Sesbania virgata (Cav.) Pers (wand riverhemp) is a fast-growing tropical legume species that has been used for revegetation of riparian forests and rehabilitation of degraded areas and that exhibits an invasive behavior in certain regions of Brazil. Preliminary studies have shown that seed leachates inhibit the germination and development of seedlings of some crop species. In this study, we report that the seed leachates of S. virgata inhibit the growth of Arabidopsis thaliana and rice. The flavonoid (+)-catechin is found in high amounts in these leachates. It was active at concentrations of 50 microg ml(-1), and its effect was not distinguishable from the (+)-catechin obtained from a commercial source. We found that (+)-catechin is located in the seed coat and is rapidly released in high concentrations (235 microg per seed) at the beginning of imbibition. Quercetin was also detected in the seed coat of S. virgata, but it was not released from the seeds. Other phytotoxic compounds in the seed leachates were also detected. The fact that S. virgata releases high amounts of (+)-catechin, which also has antimicrobial activity, and other phytotoxins from its seeds at the earliest stages of its development might represent some adaptative advantage to the seedling that contributes to its invasive behavior and successful establishment in different soils.

Erythrina speciosa Andrews (Fabaceae) is a native tree of Atlantic forest from Southern and Southeastern Brazil. Although this species is found in flooded areas, it produces highly desiccation tolerant seeds. Here, we investigated the physiological and metabolic events occurring during seed maturation of E. speciosa aiming to better understand of its desiccation tolerance acquisition. Seeds were separated into six stages of maturation by the pigmentation of the seed coat. Water potential (WP) and water content (WC) decreased gradually from the first stage to the last stage of maturation (VI), in which seeds reached the highest accumulation of dry mass and seed coat acquired water impermeability. At stage III (71% WC), although seeds were intolerant to desiccation, they were able to germinate (about 15%). Desiccation tolerance was first observed at stage IV (67% WC), in which 40% of seeds were tolerant. At stage V (24% WC), all seeds were tolerant to desiccation and at stage VI all seeds germinated. Increased deposition of the arabinose-containing polysaccharides, which are known as cell wall plasticizers polymers, was observed up to stage IV of seed maturation. Raffinose and stachyose gradually increased in axes and cotyledons with greater increment in the fourth stage. Metabolic profile analysis showed that levels of sugars, organic, and amino acids decrease drastically in embryonic axes, in agreement with lower respiratory rates during maturation. Moreover, a non-aqueous fractionation revealed a change on the proportions of sugar accumulation among cytosol, plastid, and vacuoles between the active metabolism (stage I) and the dormant seeds (stage VI). The results indicate that the physiological maturity of the seeds of E. speciosa is reached at stage V and that the accumulation of raffinose can be a result of the change in the use of carbon, reducing metabolic activity during maturation. This work confirms that raffinose is involved in desiccation tolerance in seeds of E. speciosa, especially considering the different subcellular compartments and suggests even that the acquisition of desiccation tolerance in this species occurs in stages prior to the major changes in WC.

The primary utilization of carbohydrates by cell suspension cultures of Rudgea jasminoides, a native woody Rubiaceae from tropical forests, was investigated. Sucrose, glucose + fructose, glucose, or fructose were supplied as carbon sources. The growth curves of R. jasminoides cultured in glucose + fructose, glucose, or fructose showed similar patterns to that observed when sucrose was supplied to the cells, except that an increase in dry mass was observed at the beginning of the stationary growth phase in the media containing only one monosaccharide. The increase in hexose levels in the media during the early stages of the cultures indicated extracellular hydrolysis of sucrose, which was further supported by the increase in the activity of acid invertase bound to the cell wall. Glucose was preferentially taken up, whereas uptake of fructose was delayed until glucose was nearly depleted from the medium. Measurements of intracellular sucrose content and cytoplasmatic and vacuolar invertases indicate that the enzymatic activity seems to be correlated with a decrease in the hexose flux into the cells of R. jasminoides. Our results indicate that the behavior of cell suspension cultures of R. jasminoides regarding sugar utilization seems to be similar to other dicotyledonous undifferentiated cell suspension cultures.