CHARACTERIZATION OF GROWTH INHIBITION, DISRUPTION OF MITOSIS AND DISORIENTATION OF MICROTUBULES CAUSED BY DCPA IN OAT ROOTS

JEFFREY DAVID HOLMSEN, Purdue University

Abstract

One to 5.6 (mu)M DCPA (dimethyl tetrachloroterephthalate) significantly inhibited oat root growth within 12 to 18 h. An analysis of cell division in roots treated with DCPA revealed a disruption of normal mitosis after prophase. Metaphase, anaphase and telophase division figures were absence within 8 to 10 h of treatment with 5.6 (mu)M DCPA. Concomitant with the reduction in normal division figures was an increase in aberrant division figures. The predominant type of aberrant division figure was a condensed prophase. A comparison of DCPA, colchicine and propham action in oat roots revealed differences in the disruption of mitosis and cell plate formation. DCPA was a more effective mitotic disrupter compared with colchicine and propham at concentrations which caused the same amount of root growth inhibition. DCPA was also more effective at disrupting cell plate formation. Ultrastructural observations of dividing cells in roots treated with DCPA revealed the sequence of events during aberrant mitosis and cell plate formation. Dissolution of the nuclear envelope and coiling of the chromosomes at prophase were apparently unaffected by DCPA. However, chromosomes in dividing cells remained distributed throughout the cytoplasm and did not form normal division figures. Kinetochore microtubules were present in treated roots, although they were disoriented. In contrast, spindle microtubules were absent from treated roots. Because the chromosomes were dispersed in the cytoplasm, reformation of the nuclear envelope resulted in cells with large polymorphic nuclei. The first signs of cell plate formation were evident just prior to formation of the nuclear envelope when microtubules appeared in conjunction with numerous vesicles. These sites were frequently between the lobes of polymorphic nuclei. As the cell plate formed, numerous vesicles accumulated at the margine. These vesicle accumulations often became sites at which the growing cell plate curled back on itself or branched. Microtubules were present around these sites although they were oriented in various directions. Aberrant cell walls formed in this manner and often ended in the center of the cell adjacent to lobes of polymorphic nuclei. These data suggest that DCPA inhibits growth by disrupting mitosis and cell plate formation through a selective effect on spindle microtubule formation and orientation of kinetochore and phragmoplast microtubules.

Degree

Ph.D.

Subject Area

Botany

COinS