RESUMO
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.
Assuntos
Catequina/toxicidade , Sementes/química , Sesbania/embriologia , Bioensaio , Dicroísmo CircularRESUMO
Root exudation, the process by which plants secrete compounds into the soil, is becoming accepted as a communicative process that determines organismal interactions in the rhizosphere. However, the mechanistic processes involved in the root exudation of phytochemicals have not been elucidated; traditionally, exudation has been regarded as a passive process. There is evidence that transporters in plants (and other organisms) have been involved in the movement of chemicals across different membranes. Here, we describe the involvement of different transporters in root exudation of phytochemicals by employing a pharmacological approach. We used a range of concentrations of several compounds known to inhibit different transporters, including potassium cyanide, orthovanadate, quinidine, glibenclamide, nifedipine and verapamil, to examine the effects of transporter inhibition on root exudation profiles in Arabidopsis. Generally, the exudation profile of phenolic compounds in 18-day-old plants shows more than 15 major phytochemicals. In contrast, the inhibitors listed above caused differences in the secretion of specific compounds. For instance, nifedipine and verapamil completely inhibited the exudation of the phytochemicals with molecular masses of 142 and 294, respectively. These results highlight that root exudation of phytochemicals is an active process controlled at the biochemical level and that different transporters may be involved in this root-specific mechanism.