Subcellular Manganese Compartation, Anatomic and Biochemical Changes of Two Grape Varieties in Response to Excess Manganese

Manganese (Mn) is an essential nutrient element necessary for enzymatic activities in all subcellular compartments. However, Mn is toxic when it is excessive. Studies showed that plant species could accumulate Mn to a high concentration in the shoot without showing any visible toxicity. Circumstantial evidence validated that abscisic acid (ABA) plays an important role in plant tolerance to heavy metal. It could induce a number of genes and proteins involved in stress defenses, including antioxidative enzymes and pathogenesis-related proteins.

Heavy metal stress was reported to change the morphology of chloroplast, increase the number of starch grains and plastoglobuli in plants. But the changes in cell structure and ultrastructure in response to excess Mn need to be further explored in higher plants. In recent years, grape trees have been widely cultivated in the subtropical and tropical area in southern China, and some grape cultivars exhibited good performance for plant growth in the acid soil of those areas. But the study about the response of grape to heavy metal is very limited to date.

To explore the underlying mechanism for the high tolerance to excess Mn stress in the grape species (Vitis vinifera Linn), researchers observed the subcellular compartment of Mn element, anatomic and biochemical responses of two grape cultivars (Combier and Shuijin) under excess Mn stress in semi-controlled environmental condition.

The results validated that grape species exhibited typical detoxifying or tolerant mechanism. Majority of Mn element accumulated in leaf was excluded into cell wall or comparted into cell vacuole to avoid cellular Mn-toxicity. Researchers also observed that Mn and other element were secreted into leaf surface or deposited in vascular wall. However, only small amount of Mn was located in cellular organ, and excess Mn in chloroplast was detoxified by depositing in starch granule. Although researchers did not detected obvious symptom of Mn-toxicity in this study, they observed the dessication symptom under high level of Mn treatment in the two cultivars. The findings showed that the growth inhibition and dessication symptom in the two grape cultivars could be largely associated with osmotic stress resulted from high concentration of leaf Mn.

The result has been published on Chemosphere, 2012, 89: 150-157. The paper can be downloaded from http://www.sciencedirect.com/science/article/pii/S0045653512006510.