Aerenchyma - wikipedia Aerenchyma Aerenchyma in stem cross section of a typical wetland plant. Aerenchyma is a spongy tissue that forms 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 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. 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 rhizhosphere decreases and metal ions such as iron and manganese precipitate. Aerenchyma is a modification of the parenchyma. In general, low oxygen stimulates trees and plants to produce ethylene. Ethylene slows down primary and adventitious root elongation and formation. Advantages of aerenchyma 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. Some of the oxygen transported through the aerenchyma leaks through root pores into the surrounding soil. The resulting small rhizosphere of oxygenated soil around individual roots support microorganisms that prevent the influx of potentially toxic soil components such as sulfide, iron, and manganese. References Jump up ^ Sculthorpe, C.D. 1967. The Biology of Aquatic Vascular Plants. Reprinted 1985 Edward Arnold, by London. Jump up ^ Keddy, P.A. 2010. Wetland Ecology : Principles and Conservation ( 2nd edition ). Cambridge University Press, Cambridge, UK. 497 p Jump up ^ Kozlowski, T.T. ( ed. ) 1984. Flooding and Plant Growth. Orlando, FL : Academic Press. Jump up ^ Dacey, J.W.H. 1980. Internal winds in water lilies : an adaptation for life in anaerobic sediments. Science 210 : 1017 -- 19. Jump up ^ Patrick, W.H., Jr. and Reddy, C.N. 1978. Chemical changes in rice soils. In Soils and Rice, pp. 361 -- 79. Los Ban  ̃ os, Philippines : International Rice Research Institute. Jump up ^ Kozlowski, T.T. ( ed. ) 1984. Flooding and Plant Growth. Orlando, FL : Academic Press. Jump up ^ Laing, H.E. 1940. Respiration of the rhizomes of Nuphar advenum and other water plants. American Journal of Botany 27 : 574 -- 81. Biological tissues Animals Epithelial Connective Muscular Nervous Plants Dermal tissue : Epidermis Cuticle Pavement cell Guard cell Subsidiary cell Periderm Phellem Phelloderm Vascular tissue : Phloem Sieve tube Companion cell Phloem fiber Phloem parenchyma Xylem Tracheid Vessel element Xylem fiber Xylem parenchyma Ground tissue : Parenchyma Aerenchyma Chlorenchyma Mesophyll Pith Collenchyma Sclerenchyma Sclereid Fiber Meristematic tissue : Primary Protoderm Procambium Ground meristem Secondary Cork cambium Vascular cambium Mixed : Cortex Exodermis Endodermis Stele Histology Wetlands Acrotelm A Directory of Important Wetlands in Australia Aquatic ecosystem Aquatic plants Atchafalaya Basin Backswamp Bayou Beach meadow Blackwater river Blanket bog Bog Bog garden Brackish marsh Callows Carr Cataract bog Ciénega Clean Water Act Clearwater river Coastal bog Coniferous swamp Constructed wetland Delta Waterfowl Foundation Dambo Drainage basin Ducks Unlimited Estuary Fen Flark Flood - meadow Flooded grasslands and savannas Freshwater marsh Freshwater swamp forest Grass valley Guelta Halosere Hydrosere Igapó Ings Interdunal wetland Intertidal wetland Karst Kermi bog Kettle Lagg Mangrove Marsh Marsh gas Mere Mire Misse Moorland Muck Mudflat Muskeg Oasis Palsa bog Paludification Palustrine wetland Plateau bog Pocosin Polygonal bog Pond Peat swamp forest Poor fen Pothole Ramsar Convention Raised bog Reed bed Rich fen Riparian zone River delta Salt marsh Salt pannes and pools Shrub swamp Slough String bog Swamp Telmatology Tidal marsh Upland bog Wet meadow Wetlands International Wildfowl & Wetlands Trust Will - o ' - the - wisp Várzea forest Vernal pool Whitewater river Yaéré Wikimedia Commons has media related to Aerenchyma. 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Question: aerenchyma is present in which category of plants
Answer: aquatic and wetland plants which must grow in hypoxic soils