Ultrastructural Changes Related to Frost Hardiness in the Cortical Parenchyma Cells from Mulberry Twigs<xref ref-type="fn" rid="fn1"><sup>1</sup></xref>

Abstract

Ultrastructural changes in the cortical parenchyma cells of mulberry (Morus bombyciz Koidz. cv. ‘Gorogi’) twigs were related closely to the seasonal cycle of frost hardiness. Changes in hardiness from summer to winter and vice versa took place particularly in the plasmamembrane. During stages that result in a rapid increase in hardiness, the sequence of cytological changes for the replacement of the plasmamembrane was marked invaginations of the plasmamembrane; pinching off into vesicles in the peripheral cytoplasm; engulfment of these vesicles into vacuoles; generation of numerous microvesicles by the Golgi apparatus; the appearance of these microvesicles with the plasmamembrane. Similar cytological changes that are associated with increased hardiness occur during artificial hardening at 0°C for 5 to 20 days in both the autumn and spring. In the midwinter cells, however, the plasmamembrane has a fairly smooth structure. Thus, the highly folded structure of the plasmamembrane is not always characteristic of extremely hardy cells. Ultrastructural changes associated with hardiness are discussed in terms of membrane renewal.