Aerenchyma or aeriferous parenchyma or lacunae, is a modification of the parenchyma to form a spongy tissue that creates spaces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the root. The channels of air-filled cavities (see image to right) provide a low-resistance internal pathway for the exchange of gases such as oxygen, carbondioxide and ethylene between the plant above the water and the submerged tissues. Aerenchyma is also widespread in aquatic and wetland plants which must grow in hypoxic soils. The word "aerenchyma" is Modern Latin derived from Latin ' for "air" and Greek ' for "infusion."

Aerenchyma formation and hypoxia

When soil is flooded, hypoxia develops, as soil microorganisms consume oxygen faster than diffusion occurs. The presence of hypoxic soils is one of the defining characteristics of wetlands. Many wetland plants possess aerenchyma, and in some, such as water-lilies, there is mass flow of atmospheric air through leaves and rhizomes. There are many other chemical consequences of hypoxia. For example, nitrification is inhibited as low oxygen occurs and toxic compounds are formed, as anaerobic bacteria use nitrate, manganese, and sulfate as alternative electron acceptors. The reduction-oxidation potential of the rhizosphere decreases and metal ions such as iron and manganese precipitate. In general, low oxygen stimulates trees and plants to produce

ethylene Ethylene (IUPAC name: ethene) is a hydrocarbon which has the formula or . It is a colourless, flammable gas with a faint "sweet and musky" odour when pure. It is the simplest alkene (a hydrocarbon with carbon-carbon double bonds). Ethylene i ...

Advantages

The large air-filled cavities provide a low-resistance internal pathway for the exchange of gases between the plant organs above the water and the submerged tissues. This allows plants to grow without incurring the metabolic costs of anaerobic respiration.Laing, H. E. 1940. Respiration of the rhizomes of Nuphar advenum and other water plants. American Journal of Botany 27: 574–81. Moreover, the degradation of cortical cells during aerenchyma formation reduce the metabolic costs of plants during stresses such as drought. Some of the oxygen transported through the aerenchyma leaks through root pores into the surrounding soil. The resulting small

rhizosphere The rhizosphere is the narrow region of soil or substrate that is directly influenced by root secretions and associated soil microorganisms known as the root microbiome. Soil pores in the rhizosphere can contain many bacteria and other microo ...

of oxygenated soil around individual roots support microorganisms that prevent the influx of potentially toxic soil components such as sulfide,

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

, and

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

References

{{Commonscat, Aerenchyma Plant physiology Plant cells Wetlands de:Parenchyma#hym