Miyazawa Yutaka, Nakajima Naoko, Abe Tomoko, Sakai Atsushi, Fujioka Shozo, Kawano Shigeyuki, Kuroiwa Tsuneyoshi, Yoshida Shigeo
Plant Functions Laboratory RIKEN, 2-1, Hirosawa, Wako, Saitama 351-0198, Japan.
J Exp Bot. 2003 Dec;54(393):2669-78. doi: 10.1093/jxb/erg312.
Brassinosteroids (BRs) are steroidal phytohormones that are essential for many processes in plant growth and development, such as cell expansion, vascular differentiation, and responses to stress. The effects of BRs on cell division are unclear, as attested by contradictory published results. To determine the effect of BRs on cell division, the tobacco (Nicotiana tabacum) BY-2 cell line, which is a widely-used model system in plant cell biology, was used. It was found that brassinolide (BL) promoted cell division only during the early phase of culture and in the absence of auxin (2,4-D). This promotion of cell division was confirmed by RNA gel blot analyses using cell-cycle-related gene probes. At later stages in the culturing periods of BL-supplied and 2,4-D-supplied BY-2 cells, differences in cell multiplication and cell-cycle-related gene expression were observed. Moreover, the BL-treated BY-2 cells had morphological differences from the 2,4-D-treated cells. To determine whether suppressed organellar DNA replication limited this promotion of cell division during the early culture phase, this replication was examined and it was found that BL treatment had no effect on activating organellar (plastid- and mitochondrial-) DNA synthesis. As preferential organellar DNA synthesis, which is activated by 2,4-D, is necessary during successive cell divisions in BY-2 cells, these data suggest that the mechanism of the promotion of cell division by BL treatment is distinct from that regulated by the balance of auxin and cytokinin.
油菜素甾体类化合物（BRs）是一类甾体植物激素，对植物生长发育的许多过程至关重要，如细胞扩张、维管分化以及对胁迫的响应。BRs对细胞分裂的影响尚不清楚，已发表的相互矛盾的结果证明了这一点。为了确定BRs对细胞分裂的影响，使用了烟草（Nicotiana tabacum）BY-2细胞系，这是植物细胞生物学中广泛使用的模型系统。发现油菜素内酯（BL）仅在培养早期且在没有生长素（2,4-D）的情况下促进细胞分裂。使用细胞周期相关基因探针进行的RNA凝胶印迹分析证实了这种对细胞分裂的促进作用。在供应BL和供应2,4-D的BY-2细胞培养后期，观察到细胞增殖和细胞周期相关基因表达的差异。此外，经BL处理的BY-2细胞与经2,4-D处理的细胞在形态上存在差异。为了确定在早期培养阶段抑制细胞器DNA复制是否限制了这种对细胞分裂的促进作用，对这种复制进行了检查，发现BL处理对激活细胞器（质体和线粒体）DNA合成没有影响。由于在BY-2细胞连续分裂过程中，由2,4-D激活的优先细胞器DNA合成是必需的，这些数据表明BL处理促进细胞分裂的机制与生长素和细胞分裂素平衡调节的机制不同。
