Abstract
Main conclusionPlastoglobules are ubiquitous under non-stress conditions and their morphology, closely related to their composition, changes differently depending on the specific stress that the plant undergoes.Plastoglobules are lipoprotein structures attached to thylakoid membranes, which participate in chloroplast metabolism and stress responses. Their structure contains a coating lipid monolayer and a hydrophobic core that differ in composition. Their function in chloroplasts has been studied focussing on their composition. However, we currently lack a comprehensive study that quantitatively evaluates the occurrence and morphology of plastoglobules. Following a literature search strategy, we quantified the main morphological attributes of plastoglobules from photosynthetic chloroplasts of more than 1000 TEM images published over the last 53 years, covering more than 100 taxa and 15 stress types. The analysis shows that plastoglobules under non-stress conditions are spherical, with an average diameter of 100–200 nm and cover less than 3% of the chloroplast cross-section area. This percentage rises under almost every type of stress, particularly in senescence. Interestingly, an apparent trade-off between increasing either the number or the diameter of plastoglobules governs this response. Our results show that plastoglobules are ubiquitous in chloroplasts of higher plants under non-stress conditions. Besides, provided the specific molecular composition of the core and coat of plastoglobules, we conclude that specific stress-related variation in plastoglobules attributes may allow inferring precise responses of the chloroplast metabolism.
Highlights
Since the first description of chloroplasts by Hugo von Mohl in 1837, the characterisation of the complex structure of these organelles has run in parallel with the advancements in microscopy (Staehelin 2003)
Among them the groups more frequently depicted were monocots, core eudicots, eurosids I and II and euasterids I, with the highest number of records corresponding to model and crop species, such as Arabidopsis thaliana, Nicotiana tabacum, Hordeum vulgare or Oryza sativa
To better visualise this responsiveness, the effect of each stress on PGs was displayed by a Principal component analysis (PCA) based on the effect size of each attribute (Fig. 7)
Summary
Since the first description of chloroplasts by Hugo von Mohl in 1837, the characterisation of the complex structure of these organelles has run in parallel with the advancements in microscopy (Staehelin 2003). In this endeavour, the definitive milestone was the development of the electron microscopy in the 50s, a technique that allowed enough spatial accuracy to observe chloroplast ultrastructure at 1 Å resolution The physiological roles of PGs have been the subject of several reviews (Bréhélin and Kessler 2008; Eugeni Piller et al 2012; Nacir and Bréhélin 2013; Rottet et al 2015; van Wijk and Kessler 2017; Wójtowicz and Gieczewska 2020; Michel et al 2021)
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