ABSTRACT
7-Methoxy-, 7-methyl- and 6-methylcoumarins retarded mitosis in Allium cepa root promeristem and caused chromosomal aberrations. Chromosomes became shorter and thicker, and often were lost during anaphase, forming micronuclei during interphase. Chromatid bridges were observed in anaphase and telophase, leading to the formation of a restitutional nucleus, often of irregular shape. Abnormal fragmopasts, often discontinuous, prevented normal cytokinesis. There was increased vacuolization and the mitochondria contained an electron-dense matrix. Parts of the cytoplasm, which were surrounded by ER cisternae, contained mitochondria and pieces of ER membrane. Autophagous vacuoles showed a lower density of cytoplasm, but still contained numerous pieces of ER cisternae.
ABSTRACT
At concentrations in which they occur on the plant surface and retard mitosis, coumarin and xanthotoxin lowered uptake of oxygen (by 60 and 30%, respectively) by meristematic cells ofAllium cepa root tips. They caused changes in the structure of the mitochondrial matrix to become dense, and protrusions of mitochondrial membranes were visible parallelling their hypertrophy, indicating alteration in the structure and physiology of these organelles. Coumarin and, to a lesser extent, xanthotoxin increased succinate dehydrogenase production in mitochondria and also in the cytoplasm, indicating changes in membrane permeability. Changes in oxygen uptake and mitochondrial structure, in addition to the retardation of mitosis, may be the reason these compounds act as allelochemicals after they have been removed from the plant surface and reach the root meristem.
ABSTRACT
Wheat germ protein kinase inhibits in vitro translation of Brome Mosaic virus (BMV) RNA 1 and 2, without affecting the translation of RNA 4. Inhibition of formation of BMV polypeptides 1a and 2a is due to the arrest of initiation of polypeptide synthesis. It was found that protein kinase inhibits the formation of the 80S initiation complex with BMV RNA 1 and 2, without affecting the formation of the initiation complex with BMV RNA 4. Inhibition of protein synthesis by wheat germ protein kinase is accompanied by the phosphorylation of two ribosome-associated polypeptides, with molecular weights of 32 000 and 76 000, respectively. Both polypeptides are readily dephosphorylated by the enzyme(s) present in the cell-free extract. Their dephosphorylation is accompanied by restoration of the translational capacity of the system.
