The mechanism(s) importing salt tolerance to plants remains unresolved. Although cotton (Gossypium hirsutum L.) is classified as salt‐tolerant plant, variation in salt tolerance has been observed among different cultivars. The purpose of this study was to determine if more salt‐tolerant cultivars contain higher constitutive or inducible levels of antioxidants than more salt‐sensitive cultivars. Greenhouse‐grown salt‐tolerant (cv. Acaia 1517‐88 and Acala 1517‐SR2) and salt‐sensitive (cv. Deltapine 50 and Stoneville 825) cotton plants treated with either 0 or 150 mM NaCl were analyzed for differences in growth and antioxidant capocities. The 150 mM NaCl treatment resulted in more than 40% reduction in growth of Deltapine 50 and Stoneville 825 and less than 30% reduction in the Acala cultivars. The more salt‐tolerant cultivars had higher constitutive levels of catalase (121‐215%) and u‐tocopherol (312‐420%). The salt treatment resulted in a 38 to 72% increase in peroxidase activity and a 55 to 101% increase in glutathione reductase activity in the Acala cultivars while the activities of these enzymes remained constant or decreased in the more sensitive cultivars. The Acala cultivars also exhibited a lower oxidized/reduced ascorbic acid ratio and a higher reduced/oxidized glutathione ratio than the more sensitive cultivars when grown at 150 mM NaCl. When subjected to a one‐time salt treatment, lipid peroxidation in Deltapine 50 increased 51% over Acala 1517‐88. These data indicate that protection from oxidative damage by higher levels of antioxidants and a more active ascorbate‐glutathione cycle may be involved in tbe development of salt tolerance in cotton.

A cotton (Gossypium hirsutum 1.) control and NaCI-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 NaCI-tolerant cell line exhibited no reduction in growth, whereas a 96% reduction was observed in the control lhe. The NaCI-tolerant cell line that was grown on 150 mM NaCl exhibited significantly greater catalase (341 %), peroxidase (31 9%), glutathione reductase (287%), ascorbate peroxidase (450%), y-glutamylcysteine synthetase (224%), and glutathione Stransferase (500%) activities than the intolerant control. The NaCItolerant cell line had a significantly lower dehydroascorbic acid/ascorbic acid ratio. Paraquat reduced growth by 20 and 53.7%, respectively, in the NaCI-tolerant and control cell line. The NaCI-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 NaCI-tolerant cell line. These data indicate that the NaCI-tolerant cell line exhibited a cross-tolerance to a variety of stress variables and had a more active ascorbate-glutathione cycle.When plants are subjected to environmental stress, the balance between the production of reactive O, species and the quenching activity of antioxidants is upset, often resulting in oxidative damage (Harper and Harvey, 1978;

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.

ceed plant needs or when fertilizer applications are not synchronized with plant uptake. Today, methods for Nitrogen fertilization is a required production practice for cotton predicting N status of cotton grown in the Midsouth are (Gossypium hirsutum L.) with risks arising from under-and overeither inaccurate or require additional studies before fertilization. Tissue testing for diagnosing N deficiencies in crops can use leaf blades and the total N concentration, but this practice has the critical values used in tissue testing can be accepted not been rigorously examined in cotton. The primary objective of and used by farmers and extension personnel (Bock and these experiments was to determine the leaf-N concentration of the Adams, 1980;Sabbe and Zelinski, 1990). Critical values uppermost, fully mature leaf blade below which yield loss could be are used in tissue testing to separate N-deficient from expected. Nitrogen-rate field experiments were conducted at 12 re-N-sufficient plants. Plants with tissue samples that consearch station and farm sites in the Midsouth USA in Louisiana, tain N levels above the critical value are considered Arkansas, Mississippi, and Alabama in 1996 and 1997. Leaf-blade sufficient in N and no N fertilizer would likely be needed total N concentrations associated with yield loss were 4.3% N at early while those plants with N concentrations below the critibloom (R 2 ϭ 0.50) and 4.1% N at mid-bloom (3 wk after early bloom, cal value are considered deficient in N and N applica-R 2 ϭ 0.32). The likelihood of applying N when not needed could be tions might be advisable. Inaccurate critical values can reduced by lowering the early bloom critical value to 3.9%. Only 4% result in the over-application or under-application of N. of all samples sufficient in N would have been incorrectly diagnosed N deficient at that critical value, but 44% of all deficient samples The principal method for assessing cotton-N status would have been misidentified as N sufficient. Reduced yields due under irrigated conditions is the petiole nitrate test. The to over application of N were evident in some samples with leaf N test is a snapshot of N movement to leaves because it between 4.6 and 4.8% at early bloom. These concentrations were also is an analysis of a transportable form of N, and because common for N-sufficient plants, making accurate diagnoses of the petioles or leaf stems are the conduit for nitrate transover application of N unlikely. Our leaf-N critical values probably port from roots. Petiole nitrate is a sensitive measure of differ from previously established values because earlier values were N movement to leaves, but it is probably hypersensitive derived via survey techniques and because faster fruiting cultivars because of soil moisture effects on petiole nitrate. Remay require higher leaf N.searchers have found petiole nitrate testing a better measure of soil moisture status than cotton-N status (Bock and Adams, 1980; Touchton et al., 1981). Another

The goal of this study was to construct a wetland that would detain runoff from a 162-ha watershed for the purposes of improving water quality. The volume of runoff that needed to be detained was determined to be that amount coming off the 162-ha watershed consisting of 146 ha of cultivated crop land and 16 ha of pasture that exceeded the amount that would have come off of the watershed in its natural, forested state. The Soil Conservation Service (now the Natural Resource Conservation Service [NRCS]) runoff curve number method was used to estimate runoff from the watershed in its natural, forested state and in its current state of cultivated crop land and pasture. The design of the constructed wetland was accomplished using the natural topography of the wetland site and the design criteria for a sediment containment system developed by NRCS. The SPAW (Soil-Plant-Atmosphere-Water Field & Pond Hydrology) computer model was used to model depth and volume in the wetland to determine if the constructed wetland design would accommodate typical runoff events. Construction of the wetland occurred over a 4-mo period. The capabilities of the system were verified when Hurricane Rita deposited above-normal rainfall to the wetland site area. The wetland was able to accommodate this event, allowing flow through the system for 9 d, followed by continued detention of remaining runoff for water quality improvement.