Effects of Gas Exchange Inhibition and Hypoxia on Tuberous Root Morphogenesis in Sweetpotato (Ipomoea batatas (L.) Lam.)

Gas exchange status is considered to influence tuberous root morphogenesis in sweetpotato (Ipomoea batatas (L.) Lam.). Gas exchange inhibition by using water or applying Vaseline to the young root and the development process of the root were investigated. Water can be considered as a barrier to O₂ diffusion since O₂ is only slightly soluble in water, while Vaseline can act as a barrier to all types of gases. Effects of hypoxia on root development were also examined. Tuberous roots were not formed in both the Vaseline-coated roots and submerged roots. The area of lignified region in the cross-section of the root increased due to gas exchange inhibition. Similarly, hypoxia inhibited the induction of tuberous root formation in young roots, and depressed the swelling of the roots that were in the process of tuberous root formation. The extent of lignification in roots also increased under hypoxia treatment. The results suggest that the level of O₂ is a determinant factor of tuberous root formation in sweetpotato. The induction of tuberous root morphogenesis and the subsequent expansive growth, are both inhibited due to O₂ deprivation and stress-promoted lignification within the root stele.