ABSTRACT
A stable isotope(15)N-nitrogen test (ESIMA = Ecotoxicological Stable Isotope Metabolic Assay) was developed to assess biological effects and the potential toxicological hazard of chemicals and contaminated environmental samples on plant metabolism. The assay measures the effect of toxicants on the incorporation of a(15)N labelled tracer into the total nitrogen fraction (both the nonprotein and protein fraction) of plants. Segments of Pisum arvense epicotyls are used as test substrates because of their high metabolic activity. The plant material is incubated under standardised conditions for two hours; subsequently(15)N incorporation is analysed by determining the(15)N abundance ((15)N atom-%) in the epicotyl segments. The effects of toxicants are evaluated by comparing the(15)N incorporation rates of control tissue and epicotyl segments exposed to individual chemicals or complex environmental samples. The specificity and sensitivity of effects as indicated by ESIMA were compared with effects as measured by two established ecotoxicological bioassays, the pollen tube growth test using pollen of Nicotiana sylvestris and the bacterial luminescence inhibition test using pollen of Photobacterium phosphoreum. The results of the study clearly indicate the suitability of ESIMA for assessing toxic impacts on plant nitrogen metabolism.
ABSTRACT
The key feature of tomato RNase LX localised solely outside the vacuole is the C-terminal peptide HDEF which is very similar to known endoplasmic reticulum (ER) retention signals. For functional testing of the ER-targeting ability of HDEF, different constructs including the complete RNase LX, two truncated forms without HDEF and the truncated chitinase FB7-1deltaVTP C-terminally flanked by HDEF, were expressed in Saccharomyces cerevisiae. The majority of RNase and chitinase, both containing HDEF, accumulates within the ER. However, the truncated constructs without the peptide are released into the medium. We provide compelling evidence that peptide HDEF at the C-terminus of secretory plant proteins is a new ER retention signal in yeast and most likely in plants.
