J Integr Plant Biol. ›› 1965, Vol. 13 ›› Issue (4): -.

• Research Articles •    

Site of Oxygen Absorption for Downward Transport in Seedlings of Rice and Other Plants

Sung M. S., Bai K. Z., Cui Y. Y. and Lou C. H.   

Abstract: Our earlier reports have shown that appreciable portions (ranging from 20% to 70%) of the total amount of oxygen absorbed by the aerial part can be transported downwards to roots in water cultured intact seedlings of rice, barnyard grass, wheat, pea, etc. By interrupting the alternative paths of transport, it has been demonstrated that oxygen moves downwards mainly through gaseous diffusion along the intercellularspaces in the cortex. The aim of the present investigation is to ascertain the site of oxygen absorption for downward transport in the aerial part and to show that such a transport does not necessarily involve active participation of the absorbing organ. The results are summarized below: 1. Provided that a small upper portion of the leaf is left exposed in air, flooding of the aerial part of the rice seedling does not reduce the amount of total oxygen absorption to any appreciable extent (Fig. 1). In agreement with field observation, the unflooded tip is capable of furnishing the submerged part with enough oxygen to keep it alive. 2. Nor does the complete or partial removal of leaves by cutting in seedlings of rice and pea affect downward oxygen transport appreciably, provided that the stem segment or a leaf sheath is left exposed in air. 3. The following common notion has been confirmed by actual measurement: The abnormal excessive elongation of the coleoptile in rice seedling germinated under water, which may easily extend itself above the water surface, is an adaptive device to furnish the seedling with the oxygen required for root development. 4. The "floating" roots developed at the later stage in rice culture have been demonstrated to be a possible site of oxygen absorption for downward transport. 5. When a rice seedling is held up side down, with its roots exposed in air and the shoot submerged, downward oxygen transport still takes place, although to a lesser extent than in its normal position.

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