Graduate Thesis Or Dissertation
 

Apoplastic distribution of atrazine and glyphosate in intact sunflower leaves

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/bn999b127

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  • Apoplastic distribution patterns of atrazine [2-chloro-4-(ethylamino)- 6-(isopropylamino)-s-triazine], glyphosate [N-(phosphonomethyl)- glycine], the naturally occurring apoplastic leaf solutes, and the apoplastic dye PTS (trisodium 3-hydroxy-5,8,10-pyrenetrisulfonate) were compared. Aliquots of sap were expressed from intact sunflower leaves in a pressure chamber over intervals of 0.2 to 0.4 bars. Three distinct fractions were detected in the expressed sap volume; these were tentatively identified as a petiole-midrib fraction, a minor vein-cell wall fraction, and a third fraction comprised of a decreasing minor vein-cell wall fraction and an increasing fraction of membrane-filtered cell sap. Atrazine and the naturally occurring apoplastic solutes were in a slightly higher concentration in the petiole-midrib fraction than in the minor vein-cell wall fraction. The concentration of apoplastic solutes in the third fraction was decreased with each increment of pressure to a value close to deionized water. The concentration of atrazine in the third fraction was the same as the second fraction, indicating that the plasmalemma was not a significant barrier to atrazine movement. The apoplastic distribution of PTS and glyphosate were very similar to each other, showing a marked accumulation in the minor vein-cell wall fraction. Both compounds were diluted with each successive pressure increment to a low value in the third fraction, indicating a resistance to movement into or out of the symplast. The total concentration of atrazine in the apoplast was much lower than glyphosate. Both compounds were in similar concentrations in the symplast. The apparent octanol:water partitioning coefficient for atrazine and glyphosate was determined. These values were comparable to the quotients of the symplastic and apoplastic concentrations for both atrazine and glyphosate. It was suggested that the polar nature and high water solubility of glyphosate were responsible for its slower rate of penetration into the symplast and resulting accumulation in the apoplast. These results support the intermediate permeability hypothesis; that compounds which display the apoplastic transport pattern are freely mobile between the apoplast and symplast. Compounds which are not weak acids and exhibit the symplastic transport pattern penetrate the. symplast slowly, but once absorbed, are retained for long-distance transport.
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