Identification of Casparian Strip in Roots of Metroxylon sagu, A Salt-resistant Palm

抄録

The Casparian strip refers to a modified cell wall with the deposition of suberin or lignin. The Casparian strip in the endodermis is considered to act as a barrier to dissolving ions, especially to the toxic ones, in the apoplast between the cortex and stele of plant root. The objective of the present study was to determine whether Casparian strips were present in all the plant parts of sago palm that is considered to be salt-resistant. Different positions and parts of the roots, petioles, rachis and leaflets of sago seedlings at the 10th leaf stage were observed. In the adventitious root, Casparian strips were found in the endodermal cell wall at 10 mm from the root tip and above it, and a suberin lamella was observed at 40 mm from the root tip and above it. The Casparian strip was also found in the endodermal cell walls near the root tip of lateral roots. A U-shaped thickening was detected in the cell wall of the endodermis in the mid- and basal parts of lateral roots. However, Casparian strips were not observed in the exodermis and aboveground parts such as the petiole, rachis and leaflet. The development of Casparian strips in the endodermis can be considered to be one of the important mechanical factors relating to the functional role of the avoidance mechanism for preventing the excess influx of Na⁺ into the stele and its translocation from root to shoot in sago palm.