ABSTRACT
Indian mustard (Brassica juncea L.) accumulates high tissue Se concentrations and volatilizes Se in relatively nontoxic forms, such as dimethylselenide. This study showed that the presence of bacteria in the rhizosphere of Indian mustard was necessary to achieve the best rates of plant Se accumulation and volatilization of selenate. Experiments with the antibiotic ampicillin showed that bacteria facilitated 35% of plant Se volatilization and 70% of plant tissue accumulation. These results were confirmed by inoculating axenic plants with rhizosphere bacteria. Compared with axenic controls, plants inoculated with rhizosphere bacteria had 5-fold higher Se concentrations in roots (the site of volatilization) and 4-fold higher rates of Se volatilization. Plants with bacteria contained a heat-labile compound in their root exudate; when this compound was added to the rhizosphere of axenic plants, Se accumulation in plant tissues increased. Plants with bacteria had an increased root surface area compared with axenic plants; the increased area was unlikely to have caused their increased tissue Se accumulation because they did not accumulate more Se when supplied with selenite or selenomethionine. Rhizosphere bacteria also possibly increased plant Se volatilization because they enabled plants to overcome a rate-limiting step in the Se volatilization pathway, i.e. Se accumulation in plant tissues.
ABSTRACT
: We have developed a microwave protocol for a paraffin-embedding microtechnique of the shoot apical meristem of Zea mays and have successfully applied this protocol to other plant tissues. This protocol decreases the time required for all aspects of microtechnique tissue processing, including fixation (24 hr to 15 min), dehydration (73 hr to 10 min), and infiltration (96 hr to 3 hr). Additionally, the time required to adhere paraffin ribbons to gelatin-coated slides and for the Johanson's safranin O, fast green FCF staining protocol has been significantly decreased. Using this technique, the quality of tissue preservation and subsequent in situ localization of knotted mRNA was increased by using microwaves.