Photosynthetic activity and chloroplast structural characteristics in triazine‐resistant biotypes of three weed species

Abstract

Triazine‐resistant (R) and susceptible (S) biotypes of Chenopodium album, Conyza bonaeriensis and Setaria glauca were compared in terms of photosynthetic activity, chloroplast ultrastructure, and polar‐lipid composition of thylakoid membranes. Concerning photosynthetic activity, R relative to S biotypes showed lower rates in photosystem II electron transport (R/S ratios in the 0.3‐0.5 range), which were correlated with increases in the ratio of I to P levels of the fluorescence emission curve, but similar rates in both whole‐chain electron transport by thylakoids and photosynthetic oxygen evolution at different light intensities and at temperatures of 20 and 30°C by leaf discs. Concerning chloroplast structural characteristics, R and S biotypes did not show differences in degree of thylakoid appression and chlorophyll a/b ratio. However, thylakoid polar‐lipids of R biotypes exhibited a higher degree of unsaturation, specially, in its monogalactosyl diglyceride fraction; they were richer in trans‐hexadecenoic acid in its phospholipid fraction and they had higher contents in monoglactosyl diglyceride. The above results are discussed in relation to possible differences in photosynthetic performance between R and S plants.

Changes in photosynthetic electron transfer and state transitions in an herbicide-resistant D1 mutant from soybean cell cultures

“…This mutant strain showed an unusually high content of saturated (and reduced levels of unsaturated) fatty acids in comparison with WT and, consequently, a more rigid thylakoid membrane matrix [14,16]. Changes in fatty acids unsaturation have also been reported for 14/02/2007 many other plant atrazine-resistant mutants, however, on the contrary, these mutants displayed higher levels of unsaturated lipids [17][18][19][20].…”

“…F 0 values, obtained in fluorescence experiments at room temperature, were significantly higher in the mutant as compared to WT (data no shown), lending support to this proposal. Slower rates of electron transfer from Q A to Q B have also been observed in atrazine-resistant biotypes of several plant species [19,36,37] and in some strains of Synechocystis 6714 carrying mutations in the Q B pocket [38].…”

Unusual tolerance to high temperatures in a new herbicide-resistant D1 mutant from Glycine max (L.) Merr. cell cultures deficient in fatty acid desaturation

“…Many herbicide-resistant biotypes present several other changes (like alterations in chloroplast ultrastructure) that probably develop as a compensatory mechanism to maintain a normal photosynthetic function (Burke et al 1982;Lemoine et al 1986;De Prado et al 1992). The thermal behaviour seems to be a pleiotropic eect of the mutation (Ducruet and Ort 1988;Havaux 1989;Dulai et al 1998).…”

“…Such mutants from higher plants have a single mutation in the psbA gene coding for the D1 reaction center subunit that results in an altered herbicide binding and a decrease in the rate of electron transport from the primary quinone acceptor (Q A ) to the secondary quinone acceptor (Q B ) (Hirschberg and McIntosh 1983). Atrazine-resistant mutants usually present additional pleiotropic eects such as an increased sensitivity to strong illumination (Sundby et al 1993;Alfonso et al 1996), changes in antenna size and chloroplast ultrastructure (Burke et al 1982;Lemoine et al 1986;De Prado et al 1992) or changes in lipid/fatty acid composition (Pillai and St John 1981;Burke et al 1982;Lemoine et al 1986;De Prado et al 1992). Interestingly, a higher sensitivity to heat stress has also been reported as a feature linked to the triazine-resistance trait (Ducruet and Lemoine 1985;Ducruet and Ort 1988;Havaux 1989;Dulai et al 1998).…”

Photoinhibition and recovery in a herbicide-resistant mutant from Glycine max (L.) Merr. cell cultures deficient in fatty acid unsaturation

“…In addition to this, the chloroplast membrane of STR7 accumulated an unusually high content (20%) of saturated C16:0 and reduced levels of C16:1 and C18:3 unsaturated fatty acids compared to the WT . Changes in fatty acid unsaturation have also been reported in many other atrazine-resistant mutants from plants (Pillai and St. John 1981;Lemoine et al 1986;De Prado et al 1992;Schwenger-Erger et al 2002). The relationship between the psbA mutation and fatty acid unsaturation remains unclear, but it could be related to the influence of photosynthetic electron transport on the activity of fatty acid desaturases (Kis et al 1998).…”