Gas transport through the root-shoot transition zone of rice tillers

Rice plants (Oryza sativa L.) are mainly cultivated in flooded paddy fields and are thus dependent on oxygen transport through the plant to maintain aerobic root metabolism. This gas transport is effectuated through the aerenchyma of roots and shoots. However, the efficiency of gas transport through the root¿ shoot transition zone is disputed and there are indications that the root¿shoot transition zone may represent one of the largest resistances for gas transport. Therefore, we present gas conductance measurements of the root¿shoot transition of individual rice tillers measured using SF6. SF6 was detected with a highly advanced laser based photoacoustic detection scheme allowing sensitive, high resolution measurements. In conjunction with these measurements, various plant morphological parameters were quantified. These measurements indeed indicate that the conductance at the root¿shoot transition may be much smaller than the conductance of root and shoot aerenchyma within the rice plant. Conductance was strongly correlated to tiller transverse area. After elimination of tiller area from the conductance equation, the resulting permeance coefficient was still correlated to tiller area, but negatively and related to the process of radial tiller expansion. In addition, a decrease in the permeance coefficient was also observed for increasing distance from the plant centre. No correlation was found with tiller type or age of the mother tiller. Incorporation of estimates of the conductance of the root¿shoot transition zone coupled to plant morphological parameters will allow considerable improvement of understanding and models on gas transport through plants.