Contrasting Performance and Different Tolerance of Chestnut Rose and Grape to Excess Manganese

Manganese (Mn) at adequate concentrations is an essential element for normal plant metabolism. In contrast, high leaf Mn concentrations (1,000–12,000 μg g^-1 DW) are rather toxic in plants. Toxic Mn levels may inhibit plant growth and disturb plant metabolism as a consequence of oxidative stress resulting from the accumulation of reactive oxygen species. Previous studies have revealed the mechanism of plants resistance to high Mn concentrations. That is, they may rely on Mn sequestration into vacuoles and/or endoplasmic reticulum, chelation in the cytosol, binding to some specific proteins such as metallothioneins, and induction of specific enzymes’ activities such as those involved in the management of oxidative stress. However, the physiological-biochemical response of hypertolerant plants to the extremely high Mn treatment was only marginally studied until now.

Therefore, researchers selected two plants (chestnut rose (Rosa roxburghii Tratt) and grape (Vitis vinifera L.)) to characterize the physiological basis for Mn tolerance in woody plants. The specific aims of the study were to compare the grape and chestnut rose tolerance to excess Mn and to explore the mechanisms mediating the Mn accumulation and detoxification processes in those two species.

The results indicated that chestnut rose exhibited a high sensitivity to Mn excess constraint whereas grape appeared rather tolerant to Mn excess. Stomatal density and closure rate were affected by excess Mn in chestnut rose and brittleness of the leaf vein was reported as a novel Mn toxicity symptom in this species. Linear reductions in biomass accumulation and photosynthetic pigment concentrations with increasing Mn level were observed in chestnut rose but not in grape, except under the extremely high Mn concentration (118 mM). The results showed that the contrasting performances between the two species were related to the differences in ion transfer and homeostasis. Mn was readily allocated to the photosynthetic organ in chestnut rose but was mainly restricted to the roots in grape. Excess Mn caused iron (Fe) and nitrogen (N) deficiencies in chestnut rose but not in grape. The synthesis of antioxidant phenylpropanoid compounds and chelating phytochelatins were activated in Mn-treated grape but strongly repressed in chestnut rose.

The result has been published on Journal of Plant Growth Regulation, 2012, 31: 416–426. The paper can be downloaded from http://www.springerlink.com/content/761203656071541n/.