Moderate water stress prevents the postharvest decline of ascorbic acid in spinach (Spinacia oleracea L.) but not in spinach beet (Beta vulgaris L.).

BACKGROUND: Babyleaf salads such as spinach (Spinacia oleracea L.) and spinach beet (Beta vulgaris L. subsp. cicla var. cicla) are an important dietary source of antioxidants such as ascorbic acid (vitamin C). Such compounds may be important in disease prevention in consumers but the level of these compounds in leaves frequently declines after harvest. As such, methods to maintain antioxidant levels in fresh produce are being sought. RESULTS: Irrigation deficits were used to apply water stress to S. oleracea and B. vulgaris plants. This treatment prevented postharvest decline of leaf ascorbic acid content in S. oleracea but not in B. vulgaris. Ascorbic acid levels in leaves at harvest were unaffected by the treatment in both species compared to well-watered controls. CONCLUSION: We have shown that restricted irrigation provides a viable means to maintain leaf vitamin content after harvest in S. oleracea, an important finding for producers, retailers and consumers alike. © 2015 Society of Chemical Industry.

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.

Synthesis and proteolytic degradation of nitrogenase in cultures of the unicellular cyanobacterium Gloeothece strain ATCC 27152.

In cultures of the unicellular cyanobacterium Gloeothece sp. ATCC 27152 growing under alternating 12 h light and 12 h darkness, nitrogenase activity appears as cultures enter the dark phase. Synthesis of both component proteins of nitrogenase commences immediately prior to the appearance of activity and continues until about 8 h into the period of darkness. The two components (Fe-protein and MoFe-protein) are synthesized in a molar ratio of about 3:1. Degradation of the nitrogenase proteins starts as early as 4 h into the dark period and increases markedly as cultures enter the light phase. As a result, both nitrogenase proteins are completely absent from cultures during most of the light phase. In contrast, all of the other proteins investigated appeared to be present throughout the cycle of alternating light and darkness. Degradation of nitrogenase depends upon protein synthesis during the last 6 h of darkness and is prevented by addition of protease inhibitors. Two proteins, of M(r) 47,000 and 29,000, are specifically synthesized during this period and it is possible that they have a role in nitrogenase degradation. Proteolytic activity of extracts of Gloeothece, measured as the ability to degrade azocasein, increased markedly during the early part of the light period, but this increase did not depend on protein synthesis. This activity does not therefore correspond to that specifically involved in nitrogenase catabolism, though it may act on initial breakdown products generated by a nitrogenase-specific degradative system. A phycobiliprotein appears to act as a temporary store of the degradation products of nitrogenase.