Seeds of a tropical tree species from Brazil, Astronium fraxinifolium, or zebrawood, were germinated, for the first time in microgravity, aboard the International Space Station for nine days. Following three days of subsequent growth under normal terrestrial gravitational conditions, greater root length and numbers of secondary roots was observed in the microgravity-treated seedlings compared to terrestrially germinated controls. Suppression subtractive hybridization of cDNA and EST analysis were used to detect differential gene expression in the microgravity-treated seedlings in comparison to those initially grown in normal gravity (forward subtraction). Despite their return to, and growth in normal gravity, the subtracted library derived from microgravity-treated seedlings was enriched in known microgravity stress-related ESTs, corresponding to large and small heat shock proteins, 14-3-3-like protein, polyubiquitin, and proteins involved in glutathione metabolism. In contrast, the reverse-subtracted library contained a comparatively greater variety of general metabolism-related ESTs, but was also enriched for peroxidase, possibly indicating the suppression of this protein in the microgravity-treated seedlings. Following continued growth for 30 days, higher concentrations of total chlorophyll were detected in the microgravity-exposed seedlings.

A ocorrência de poliembrionia foi investigada em 75 espécies lenhosas do Cerrado do Brasil central e da Caatinga xerófila do nordeste brasileiro. Quatorze espécies apresentaram poliembrionia, uma modalidade de reprodução anômala em angiospermas. Poliembrionia é relatada pela primeira vez para nove gêneros, Astronium, Byrsonima, Cariniana, Copaifera, Hancornia, Magonia, Myracrodruon, Tabebuia e Tapirira. A correlação positiva encontrada entre poliembrionia, reprodução sexual e processos apomíticos sugere que parte das espécies de angiospermas faça uso regular de sistemas de cruzamento múltiplos.

The occurrence of polyembryony was investigated in 75 woody species of the Cerrado in central Brazil and the xerophilous Caatinga vegetation in northeastern Brazil. Fourteen species showed polyembryony, a type of anomalous angiospermous reproduction. Polyembryony is reported for the first time for nine genera, Astronium, Byrsonima, Cariniana, Copaifera, Hancornia, Magonia, Myracrodruon, Tabebuia, and Tapirira. The positive correlation found between polyembryony, sexual reproduction, and apomictic processes suggests that a number of angiospermous species may make regular use of multiple breeding systems.