The response of cortical microtubules to low temperature and freezing was assessed for root tips of cold-acclimated and nonacclimated winter rye (Secale cerea/e L. cv Puma) seedlings using indirect immunofluorescence microscopy with antitubulin antibodies. Roots cooled to 0 or -30C were fixed for immunofluorescence microscopy at these temperatures or after an additional hour at 40C. Typical arrays of cortical microtubules were present in root-tip cells of seedlings exposed to the cold-acclimation treatment of 40C for 2 days. Microtubules in these cold-acclimated cells were more easily depolymerized by a 0°C treatment than microtubules in root-tip cells of nonacclimated, 22°C-grown seedlings. Microtubules were still present in some cells of both nonacclimated and cold-acclimated roots at 0 and -30C; however, the number of microtubules in these cells was lower than in controls. Microtubules remaining during the -30C freeze were shorter than microtubules in unfrozen control cells. Repolymenzation of microtubules after both the 0 and -30C treatments occurred within 1 h. Root tips of nonacclimated seedlings had an LT-50 of -90C. Cold acclimation lowered this value to -140C. Treatment of 22°C-grown seedlings for 24 h with the microtubulestabilizing drug taxol caused a decrease in the freezing tolerance of root tips, indicated by a LT-50 of -30C. Treatment with Dsecotaxol, an analog of taxol that was less effective in stabilizing microtubules, did not alter the freezing tolerance. We interpret these data to indicate that a degree of depolymerization of microtubules is necessary for realization of maximum freezing tolerance in root-tip cells of rye.

The cold stability of cortical microtubules in root-tip cells of winter rye (Secale cereale L. cv Puma) is altered by growth temperature (GP Kerr, JV Carter (1990] Plant Physiol 93:77-82).One hypothesis for the basis of this alteration is that different tubulin isotypes are present at different growth temperatures, and that the cold stability of microtubules is affected by these isotypic differences. We have explored the first part of this hypothesis by comparing protein extracts from roots of seedlings grown for 2 days at 220C (nonacclimated) or for an additional 2 or 4 days at 4°C (cold-acclimated). Immunoblots of two-dimensional polyacrylamide gels were probed with monoclonal antibodies to a-and ,8-tubulin. At least six a-and seven #-tubulins were present in the extracts from both the nonacclimated and coldacclimated roots. Changes in electrophoretic mobility and isotype number of both a-and j5-tubulin were observed after only 2 days at 40C. Further changes in tubulin were observed after 4 days at 40C. Changes in a-tubulin were more pronounced than those in ,8-tubulin.

We have used double fluorescence labelling to investigate the effect of freezing on microtubules and microfilaments in root‐tip cells of rye (Secale cereale L. cv Rymin). Freezing to ‐5°C (which does not kill these cells) caused partial depolymerization of both, but microfilaments were more resistant than microtubules. When microtubules were stabilized against freeze‐induced depolymerization by pre‐treating seedlings with taxol, microfilaments exhibited enhanced stability as well. Almost all the frozen cells containing taxol‐stabilized microtubules also contained microfilaments. When seedlings were treated with the microtubule‐destabilizing drug APM prior to freezing, microfilaments became more susceptible to freeze‐induced depolymerization than in controls. These data suggest a physical interaction between microtubules and microfilaments in these cells.

Leaching of salt from container media was investigated by means of the miscible displacement theory for 6 peat-perlite-glass bead combinations plus 4 other mixes. Columns were salinized with 15 meq 1−1 each CaCl2 and NaCl, then allowed to equilibrate. Electrical conductivity of the effluent was recorded as columns were leached, using 1 cm constant water head, with solutions of 1, 4, or 7 meq 1−1 each of CaCl2 and NaCl. The replacement efficiency of the soil solution by the leaching solution increased as glass bead content increased. Replacement efficiency of the soil solution had high correlation with mixture physical properties. No relationship to particle size distribution could be ascertained. Leaching solution concentration did not influence replacement efficiency and, generally, after 1 to 1.5 container capacities of effluent, removal of the original soil solution decreased substantially.

The report of Poole and Chase (1) continues a misconception that exists concerning the determination of potting soil salinity characteristics, namely, that potting soil conductivity can be determined from the leachate.