The germination of three cerrado herbaceous species: Bidens gardneri, Vernonia herbacea (Asteraceae) and Psychotria barbiflora (Rubiaceae) was studied using seeds stored in cerrado soil and in refrigerator at 4°C. The field experiment was carried out at a preserved area of cerrado, the Reserva Biológica e Estação Experimental de Mogi-Guaçu, State of São Paulo, Brazil. The soil was collected in the same cerrado where the experiment was carried out. The achenes of Bidens gardneri are light sensitive, but this sensitivity disappeared when the achenes were stored in soil. With 3 months storage in cerrado soil no differences in germination in light or darkness were detected. The number of intact achenes retrieved from storage in soil decreased with increasing time of storage. A large number of seeds had already germinated during the 3 months storage in soil. The longevity of seeds of this species stored for nearly 10 years at 4°C was checked: the achenes were viable for a long period of time but less than 10 years. Intact achenes of Vernonia herbacea could be retrieved from the soil only with 1 month storage. Germination was always very low and only 15% of the achenes possessed embryos. The number of intact seeds of Psychotria barbiflora decreased the longer the period of storage in soil. Germination of seeds stored at 4°C or in the soil was always very low. From the germination studies of stored seeds in cerrado it can be concluded that Vernonia herbacea does not form a seed bank and Bidens gardneri and Psychotria barbiflora may form a temporary seed bank in cerrado.

Two saprophytic fungi (Mucor ramosissimus and Rhizopus sp.) were tested for their ability to induce phytoalexin production by seeds of frog-eye leaf spot and stem canker-resistant and -susceptible soybean (Glycine max L.) cultivars. Only M. ramosissimus was shown to elicit a response and qualitative differences in phytoalexin accumulation were found between the susceptible and resistant cultivars. Glyceollins I, II, and III and glycinol were isolated from the susceptible cultivar, whereas Glyceollins I, II, and III, glycinol, glyceocarpin, genistein, isoformononetin, and N-acetyltyramine accumulated in the resistant cultivar in response to the same fungal elicitor. Genistein was found to be an inducibly formed isoflavonoid instead of a constitutive metabolite in the resistant cultivar, whereas N-acetyltyramine is described for the first time as a soybean phytoalexin. All the compounds, except genistein, showed fungitoxic activity against Cladosporium sphaerospermum. Spectral data of the pterocarpan phytoalexins, genistein, and N-acetyltyramine are also given in this work.

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-(Effects of moisture content and temperature during storage on germination of the achenes of Bidens gardneri Baker). Bidens gardneri is a herbaceous species of the cerrados, whose seeds are light sensitive at 25°C, but they become indifferent to light when stored in soil. In this work the effects of moisture content, temperature and light (during storage) upon light sensitivity during germination were studied. Ripe achenes were collected in the cerrados of Itirapina and Moji Guaçu, State of São Paulo, Brazil. The storage conditions of the achenes varied in each experiment. Achenes were stored in darkness or light, in closed bottles, at 4°C, 20/30°C or 25°C. Achenes were imbibed for 24 h at 4°C, 25°C or 20/30°C (in darkness) and then stored for 1, 10, 20, 30 and 40 days (40 days only for 4°C and 25°C). Germination tests were conducted at 25°C and 20/30°C. The achenes not previously imbibed showed sensitivity to light during germination. High moisture content did not affect light sensitivity of the achenes during germination but high moisture content together with storage temperatures of 25°C and 20/30°C had a deleterious effect upon the longevity of the achenes. Alternate temperatures during germination did not change the light sensitivity of newly collected achenes from Itirapina but changed the light sensitivity of the achenes stored imbibed at 4°C in darkness. Alternate temperatures during storage of achenes with low moisture content did not change their photoblastism when germination was carried out at 25°C. Alternate temperatures during storage of achenes with high moisture content followed by alternate temperatures during germination changed the light sensitivity of the achenes.RESUMO -(Efeito do conteúdo de água e temperatura durante o armazenamento na germinação dos aquênios de Bidens gardneri Baker). Bidens gardneri é uma espécie herbácea dos cerrados, cujas sementes são fotoblásticas positivas a 25°C, mas tornam-se indiferentes à luz quando armazenadas em solo. Neste trabalho, foram estudados os efeitos do conteúdo de água dos aquênios, da temperatura e da luz (durante o armazenamento) na sensibilidade à luz durante a germinação. Os aquênios foram coletados nos cerrados de Itirapina e de Moji Guaçu, estado de São Paulo, Brasil. As condições de armazenamento variaram em cada experimento. Os aquênios foram armazenados no escuro ou em luz, em vidros fechados a 4°C, 25°C e 20/30°C. Os aquênios foram embebidos por 24 horas a 4°C, 25°C e 20/30°C (no escuro) e então armazenados por 1, 10, 20, 30 e 40 dias (40 dias somente para 4°C e 25°C). Os testes de germinação foram conduzidos a 25°C e 20/30°C. Os aquênios que não foram embebidos apresentaram sensibilidade à luz durante a germinação. O conteúdo alto de água durante o armazenamento não afetou a resposta à luz dos aquênios durante a germinação, mas o conteúdo alto de água em temperaturas de armazenamento de 25°C e 20/30°C tiveram efeito deletério na longevidade dos mesmos. As temperaturas alternadas durante a germinação não alteraram a resposta à lu...