Ultrastructural features of pollen tubes of Endymion non-scriptus modified by cytochalasin D

Summary

The cytochalasins, known as inhibitors of various processes involving motility in plant and animal cells, induce far-reaching structural changes in the cytoplasm and walls of pollen tubes without destroying the capacity for subsequent growth in normal media. The fine structure of tubes of Endymion non-scriptus modified by cytochalasin D suggests that the changes all stem directly or indirectly from the interruption of the longrange cyclosis along the tube axis, which is sustained throughout the period of normal growth. The elimination of this movement breaks down the the pattern of flow responsible for the sorting-out process that maintains the characteristic zonation of organelles and other inclusions at the apex of the extending tube, and leads gradually to re-distribution of the vacuoles and membranes in the vegetative cell, the disposition of which is normally correlated with the longitudinally oriented flow pathways. Random local migrations of organelles and other inclusions of greater amplitude than is to be expected from Brownian movement continue in the tubes in the presence of cytochalasin D, indicating that the motility system is not wholly destroyed. Following the interruption of concerted axial movement, the polysaccharide wall-precursor bodies (P-particles), normally inserted into the wall mainly in the apical part of the tube during tip growth, gradually become dispersed throughout the tube and are incorporated in the wall at random, entering even into the intine of the parent pollen grain.