Order of arrival shifts endophyte-pathogen interactions in bean from resistance induction to disease facilitation.

Endophytic fungi colonize plants without causing symptoms of disease and can enhance the resistance of their host to pathogens. We cultivated 53 fungal strains from wild lima bean (Phaseolus lunatus) and investigated their effects on pathogens using in vitro assays and experiments in planta. Most strains were annotated as Rhizopus, Fusarium, Penicillium, Cochliobolus, and Artomyces spp. by the sequence of their 18S rRNA gene. In vitro confrontation assays between endophytes and three pathogens (the bacteria Pseudomonas syringae pv. syringae and Enterobacter sp. strain FCB1, and the fungus Colletotrichum lindemuthianum) revealed strong and mainly symmetric reciprocal effects: endophyte and pathogen either mutually inhibited (mainly Enterobacter FCB1 and Colletotrichum) or facilitated (P. syringae) the growth of each other. In planta, the endophytes had a strong inhibitory effect on P. syringae when they colonized the plant before the bacterium, whereas infection was facilitated when P. syringae colonized the plant before the endophyte. Infection with Enterobacter FCB1 was facilitated when the bacterium colonized the plant before or on the same day with the endophyte, but not when the endophyte was present before the bacterium. The order of arrival determines whether fungal endophytes enhance plant resistance to bacterial pathogens or facilitate disease.

Short-term proteomic dynamics reveal metabolic factory for active extrafloral nectar secretion by Acacia cornigera ant-plants.

Despite the ecological and evolutionary importance of nectar, mechanisms controlling its synthesis and secretion remain largely unknown. It is widely believed that nectar is 'secreted phloem sap', but current research reveals a biochemical complexity that is unlikely to stem directly from the phloem. We used the short daily peak in production of extrafloral nectar by Acacia cornigera to investigate metabolic and proteomic dynamics before, during and after 2 h of diurnal secretion. Neither hexoses nor dominating nectar proteins (nectarins) were detected in the phloem before or during nectar secretion, excluding the phloem as the direct source of major nectar components. Enzymes involved in the anabolism of sugars, amino acids, proteins, and nectarins, such as invertase, ß-1,3-glucanase and thaumatin-like protein, accumulated in the nectary directly before secretion and diminished quantitatively after the daily secretion process. The corresponding genes were expressed almost exclusively in nectaries. By contrast, protein catabolic enzymes were mainly present and active after the secretion peak, and may function in termination of the secretion process. Thus the metabolic machinery for extrafloral nectar production is synthesized and active during secretion and degraded thereafter. Knowing the key enzymes involved and the spatio-temporal patterns in their expression will allow elucidation of mechanisms by which plants control nectar quality and quantity.

Callus and suspension culture induction, maintenance, and characterization.

Callus and cell suspension can be used for long-term cell cultures maintenance. This chapter describes procedures for the induction of somatic embryos of garlic, keeping a regeneration capacity for more than 5 yr, as well as the maintenance of a tobacco suspension culture (NT-1 cells), for more than 10 yr. Methods for plant regeneration and growth kinetics of garlic cultures are described, as well as for cell viability of NT-1 cells stained with 2,3,5 triphenyltetrazolium chloride. The packed cell volume determination as a parameter of growth is detailed.