Relationship between Freezing Tolerance of Root-Tip Cells and Cold Stability of Microtubules in Rye (Secale cereale L. cv Puma)

Abstract

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.

Effect of Microtubule Stabilization on the Freezing Tolerance of Mesophyll Cells of Spinach

“…Our results are not inconsistent with the change in LT5o from -9°to -3°C in root-tip cells of rye following taxol treatment (10). Based on the rye study the suggestion was made that microtubule depolymerization during freezing may be necessary if the tissue is to survive to its normal LT5o (10).…”

“…Taxol, a taxane alkaloid derived from the western yew, Taxis brevifolia (16), stabilizes microtubules at sub-stoichiometric concentrations relative to tubulin concentration. It stabilizes microtubules in the mitotic spindle (2,9) and cytoplasm (12), in root-tip cells of rye (10), and stabilizes in vitro microtubules from several species (5,13). The finding that root-tip cells of rye containing taxol-stabilized microtubules are less freezing-tolerant than are non-taxol-treated controls (10) suggests that microtubule depolymerization during freezing may have important consequences.…”

“…Several chemical compounds, ions, and environmental conditions shift the equilibrium toward depolymerization (8 Freezing promotes microtubule depolymerization in several plants including onion (4), rye (10), spinach (3), and winter rape (Boyang Chu, personal communication). Low temperature also promotes microtubule depolymerization in a variety ofplant species (3,4,10,14). The implications of microtubule depolymerization induced by low temperature and freezing, however, are not well known.…”

Identification and characterization of a low temperature regulated gene encoding an actin‐binding protein from wheat

“…The higher accumulation of an ABP in the tolerant species may be related to their capacity to modulate the intracellular actin structure needed to develop higher freezing tolerance. It has been reported that low temperature causes microtubule depolymerization in winter rye root tips [2]. The level of depolymerization was related to the degree of freezing tolerance.…”

“…These modifications are associated with a reduction in cell water content, increase in intracellular solutes, reduction in cell volume, and an increase in plant erectness [1]. It has been reported that low temperature causes microtubule depolymerization in winter rye root tips [2]. The level of depolymerization was related to the degree of freezing tolerance, suggesting that microtubule depolymerization is important for achieving maximal freezing tolerance.…”