Abstract
ABSTRACT The effects of manganese on the morphology and ultrastructure of root cells were studied in in vitro selected plantlets tolerant to high concentrations (5 mM) of Mn which, in a previous investigation, had shown a significant reduction in root growth when compared to the control (0.1 mM Mn). A decrease in the length of the root cap and meristematic region was observed. The most serious effects of Mn toxicity occurred in the outer root cap and outer meristematic cells where extensive cytoplasmic disorganisation was observed. The plasma membrane, in particular, displayed ruptures associated with the formation of vesicular and multi-lamellar bodies. Mitochondria also revealed strong structural alterations. However, the cells in the inner regions of the meristem showed better preserved subcellular components and exhibited normal mitotic activity. These last conditions suggest a possible resistance strategy which permits root development to continue. The primary root structure was not affected by the metal, except the central cylinder where 5 mM Mn induced precocious xylem differentiation (protoxylem and metaxylem), while in the corresponding zone control roots showed protoxylem elements only. Moreover, the epidermis-esoderm cell morphology seemed to be influenced by the metal.
Published Version
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