Varietal differences in growth and Cs allocation of blackgram (Vigna mungo) under water stress

• Drought stress reduced 137Cs concentrations of blackgram.
• Hydraulic conductivity correlated positively with the 137Cs concentrations.
• Different blackgram varieties differed in 137C concentrations in each organ.
• K moved more freely than 137Cs to aerial parts for drought tolerance variety.
• Distribution of 137Cs was influenced by growth performance and water movement.

Plant uptake and distribution of radioactive caesium (137Cs) was examined in an effort to determine how plant-water interactions differ between two blackgram plant varieties with different salt tolerance. Salt-tolerant U Taung-2 (BT) and the salt-sensitive variety Mutpe Khaing To (BS) were grown in pots filled with 137Cs-contaminated soil obtained from Nihonmatsu, Fukushima, Japan. The average soil 137Cs concentration was 1084 Bq kg−1, and the soil type comprised sandy clay loam, where the sand: silt: clay proportion was 62:18:20. After growing for 15 days in a temperature-controlled growth chamber, plants were subjected to drought stress conditions by addition of either 10 or 20% polyethylene glycol (PEG 6000) to the soil to reduce the osmotic potential of the soil, or to field capacity conditions (0% PEG).Analysis of the growth traits and water relations revealed the different strategies employed by the two blackgram varieties under water stress conditions. No differences were observed among the two varieties under field capacity conditions. However, under both drought stress conditions (10 or 20% PEG), the reduction in total leaf area, total biomass and plant growth analysis parameters, in addition to the relative water content, were higher in BS than in BT plants. Both plant varieties exhibited lower 137Cs concentrations in the leaves, shoots and roots under drought stress conditions compared to plants subjected to field capacity conditions. Under drought stress conditions, BT plants showed uptake and translocation of 137Cs from the roots to shoots and leaves, while this activity was seriously limited in BS plants, and especially in the leaf portion of BS plants treated with 20% PEG. In BT plants, potassium moved more freely than Cs from roots to the aerial parts of the plant under water stress conditions, while this was not the case in BS plants. Examination of the hydraulic conductivity showed a positive correlation with the 137Cs concentration in leaf and stem. Our results showed that the accumulation and distribution patterns of 137Cs among part of the blackgram tissues were dependent on plant growth performance, water movement pathways, and selective absorption.