The neem tree (Azadirachta indica A.Juss.) contains a range of biologically active compounds-mainly triterpenoids produced in single secretory cells, which are distributed among all plant parts. Neem secretions are toxic to animal cells, triggering autolytic mechanisms that culminate in cell disruption. However, little is known about the self-toxicity of these secretions to the cells that produce them. We carried out an anatomical, histochemical, and ultrastructural investigation of neem's single secretory cells in the shoot apex and in young leaves. We evaluated the morphological changes as possible evidences of stress reactions to their own secretions. The subcellular apparatus involved in synthesis and compartmentation was consistent with hydrophilic and lipophilic secretions. Polymorphic plastids devoid of thylakoids and abundant smooth endoplasmic reticulum in the later stages of differentiation are comparable with previous reports on neem cotyledons with regard to terpenoid synthesis. However, secretions were compartmentalized within autophagic vacuoles and periplasmic spaces instead of in terpenoid vesicles. Cellular swelling, increased vesiculation, dilatation of endoplasmic reticulum cisternae, mitochondrial hypertrophy in the cristolysis process, autolytic vacuoles, and vacuolar degeneration culminating in protoplast autolysis are all consistent with early indications of autotoxicity. The signaling stress reaction mechanism was expressed as cytoplasmic deposits of calcium salt and by the expression of a 70-kDa heat-shock protein. The morphological and histochemical changes in the secreting cells are comparable with those described in animal cells exposed to neem oil. Our data provide evidence of cell damage and signaling reactions linked to these cells' own secretions before autolysis.

中文翻译：

---

印楝分泌细胞：发育细胞学和细胞自体毒性的适应症

印楝树 (Azadirachta indica A.Juss.) 含有一系列生物活性化合物——主要是在单个分泌细胞中产生的三萜类化合物，它们分布在植物的所有部位。印楝分泌物对动物细胞有毒，会触发自溶机制，最终导致细胞破裂。然而，关于这些分泌物对产生它们的细胞的自身毒性知之甚少。我们对茎尖和嫩叶中印楝的单个分泌细胞进行了解剖学、组织化学和超微结构研究。我们评估了形态变化，作为对其自身分泌物的应激反应的可能证据。参与合成和分隔的亚细胞装置与亲水性和亲脂性分泌物一致。在分化后期缺乏类囊体和丰富的光滑内质网的多态性质体与之前关于萜类化合物合成的印楝子叶的报道相当。然而，分泌物被分隔在自噬泡和周质空间内，而不是在萜类囊泡中。细胞肿胀、水泡增多、内质网池扩张、脆化过程中的线粒体肥大、自溶液泡和最终原生质体自溶的液泡变性都与自体毒性的早期迹象一致。信号应激反应机制表现为钙盐的细胞质沉积物和 70 kDa 热休克蛋白的表达。分泌细胞的形态和组织化学变化与暴露于印楝油的动物细胞中描述的变化相当。我们的数据提供了细胞损伤和信号反应与自溶前这些细胞自身分泌物相关的证据。