Within a plant, the apoplast is the free diffusional space outside the plasma membrane. It is interrupted by the Casparian strip in roots, air spaces between plant cells and the cuticula of the plant. Divisions Land plants (embryophytes) Non-vascular plants (bryophytes) Marchantiophyta - liverworts Anthocerotophyta - hornworts Bryophyta - mosses Vascular plants (tracheophytes) Lycopodiophyta - clubmosses Equisetophyta - horsetails Pteridophyta - true ferns Psilotophyta - whisk ferns Ophioglossophyta - adderstongues Seed plants (spermatophytes) †Pteridospermatophyta - seed ferns Pinophyta - conifers Cycadophyta - cycads Ginkgophyta - ginkgo Gnetophyta - gnetae Magnoliophyta - flowering plants Adiantum pedatum (a fern... Suberin is a waxy substance found in higher plants. ... Primary and secondary roots in a cotton plant In vascular plants, the root is that organ of a plant body that typically lies below the surface of the soil (compare with stem). ... on leaves: a water-repelling surface that protects plants from uncontrolled transpiration and mechanical damages. ...

The apoplast is important for all the plant's communication to its environment. The main carbon source (carbon dioxide) needs to be solubilized in the apoplast before it is to be taken up by chloroplasts and consumed during photosynthesis. In the roots, ions diffuse into the apoplast of the epidermis before being taken up into the symplast by specific ion channels and being pulled by the plant's transpiration stream, which also occurs completely within the boundaries of the apoplast. Similarly, all gaseous molecules emitted and received by plants such as plant hormones and other pheromones must pass the apoplast. The apoplast is also a site for cell-to-cell communication. During local oxidative stress, hydrogen peroxide and superoxide anion can diffuse through the apoplast and transport a warning signal to neighbouring cells. In addition, a local alkalinization of the apoplast due to such a stress can travel within minutes to the rest of the plant body via the xylem and trigger systemic acquired resistance (Felle et al., 2005). Carbon dioxide is an atmospheric gas comprised of one carbon and two oxygen atoms. ... The inside of a chloroplast Chloroplasts are organelles found in plant cells and eukaryotic algae that conduct photosynthesis. ... Leaf. ... Epidermis could refer to: In plants, the outermost layer of cells covering the leaves and young parts of a plant is the epidermis. ... In plants, the transpiration stream is the uninterrupted stream of water which is taken up by the roots and, via the xylem vessels, transported to the leaves where it will eventually evaporate at the air/apoplast-interface of the substomatal cavity. ... Plant hormones (or plant growth regulators, or PGRs) are internally-secreted chemicals in plants that are used for regulating the plants growth. ... It has been suggested that Bombykol be merged into this article or section. ... Oxidative stress is a medical term for damage to animal cells (and thereby the organs and tissues composed of those cells) caused by reactive oxygen species, which include superoxide, peroxynitrate, or hydrogen peroxide. ... Flash point Non-flammable. ... Superoxide is a reactive anion and free radical, formally O2-. It is produced most easily by burning rubidium or caesium in oxygen. ... It has been suggested that Vessel element be merged into this article or section. ... In plants, the transpiration stream is the uninterrupted stream of water which is taken up by the roots and, via the xylem vessels, transported to the leaves where it will eventually evaporate at the air/apoplast-interface of the substomatal cavity. ...

Notes

1. Apoplast was previously defined as "everything but the symplast, consisting of cell walls and spaces between cells in which water and solutes can move freely". However, since solutes can neither freely move through the air spaces between plant cells nor through the cuticula, this definition has been changed. When referring to "everything outside the plasma membrane", the term "extracellular space" is in use.
2. The word apoplasm is also in use with similar meaning as apoplast, although less common.

A cell wall is a more or less solid layer surrounding a cell. ... Cells in culture, stained for keratin (red) and DNA (green). ... A girl in a swimming pool Water (from the Old English waeter; c. ... A substance is soluble in a fluid if it dissolves in the fluid. ...

References

1. Felle HH, Herrmann A, Hückelhoven R, Kogel K-H (2005) Root-to-shoot signalling: apoplastic alkalinization, a general stress response and defence factor in barley (Hordeum vulgare). Protoplasma 227, 17 - 24.
2. Salibury F, Ross C (1991) Plant Physiology. Brooks Cole, pp 682, ISBN 0534151620.

See also

• Symplast
• Tonoplast