Combining extensibility, robustness and protective functionsPlant cells are distinguished by their extraordinary ability to use solar energy to convert atmospheric carbon dioxide (CO2) into sugars. The latter are an inexhaustible source not only of energy, but also of building materials. Like links in a chain, sugars can assemble to form long polymers, known as polysaccharides. Arranged in a complex network around the plasma membrane of plant cells, these polysaccharides help build the cell wall. The cell wall acts both as a protective barrier and as the support for a pressurized, extensible skeleton, giving the plant its rigidity while allowing plant cells to expand. When these cells change shape, grow or divide, they have to remodel their cell wall architecture.
Growth without explosionOne question remains, however: how do plant cells organize their cell wall structure so that they can grow without the risk of exploding? This issue, central to plant biology, lies at the heart of understanding the key mechanisms of plant growth and adaptation to constantly changing environmental conditions.
Unidirectional growthIn a study just published in Science, the group led by Julia Santiago Cuellar , Associate Professor in the Department of Plant Molecular Biology in the Faculty of Biology and Medicine at the University of Lausanne, in collaboration with a group of scientists from the Institut national de la recherche agronomique (INRAE) in Versailles (France), provides some answers. We have identified an active mechanism which, via a protein complex, interacts directly with the polysaccharides of the cell wall, assembling them according to a particular pattern that favours unidirectional expansion", explains the Lausanne-based professor in charge of the research.
Highly resistant web-like fibersTo analyze this process in detail, the scientists used as models the pollen tubes of Arabidopsisthaliana, a fast-growing, single-celled plant structure measuring around 5 um. Their study used a multidisciplinary approach, combining biochemical, genetic and state-of-the-art super-resolution microscopy techniques to dissect the heart of this mechanism both in vitro and in planta.
Our data show how an activated protein complex is responsible for knitting unstructured sugar chains, pectins, into an organized pattern of cross-linked filaments", explains Julia Santiago Cuellar. This three-dimensional arrangement of web-like fibers thus enables the cell walls of pollen tubes to withstand high turgor (growing) pressure by sustaining continuous growth, without exploding. This structure resembles a solid support system, like an explosion-proof water pipe.
Our discovery provides molecular evidence that plant cells orchestrate the appropriate physical and chemical organization of their cell walls to support plant growth and development", comments the biologist.