RESUMO
Root hairs are single cells that develop by tip growth, a process shared with pollen tubes, axons, and fungal hyphae. However, structural plant cell walls impose constraints to accomplish tip growth. In addition to polysaccharides, plant cell walls are composed of hydroxyproline-rich glycoproteins (HRGPs), which include several groups of O-glycoproteins, including extensins (EXTs). Proline hydroxylation, an early post-translational modification (PTM) of HRGPs catalyzed by prolyl 4-hydroxylases (P4Hs), defines their subsequent O-glycosylation sites. In this work, our genetic analyses prove that P4H5, and to a lesser extent P4H2 and P4H13, are pivotal for root hair tip growth. Second, we demonstrate that P4H5 has in vitro preferred specificity for EXT substrates rather than for other HRGPs. Third, by P4H promoter and protein swapping approaches, we show that P4H2 and P4H13 have interchangeable functions but cannot replace P4H5. These three P4Hs are shown to be targeted to the secretory pathway, where P4H5 forms dimers with P4H2 and P4H13. Finally, we explore the impact of deficient proline hydroxylation on the cell wall architecture. Taken together, our results support a model in which correct peptidyl-proline hydroxylation on EXTs, and possibly in other HRGPs, is required for proper cell wall self-assembly and hence root hair elongation in Arabidopsis thaliana.
Assuntos
Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Raízes de Plantas/crescimento & desenvolvimento , Prolil Hidroxilases/metabolismo , Arabidopsis/genética , Arabidopsis/crescimento & desenvolvimento , Regulação Enzimológica da Expressão Gênica , Regulação da Expressão Gênica de Plantas , Glicosilação , Hidroxilação , Hidroxiprolina/metabolismo , Família Multigênica , Raízes de Plantas/enzimologia , Raízes de Plantas/genética , Prolil Hidroxilases/genéticaRESUMO
BACKGROUND AND AIMS: The distinction between pearl bodies (or pearl glands) and food bodies (FBs) is not clear; neither is our understanding of what these structures really represent. The present work examined the ontogenesis, structure, ultrastructure and histochemical aspects of the protuberances in Cissus verticillata, which have been described since the beginning of the 19th century as pearl glands or pearl bodies, in order to establish a relationship between their structure and function. METHODS: Segments of stems and leaves in different stages of development were collected and fixed for study under light microscopy as well as electron transmission and scanning microscopy. Samples of FBs were subjected to chemical analysis using thin-layer chromatography. KEY RESULTS: The FBs in C. verticillata are globose and attached to the plant by a short peduncle. These structures are present along the entire stem during primary growth, and on the inflorescence axis and the abaxial face of the leaves. The FBs were observed to be of mixed origin, with the participation of both the epidermis and the underlying parenchymatic cells. The epidermis is uniseriate with a thin cuticle, and the cells have dense cytoplasm and a large nucleus. The internal parenchymatic cells have thin walls; in the young structures these cells have dense cytoplasm with a predominance of mitochondria and plastids. In the mature FBs, the parenchymatic cells accumulate oils and soluble sugars; dictyosomes and rough endoplasmic reticulum predominate in the cytoplasm; the vacuoles are ample. Removal of the FBs appears to stimulate the formation of new ones, at the same place. CONCLUSIONS: The vegetative vigour of the plant seems to influence the number of FBs produced, with more vigorous branches having greater densities of FBs. The results allow the conclusion that the structures traditionally designated pearl glands or pearl bodies in C. verticillata constitute FBs that can recruit large numbers of ants.
Assuntos
Cissus/anatomia & histologia , Cissus/metabolismo , Epiderme Vegetal/citologia , Epiderme Vegetal/metabolismo , Animais , Formigas/fisiologia , Cissus/citologia , Cissus/ultraestrutura , Epiderme Vegetal/parasitologia , Epiderme Vegetal/ultraestruturaRESUMO
BACKGROUND AND AIMS: Food bodies (FBs) are structures that promote mutualism between plants and ants, which help protect them against herbivores. The present study aims to describe the anatomical organization, ultrastructure and chemical composition of the FBs in Hovenia dulcis, which represent the first structures of this type described in Rhamnaceae. METHODS: Leaves in various stages of development were collected and fixed for examination under light, transmission and scanning electron microscopy. Samples of FBs were subjected to chemical analysis using thin-layer chromatography and nuclear magnetic resonance of (1)H and (13)C. KEY RESULTS: The FBs vary from globose to conical and are restricted to the abaxial leaf surface, having a mixed origin, including epidermis and parenchyma. The FB epidermis is uniseriate, slightly pilose and has a thin cuticle. The epidermal cells are vacuolated and pigments or food reserves are absent. The parenchyma cells of immature FBs have dense cytoplasm showing mitochondria, endoplasmic reticulum and plastids. Mature FB cells store oils, which are free in the cytosol and occupy a large portion of the cell lumen. In these cells the plastids accumulate starch. CONCLUSIONS: The lipids present in FBs are glycerin esters characteristic of plant energy reserves. Ants were observed collecting these FBs, which allows us to infer that these structures mediate plant-ant interactions and can help protect the young plants against herbivores, as these structures are prevalent at this developmental stage.