Differences in lysigenous aerenchyma formation and patterns of radial O
loss (ROL) in rice roots under drained soil conditions and waterlogged soil conditions. Under drained soil conditions, lysigenous aerenchyma is constitutively formed, but a barrier to ROL is not formed; thus ROL at the basal part of the root decreases O2 diffusion to the apical part. By contrast, under waterlogged soil conditions lysigenous aerenchyma formation is enhanced and formation of the barrier to ROL is induced, resulting in the promotion of longitudinal O2 diffusion to the root apex. Under drained soil conditions, lysigenous aerenchyma is constitutively formed at the basal part of the roots (a), but it is not usually formed at the apical part of the roots (b). Under waterlogged soil conditions, lysigenous aerenchyma is induced at the basal part (c) and the apical part (d) of the roots. Lysigenous aerenchyma is more highly developed at the basal part of the roots (a, c) than at the apical part (b, d). Arrow thickness reflects the amount of O2 available. Ep, epidermis; Ex, exodermis; Sc, sclerenchyma; Co, cortex; En, endodermis.