Laboratório de Fisiologia Vegetal, Departamento de Botânica, Instituto de Biologia, CCS, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, Brasil.
Pós-graduação em Biotecnologia Vegetal, Universidade Federal do Rio de Janeiro, Cidade Universitária, Rio de Janeiro, Brasil.
Ann Bot. 2018 May 11;121(6):1163-1172. doi: 10.1093/aob/mcx217.
Setaria viridis is being promoted as a model C4 photosynthetic plant because it has a small genome (515 Mb), a short life cycle (60 d) and it can be transformed. Unlike other C4 grasses such as maize, however, there is very little information about how C4 leaf anatomy (Kranz anatomy) develops in S. viridis. As a foundation for future developmental genetic studies, we provide an anatomical and ultrastructural framework of early shoot development in S. viridis, focusing on the initiation of Kranz anatomy in seed leaves.
Setaria viridis seeds were germinated and divided into five stages covering development from the dry seed (stage S0) to 36 h after germination (stage S4). Material at each of these stages was examined using conventional light, scanning and transmission electron microscopy.
Dry seeds contained three embryonic leaf primordia at different developmental stages (plastochron 1-3 primordia). The oldest (P3) leaf primordium possessed several procambial centres whereas P2 displayed only ground meristem. At the tip of P3 primordia at stage S4, C4 leaf anatomy typical of the malate dehydrogenase-dependent nicotinamide dinucleotide phosphate (NADP-ME) subtype was evident in that vascular bundles lacked a mestome layer and were surrounded by a single layer of bundle sheath cells that contained large, centrifugally located chloroplasts. Two to three mesophyll cells separated adjacent vascular bundles and one mesophyll cell layer on each of the abaxial and adaxial sides delimited vascular bundles from the epidermis.
The morphological trajectory reported here provides a foundation for studies of gene regulation during early leaf development in S. viridis and a framework for comparative analyses with other C4 grasses.
柳枝稷被宣传为一种模型 C4 光合植物，因为它具有小基因组（515Mb）、短生命周期（60d）且易于转化。然而，与其他 C4 禾本科植物（如玉米）不同，关于柳枝稷 C4 叶片解剖结构（Kranz 解剖结构）如何发育的信息非常少。作为未来发育遗传研究的基础，我们提供了柳枝稷早期芽发育的解剖学和超微结构框架，重点关注种子叶中 Kranz 解剖结构的起始。
柳枝稷种子萌发并分为五个阶段，涵盖从干种子（S0 期）到萌发后 36 小时（S4 期）的发育过程。在这些阶段的每个阶段使用常规光、扫描和透射电子显微镜检查材料。
干种子中包含三个处于不同发育阶段的胚胎叶原基（1-3 个叶原基）。最老的（P3）叶原基具有几个原形成层中心，而 P2 仅显示基生组织。在 S4 期 P3 原基的顶端，C4 叶片解剖结构典型的苹果酸脱氢酶依赖的烟酰胺二核苷酸磷酸（NADP-ME）亚型是明显的，即维管束缺乏中柱层，被单层鞘细胞包围，这些细胞含有大的、离心定位的叶绿体。两个到三个叶肉细胞分隔相邻的维管束，每一个背面和腹面的两个叶肉细胞层将维管束与表皮分隔开来。
这里报道的形态轨迹为柳枝稷早期叶片发育过程中基因调控的研究提供了基础，并为与其他 C4 禾本科植物的比较分析提供了框架。
