Impact of Miscanthus x giganteus senescence times on fast pyrolysis bio-oil quality.

In this study the impact of senescence and harvest time in Miscanthus on the quality of fast pyrolysis liquid (bio-oil) was investigated. Bio-oil was produced using a 1 kg h(-1) fast pyrolysis reactor to obtain a quantity of bio-oil comparable with existing industrial reactors. Bio-oil stability was measured using viscosity, water content, pH and heating value changes under specific conditions. Plant developmental characteristics were significantly different (P≤0.05) between all harvest points. The stage of crop senescence was correlated with nutrient remobilisation (N, P, K; r2=0.9043, r2=0.9920, r2=0.9977 respectively) and affected bio-oil quality. Harvest time and senescence impacted bio-oil quality and stability. For fast pyrolysis processing of Miscanthus, the harvest time of Miscanthus can be extended to cover a wider harvest window whilst still maintaining bio-oil quality but this may impact mineral depletion in, and long term sustainability of, the crop unless these minerals can be recycled.

Involvement of abscisic acid-dependent and -independent pathways in the upregulation of antioxidant enzyme activity during NaCl stress in cotton callus tissue.

The role of abscisic acid (ABA) in the signal transduction pathway associated with NaCl-induced up-regulation of antioxidant enzyme activity was examined in a NaCl-tolerant cotton callus cell line treated with NaCl, ABA, paraquat, or H2O2 in the presence and absence or fluridone, an inhibitor of terpene, and therefore, ABA synthesis. Treatment with NaCl resulted in a rapid increase (within 30 minutes) in the ABA levels of the callus tissue, and the NaCl, ABA, and paraquat treatments induced rapid increases in the activities of superoxide dismutase, catalase, peroxidase, and glutathione reductase. Pre-treatment with fluridone significantly suppressed the NaCl-induced increases, but only slightly delayed the increases in tissue subjected to exogenous ABA treatment. This implies that ABA is involved in the signal transduction pathway associated with the NaCl-induced up-regulation of these antioxidant enzymes. Pre-treatment with fluridone had no effect on the paraquat-induced increases, suggesting that these enzymes can also be up-regulated by a pathway other than the one mediated by ABA. Both the NaCl and paraquat treatments produced significant increases in the superoxide levels within the callus, but the increase resulting from the paraquat treatment was significantly higher than the increase resulting from the NaCl treatment. These data suggest that NaCl stress results in the production of reactive oxygen intermediates (ROI) which signals the induction of an ABA-dependent signaling pathway. The production of very high levels of ROI, such as those that occur with paraquat treatment or perhaps during periods of prolonged or extreme stress, may induce an ABA-independent signaling pathway.

The influence of alpha-amanitin on the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus tissue.

Liquid suspensions of cotton callus tissue from a NaCl-sensitive cell line and a NaCl-tolerant cell line were subjected to the following treatments: (a) 0 and 150 mM NaCl, respectively (controls); (b) 75 and 250 mM NaCl, respectively; (c) 100 ng ml(-1) alpha-amanitin; or (d) pretreatment for 2 h with 100 ng ml(-1) alpha-amanitin followed by the respective NaCl treatments. The callus tissue was harvested at 0, 0.5, 1, 2, 4, and 8h and analyzed for antioxidant enzyme activity. In the NaCl-tolerant callus, the 250 mM NaCl treatment resulted in transient 2- to 4-fold increases above the control levels in the activities of ascorbate peroxidase, catalase, glutathione reductase, and peroxidase within 1 h after treatment, while superoxide dismutase activity increased 4-fold within 4 h. This rapid increase suggests that the up-regulation of antioxidant capacity is an early response to NaCl stress and perhaps provides protection against oxidative damage until other acclimating mechanisms can be invoked. In the control callus, peroxidase activity remained unchanged, and significant increases in the other enzymes were not observed until 8 h after treatment with 75mM NaCl. Pre-treatment with alpha-amanitin prior to the NaCl treatment completely inhibited the NaCl-induced increase in the activities of all five enzymes in both cell lines. This data supports the conclusion that the NaCl-induced up-regulation of antioxidant enzyme activity in cotton callus tissue is transcriptionally regulated, proceeding via a de novo synthesis of poly(A)+RNA and is not due to the translation of existing transcripts or the mobilization of existing enzyme pools. In addition, the results suggest that it is not only the up-regulation of antioxidant activity that bestows a degree of tolerance to environmental stress, but also the speed with which this response occurs.

The relationship between yield and the antioxidant defense system in tomatoes grown under heat stress.

Four putative heat-tolerant tomato (Lycopersicum esculentum) cultivars (Tamasabro, Heat Wave, LHT-24, and Solar Set) and one putative heat-sensitive tomato cultivar (Floradade) were grown in the field under non-stress (average daily temperature of 26 degrees C) and heat-stress (average daily temperature of 34 degrees C) conditions. At anthesis, approximately five weeks after being transplanted to the field, leaf samples were collected for antioxidant analyses. Yield was determined by harvesting ripe fruit seven weeks after the collection of leaf samples. Heat stress resulted in a 79.1% decrease in yield for the heat-sensitive Floradade, while the fruit yield in the heat-tolerant cultivars Heat Wave, LHT-24, Solar Set, and Tamasabro was reduced 51.5%, 22.1%, 43.8%, and 34.8% respectively. When grown under heat stress, antioxidant activities were also greater in the heat-tolerant cultivars. Superoxide dismutase (SOD) activity increased up to 9-fold in the heat-tolerant cultivars but decreased 83.1% in the heat-sensitive Floradade. Catalase, peroxidase, and ascorbate peroxidase activity increased significantly in all cultivars. Only Heat Wave showed a significant increase in glutathione reductase in response to heat stress but all heat-tolerant cultivars exhibited significantly lower oxidized ascorbate/reduced ascorbate ratios, greater reduced glutathione/oxidized glutathione rations, and greater alpha-tocopherol concentrations compared to the heat-sensitive cultivar Floridade. These data indicate that the more heat-tolerant cultivars had an enhanced capacity for scavenging active oxygen species and a more active ascorbate-glutathione cycle and suggest a strong correlation between the ability to up-regulate the antioxidant defense system and the ability of tomatoes to produce greater yields when grown under heat stress.

Antioxidant Response to NaCl Stress in a Control and an NaCl-Tolerant Cotton Cell Line Grown in the Presence of Paraquat, Buthionine Sulfoximine, and Exogenous Glutathione.

A cotton (Gossypium hirsutum L.) control and NaCl-tolerant cell line (cv Coker 312) were grown on media with or without NaCl in the presence or absence of paraquat, buthionine sulfoximine, and oxidized glutathione. On medium with 150 mM NaCl the NaCl-tolerant cell line exhibited no reduction in growth, whereas a 96% reduction was observed in the control line. The NaCl-tolerant cell line that was grown on 150 mM NaCl exhibited significantly greater catalase (341%), peroxidase (319%), glutathione reductase (287%), ascorbate peroxidase (450%), [gamma]-glutamylcysteine synthetase (224%), and glutathione S-transferase (500%) activities than the intolerant control. The NaCl-tolerant cell line had a significantly lower dehydroascorbic acid/ascorbic acid ratio. Paraquat reduced growth by 20 and 53.7%, respectively, in the NaCl-tolerant and control cell line. The NaCl-tolerant cell line also showed a slight tolerance to buthionine sulfoximine. In the buthionine sulfoximine experiments reduced glutathione restored growth in both cell lines, whereas oxidized glutathione restored growth only in the NaCl-tolerant cell line. These data indicate that the NaCl-tolerant cell line exhibited a cross-tolerance to a variety of stress variables and had a more active ascorbate-glutathione cycle.

The effects of NaCl on antioxidant enzyme activities in callus tissue of salt-tolerant and salt-sensitive cotton cultivars (Gossypium hirsutum L.).

To determine NaCl effects on callus growth and antioxidant activity, callus of a salt-tolerant and a salt-sensitive cultivar of cotton was grown on media amended with 0, 75, and 150 mM NaCl. Callus of the salt-tolerant cultivar, Acala 1517-8 8, grown at 150 mM NaCl, showed significant increases in superoxide dismutase, catalase, ascorbate peroxidase, peroxidase and glutathione reductase activities compared to callus tissue grown at 0 mM NaCl. In contrast, callus tissue of the salt-sensitive cultivar, Deltapine 50, grown at 0, 75, and 150 mM NaCl, showed no difference in the activities of these enzymes. At the 150 mM NaCl treatment, peroxidase was the only antioxidant enzyme from Deltapine 50 with an activity as high as that observed in Acala 1517-88. The NaCl-induced increase in the activity of these enzymes in Acala 1517-88 indicates that callus tissue from the more salt-tolerant cultivar has a higher capacity for scavenging and dismutating superoxide, an increased ability to decompose H2O2, and a more active ascorbate-glutathione cycle when grown on media amended with NaCl.

Scanning electron microscope studies of Agrobacterium tumefaciens attachment to Zea mays, Gladiolus sp., and Triticum aestivum.

Scanning electron microscope studies demonstrated that cells of Agrobacterium tumefaciens strains attach to cells on the cut surfaces of corn and wheat seedlings and to gladiolus disks. Bacterial cells attached to these monocots in the same manner as they attached to the dicots tested. Of the strains tested, A66 and T37 covered more of the cut surfaces of these monocots in a nonrandom fashion than did cells of other isolates. These bacteria attached to cells of intact monocotyledonous plants and had the greatest affinity for tissues located within the vascular bundles. They attached in large numbers to cells in these areas in all three monocots tested.