Comparative study of root growth and sucrose-cleaving enzymes in metallicolous and non-metallicolous populations of Rumex dentatus under copper stress.

Sucrose metabolism in roots of metallophytes is very important for root growth and maintenance of heavy metal tolerance. However, rare researches have been carried out on this topic so far. We tested here a hypothesis that roots of copper-tolerant plants should manifest higher activities of sucrose-cleaving enzymes than non-tolerant plants for maintaining root growth under Cu stress. Plants of two contrasting populations of metallophyte Rumex dentatus, one from an ancient Cu mine (MP) and the other from a non-mine site (NMP), were treated with Cu in controlled experiments. Cu treatment resulted in a higher root biomass and root/shoot biomass ratio in MP compared to NMP. More complicated root system architecture was showed in MP under Cu stress. Activities and transcript levels of acid invertase as well as contents of sucrose and reducing sugar in MP were elevated under Cu treatment, while activities of neutral/alkaline invertase and sucrose synthase showed no significant differences between two populations. The results indicate important roles of acid invertase in governing root growth under Cu stress.

Effects of copper on phenology and reproduction in Rumex dentatus from metalliferous and non-metalliferous sites.

The responses of phenology and reproductive traits to copper stress in two populations of Rumex dentatus were comparatively studied with pot culture experiments. Seeds used for the experiments were, respectively, collected from metalliferous and normal soils. It was found that the responses of phenology and reproductive traits to Cu treatment between the two populations were significantly different. Compared to the non-metallicolous population, the metallicolous population of R. dentatus had a short life cycle, large reproductive effort, and high fertility under Cu stress. In addition, the reproductive effort in metallicolous population of R. dentatus was maintained at the expense of a curtailment of vegetative development. The results suggested that change in phenological traits and more resources allocation to reproduction might play an important role in the adaptation of metallicolous population of R. dentatus to the Cu-enriched mine soils.