Die räumliche Verteilung von35S und die Art der markierten Verbindungen in Spinatblättern nach Begasung mit35SO2

The concurrent exchange of SO2 and H2O vapor between the atmosphere and foliage of Geraium caroinianun was investigated using a wholeplant gas exchange chamber. Total leaf flux of S02 was partitioned Into leaf surface and internal fractions. The emission rate of SOrinduced H2S was measured to develop a net leaf budget for atmospherically derived sulfur. Stomatal resistance to SO2 flux was estimated by two techniqe:(a) Rn' from 50 data using anaiog modeling techniques ad (b) R!% from analogy to H2O (Lc. 1.89 R?'O).The emission of H2S was positively correlated with the rate of SO flux into the leaf interior. An accounting of the simultaneou, bidirectonal flux of gaseous sulfur compounds during poUlutant exposure showed that sulfur accumulation in the leaf interior of G. caroliaumn was 7 to 15% lower than that estimated solely from mass-balance calculations of SO2 flux data (ie. ignoring HsS emissions).The esimate of stomatal resistance to poDutant flux from the SO, data (Rn) was consistently less than the simultaneous estimate derived from analogy to H20 vapor (Rn). The resultant of R?0' -R!, which was always negative, is indicative of a residual resistance to SO flux into the leaf interior. On a comparative basis, SOs molecules experienced less pathway resistance to diffusion than effluxing H2O molecules. It is proposed that the SO,:H1O path length ratio is less than unity, as a conquence of the pollutant's high water solubility and unique chemical reactivity in solution. Thus, the diffusive paths for H2O and SO2 in G. carominiauwn are not completely synonymous.resistance but rather to physicochemical properties of the mesophyll tissue that imparted a greater S02 sink capacity in pea as compared with corn (19). More recently, Hallgren et al (15) observed changes in S02 flux to needles of scots pine (Pinus sylvestris) that were not correlated with stomatal responses.Estimates of S02 flux into the leaf interior are frequently calculated from the ratio of the atmospheric S02 concentration to gas phase resistance to S02, the latter being derived from the sum of boundary layer and stomatal resistance to H20. This assumes (a) an S02 concentration ofzero in the leafinterior, (b) a combined gas and aqueous pathway resistance to S02 that is analogous to H20 including an identical path length, and (c) an accurate analytical measurement of S02 without interference from other sulfur-containing gases. Accurate S02 measurement is important because S02-exposed plants emit H2S in the light (5), which is indistinguishable from S02 by flame photometry (38), a common technique for measuring SO2. Because this technique measures all sulfur species in the air stream, the concentration gradient for SO2 is overestimated. Moreover, mass-balance calculations of SO2 flux to foliage would be in error (underestimated) because the true chamber/cuvette outlet SO2 concentration is less than the instrument reading. To investigate the factors controlling S02 flux into the leaf interior, the concurrent fluxes of H20, SO2, and H2S were meas...

Section: Resultsmentioning

confidence: 99%

Sulfur Dioxide Flux into Leaves of Geranium carolinianum L.

Taylor¹,

Tingey²

1983

“…S02-fumigated plants can accumulate sulfate (9,30), which has been reported to be both relatively harmless (8,27) and to quite effectively inhibit photosynthesis in isolated chloroplasts (4,27). We treated isolated pea chloroplasts with sulfate in order to compare effects with those of sulfite.…”

mentioning

confidence: 99%

“…We observed an even higher inhibition (54% with 0.4 mm sulfite, see 'Results") than has been reported previously (50% with 5 and 1.6 mM sulfite, respectively, depending on the PPi concentration, [271). This may be because we treated the chloroplasts with sulfite in the dark prior to illumination, since in the light sulfite is assimilated and oxidized to sulfate (9,30). Damage of pea and tomato plants after SO2 exposure in the dark is reported to be greater than in the light (22).…”

mentioning

confidence: 99%

Effects of Arsenite, Sulfite, and Sulfate on Photosynthetic Carbon Metabolism in Isolated Pea (Pisum sativum L., cv Little Marvel) Chloroplasts

Marques¹,

Anderson²

1986

Photosynthetic C02-fixation in isolated pea (Pisum sativum L., cv Little Marvel) chloroplasts during induction is markedly inhibited by 0.4 millimolar sulfite. Sulfate at the same concentration has almost no effect.The "C02-fixation pattern indicates that the primary effect of sulfite is inhibition of the reaction catalyzed by ribulose bisphosphate carboxylase and a stimulation of export of intermediates out of the chloroplasts. Inhibition of light modulation of stromal enzyme activity does not appear to account for the toxicity of SO2 in this Pisum variety. Arsenite at 0.2 millimolar concentrations inhibits light activation and inhibits photosynthetic CO2 fixation. The '4C02-fixation pattern indicates that the primary effect of arsenite is inhibition of light activation of reductive pentose phosphate pathway enzyme activity.Several sites of action have been proposed to explain the effect of SO2, one of the major air pollutants, on plants. In chloroplasts sulfite (at pH 8.2: 9.2% HSO3-and 90.8% S032-) and effectors induced by SO2 fumigation can attack reactions of photosynthetic electron transport (7, 26), photophosphorylation (5, 27), and the reductive pentose phosphate pathway (10,14,17,24,29,(31)(32)(33). Light modulation of stromal enzyme activity in the chloroplast is known to be sulfite sensitive (3,20,21).In previous experiments involving '4C02 fixation in intact chloroplasts the RPP3 pathway intermediates were only partially resolved (16). To verify the reported SO2 effects and to determine their significance in situ, we have examined the effect of sulfite on the "4CO2 fixation pattern and the distribution of '4C-labeled metabolites between chloroplasts and the incubation medium during photosynthetic induction.S02-fumigated plants can accumulate sulfate (9, 30), which has been reported to be both relatively harmless (8,27) and to quite effectively inhibit photosynthesis in isolated chloroplasts (4,27). We treated isolated pea chloroplasts with sulfate in order to compare effects with those of sulfite.The major causes of the sulfite-induced reduction in the pho-'Supported

“…This fact has been remarked on by several workers in the air pollution field (9,28,31). Rates of sulfite metabolism within the cell, be it oxidative or reductive (27,29), vary with plant species and age (7). Within any given cell, concentrations of sulfite are likely to vary from subcellular compartment to compartment, as is evidenced by the data of Ziegler (32) from control and exposed plants 3 h and 2 d after the onset of illumination.…”

mentioning

confidence: 76%

Effects of SO₂ on Stomatal Metabolism in Pisum sativum L.

Rao¹,

Amundson²,

Alscher-Herman³

et al. 1983

Pea (Pisum sativum L. cv 'Little Marvel') plants were exposed to SO2 for short term (3 hours) and long term (2 days) at 0.2 and at 0.5 microliter per liter (ppm) levels. The effect of this treatment on the activity of phosphoenolpyruvate carboxylase, NAD-and NADP-malate dehydrogenases, and alanine aminotransferase from epidermis and whole leaves was investigated. Short-term exposure to SO2 at 0.2 or 0.5 ppm decreased the activity of the carboxylase and the dehydrogenases in the epidermis. In contrast, the activity of the same three enzymes increased in whole leaves with either short-or long-term exposure to SO2. Alanine aminotransferase in epidermis or whole leaves was not much affected by short-term exposure, but the epidermal activity was decreased and whole leaf activity was increased with long-term exposure. SO2 exposure which was initiated prior to illumination decreased the free thiol content of both epidermis and of whole leaf. Net photosynthesis was reversibly inhibited by long-term exposure to SO2 at 0.5 ppm. No effect of 0.5 ppm SO2 on stomatal conductance was detectable after 3 hours. Stomatal conductance appeared to decrease after longer exposure times (2 days) at 0.5 ppm.Stomates play an important regulatory role in leaf physiological processes as the primary pathway for exchange of gases between internal leaf surfaces and the atmosphere. The closing of stomata as a result of exposure to SO2 concentrations above 0.5 ,il/l has been reported for a wide variety of species (10,17). In contrast, S02-induced stomatal opening has been demonstrated for Vicia faba up to S02 levels of 0.35 ,Al/ (6). Other environmental variables, such as C02, light, and humidity, affect the magnitude and the direction of the response of stomates to SO2 (6,13,17). Stomatal movements are known to be caused by changes in guard cell turgor arising from the movement of K+ and H+ with electroneutrality being maintained by movement of Cl-or internal production of malate (18,21). The bulk of this malate is assumed to be derived from CO2 fixation by P-enolpyruvate carboxylase.The presence of both photosystems in guard cells has been demonstrated by Outlaw and coworkers who suggested that one of the important physiological changes associated with H20 oxidation by photosynthetic electron transport might be the modulation of enzyme activity in guard cells (18 ' Address reprint requests to this author. dithiol groups within the chloroplasts apparently by the reduction ofdisulfide bonds (2). The capacity for light modulation ofenzyme activity in pea leaf chloroplasts is diminished by brief exposure to sodium sulfite or atmospheric S02 (3,4). Alscher-Herman (1) has found that light activation of fructose 1,6-bisphosphatase in a S02-sensitive soybean cultivar is more sulfite sensitive than is light activation in a S02-insensitive cultivar; Alscher-Herman and Jeske (unpublished) have demonstrated the accumulation of sulfite and a delay in light activation of alkaline fructose 1,6-bisphosphatase in chloroplasts of a more S02-suscept...