Changes in Carbohydrate Levels in Red Kidney Bean (Phaseolus vulgaris L.) Exposed to Sulphur Dioxide

Red kidney bean (Phaseolus vulgaris L.) was exposed to variousconcentrations of SO² for 24 h (16 h light/8 h dark photoperiod)with continuous monitoring of photosynthetic and respiratoryactivity. Plants were harvested at the end of the dark periodinto samples of mature and immature leaf tissue, stems, androots for determination of sugar and starch levels. In all tissue samples the levels of total sugars were increasedby exposure to the lower concentrations of SO², but decreasedby the higher concentrations. Starch levels in leaves followeda similar trend. Increases in sugar and starch levels precededsymptoms of visible injury. Decreasing rates of photosynthesiswere correlated with increasing rates of respiration, the occurrenceof visible injury, and the depletion of sugar and starch levels.     

Uptake of SIV Anions and the Induction of Gaseous Emissions in Leaf Segments of SO2-Sensitive and Resistant Genotypes of Lolium perenne L.

Koziol, M. J., Shelvey, J. D. and Beedham, B. 1986 Uptake ofS'v anions and the induction of gaseous emissions in leaf segmentsof SO2-sensitiveand resistant genotypes of Lolium perenne L.—J.exp.Bot. 37: 556–571. At pH 3?0 and over a range of concentrations from 5 to 100 molm^–3 NaHSO₂ the SO₂ genotype (S23) took up less and showed a lower metabolic thresholdfor the induction of gaseous emissions than the SO₂ genotype(BR). Emission of H₂S from leaf segments of S23 was inducedat an estimated sulphite concentration of 605 ng g^–1 fr.wt. compared with 932 ng g^–1 fr. wt. in BR. Although theuptake of sulphite by leaf segments incubated on NaHSO₃ solutionsat pH 7?0 was similar to that of leaf segments incubated atpH 3?0, very little ethane, ethylene or H₂S were emitted. Afree radical scavenging mechanism is proposed to explain theseobservations. At pH 6?0 and concentrations of NaHSO₃ equivalent to low tomoderate exposure concentrations of gaseous SO² BR took up moresulphite than S23. Uptake in both genotypes was partially inhibitedby CCCP and by pre-loading the leaf segments with sulphate,indicating an active uptake mechanism transporting both sulphateand sulphite. Key words: Bisulphite/sulphite, gaseous emissions, uptake, Lolium perenne L     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: III. EFFECTS ON FREE AND STORAGE CARBOHYDRATE CONCENTRATIONS

Exposure of ryegrass (Lolium perenne L.) cv. S23 to 0, 50, and400 µg m^–3 SO₂ for an initial 29 d (first harvest),and for an additional 22 d period of regrowth (second harvest),resulted in distinct alterations in carbohydrate metabolismat each harvest. At the first harvest, exposure to 50 µgm^–3 increased concentrations of free and total carbohydrates,whereas exposure to 400 µg m^–3 resulted in concentrationshardly different from those in control plants. At both SO₂ concentrations,more assimilate was retained as free carbohydrate rather thanas storage carbohydrate. Comparison of assimilate distributionat the end of the light, and at the end of the dark period atthe first harvest led to the conclusion that light-mediatedmetabolism is more sensitive to SO₂ exposure than dark metabolism,and that assimilate distribution might be controlled by at leasttwo processes exhibiting different SO₂ sensitivities.     

Monitoring Gas Concentrations in Pollutant Exposure Systems: Defining Exposure Concentrations

Several reasons have been offered in the recent literature toexplain the disagreement in experimental results on the effectsof SO² on plants. The tacit assumption that each research groupis monitoring exposure concentration in a comparable manneris challenged. For example, in well-stirred chambers exposureconcentrations are identical with outlet concentrations, yetseveral studies have interpreted plant response in terms ofsupply (i.e. inlet) concentrations. Experiments are presentedthat illustrate the extent to which supply concentrations canbe depleted within chambers, and the magnitude of error in assumingsupply to represent exposure concentrations. Definitions forexposure concentration in chamber, wind tunnel, and glasshousesystems are suggested.     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: I. EFFECTS ON PHOTOSYNTHESIS AND RESPIRATION

The effects of exposure to SO₂ (50 and 400 µg m^–3SO₂) on the growth, photosynthesis, and respiration of perennialryegrass (Lolium perenne L.) cv. S23 were examined in two successivegrowth periods of 29 and 22 d. At the higher concentration ofSO₂, there was some visible injury of the leaves and specificleaf area was reduced, but yield, net photosynthesis, and darkrespiration of the plants were not significantly affected byexposure. The treatment was also without effect on the transpirationcoefficient of the plants and their number of tillers. The plantsexposed to the lower concentration of SO₂ showed no signs ofinjury and did not differ in any of the measured characteristicsfrom plants grown in SO₂-free air. Content of S in the shootsincreased linearly with the concentration of SO₂, the additionalS being found in the sulphate fraction whilst organic S wasunchanged. The results are discussed in relation to earlierfindings that yield of ryegrass exposed to SO₂ may be reducedwithout visible signs of injury.     

Growth of Ryegrass (Lolium perenne L.) Exposed to SO2: II. CHANGES IN THE DISTRIBUTION OF PHOTO ASSIMILATED 14C

Perennial ryegrass (Lolium perenne L.) cv. S23 was exposed to0, 50, and400 µg m– ³ SO₂ for a 29 d period, harvested,and then exposed under the same regime for a further 22 d periodof regrowth. Leaves from plants representing each exposure concentrationwere photosynthetically fed ¹⁴CO₂ for 5 min at the end of eachperiod. A significant increase in photoassimilation of ¹⁴CO₂and retention of ^I4C, concomitant with significant decreasesin [¹⁴C]glycine and [¹⁴C]serine with increasing SO₂ concentration,implied that there was an inhibition of the photorespiratorypathway. At the second harvest, leaves from plants exposed to400 µg m– ³ SO₂ also exhibited significant increasesin [¹⁴C]sucrose and [¹⁴C]fructose.