Cell-wall pectins in the roots of Apiaceae plants: adaptations to Cd stress

Abstract

The influence of Cd stress on changes in the pectin content of root cell walls (CWs), and the Cd content in the initial growth of plants of two species of Apiaceae L. (parsnips and celeriac) were investigated. Plants were grown in hydroponic systems under controlled environmental conditions, with and without the addition of Cd2+ ions. It was noted that pectin content and its degree of methylation (DM) increased, and pectin methylesterase (PME) activity decreased in parsnip root CWs under Cd stress. With regard to celeriac, a decrease in pectin content and its DM occurred with increasing PME activity. The total soluble pectin content under Cd stress was predominantly related to changes in the diluted alkali (sodium carbonate)-soluble pectin (DASP). Higher amounts of Cd2+ ions were taken up and accumulated in the roots of the parsnips comparing to those in celeriac. Similar amounts of CW-bound Cd2+ in both species were caused by an increase in pectin content (parsnip) or a decrease in DM pectin (celeriac), related to an increase in PME activity under stress. It was noted that CW had no significant effect on the Cd uptake and binding in tested root vegetables.