Krzeslowska M, Lenartowska M, Mellerowicz EJ, Samardakiewicz S, Wozny A
Pectinous cell wall thickenings formation-A response of moss protonemata cells to lead
Environmental and Experimental Botany: 2009 65:119-131

Lead poisoning constitutes one of most detrimental environmental hazards to all living organisms. Plants developed a variety of avoidance and tolerance mechanisms that are activated in response to lead exposure. Plant cell walls were suggested to play important role in these reactions by creating an efficient barrier to lead entry to the protoplasts, but the molecular mechanisms involved in such shielding reaction have not been elucidated. Tip growing protomemata of Funaria hygrometrica (Hedw.) were used as model for studying effects of lead exposure on plant cell walls (CWs). Forty-eight hour-treatment 4 μM PbCl2 resulted in the appearance of cell wall thickenings (CWTs) at the tip of the apical cell, which is the lead entry site to the cell protoplast [Krzesłowska, M., Woźny, A., 1996. Lead uptake localization and changes in cell ultrastructure of Funaria hygrometrica protonemata. Biol. Plant. 38, 253–259]. The nature of these thickenings differed from the one of cell wall in unexposed plants as revealed by immunolabelling with monoclonal antibodies and histochemical analyses. The most striking difference was the appearance high amount of low-esterified (JIM5 epitope) and unesterified (PAM1 epitope) homogalacturonan, which were absent from the tip cell wall of control protonemata and are known as the compounds able to bind and immobilise Pb2+. Furthermore, the cell wall thickenings commonly contained callose and at least two kinds of lipid compounds known as the substances preventing metal ions entry to the protoplast.

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