Departamento de Botânica, Museu Nacional, Universidade Federal do Rio de Janeiro, Rio de Janeiro, RJ, 22940-040, Brazil.
Departamento de Botânica, Instituto de Biociências, Universidade Estadual Paulista, Botucatu, SP, 18618-000, Brazil.
Protoplasma. 2019 May;256(3):745-761. doi: 10.1007/s00709-018-01336-0. Epub 2018 Dec 15.
Perfect flowers of Maytenus obtusifolia have partial sterility of pollen grains, resulting in collapsed and developed free microspores. However, the cellular events resulting in partial male sterility have not been determined. In pistillate flowers of this species, male sterility is related to the premature programmed cell death (PCD) in tapetum and sporogenic cells. The process occurs through autophagy via macroautophagy and massive autophagy and is associated with sporophytic cytoplasmic male sterility (CMS). Here, we characterised the development of pollen grains and investigated the cellular events that result in tapetum cells and free microspores PCD in perfect flowers, using light and transmission electron microscopy combined with the TUNEL (Terminal deoxynucleotidyl transferase mediated dUDP end-Labeling) assay and the ZIO (Zinc iodide-osmium tetroxide) method. Pollen grain development in perfect flowers was divided into eight developmental stages based on the characteristics of the pollen grains. Tapetum cells undergo PCD at the free microspore stage, through a macroautophagic process, by formation of autophagosomes and by autophagosomes giving rise to lytic vacuoles at maturity. In the final stage of PCD, massive autophagy occurs by rupture of the tonoplast. The development of viable and inviable microspores diverges at the vacuolated microspore stage, when PCD occurs in some free microspores, causing interruption of pollen development through necrosis. These events result in the observed partial male sterility. Viable microspores undergo mitosis and develop into tricellular pollen grains. Male sterility in hermaphrodite individuals is here interpreted as gametophytic CMS.
五月茶（Maytenus obtusifolia）的完全花花粉粒存在部分不育现象，导致花粉粒皱缩和游离小孢子发育。然而，导致部分雄性不育的细胞事件尚未确定。在该物种的雌性花中，雄性不育与绒毡层和造孢细胞的过早程序性细胞死亡（PCD）有关。这一过程通过巨自噬和大量自噬发生，与孢子细胞质雄性不育（CMS）有关。在这里，我们使用光镜和透射电子显微镜结合末端脱氧核苷酸转移酶介导的 dUDP 末端标记（TUNEL）检测和碘化锌-锇四氧化物（ZIO）方法，描述了完全花花粉粒的发育，并研究了导致绒毡层细胞和游离小孢子 PCD 的细胞事件。根据花粉粒的特征，将完全花花粉粒的发育分为八个发育阶段。绒毡层细胞在游离小孢子期通过巨自噬过程发生 PCD，通过形成自噬体和自噬体成熟时形成溶酶体。在 PCD 的最后阶段，通过液泡膜破裂发生大量自噬。在有空泡的小孢子期，有活力和无活力的小孢子的发育开始分叉，此时一些游离小孢子发生 PCD，导致花粉发育中断坏死。这些事件导致了观察到的部分雄性不育。有活力的小孢子经历有丝分裂并发育成三细胞花粉粒。雌雄同体个体中的雄性不育在这里被解释为配子细胞质 CMS。
