Department of Biology, University Roma Tre, 00146 Rome, Italy.
Plant Physiol. 2011 Sep;157(1):200-15. doi: 10.1104/pp.111.173153. Epub 2011 Jul 11.
Spermidine (Spd) treatment inhibited root cell elongation, promoted deposition of phenolics in cell walls of rhizodermis, xylem elements, and vascular parenchyma, and resulted in a higher number of cells resting in G(1) and G(2) phases in the maize (Zea mays) primary root apex. Furthermore, Spd treatment induced nuclear condensation and DNA fragmentation as well as precocious differentiation and cell death in both early metaxylem and late metaxylem precursors. Treatment with either N-prenylagmatine, a selective inhibitor of polyamine oxidase (PAO) enzyme activity, or N,N(1)-dimethylthiourea, a hydrogen peroxide (H(2)O(2)) scavenger, reverted Spd-induced autofluorescence intensification, DNA fragmentation, inhibition of root cell elongation, as well as reduction of percentage of nuclei in S phase. Transmission electron microscopy showed that N-prenylagmatine inhibited the differentiation of the secondary wall of early and late metaxylem elements, and xylem parenchymal cells. Moreover, although root growth and xylem differentiation in antisense PAO tobacco (Nicotiana tabacum) plants were unaltered, overexpression of maize PAO (S-ZmPAO) as well as down-regulation of the gene encoding S-adenosyl-l-methionine decarboxylase via RNAi in tobacco plants promoted vascular cell differentiation and induced programmed cell death in root cap cells. Furthermore, following Spd treatment in maize and ZmPAO overexpression in tobacco, the in vivo H(2)O(2) production was enhanced in xylem tissues. Overall, our results suggest that, after Spd supply or PAO overexpression, H(2)O(2) derived from polyamine catabolism behaves as a signal for secondary wall deposition and for induction of developmental programmed cell death.
亚精胺（Spd）处理抑制根细胞伸长，促进细胞壁中酚类物质在根表皮、木质部元素和维管束薄壁组织中的沉积，并导致玉米（Zea mays）初生根尖中更多的细胞停留在 G1 和 G2 期。此外，Spd 处理诱导核浓缩和 DNA 片段化以及早期木质部和晚期木质部前体细胞的早熟分化和细胞死亡。用 N- prenylagmatine（多胺氧化酶（PAO）酶活性的选择性抑制剂）或 N,N（1）-二甲基硫脲（H2O2 的清除剂）处理，均可逆转 Spd 诱导的自发荧光增强、DNA 片段化、根细胞伸长抑制以及 S 期核比例降低。透射电子显微镜显示，N-prenylagmatine 抑制了早期和晚期木质部元素以及木质部薄壁细胞的次生壁的分化。此外，尽管反义 PAO 烟草（Nicotiana tabacum）植物的根生长和木质部分化没有改变，但玉米 PAO（S-ZmPAO）的过表达以及通过 RNAi 下调编码 S-腺苷甲硫氨酸脱羧酶的基因在烟草植物中促进了血管细胞分化，并诱导根冠细胞程序性细胞死亡。此外，在玉米中用 Spd 处理和在烟草中过表达 ZmPAO 后，木质部组织中体内 H2O2 的产生增加。总之，我们的结果表明，在 Spd 供应或 PAO 过表达后，多胺分解产生的 H2O2 作为沉积次生壁和诱导发育性程序性细胞死亡的信号。
