Abstract

Vascular plants with secondary growth develop a periderm mostly composed of dead suberized cork cells to face environmental hostile conditions. Cork oak has a highly active and long-living phellogen forming a remarkably thick periderm that is periodically debarked for industrial purposes. This wounding originates the quick formation of a new traumatic periderm, making cork oak an exceptional model to study the first periderm differentiation during normal development in young sprigs and traumatic (wound) periderm formation after debarking. Here, we studied the poorly known first periderm differentiation steps that involve cell wall suberization, polyphenolic accumulation and programmed cell death (PCD) by combining transmission electron microscopy, histochemical and molecular methods in periderms from young sprigs. These processes were further compared with traumatic periderms formed after wounding using molecular and histochemical techniques, such as the polyphenolic accumulation. In the first periderms from young sprigs, four distinct differentiation stages were defined according to the presence of PCD morphological features. First young and traumatic periderms showed an upregulation of genes related to suberin biosynthesis, proanthocyanidins biosynthesis and transport, autophagy, and PCD. Traumatic periderms revealed an overall upregulation of these genes, likely resulting from ontogeny differences and distinct phellogen origin associated with a faster metabolism, highlighting the impact of wounding on phellogen activity after debarking. First periderms from young sprigs showed gradual accumulation of proanthocyanidins in the vacuoles throughout PCD stages until total filled lumens, whereas in traumatic periderms, these compounds were found cell wall linked in already empty cells. This work enabled a comprehensive overview of the cork cells differentiation processes contributing to deepening the knowledge of the fundamental ontogenic program of this protective tissue, which is also a unique forest product, constituting the basis of a sustainable and profitable industry.

中文翻译：

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软木橡木周皮中的软木细胞经历程序性细胞死亡和原花青素沉积

摘要

具有二次生长的维管植物会形成主要由死栓塞细胞组成的周皮，以应对恶劣的环境条件。软木橡木具有高活性和长寿命的腐生菌，形成非常厚的外皮，定期剥皮用于工业用途。这种伤口导致了新的外伤周皮的快速形成，使软木橡木成为研究幼枝正常发育过程中第一次周皮分化和剥皮后外伤（伤口）周皮形成的特殊模型。在这里，我们通过结合透射电子显微镜、组织化学和分子方法在年轻小枝的周皮中研究了鲜为人知的第一周皮分化步骤，这些步骤涉及细胞壁松软、多酚积累和程序性细胞死亡 (PCD)。这些过程进一步与使用分子和组织化学技术（如多酚积累）受伤后形成的外伤性外皮进行了比较。在幼枝的第一周皮中，根据 PCD 形态特征的存在定义了四个不同的分化阶段。第一个年轻的外伤性外皮显示与木栓质生物合成、原花青素生物合成和运输、自噬和 PCD 相关的基因上调。外伤性外皮揭示了这些基因的整体上调，这可能是由于个体发育差异和与更快代谢相关的不同的腐臭素起源所致，突出了剥皮后伤口对腐臭素活性的影响。来自年轻小枝的第一周皮显示在整个 PCD 阶段的液泡中逐渐积累原花青素，直到完全充满管腔，而在外伤周皮中，发现这些化合物与已经空的细胞中的细胞壁相连。这项工作能够全面概述软木细胞分化过程，有助于加深对这种保护组织的基本个体发生程序的了解，这也是一种独特的林产品，构成了可持续和有利可图的行业的基础。