Phloem translocation of strong acids—glyphosate, substituted phosphonic and sulfonic acids—in Ricinus communis L

Abstract

The mobility in phloem of several substituted phosphonic acids and a sulfonic acid was studied in the castor bean plant, Ricinus communis L. For a series of14C‐labelled phosphonate mono‐esters applied to the petioles of mature leaves, phloem transport was modest, becoming poor over longer distances in the plant. Substituted phenylphosphonic acids were more efficiently moved in phloem; uptake from the petiole and subsequent redistribution were slow, but these dibasic compounds were very stable in plants and substantial amounts reached the roots after 72 to 120 h. Glyphosate was very efficiently transported to phloem sinks even within 24 h, with high concentrations in phloem sap. Toluene‐4‐sulfonic acid moved predominantly in the xylem to the mature leaves and its phloem transport was poor. Transport patterns are considered in relation to the physico‐chemical properties of the compounds. Ion trapping appears to play little part in the phloem transport of these strong acids, though the good accumulation and transport in phloem of the complex molecule glyphosate cannot at present be explained.

Phloem Transport of d,l-Glufosinate and Acetyl-l-Glufosinate in Glufosinate-Resistant and -Susceptible Brassica napus

“…However, the phloem mobility of d,l-glufosinate was low compared with that of other compounds with similar properties. For example, glyphosate (pK a values of 2.6, 5.6, and 10.3; log K ow ϭ Ϫ2.7 to Ϫ3.2) is very phloem mobile in most species (Devine, 1989;Bromilow et al, 1993). Since d-glufosinate was much more phloem mobile than d,lglufosinate (Table IV), and only the l-isomer of glufosinate is herbicidal (Manderscheid and Wild, 1986), we conclude that the phytotoxic effect of l-glufosinate on the plant limits its own translocation.…”

“…Glufosinate is not translocated extensively from the site of application in susceptible plants (Bromilow et al, 1993;Steckel et al, 1997), but the reason for this limited transport is unknown. Based on its physicochemical properties (pK a ϭ Ͻ2, 2.9, and 9.8; log K ow estimated at Ϫ3.9), glufosinate has the requisite characteristics for phloem mobility (Kleier, 1988;Hsu and Kleier, 1990).…”

Nutrient Accumulation and Photosynthesis in Glyphosate-Resistant Soybeans Is Reduced Under Glyphosate Use

“…The data presented here, showed that younger plants (V4 growth stage) are more sensitive to glyphosate effects than plants receiving glyphosate at a later growth stage (V7). Because a single application contains the total dose, it differs from sequential application in which the same dose is fragmented (50%-50%), thus, using a single application, the plant has less time to recover from the likely chelating effects of the higher glyphosate rate (Jaworski, 1972;Kabachnik et al, 1974;Madsen et al, 1978;Glass, 1984;Bromilow et al, 1993;Coutinho and Mazo, 2005;Eker et al, 2006;Zobiole et al, 2010). Since glyphosate forms insoluble metal complexes (Madsen et al, 1978;Glass, 1984;Coutinho and Mazo, 2005), the decrease in micronutrient accumulation could also affect the main function of chloroplast, i.e.…”

“…It is translocated throughout the plant continually through the phloem and accumulates in young leaves, roots, and meristems (Bromilow et al, 1993). Glyphosate inhibits 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) in the shikimate pathway responsible for the biosynthesis of aromatic amino acids (Sprankle et al, 1975).…”

“…The first mode of action reported for glyphosate was as a metal chelator, and the molecule was initially patented for that purpose (Jaworski, 1972;Bromilow et al, 1993), therefore, it could be hypothesized that its application can exert negative side-effects on plant growth and nutritional status under some conditions, even in transgenic, GR soybean.…”