Diurnal changes in radial oxygen loss and ethanol metabolism in roots of submerged and non‐submerged rice seedlings

Abstract

S U IVl .VI .\ R YThe effects of shoot submergence on root aeration were examined using floodwater flushed with 1 or 2 kPa CO., plus 1 0 or 21 kPa ().,, or with air; the rooting media were stagnant. Oxygen regimes within the roots were evaluated from measurements ot radial ()., loss to polarographic electrodes sleeving the extension zone of nodal roots, or, from dissolved O., and ethanol in the rooting medium.With shoots submerged, root O^ and extension, as well as O., and ethanol concentrations in the rooting medium underwent marked diurnal changes. In the dark, the radial ()., loss fell rapidly until root surface O., became (0-001 mol m"'' (gas-phase equivalent <()'l kPa) and root extension slowed down or ceased. Oxygen, previously accumulated in the rooting medium, also declined markedly, whilst ethanol accumulated rapidly. When the lights come on, radial O., loss resumed within 3 min and surged to a peak at c. 30 min before decreasing gradually to a lower level. Root extension also resumed, and a steady rise in dissoh'ed ()., was accompanied by a decline in ethanol concentration. The expression of a diurnal cycling of O,, was attributed to high boutidary-layer resistance to gas exchange between leaf and water, to CO,^ supply and to a buffering eftect by oxygen in the floodwater. Thus, during the day the escape of photosynthetic ()., was hindered, while at night, ()., How from floodwater to leaf was restricted. Fluctuations in ethanol were attributed to the generation and subsequent consumption of ethanol by the roots in response to lower and higher internal O,, concentration. The O., surge at dawn was partly attributed to enhanced photosynthesis from accumulated internal CO.,, and partly to a decline in O,, demand during the night as a result of substrate depletion in the plant. Stagnant floodwaters around the shoots led to much higher daytime rates of radial O,^ loss from the roots, and to unexpected oscillations in radial O., loss attributed to pressurisation and de-pressurization during the expansion and subsequent release of O.,-enriched bubbles from the leaves.With non-submerged plants, the diurnal cycles in O., and ethanol concentrations were smaller and in the case of O,,, different in pattern: although, initially at night, radial O., loss declined, it often rose again later. T his trend would be consistent with a reduction in respiration during the night following rapid substrate depletion at the high temperatures. Short roots grew day and night, but as roots became longer, apical O., concentration declined and, because of this, growth ceased at c. 80 mm. The considerable influence of high temperatures on root aeration was confirmed by rapid increases in radial O., loss when temperatures were lowered from 32 to 23 °C.The ecological significance of the landings is discussed and it is concluded that {a) a diurnal periodicity ot root growth and of localized internal anoxia may be a normal feature of roots in submerged and even non-submerged rice, and (b) ethanol production may play an important role in ...

Microsensor Analysis of Oxygen in the Rhizosphere of the Aquatic Macrophyte Littorella uniflora (L.) Ascherson

“…The light dependence of root oxygen release is also strong for numerous other wetland species (Waters et al, 1989;Armstrong and Armstrong, 1990;Grosse et al, 1991). In the light these plants are capable of creating a convective flow of gases in the lacunae due to temperature-and humidity-induced pressurization (Dacey, 1981), whereas in the dark gases move more slowly by diffusion in a stagnant interna1 atmosphere.…”

Aerobic Toluene Degraders in the Rhizosphere of a Constructed Wetland Model Show Diurnal Polyhydroxyalkanoate Metabolism

“…In addition, the helophytes usually grown in CWs channel oxygen into their roots and the rhizosphere through a specific tissue, the aerenchyma (13), thereby fostering aerobic microbial processes. The release of oxygen and organic carbon by any plant root depends on photosynthesis and therefore may exhibit diurnal oscillations (14,15). These oscillations were indeed described for root exudation by Juncus effusus, a common wetland plant (16,17).…”

The role of oxygen in submergence‐induced petiole elongation in Rumex palustris: in situ measurements of oxygen in petioles of intact plants using micro‐electrodes

“…In submerged, green shoot organs O # and CO # concentrations vary considerably owing to the effects of photosynthetic rate, pH, inorganic carbon content and photosynthetic flux density (Gleason & Zieman, 1981 ;Raskin & Kende, 1984). In turn, any changes in the oxygen regime of shoots can rapidly and substantially affect root aeration (Gaynard & Armstrong, 1987 ;Waters et al, 1989).…”