Redroot Pigweed (Amaranthus retroflexus L.) is an important weed that is highly competitive with common bean. Photosynthetic pigments, the activity of antioxidant enzymes, the relative expression of a number of antioxidant enzyme and light response genes, were studied in three of common bean cultivars and in V4 and R7 stages under Redroot Pigweed free and infested. The presence of weeds reduced the content of chlorophyll, relative chlorophyll and anthocyanin of common bean leaves. With the increase of weed competition, the expression of antioxidant genes and enzymes increased, which indicates the increase of their activity in order to reduce the amount of reactive oxygen species. Among the studied antioxidant enzymes, the activity of catalase and ascorbate peroxidase produced in the leaves was higher than that of superoxide dismutase. With the increase of weed interference, the expression of phytochrome interacting factor 3 (PIF3) gene as a positive regulator of light signals is increased and the expression of phytochrome rapidly regulated1 (PAR1) gene as a negative regulator is decreased. Chlorophyll a/b-binding protein (CAB1) and auxin-responsive protein IAA8 (IAA8) genes also down-regulated with increasing competition. Along with the decrease of CAB expression in the conditions of competition with weeds, the chlorophyll a, b content also decreased. Correlation between gene expression and physiological traits related to them highlights the prominent role of CWCP in maintaining yield potential.

Redroot Pigweed (Amaranthus retroflexus L.) is an important weed that is highly competitive with common bean. The aims of this study were to evaluate the relative expression of a number of antioxidant enzyme and light response genes and investigate the activity of antioxidant enzymes, anthocyanins and photosynthetic pigments of several red common bean cultivar/lines (Sayad, Derakhshan, and Line D81083) in third trifoliate leaf (V4) and pod formation (R7) stages under Redroot Pigweed free and infested conditions. At V4, enzymatic activity and gene expression decreased while with the increase of common bean competition with weeds, the expression of genes and enzymes activity increased. The activity of antioxidant enzymes increased in the R7 as compared to the V4, indicating the production of reactive oxygen species (ROS) upon competition with weed and increased enzymatic activity for the elimination of ROS. Sayad and D81083 exhibited the highest catalase contents under weed interference whereas demonstrated the lowest catalase enzyme amount under weed-free conditions. Thus, response of common bean to competition with weed depends on bean growth stage and genotype.