Growth, physiological, biochemical and DNA methylation responses to cadmium stress of bean (phaseolus vulgaris L) grown under different irrigation levels

The aim of this study is to evaluate the physiological, biochemical and morphological characteristics of bean in different irrigation (I1: 100%, I2: 75% and I3: 50%) and Cd levels (T1: 0 mg/kg, T2: 100 mg/kg, T3: 150 mg/kg and T4: 200 mg/kg Cd), combined or separately. Also, methylation pattern changes in samples exposed to drought and Cd stress were examined by methylation-sensitive amplified polymorphism (MSAP) technique and genomic stability was confirmed by ISSR technique. As a result of this study, significant decreases in plant growth occurred in parallel with increased drought stress and Cd dose. In addition, a sharp decrease in morphological properties of bean occurred when these two stress factors were combined. In T4I3, plant fresh and dry weight and root fresh and dry weight of bean seedlings reduced by 74.5%, 66.8%, 59.6% and 61.9%, respectively as compared to the control. While electrical lekeage (EL) increased with Cd and drought stress, leaf relative water content (LRWC), photosynthetic activity [photosynthesis (Pn), transpiration (Tr), CO2 (Ci) and stomatal conductivity (gs)] and chlorophyll content of bean reduced. Both Cd alone and combined stress treatments have increased Cd content of leaf and root. It was observed that lower irrigation levels (I2 and I3) and Cd stress significantly increased the content of hydrogen peroxide (H2O2), malondialdehyde (MDA), proline and sucrose in bean seedlings. In addition, there was an increase in antioxidant enzyme activity [catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD)] in bean seedlings due to the increased stress level. The negative effects on plant morphological, physiological and biochemical properties occurred more with the coexistence of both stress factors. We also determined by the MSAP technique that the total methylation level was relatively high with I3 and T4 treatment compared to the control. Under water deficit conditions, DNA methylation decreased by 1.7% and 2.6% in I2 and I3 irrigation level respectively, while in Cd applications it decreased by 1.7%, 2.6% and 9.7% in T2, T3 and T4, respectively. According to ISSR results, our findings confirmed that the rate of genomic template stability (GTS) decreased as the water deficit and Cd applications increased. As a result, it is thought that all these reactions, which occur with the combination of the two stress factors, occur by revealing the effects of drought stress by limiting water use as well as the reactions of metal stress itself.

Automated summary

The aim of this study is to evaluate the physiological, biochemical and morphological characteristics of bean under different irrigation and Cd levels, combined or separately. The results showed that drought stress and Cd dose led to significant decreases in plant growth, and the morphological properties of bean decreased sharply when both stresses were combined. Furthermore, water deficit and Cd stress increased the content of hydrogen peroxide, malondialdehyde, proline and sucrose in bean seedlings, and also increased the activity of antioxidant enzymes.