Jesse H. Bennett

Differential ozone tolerance in soybean and snapbeans: Analysis of ascorbic acid in O3-susceptible and O3-resistant cultivars by high-performance liquid chromatography

The relationship between foliar ozone (O3) tolerance and leaf ascorbic acid (AA) concentrations in O3-susceptible (O3-S) and O3-resistant (O3-R) cultivars of soybean (Glycine max L.) cv. ‘Hark’ (O3-S) and ‘Hood’ (O3-R), and in snapbean (Phaseolus vulgaris L.) cv. ‘BBL-290’ (O3-S) and ‘Astro’ (O3-R) was examined by use of high-performance liquid chromatography (HPLC). Isocratic separation of AA for leaf tissues was accomplished in < 5 min on a μBondapak C-8 reverse phase column using 2% NH4H2PO4 (pH 2.8) as the solvent. Tissues were wxtracted with 6% metaphosphoric acid containing 1 × 10−6 M EDTA. Results showed that resistant genotypes contained more AA in their trifoliate leaves than did the correspnding susceptible genotypes. Young trifoliate leaves were highly tolerant to O3 and had proportionally higher AA concentrations than newly expanded leaves. A threshold concentration of approximately 1000 μg AA/g leaf fresh weight was required for good O3 protection. Ascorbic acid is an antioxidant and is a free radical scavenger which at physiological levels can protect against lipid peroxidation and leaf damage. Ozone stress was shown to induce the production and accumulation of AA in O3-treated leaves. Possible mechanisms for enhanced tolerance to O3 stress are discussed.

The effects of photochemical oxidants on the yield of snap beans

Abstract Effects of photochemical oxidants (primarily ozone) in the ambient air of Eastern United States on the yields of selected snap bean ( Phaseolus vulgaris L.) cultivars grown from the seedling stage to maturity in “open-top” field chambers were studied. The chambers were supplied with either carbon-filtered or nonfiltered air. The research was conducted at Beltsville, Maryland, near Washington, D.C. during 1972–1976 and at Raleigh, North Carolina, in 1972. Cultivars Bush Blue Lake (BBL) 290, BBL 274 and Gallatin 50 represented processing type beans and Astro, fresh market beans. Two crops, an early and a late crop, were grown each year. At Beltsville from 1972 to 1974, BBL 290, the most sensitive cultivar to oxidants, averaged 14% less bean yield (range 5–27%) in nonfiltered air than in filtered air. Gallatin 50 and Astro, two oxidant tolerant cultivars, yielded about the same in the two environments. The results were similar in North Carolina. In 1975 yields were greatly reduced due to heavy rains. Consequently, no measurable yield effects attributable to oxidants could be determined. In the late crop in 1976, however, BBL 274 yielded 22% less in the nonfiltered air. The other three cultivars did not exhibit statistically significant oxidant induced yield losses. Yields in ambient air field plots without chambers were essentially equivalent to those in the nonfiltered chambers indicating that chamber effects per se were minimal. The microclimates of the chambers are described in an Appendix.

Photochemical reduction of iron. II. Plant related factors

Abstract Photochemical reduction of ferric iron induced by ultraviolet (UV) and blue radiation is enhanced by certain di‐ and tri‐carboxylic acids. Iron photoreduction proceeds according to the following relative rates in Fe3+‐organic acid solutions containing the major plant acids listed: tartaric >oxalic>citric> malic>aconitic > fumaric ≥succinic≥FeCl3 (control). Any sensitized ferric to ferrous photoreduction occurring in plant foliage exposed to sunlight or artificial light would make iron more available to the tissues for metabolism. Iron is translocated within plants primarily complexed with citric acid (Tiffin, 1972). Citric acid is decarboxylated during Fe‐citrate photoreduction‐oxidation. Ferric iron photoreduction is thus accompanied by citrate degradation. In plant foliage, the fate of ferric citrate taken up the stem depends upon many plant‐related factors. Chelated iron is translocated predominately to actively growing regions where enzymatic reactions largely determine the immediate fate. In...

Photochemical reduction of iron. I. light reactions

Abstract The role of spectral quality in the photochemical reduction of Fe3+ in vitro was investigated under various lamps to determine the basis for severe chlorosis observed in certain species and cultivars under low pressure sodium (LPS) lamps when used as a sole source of artificial light in plant growth chambers. The comparative efficacy of LPS and cool white fluorescent (CWF) lamps was evaluated by means of an automated spectroradiometer with capability of measuring spectral irradiance every nanometer from 250 nm to 840 nm; by visible appearance of the plants (e.g., extent of greening and morphological development); by physiological measurements (e.g., of biomass and chlorophyll content); and by use of ferrozine as a chemical actinometer. Reduction of Fe3+ to Fe2+, measured as Fe2+ ferrozine (at 562 nm) was more than 4 times as great under CWF lamps, which emit appreciable amounts of UV and blue irradiance, as under LPS lamps, which are deficient in these wavelengths. By use of appropriate filters t...

Photochemical oxidants potentiate yield losses in snap beans attributable to sulfur dioxide.

Field-grown snap beans (Phaseolus vulgaris) were given recurring midday exposures to sulfur dioxide in open-top field chambers containing ambient photochemical oxidants. There was a linear correlation (correlation coefficient = –.99) between increasing concentrations of sulfur dioxide and the yields of snap beans. Synergism was indicated for the mixtures of ambient ozone plus sulfur dioxide, leading to threefold greater yield losses in nonfiltered air than in charcoal-filtered air (to remove the ozone). Even the lowest sulfur dioxide dose in nonfiltered air reduced the yields of Astro, a cultivar that exhibited no visible pollutant-induced foliar injury.

Soluble carbohydrates in bean leaves transformed into oxidant-tolerant tissues by EDU treatment

Abstract Improved gas-liquid chromatography techniques were used to evaluate the effects of EDUa on soluble leaf carbohydrates in Phaseolus vulgaris L. ‘Bush Blue Lake 290’. This snap bean cultivar is normally rather sensitive to 0 3 but becomes highly tolerant when treated systemically with EDU. Less than 24 h is required to induce the resistance. Standardized trifoliate leaves from EDU-treated and control plants were sampled 48 h after treatment. Additional plants were sampled 48 h after treatment. Additional plants were exposed to 0 3 one day after EDU soil application to assess the plant tolerance induced. The optimal dose required to enhance oxidant tolerance was 50 mg/pot. Major sugars in both EDU-treated (0 3 -tolerant) and untreated (0 3 -sensitive) leaves were glyceraldehyde, erythritol, fructose, glucose and sucrose. Myo -inositol, ribose and arbitol were present in lesser or trace amounts. EDU-treatment resulted in significant increases (35–62%) in all soluble carbohydrates except glyceraldehyde and myo -inositol. Implications relating to plant tolerance, to oxidants and stress-induced senescence are discussed.

Inhibition of photosynthesis and leaf conductance interactions induced by SO2, NO2, and SO2 + NO2.

Abstract Effects of 2-h exposures to 0–1 μmol mol −1 SO 2 , NO 2 and (1:1) SO 2 + NO 2 on CO 2 uptake by standardized snap bean leaves were studied. Interactions resulting from pollutant-induced changes in leaf conductance were evaluated. Minimum exposure concentrations required to depress CO 2 exchange rates (CER) under the test conditions were:0.17 μmol mol −1 SO 2 , 0.38 μmol mol −1 NO 2 , and 0.08 μmol mol −1 of each pollutant in the 1:1 mixture. Treatments with 1 μmol mol −1 NO 2 reduced CER 10% without affecting leaf conductance. One μmol mol −1 SO 2 depressed CER by 50%. Leaf conductances increased in SO 2 -treated leaves showing 30% inhibition of CER. Greater inhibition led to subsequent stomatal closure. Inhibition caused by the individual pollutants (applied singly) was linear over the range of concentrations investigated. The dual-pollutant mixture produced a synergistic response that was most pronounced at the lower pollutant concentrations. The potentiated effect was correlated with marked stomatal closure. Experimental plants for this study were grown under low moisture stress conditions to enhance stomatal opening in the plant stock material and reduce (damp) the potential for further SO 2 -induced stimulation of stomatal opening. The experiments were designed to obtain limiting data for the test conditions.