02382nas a2200229   4500008004100000245010700041210006900148260001200217300001600229490000700245520162100252653002601873653001101899653002401910653001601934653001201950653002101962653001901983653001602002100001802018856011602036       2004                        eng d00aRegulation of root anaerobiosis and carbon translocation by light and root aeration in Isoetes alpinus0 aRegulation of root anaerobiosis and carbon translocation by ligh  c2004///  a1102 - 11110 v273 aThe activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15-0.35 × 10-6 mol g-1 fresh weight s-1) over the entire plant depth range (3-7 m depth), and was intermediate to that developed in excised roots after 1-week exposure to either dissolved oxygen at air-saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot-to-root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of 14C-labelled photo-assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high 14C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning.10aAlcohol dehydrogenase10aAnoxia10aAquatic macrophytes10aAssimilates10aLacunae10aOxygen transport10aPhotosynthesis10aRespiration1 aSorrell, B.K.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-4544301436&partnerID=40&md5=3f174fe3d7839650597cfe52d3369b9102405nas a2200205   4500008004100000245014300041210006900184260001200253300001400265490000700279520168800286653000801974653001401982653001901996653000702015653002602022100001802048700001702066856011602083       2004                        eng d00aWater velocity and irradiance effects on internal transport and metabolism of methane in submerged Isoetes alpinus and Potamogeton crispus0 aWater velocity and irradiance effects on internal transport and   c2004///  a189 - 2020 v793 aSubmerged aquatic macrophytes are important methane (CH4) transport pathways, but little is known about how water velocity and illumination affect plant CH4 transport. We studied CH4 transport in vitro in fully-submerged plants of two aquatic macrophytes, Isoetes alpinus and Potamogeton crispus, comparing transport between two water velocities (0.5 and 90 mm s-1) and light versus dark treatments at the shoots. In I. alpinus, CH4 taken up by the roots accumulated in the lacunar system of the leaves at concentrations &gt;40 μmol l-1 at both flow rates, but there was no release from the shoots to the water at flow = 0.5 mm s-1, whereas at 90 mm s-1 release from the shoots to the water was always &gt;0.15 μmol (CH4 g-1 dry wt. h-1). Uptake of CH4 by the roots was 1.5 times greater at the higher than the lower water velocity. In P. crispus, a gradient in lacunar [CH4] developed from the base to the apex of the shoot and was steeper at the higher than the lower water velocity. CH4 release rates from the shoots were &lt;0.1 μmol (CH4 g-1 dry wt. h-1) at both water velocities in this species, due to CH 4 consumption by epiphytic methanotrophic bacteria. Irradiance and its associated root aeration had no effect on CH4 transport in I. alpinus, but decreased root to shoot CH4 transport and release more than 10-fold in P. crispus, apparently by alleviating effects of hypoxia on the root-associated methanotrophic bacteria. Our data support the view that plant-associated methanotrophs are important CH4 sinks in freshwater habitats, and demonstrate the importance of flow velocity in the CH4 dynamics of submerged macrophytes. © 2004 Elsevier B.V. All rights reserved.10aCH410aDiffusion10aLacunar system10aO210aSubmerged macrophytes1 aSorrell, B.K.1 aDownes, M.T.  uhttp://www.scopus.com/inward/record.url?eid=2-s2.0-2642545092&partnerID=40&md5=9d9974a9e87e34dbe2225f98137ef822