Callus Accumulation Research Articles

Effects of glyphosate on synthesis and degradation of chlorophyll in soybean and tobacco cells

Summary:The chlorophyll content increased with time in callus cultures of soybean (Glycine max L., cv. Chippewa) and tobacco (Nicotiana tabacum L., cv. White Gold) grown in the light on a standard medium. Addition of 0.5 mmol/1 glyphosate [N‐(phosphonomethyl) glycine] to the medium completely inhibited chlorophyll accumulation in the tobacco callus. Soybean callus required 40 times more glyphosate to initiate inhibitory effects on chlorophyll content. The inhibition was not reversed by simultaneous addition of casein hydrolysate or aromatic amino acids, suggesting that aromatic amino acid levels were not limiting for chlorophyll synthesis. In leaf discs of soybean and tobacco, glyphosate accelerated chlorophyll degradation in the light, but not in the dark; there was little difference in response between the two plant species. Young leaves of tobacco were more sensitive than mature leaves to glyphosate effects with glyphosate‐induced net losses of chlorophyll of 24 and 14% respectively after 5 days. Such rates of loss cannot explain the complete inhibition of chlorophyll accumulation in the callus tissue, suggesting that there was an inhibition of chlorophyll synthesis by glyphosate.