ENVIRONMENTAL-ANALYSIS OF AERIAL O-2 TRANSPORT THROUGH LEAVES FOR ROOT RESPIRATION IN RELATION TO WATER-UPTAKE IN CUCUMBER PLANTS (CUCUMIS-SATIVUS L) IN O-2-DEFICIENT NUTRIENT SOLUTION

Aerial O-2, transport through leaves for root respiration was examined in relation to water uptake in cucumber plants (Cucumis sativus L.) b y using an airtight hydroponic system and by O-18(2), tracing. Root re spiration clearly responded to aerial O-2 to which, in darkness, the l eaves were exposed. Root respiration in an O-2-deficient nutrient solu tion increased with a higher aerial O-2 concentration and decreased wi th a lower aerial O-2, concentration. Water uptake was promoted in dar kness with aerial O-2, and appeared simultaneous in dynamics with root respiration. For tracing aerial O-2 transport through leaves for root respiration, leaves were exposed to aerial O-18(2), and (H2O)-O-18 pr oduced by respiration in roots was analysed. A significant difference in O-18 isotopic abundance in roots was noted between O-18(2)-treated 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 con clude that aerial O-2 can be transported through leaves and gas-filled intercellular spaces among cells for root respiration in cucumber pla nts grown in an O-2-deficient root environment, and this results in im provement of water uptake in darkness.