C. Dominguez

Physiological and Biochemical Characteristics in Triazine Resistant Biotypes of Four Amaranthus Species

Summary A comparative study was made of the photosynthetic activity, growth and productivity of triazine-resistant (R) and -susceptible (S) biotypes of A. albus, A. blitoides, A. hybridus and A. retroflexus collected from various areas in Spain. Fluorescence assay showed that herbicide treatment totally inhibited electron transport in S plants but not in their R counterparts. Electron flow from QA to QB was lower in R plants, but no difference was observed for the electron flow rate through PSII + PSI nor for photosynthetic activity at different light intensities. Growth studies revealed that S biotypes were more vigorous than in R in A. hybridus and A. retroflexus; R and S were similar in A. albus, but S biotypes of A. blitoides showed greater growth at the first development stage (3-week-old plants), althoughRandS plants were not significantly different at 5 and 6 weeks. No uniformity in productivity was observed across the 4 species.

Lipid Composition and Chloroplast Ultrastructure in Triazine Resistant Biotypes of Amaranthus Species

Summary A study was made of thylakoid membrane polar lipid composition and of chloroplast ultrastructure in triazine resistant (R) and susceptible (S) biotypes of four Amaranthus species. R biotypes showed higher values for MGDG/DGDG (monogalactosyl-diacylglycerides/digalactosyl-diacylglycerides) and MGDG/PL (monogalactosyl-diacylglycerides/phospholipids) ratios. For fatty acid composition, when R were compared with S biotypes, they showed higher trans-hexadecenoic acid content in the PL fraction, higher linolenic acid content in TL, MGDG and DGDG, and lower linoleic acid content in TL, MGDG and DGDG. Studies of chloroplast ultrastructure revealed no appreciable difference between RandS biotypes with regard to the chlorophyll a/b ratio or the extent of thylakoid appression.