Dynamics of cytoskeleton in differentiation of xylem cells of trees grown under the environmental stress

树木形成层细胞的分裂及其衍生物的分化产生可持续的木材生物量。木材的数量和质量取决于树木生长的环境条件。树木通常在高温或低温、干旱、酸雨、臭氧等环境胁迫下生长。这种胁迫通过抑制形成层活性导致木材数量减少。在本项目中，我们分析了低温作为环境胁迫之一，如何影响形成层活性和木质部分化的细胞机制。活性形成层细胞中的微管在低温下会解聚，因此，在固定样品时通常需要避免低温。然而，在冬季中期，当温度低于零度时，我们在休眠的形成层细胞中发现了清晰的微管束。此外，休眠形成层细胞中的微管在低温下固定样品时不会解聚。这些观察结果表明，休眠形成层中的微管在低温下具有稳定性。这种稳定性可能与形成层细胞的内源因素有关，因为微管的冷稳定性可以被植物激素（如赤霉素和脱落酸）修饰。此外，活性和休眠形成层细胞中的微管可能由不同的微管蛋白组成，这些微管蛋白的聚合表现出不同程度的冷稳定性。我们认为，微管的冷稳定性与树木对环境条件的适应密切相关，从而控制木材生物量的数量和质量。

The cell division of cambial cells and differentiation of their derivatives in trees produce sustainable wood biomass. The quantity and quality of wood vary depending on the environmental conditions of growth of trees. Trees usually grow under the several environmental stresses such as high or low temperature, drought, acid rain, and ozone etc. Such stresses result in decrease in wood quantity through the inhibition of cambial activity. In this project, we analyzed the cellular mechanism how low temperature, one of environmental stresses, affects the cambial activity and xylem differentiation. Microtubules in active cambial cells depolymerize in response to low temperatures and, thus, it is generally necessary to avoid low temperatures during the fixation of samples. However, we found clear bundles of microtubules in dormant cambial cells in mid-winter, when the temperature was below zero. In addition, microtubules in dormant cambial cells did not depolymerize by the fixation of samples under low temperature. These observations suggest the stability of microtubules in dormant cambium at low temperatures. Such stability might be related to endogenous factors in cambial cells since the cold stability of microtubules can be modified by plant hormones, such as gibberellin and abscisic acid. In addition, it is likely that microtubules in active and dormant cambial cells consist of different isotypes of tubulin whose polymerization exhibits different degrees of cold stability. We conclude that the cold stability of microtubules is closely related to the adaptation to environmental conditions of trees, therefore controlling the quantity and quality of wood biomass.