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BIOL 462
Barry Warner

Plant Adaptations: Adaptation to Anoxia: Oxygen poor condition A) Structural adaptations: aerenchyma o Rooted wetland plants form internal gas-transport systems of large gas filled lacunae(gaps)– lacunae are together in porous tissue called aerenchyma o Aerenchyma increases with increased reduced conditions  10-12% root X-sectional area in flood intolerant plants  50-60% root X-sectional area in flood tolerant plants o Allows gases to be stored – EX) cattails nearly ½ total leaf volume is gas space, C02 may be up to 18* greater than in atmosphere B) Root Adaptation o Adventitious roots: new roots that form laterally from the main stem within days of flooding ; forms in oxygen rich water and less root biomass : PLANT HORMONE: AUXIN o Shallow rooting: both woody and herbaceous plants tend to have shallower roots than in terrestrial conditions  Gives roots access to oxygen and nitrate o Pneumatophores: modified erect roots that grow upward from roots ( knees)  Height corresponds to maximum water height  Take in oxygen and release 3-22% more carbon dioxide than equivalent truck area - have lenticels o Prop and Drop roots: Develop from lower part of stems, and branches- grow outward toward substrate  Covered with lenticels that allow oxygen to diffuse into plant  Help with anchoring plant NOTE: Lenticels: One of many raised pores in the stem of a woody plant that allow gas exchange between the atmosphere and plant tissues. C) Stem Adaptations: o Rapid underwater root extension: brings plants near or above water surface for light, oxygen, and carbon dioxide. Hormone: ETHYLENE o Hypertrophy: Swelling at stem base in response to flooding in herbaceous/woody plants- due to accelerated cell expansion caused by cell separation/rupture- buttress tree trunks o Stem buoyancy: for taking up Oxygen and Carbon dioxide; slime D) Gas Transport Mechanism:  Enhances gas diffused/enable plant to live in anoxic \  Aerenchyma: paces or air channels in the leaves, stems and roots of some plants, which allows exchange of gases between the shoot and the rooThe 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. o Passive molecular diffusion: most prevalent; physical process where substances moves from site of lower concentration/partial pressure to site of high concentration/partial pressure  Aerial part of plant(leaves/stems) has oxygen concentrations close to atmospheric (21%) and about 4% in rhizomes/roots o Pressurized ventilation: air moves into plant through stomata of younger leaves, down stems to rhizomes, than back up to older leaves and out  younger leaves= higher pressure, older leaves= low pressure • young leaves have greater pressure because of smaller stomata: contributes to differences in humidly, water vapour than in older leaves o Underwater gas exchange: based on exchange of gases between submerged plant tissue/surrounding water  Ex) pneumatophores, adventitious roots o Ventri-induced convection: based on gradient in wind velocity:  tall stems: exposed to h
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