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

Grape (cultivar Jinshou) and chestnut rose (cultivar Gui 4) were exposed to excess manganese (Mn) treatments to characterize the physiological basis for Mn tolerance in woody plants. Chestnut rose exhibited a high sensitivity to this environmental 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). Our 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 importance of these parameters in the overall strategy of Mn tolerance in grape is discussed.