Rapid endocytosis is triggered upon imbibition in Arabidopsis seeds

Abstract

Abbreviations: BFA, brefeldin A; DMSO, dimethylsulphoxide; FM4-64, N-(3-triethylammoniumpropyl)-4-(6-(4-diethylaminophenylhexatrienyl)pyridinium dibromide; RG-II, rhamnogalacturonan-II During seed imbibition and embryo activation, rapid change from a metabolically resting state to the activation of diverse extracellular and/or membrane bound molecules is essential and, hence, endocytosis could be activated too. In fact, we have documented endocytic internalization of the membrane impermeable endocytic tracer FM4-64 already upon 30 min of imbibition of Arabidopsis seeds. This finding suggest that endocytosis is activated early during seed imbibition in Arabidopsis. Immunolocalization of rhamnogalacturonan-II (RG-II) complexed with boron showed that whereas this pectin is localized only in the cell walls of dry seed embryos, it starts to be intracellular once the imbibition started. Brefeldin A (BFA) exposure resulted in recruitment of the intracellular RG-II pectin complexes into the endocytic BFA-induced compartments, confirming the endocytic origin of the RG-II signal detected intracellularly. Finally, germination was significantly delayed when Arabidopsis seeds were germinated in the presence of inhibitors of endocytic pathways, suggesting that trafficking of extracellular molecules might play an important role in the overcome of germination. This work constitutes the first demonstration of endocytic processes during germination and opens new perspectives about the role of the extracellular matrix and membrane components in seed germination.

Xyloglucan Metabolism Differentially Impacts the Cell Wall Characteristics of the Endosperm and Embryo during Arabidopsis Seed Germination

“…The latter seems more likely, since ubiquitous cell wall labeling was observed at earlier stages and decreased XyG abundance correlated with concomitant labeling of intracellular vesicles. In accordance, inhibitors of endocytosis have previously been shown to significantly delay germination, indicating that internalization of extracellular molecules plays an important function (Pagnussat et al, 2012). Interestingly, the differential XyG accumulation was observed in a region just above the radicle tip previously described as the embryo elongation zone during germination (Sliwinska et al, 2009).…”

How membranes organize during seed germination: three patterns of dynamic lipid remodelling define chilling resistance and affect plastid biogenesis

“…The PA level was 6.38 nmol/mg in dry seeds (Table 1), which was much higher than that previously reported in leaves (Crowe & Crowe, 1992, Li, Wang, Liu, Cui, Chen, Zhang, Jiang, Xu, Li, Li, Zhao & Chen, 2013, Welti et al , 2002). PA levels in leaves are usually around 1 nmol/mg, but can increase 2–10-fold under stress conditions, such as freezing and desiccation (Li et al , 2008, Pagnussat et al , 2012, Welti et al , 2002). The higher PA levels in dry seeds are consistent with previous data(Devaiah et al, 2006) and support the hypothesis that their cellular membranes are commonly in the hexagonal II phase, which is characteristic of disordered membranes (Simon, 1974).…”

“…Previous studies focused primarily on the morphology, physiology, primary metabolism, and phytohormonal regulation of germination. However, recent studies that involved transcriptomic and proteomic approaches have provided new insight into the molecular mechanisms of germination (Bhardwaj et al , 2012, Demarsy et al , 2012, Holdsworth et al , 2008, Law et al , 2012, Pagnussat et al , 2012, Parrish & Leopold, 1977, Swigonska & Weidner, 2013). Although the essential role of membranes in germination is widely accepted, the concept that describes membrane reorganization is built on simple and in vitro biophysical models (Simon, 1974).…”

“…The biological events that take place during germination were recently revealed by transcriptomic (Bhardwaj, Anand & Nagarajan, 2012, Demarsy, Buhr, Lambert & Lerbs-Mache, 2012, Holdsworth, Bentsink & Soppe, 2008, Parrish & Leopold, 1977) and proteomic analyses (Cheng, Gao, Li, Shi, Javeed, Jing, Yang & He, 2010, Han, Yin, He & Yang, 2013, Law, Narsai, Taylor, Delannoy, Carrie, Giraud, Millar, Small & Whelan, 2012, Pagnussat, Burbach, Baluska & de la Canal, 2012, Swigonska & Weidner, 2013, Yang, Liu, Liu, Chen, Chen & Shen, 2009), and can basically be classified into two types. The first involves the metabolic quiescence of dry seeds being reversed after imbibition.…”

How to let go: pectin and plant cell adhesion

“…Given the adhesion defects described above, when actin is disrupted, it is plausible that actin-mediated endocytosis might also be involved in maintaining cell wall integrity. Recycling of cell wall components has been demonstrated in germinating Arabidopsis seeds and maize root tip cells ( Baluška et al, 2002 ; Pagnussat et al, 2012 ). Cell wall modifying proteins may also be recycled, as seen in the case of PMEI endocytosis in growing pollen tubes ( Röckel et al, 2008 ).…”