Studies on effects of gibberellin on microtubule-stabilization

1. 研究了赤霉素对矮豆节间表皮细胞皮层微管排列和冷稳定性的影响，发现赤霉素处理的细胞皮层微管以横向排列为主，而未处理的细胞皮层微管以平行于细胞长轴排列为主。纵向微管对低温处理有抗性，而横向微管对低温处理敏感。这些结果表明，赤霉素引起了横向微管的优势，从而降低了微管的冷稳定性。研究了烟草悬浮细胞“BY-2”皮层微管的冷稳定性。烟草细胞皮层微管对低温处理具有抗性，但在离体烟草微管蛋白中聚合的微管在低温处理下被破坏。烟草原生质体皮层微管对低温处理敏感，而培养后细胞壁再生的细胞皮层微管对低温处理产生抗性。这些结果表明细胞壁对微管的稳定性起着重要的作用。接下来，我们检测了提供给原生质体介质的各种物质对微管稳定的影响，发现聚赖氨酸和精胺稳定了原生质体的皮质微管。这表明细胞壁上的一些多阳离子参与了皮层微管的稳定。为了研究植物细胞微管稳定性与微管蛋白翻转的关系，我们建立了微管蛋白含量的灵敏测定方法、微管蛋白合成活性和降解活性的测定方法。这些方法表明，在分离的百日草叶肉细胞气管元件分化过程中，微管蛋白降解活性与微管稳定性有关。

1. We studied the effects of gibberellin on the arrangement and the cold stability of cortical microtubules in epidermal cells of dwarf pea internodes and found that transverse arrays of cortical microtubules are predominant in gibberellin-treated cells, while cortical microtubules parallel to the long axis of the cells are predominant in non-treated cells. Longitudinal microtubules are resistant to low-temperature treatment, but transverse microtubules are sensitive to it. These results suggest that gibberellin gives rise to a predominance of transverse microtubules and thereby to the decrease in cold stablity of microtubules.2. We examined the cold stabilty of cortical microtubules of tobacco suspension cells "BY-2". The cortical microtubules in tobacco cells were resistant to low-temperature treatment, although microtubules which had been polymerized in vitro from isolated tobacco tubulin were disrupted by low-temperature treatment. Cortical microtubules in tobacco protoplasts were sensitive to low-temperature treatment, but those in cells which had regenerated cell walls after culture became resistant to the treatment. These results indicate that cell walls play an important role in the stability of microtubules. Next, we examined the effects of various substances supplied to the medium of protoplasts on the stabilization of microtubules, and found that polylysine and spermine stabilize cortical microtubules in protoplasts. This suggests that some polycations in cell walls are involved in the stabilization of cortical microtubules.3. We established a sensitive method to measure tubulin content, methods to measure tubulin synthetic activity and degrading activity in order to study a relationship between microtubule stability and the turn over of tubulin in plant cells. These methods revealed that tubulin degrading activity is associated with microtubule stability during tracheary element differentiation in isolated Zinnia mesophyll cells.