COLD-STABILITY IN THE POLLEN-TUBE CYTOSKELETON

In 3- and 12-hour-old pollen tubes of Nicotiana tabacum microtubules (MTs) most resistant to cold-depolymerization were located in the generative cell (GC). The most cold-sensitive MTs occurred in the apical region of the pollen tube. In the basal part of the tube, the cold-resistance of MTs increased, especially in 12-hour-old tubes. The cold depolymerization pattern of MTs with accumulation of tubulin at the cell and nuclear membranes suggested that binding of MTs to membranes might increase their stability. The IF microscopy and staining with fluorochrome-conjugated phallotoxins indicated that microfilaments (MFs) unlike MTs remained polymerized in cold-treated pollen tubes. Recording of the positions of the vegetative nucleus (VN) and GC in the control and cold-treated pollen tubes in different ages showed clearly that low temperature stopped sharply the movement of the VN and GC into the young tubes while no drastic effects were recorded in the old tubes. The cessation and recovery of the movement correlated well with de- and reassembly of MTs, which indicated that MTs in addition to MFs may be necessary for the movement of VN and GC. The immunoblot results showed that the levels of tubulin and actin monomers in the cold-treated tubes were comparable to those present in the control tubes, which might be a prerequisite for the rapid recovery of the structure and function of the cytoskeleton recorded after the return of the cold-treated pollen tubes to normal temperature.