Environmental analysis of aerial O₂ transport through leaves for root respiration in relation to water uptake in cucumber plants (Cucumis sativus L.) in O₂-deficient nutrient solution

Aerial O₂ transport through leaves for root respiration was examined in relation to water uptake in cucumber plants (Cucumis sativus L.) by using an airtight hydroponic system and by ¹⁸O₂ tracing. Root respiration clearly responded to aerial O₂ to which, in darkness, the leaves were exposed. Root respiration in an O₂-deficient nutrient solution increased with a higher aerial O₂ concentration and decreased with a lower aerial O₂ concentration. Water uptake was promoted in darkness with aerial O₂, and appeared simultaneous in dynamics with root respiration. For tracing aerial O₂ transport through leaves for root respiration, leaves were exposed to aerial ¹⁸O₂, and H₂ ¹⁸O produced by respiration in roots was analysed. A significant differ ence In ¹⁸O₂ isotopic abundance in roots was noted between 18 and untreated plants at the 1% level. On the other hand, no aerenchyma was present in the cortex of cucumber roots. From these facts, we conclude that aerial O₂ can be transported through leaves and gas-filled intercellular spaces among cells for root respiration in cucumber plants grown in an O₂ root environment, and this results in improvement of water uptake in darkness.