Differential modulation of photosynthesis and defense strategies towards copper toxicity in primary and cotyledonary leaves of Ricinus communis L.

Abstract

Copper (Cu) is an essential element associated with different metabolic processes in plants. However, at concentrations higher than the threshold level, it becomes a potential stress factor. In the present investigation, the Cu-induced photosynthetic changes and prominent Cu detoxification methods were evaluated in Ricinus communis seedlings. Exposure of one-month-old seedlings of R. communis to 0.2 mM CuSO4 in Hoagland solution for 6 d slightly reduced the plant growth and photosystem activities in the primary leaves. However, these features were significantly reduced in the cotyledonary leaves. The comparative analysis of chlorophyll a fluorescence kinetics measured in cotyledonary and primary leaves of castor seedlings subjected to Cu stress indicates that photosynthesis is highly sensitive to Cu-induced stress, and it was predominant in cotyledonary leaves. In order to counteract this metal-induced oxidative damage and to scavenge the reactive oxygen species (ROS), various anti-oxidation processes get enhanced in both the leaves and roots. However, cellular redox homeostasis was better maintained in the primary leaves. The functional groups associated with cell wall materials take part in the sequestration of Cu to the cell wall by forming stable complexes with Cu to reduce the toxicity in the cytoplasm, which was common in both the cotyledonary and primary leaves, observed as structurally similar absorption peaks in FT-IR spectrum.