High- but not low-intensity light leads to oxidative stress and quality loss of cold-stored baby leaf spinach.

BACKGROUND: Quality management in the fresh produce industry is an important issue. Spinach is exposed to various adverse conditions (temperature, light, etc.) within the supply chain. The present experiments were conducted to investigate the effect of light conditions (dark, low-intensity light (LL) and high-intensity light (HL)) and photoperiod (6 h HL and 18 h dark) on the quality changes of cold-stored spinach. RESULTS: HL exposure resulted in oxidative stress, causing tissue damage and quality loss as evidenced by increased membrane damage and water loss. The content of total ascorbic acid was reduced under HL conditions. On the other hand, storage of spinach under LL conditions gave promising results, as nutritional quality was not reduced, while texture maintenance was improved. No significant differences, with the exception of nutritional quality, were found between spinach leaves stored under continuous (24 h) low-intensity light (30-35 µmol m(-2) s(-1)) and their counterparts stored under the same light integral over 6 h (130-140 µmol m(-2) s(-1)). CONCLUSION: LL extended the shelf-life of spinach. The amount of light received by the leaves was the key factor affecting produce quality. Light intensity, however, has to be low enough not to cause excess oxidative stress and lead to accelerated senescence.

New, quick tests for herbicide resistance in black-grass (Alopecurus myosuroides Huds) based on increased glutathione S-transferase activity and abundance.

Black-grass (Alopecurus myosuroides Huds) is a major grass weed in winter cereals in Europe. It reduces yields and can act as a secondary host for a range of diseases. Herbicide resistance in this species was first detected in the UK in the early 1980s, and has now been reported in thirty counties. To successfully manage herbicide resistance it is vital that suspect populations are tested so that appropriate action can be taken. Ideally, a test will be quick, cheap and easy to use. Furthermore, it should provide an unequivocal result before post-emergence herbicides are to be applied, allowing alternative strategies to be adopted where necessary. This paper reports the development of new tests for herbicide resistance based on our observation that the resistant black-grass biotype Peldon contains approximately double the activity of the enzyme glutathione S-transferase (GST) compared with susceptible biotypes. Data are presented on the production of a monoclonal antiserum to a novel 30 kDa GST polypeptide purified from the biotype Peldon. An ELISA using this antiserum is described and the utility of this assay to detect resistant black-grass biotypes in plants grown under glass and in the field is presented. In addition, a microtitre assay for GST activity is described, which allows the rapid assessment of GST activities of plants. Both abundance and activity of GSTs are discussed as markers for herbicide resistance in black-grass.

Use of a potentiometric vital dye to determine the effect of the herbicide bromoxynil octanoate on mitochondrial bioenenergetics in Chlamydomonas reinhardtii.

BACKGROUND: The aims of the present study were to validate a vital mitochondrial potentiometric staining method in Chlamydomonas reinhardtii and to utilise this method to examine the effect of the herbicide bromoxynil octanoate on mitochondrial potential in this species. A range of stains was investigated, including Rhodamine 123, DASPMI, Mitotracker Green, Mitotracker Orange and JC-1. RESULTS: Rhodamine 123 (R123) had the highest utility of several candidate stains. Incubation with both 5 and 10 µM carbonyl cyanide 3-chlorophenylhydrazone caused significant fluorescence collapse [Dunn's post test (40.00, P < 0.01) and (45.49, P < 0.01) respectively], demonstrating that the R123 fluorescence reported mitochondrial potential. The effect of the herbicide bromoxynil octanoate was examined. Exposure to 0.1 mM of bromoxynil resulted in a significant increased mitochondrial fluorescence compared with the baseline (Mann­Whitney U = 222, P < 0.002), while concentrations of 1 mM and greater resulted in significant, almost complete loss of mitochondrial potential [mean fluorescence ratio = 1.193­1.289 (where a ratio of 1 represents total potential loss), Mann­Whitney U = 0.0, P < 0.001 (1 mM), 0.0, P < 0.0001 (2 mM), 0.0, P < 0.0001 (5 mM)]. EC50 of the collapse in mitochondrial potential owing to bromoxynil incubation occurred at 0.72 mM, and the mean t50 of bromoxynil octanoate action was 93 s. CONCLUSIONS: R123 is a sensitive potentiometric dye in C. reinhardtii that may find further use in investigations of both mitochondrial bioenergetics in plants and environmental toxicology.