A serine-to-threonine substitution in the triazine herbicide-binding protein in potato cells results in atrazine resistance without impairing productivity.

A mutation of the psbA gene was identified in photoautotrophic potato (Solanum tuberosum L. cv Superior x U.S. Department of Agriculture line 66-142) cells selected for resistance to 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine). Photoaffinity labeling with 6-azido-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine detected a thylakoid membrane protein with a M(r) of 32,000 in susceptible, but not in resistant, cells. This protein was identified as the secondary quinone acceptor of photosystem II (QB) protein. Atrazine resistance in selected cells was attributable to a mutation from AGT (serine) to ACT (threonine) in codon 264 of the psbA gene that encodes the QB protein. Although the mutant cells exhibited extreme levels of resistance to atrazine, no concomitant reductions in photosynthetic electron transport or cell growth rates compared to the unselected cells were detected. This is in contrast with the losses in productivity observed in atrazine-resistant mutants that contain a glycine-264 alteration.     

Assessing the relative contributions of phytochelatins and the cell wall to cadmium resistance in white lupin

In response to Cd stress, higher plants utilise a number of defence systems, such as retention in cell walls, binding by organic molecules in the cytosol and sequestration in the vacuole. White lupin is a Cd-resistant legume that is of interest for phytoremediation of acidified and Cd-contaminated soils. The aim of this research was to evaluate the contributions of various mechanisms of Cd detoxification used by this species, focusing on cell-wall retention and binding by thiol-rich compounds. Retention of Cd by the cell wall of white lupin was well described by a Langmuir isotherm model. The percentage of total Cd adsorbed by the cell wall ranged from 29 to 47% in leaves, from 38 to 51% in stems and from 26 to 42% in roots depending on the Cd supply. Cadmium induced the synthesis of high levels of phytochelatins (PCs) in lupin plants, mainly in roots, with PC₃ being the major PC. The amount of Cd complexed by thiols accounted for approximately 20% of the total Cd in leaves, 40% in stems and 20% in roots. Therefore, cell-wall retention could account for more than twice the amount of Cd complexed by PCs in leaves and roots. In stems, both mechanisms contributed equally to Cd detoxification. These studies indicate that white lupin plants use cell-wall binding and, secondarily, the production of PCs, as effective mechanisms of Cd detoxification.     

The analysis of the distribution of restriction endonuclease sites in repetitive DNAs.

A method is described which permits the determination of the frequency of modified restriction endonuclease sites in tandem arrays of repeating sequences using the Southern transfer procedure.     

Salicylic acid-inducible binding of a tobacco nuclear protein to a 10 bp sequence which is highly conserved amongst stress-inducible genes

A 10 bp sequence motif (TCATCTTCTT) which is repeated several times in the 5' non-transcribed region of a barley β-1,3-glucanase gene is also present in the non-translated regions of over 30 different plant genes which are known to be induced by one or more forms of stress. Gel retardation assays and South-western blotting experiments provide evidence that the motif is the binding site for a tobacco nuclear protein with an apparent molecular weight of 40 kDa. Binding activity is increased when nuclear extracts from salicylic acid-treated plants are analysed compared with extracts from control plants, indicating that the protein itself is either induced or modified under conditions of stress. These observations suggest roles for the 10 bp motif and its binding protein as cis - and trans -acting regulators of gene expression during response to stress.