Institute of Plant Biology and Biotechnology, University of Muenster, Schlossplatz 8, 48143, Muenster, Germany.
Matthias Schleiden Institute for Genetics, Bioinformatics and Molecular Botany, Friedrich Schiller University Jena, Dornburgerstrasse 159, 07743, Jena, Germany.
J Plant Physiol. 2022 Apr;271:153643. doi: 10.1016/j.jplph.2022.153643. Epub 2022 Mar 1.
Cucurbits have been used as phloem research models for many decades because their exudates can be accessed with ease. However, cucurbit plants possess two distinct phloem systems known as the fascicular phloem (FP) and extrafascicular phloem (EFP). Therefore, the molecular composition and function of certain exudates can be misinterpreted due to their unclear origin. To characterize the anatomy and function of the different phloem systems more clearly, we generated specific antibodies against marker proteins (PP1 homologs) allowing the clear identification of the EFP at the organ, tissue and cellular levels by immunological staining. We also used detailed microscopy to determine common and unique anatomical features of the FP and EFP sieve elements (SEs) in cucumber (Cucumis sativus). The comparison of exudation rates and the dynamic viscosity, density and sugar content of the exudates from plants grown in the light and dark revealed the consistent composition and behavior of the EFP exudate even when photosynthesis was prevented, thus differing from the properties of the FP exudate. Furthermore, the analysis of phloem transport using a fluorescein disodium salt showed only wound-induced exudation of dye from the EFP, indicating the absence of transport in this tissue. Our results show that it is important to distinguish between the EFP and FP in cucurbits, particularly their differing behaviors in response to wounding.
葫芦科植物因其泌物流出较为容易，已被用作韧皮部研究模型数十年。然而，葫芦科植物具有两种不同的韧皮部系统，即束状韧皮部（FP）和束间韧皮部（EFP）。因此，由于其来源不明确，某些泌物的分子组成和功能可能会被误解。为了更清楚地描述不同韧皮部系统的解剖结构和功能，我们生成了针对标记蛋白（PP1 同源物）的特异性抗体，通过免疫染色可以在器官、组织和细胞水平上清楚地识别 EFP。我们还使用详细的显微镜技术来确定黄瓜（Cucumis sativus）FP 和 EFP 筛管（SE）的共同和独特的解剖特征。比较在光照和黑暗条件下生长的植物的泌出率以及泌出物的动态粘度、密度和糖含量，结果表明，即使阻止了光合作用，EFP 泌出物的组成和行为仍然一致，与 FP 泌出物的性质不同。此外，使用荧光素二钠盐分析韧皮部运输，结果仅显示 EFP 中染料的创伤诱导泌出，表明该组织中不存在运输。我们的研究结果表明，区分葫芦科植物中的 EFP 和 FP 很重要，特别是它们在应对创伤时的不同行为。
