Multiple strains of Bacillus subtilis were demonstrated to stimulate plant defense responses, and cyclic lipopeptides may be involved in the elicitation of this induced systemic resistance phenomenon. Here, we further investigated molecular events underlying the interaction between such lipopeptides and plant cells. Addition of surfactin but not fengycin or iturin in the micromolar range to tobacco cell suspensions induced defense-related early events such as extracellular medium alkalinization coupled with ion fluxes and reactive oxygen species production. Surfactin also stimulated the defense enzymes phenylalanine ammonia lyase and lipoxygenase and modified the pattern of phenolics produced by the elicited cells. The occurrence of these surfactin-elicited early events is closely related to Ca(2+) influx and dynamic changes in protein phosphorylation but is not associated with any marked phytotoxicity or adverse effect on the integrity and growth potential of the treated tobacco cells. Reduced activity of some homologues also indicates that surfactin perception is dictated by structural clues in both the acyl moiety and cyclic peptide part. Our results suggest that these molecules could interact without irreversible pore formation but in a way sufficient to induce disturbance or transient channeling in the plasma membrane that can, in turn, activate a biochemical cascade of molecular events leading to defensive responses. The present study sheds new light not only on defense-related events induced following recognition of amphiphilic lipopeptides from Bacillus spp. but also more globally on the way elicitors from beneficial bacteria can be perceived by host plant cells.

No abstract

A method using Ion Chromatography hyphenated to an Inductively Coupled Plasma-Mass Spectrometer has been developed to accurately determine arsenite (As III ), arsenate (As V ), mono-methylarsonic acid (MMAA V ), dimethylarsinic acid (DMAA V ) and arsenobetaine (AsBet) in different water matrices. The developed method showed a high sensitivity with detection limits for each arsenic species close to 0.4 pg injected. Arsenite and arsenate were the major species found in surface and well waters, but AsBet and DMAA V were found in some surface waters, which has never been reported before, while in some natural mineral waters located in volcanic region, the arsenic content exceeded the maximal admissible arsenic content by European legislation standards and the predominant form was As V .

Both cultivars of L. siceraria should be harvested at 50 DAFS owing to the good nutritional properties of their seeds and oils. However, to obtain best-quality proteins, round and oval berry cultivars should be harvested at 30 DAFS and CPW respectively. The results of this study will be useful in reducing the production time of fruits and improving the nutritional quality of their seeds.