|Budget Amount *help
¥1,900,000 (Direct Cost : ¥1,900,000)
Fiscal Year 1995 : ¥600,000 (Direct Cost : ¥600,000)
Fiscal Year 1994 : ¥1,300,000 (Direct Cost : ¥1,300,000)
Effects of abscisic acid (ABA), which is a kind of phytohormone known to induce stomatal closure, was investigated on the arrays of microtubules in guard cells of Vicia faba by immunofluorescence microscopy. Treatment of epidermal strips for 1 h with 10muM ABA resulted in disruption of microtubules in the guard cells with concomitant closure of stomata. This effect of ABA was reversible, and arrays of microtubules were reorganized within 1 h after the removal of ABA.Stomatal closure caused by treatment with 0.1 M mannitol was not, however, associated with the disruption of microtubules. The disruption of microtubules was preceded by stomatal closure when ABA was applied and the depolymerization of microtubules by propyzamide, an inhibitor of the polymerization of microtubules, did not induce stomatal closure. These observations suggest that the disruption of microtubules in guard cells is probably not directly necessiated by stomatal closure.
In natural conditions, changes in the arrays of microtubules in guard cells were examined during a day from an early morning. The size of stomatal aperture gradually increased till noon, when the size attained the maximum. The size became smaller again after then and ultimately got the minimum at 0 : 00 to 3 : 00. The microtubules in guard cells were aligned at random and some of them were in the segmented state at 6 : 00., and then they were aligned preferentially transversely with respect to long axis of the cell at 12 : 00 to 15 : 00. Thereafter, the microtubules were gradually segmented and disrupted at about 3 : 00. Thus, the change of arrays of microtubules showed circadian rhythm as well as the stomatal aperture. These results suggest some parallelism between the size of stomatal aperture and the arrays of microtubules.