 8, 16, 24, 32 Morphogenesis and Structural Characteristics of Regrowth of Brachiaria brizantha cv. Marandu Assigned to Three Nitrogen LevelsABSTRACT -An experiment was arranged in a randomized blocks design, in a 3 x 8 factorial scheme, three nitrogen (N) levels (0, 20 e 40 mg dm -3 week -1 of N) and eight regrowth ages (0, 2, 4, 8, 16, 24, 32 F showed significant effect as the nitrogen level increased. Plants that received 40 mg dm -3 week -1 of N showed phyllochrons inferior (6.99 days leaf -1 ) than those observed in the control (12.20 days leaf -1 ). TA l F was very sensible to the N application and increased as the N level increased (185.24 and 264.32%, respectively, for plants that received 20 and 40 mg dm -3 week -1 of N). CMF showed positive and significant effect, as the nitrogen level increased. N levels and regrowth age showed significant and positive effect on NFVP and PMP. Although the higher NFVP, plants that received N levels had higher loss by senescence. The quantitative factors also showed significant and positive effect on DP.

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Recebido em 11/2/03; aceito em 13/8/03CONTENT AND COMPOSITION OF THE ESSENTIAL OIL OF FIVE ACCESSES OF MENTRASTO. This study aimed to analyse the content and the composition of the essential oil of five accesses of mentrasto (Ageratum conyzoides). Five accesses of mentrasto with three repetitions were used. The accesses were obtained in Mariana-MG (AMA), Piranga-MG (API), Visconde do Rio Branco (ARB) and Viçosa-MG (AVB and AVP). The essential oil was obtained by hydrodistillation and the identification of the oil components by CG and GC/MS. The ARB access presented the higher essential oil content, that is 0.70% (P < 0.05). Eleven chemical compounds were identified. The precocene I was the main constituent in the access API, and the precocene II was the main constituent in the accesses AMA, ARB, AVB and AVP.

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Aluminum (Al) effects on fatty acid composition and on the lipid peroxidation of a puri®ed plasma membrane fraction of root apices of two sorghum cultivars were studied. Palmitic and linoleic acids were the major fatty acids in the root apices of sorghum, independent of the Al presence in nutrient solution. After Al treatment, the C18:0aC18:3 and C18:2aC18:3 ratios increased, while the C18:2aC16:0 ratio remained unchanged in the Al-sensitive cultivar but all three ratios decreased in the Al-tolerant cultivar. The double bond index and unsaturated JOURNAL