1996 Volume 65 Issue 2 Pages 309-314
Aging pattern of rice seminal root system grown under submerged soil conditions was evaluated by the measurement of succinic dehydrogenase (SDH) and peroxidase (POD) activities with special reference to the difference between the basal 11 cm-portion of the seminal root axis (SRA) and the lateral roots (LR) initiated from this portion. SDH activity in both SRA and LR showed high levels just after their initiation, and subsequently these activities decreased sharply with aging. The activity in LR always exceeded that in SRA. The percentage of the LR that positively reacted to the reduction assay of triphenyltetrazolium chloride was 100% in the first 4 days after initiation, followed by a drastic decrease ranging from 14 to 24%. Even at heading stage, however, about 8% of the LR still showed a positive reaction. In contrast, POD activity in both SRA and LR increased with aging. The activity in LR, again, always exceeded that in SRA, and attained the highest level which was 3.6 times higher than that in SRA at heading. This elevation of POD activity with aging was discussed in terms of induced protective reaction which may delay senescence. These results indicated that the senescence of SRA precedes that of LR, and LR plays a major role in the physiological activity of the seminal root system. In addition, the rice seminal root system was found to be alive up to the heading.