Sánchez María de la Paz, Gurusinghe Sunitha H, Bradford Kent J, Vázquez-Ramos Jorge M
Departamento de Bioquímica, Facultad de Química, UNAM, México D.F. 04510, México.
J Exp Bot. 2005 Feb;56(412):515-23. doi: 10.1093/jxb/eri029. Epub 2004 Nov 15.
The proliferating cell nuclear antigen (PCNA) is a protein factor required for processive DNA synthesis that is associated with G(1) cell cycle proteins. It has been demonstrated previously that, in germinating maize (Zea mays) embryonic axes, PCNA forms protein complexes with two Cdk-A proteins (32 and 36 kDa) and with a putative D-type cyclin. These complexes exhibit protein kinase activity on histone H1 and on the maize homologue of the pRB (retinoblastoma) protein. Flow cytometry has been used to study the influence of the phytohormones benzyladenine (BA) and abscisic acid (ABA) on cell cycle advancement during maize germination. It was found that, while BA accelerates the passage of cells from G(1) to G(2), ABA delays cell cycle events so that most cells seem to remain in G(1). The amounts of PCNA and Cdk-A proteins also vary according to the hormone treatment. In embryonic axes, PCNA increases rapidly during early germination in BA, compared with a gradual increase in water, while ABA treatment had only a marginal effect. However, of the two Cdk-A proteins, the 32 kDa protein is strongly reduced after 15 h of imbibition in water while this occurs later when axes are imbibed in BA or ABA. The PCNA-associated protein kinase activity in the BA and ABA treatments falls after 3 h of imbibition compared with activity in the control; however, while kinase activity in the BA treatment continues to decline during imbibition, it remains relatively constant until 24 h of imbibition in the ABA treatment. By contrast, a p13(Suc1)-associated Cdk-A kinase is activated after 15 h of imbibition under all treatments, particularly in ABA. These results suggest that, in maize, ABA delays the germination process by affecting cell cycle advancement, stopping cells mostly in a G(1) state.
增殖细胞核抗原（PCNA）是进行性DNA合成所需的一种蛋白质因子，它与G1期细胞周期蛋白相关。先前已经证明，在萌发的玉米（Zea mays）胚轴中，PCNA与两种Cdk-A蛋白（32 kDa和36 kDa）以及一种假定的D型细胞周期蛋白形成蛋白复合物。这些复合物对组蛋白H1和玉米pRB（视网膜母细胞瘤）蛋白的同源物具有蛋白激酶活性。流式细胞术已被用于研究植物激素苄基腺嘌呤（BA）和脱落酸（ABA）对玉米萌发过程中细胞周期进程的影响。结果发现，虽然BA加速细胞从G1期进入G2期，但ABA会延迟细胞周期事件，以至于大多数细胞似乎停留在G1期。PCNA和Cdk-A蛋白的量也因激素处理而有所不同。在胚轴中，与在水中逐渐增加相比，在BA处理下早期萌发期间PCNA迅速增加，而ABA处理只有轻微影响。然而，在两种Cdk-A蛋白中，32 kDa的蛋白在吸水15小时后在水中强烈减少，而当胚轴在BA或ABA中吸水时这种情况发生得较晚。与对照相比，在吸水3小时后，BA和ABA处理中与PCNA相关的蛋白激酶活性下降；然而，虽然BA处理中的激酶活性在吸水过程中持续下降，但在ABA处理中直到吸水24小时它都保持相对恒定。相比之下，在所有处理下，尤其是在ABA处理中，吸水15小时后一种与p13(Suc1)相关的Cdk-A激酶被激活。这些结果表明，在玉米中，ABA通过影响细胞周期进程来延迟萌发过程，使细胞大多停滞在G1期。
