An ultrastructural study of Triticum monococcum cell suspension cultures during aging and after treatment with the herbicide Diclofop-methyl (methyl-2-(4-(2′,4′-dichlorophenoxy)phenoxy)propanoate)

Cell suspensions from root-derived callus tissues of Triticum monococcum L. were examined during growth and senescence. The fine structure of control cultures was compared with the ultrastructural modifications in cultures treated with the compound, methyl-2-(4-(2′,4′-dichlorophenoxy)phenoxy)propanoate (Diclofop-methyl). The control cell suspensions were observed during the cell division phase, the log phase, and the early stationary phase of growth. Senescence is characterized by a loss of ribosomes, alteration of internal membranes of the plastids, vesiculation, formation of granular material in the cytoplasm, rupture of the tonoplast, and an increase in number of lipid bodies. Cells in advanced stages of senescence had few organelles, but rather the cytoplasm consisted almost exclusively of lipid bodies and vesicles. The fine structure of the nuclei and mitochondria was least affected during aging. The ultrastructural effects of herbicide treatment did not completely parallel those of senescing cells, although any distinctions were difficult to sort out. The intensity of herbicide damage depended on both concentration and time (and undoubtedly the physiological state of any particular cell at the time of treatment). Low concentrations (4 μM) at 12 h resulted in plastid damage (analogous to chloroplast damage in photosynthetic tissues treated with herbicides) and in the formation of some myelin figures. At 20 μM concentration for 12 h, very extensive formation of myelin figures was observed in all cells. By 70 h, cells treated with 4 μM herbicide ranged from those with little or no damage to cells with extensive vesicle formation. In contrast, all cells treated with 20 μM herbicide at 70 h were damaged greatly. Some nuclei were present, although the nuclear envelopes were altered. Most organelles were barely recognizable. Extensive vesiculation and lipid formation occurred. These effects were more pronounced in cells treated with 40 μM herbicide at 70 h than in cells treated with lesser concentrations for shorter times. In this case, some organelles were recognizable (plastids and mitochondria) but they were abnormal in that the contents were often granular with only remnants of membranes. Some cells appeared as though the physiological processes were stopped so rapidly that hydrolytic enzymes could not function totally.