Ni-inhibited radicle growth in germinating wheat seeds involves alterations in sugar metabolism.

Nickel (Ni) is a trace element essential for the growth and development of plants. Conversely, when in excess, Ni inhibits seed germination and reduces seedling growth. Therefore, we investigated the effect of Ni (5-50 μM; supplied as nickel sulfate: NiSO·6HO) on the activity of enzymes involved in sugar metabolism of wheat ( Triticum aestivum L.) seedlings after 96 h of exposure to the metal. Ni treatment reduced root and coleoptile length of emerging wheat seedlings and the effect was more pronounced on the root length. Ni (5-50 μM) treatment significantly enhanced carbohydrate content by 21-100 % over that of the control. In contrast, protein and reducing sugar contents declined by 17-43 and 22-69 %, respectively. The reduction in total protein content was confirmed by SDS-PAGE analysis. The activities of starch-metabolizing enzymes declined upon Ni stress in a concentration-dependent manner. Activities of α- and β-amylases, acid and alkaline invertases, acid and alkaline phosphatases, and starch phosphorylase declined by 18-74 and 24-85 %, 42-76 and 21-73 %, 15-54 and 28-72 %, and 50-83 %, respectively, when compared to the control. The study concludes that Ni impairs sugar metabolism as indicated by decline in the activity of sucrose and starch hydrolyzing enzymes. It resulted in decrease in the availability of biochemical energy and sugars required for the synthesis, leading to inhibition of radicle growth in germinating wheat seeds. [ABSTRACT FROM AUTHOR]