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

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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.