Anatomical Features of the Cell Wall Ingrowth in the Cortical Cells outside the Endodermis and the Development of the Casparian Strip in Loquat Trees

Abstract

Cell wall ingrowth, an unusual secondary cell wall thickening, in several layers of cortical tissue adjacent to the endodermis and the development of the Casparian strip within the endodermal cells were observed. The cell wall thickened inwardly, but unevenly until it had the appearance of an oblong ball. These cells exhibiting the ingrowth formed a single layer ring adjacent to the endodermis of young roots. Cell wall ingrowth subsequently occurred in several layers of the cortex as the roots aged. Using fluorescent microscopy, the Casparian strip in the endodermis became visible during vascular bundle development, concurrently with secondary vascular cylinder formation when a separation zone occurred between the cortical cells with ingrowths and the endodermis. Upon separation of the cortex and new cells within the endodermis increased laterally and the Casparian strip appeared. Following cortical separation, the outer region of the endodermis began to form cork-like tissue. The anatomical changes, relating to cortical cell ingrowth and the formation of the Casparian strip in the endodermis may play an important role in protecting loquat roots from water and solute loss.