Further evidence for gaseous CO ₂ transport in relation to root uptake of CO ₂ in rice plant

Abstract

In order to make clear the mechanism of transport of CO2, absorbed by rice roots, several experiments were carried out. The amount of CO2, derived from root uptake in rice seedlings was significantly larger than that in wheat seedlings. As CO2, concentration in the culture solution increased, the predominate uptake by rice roots became more obvious. 2,4-Dinitro-phenol and sodium azide constantly inhibited dark CO2, fixation in roots of rice and wheat, while their effects on the CO2, transport to the shoots were not significant. In the case of mannitol treatment, CO2, transport from roots to shoots in wheat decreased by 50%, while no strong inhibition was observed in rice. CO2, gas analysis in roots indicated that the CO2, enrichment in the culture solution led to the increase of CO2, gas content in rice roots. The volume of the gas phase in rice roots was ten times as large as that in wheat roots and CO2, gas contents in rice roots were by far higher than those in wheat roots. These results as well as other experimental data may suggest that a large part of CO2, absorbed by rice roots moves to the shoots in the gaseous state. Further, it can be postulated that the principal gasification site in rice plants is located in the root cortex where lysigenous intercellular spaces are present.