Biochemical effects on potato tubers irradiated by γ-ray with sprout-inhibition dose

Abstract

A study was carried out to investigate the biochemical effects on sproutinhibition of potato tubers by $\gamma$-ray irradiation. The tubers, which were treated at low temperature $4\,^\circ\!C$ for 4 weeks, were irradiated with a dose of 0.12 kGy from 60 Co sources and stored at $20\pm2\,^\circ\!C$ and 70-90\% humidity for 5 weeks. Changes of several enzyme activities such as $\alpha$-amylase, peroxidase, indole acetic acid oxidase, and indole acetic acid synthesizing enzyme were determined. In addition, treatment of plant hormone (gibberellin or indole acetic acid) on these tubers irradiated were carried out to test reversion of sprout-inhibition of irradiated tubers. The experimental results are as follows; 1. The enzymes tested appeared to be located mainly in the potato skin and cortex. Irradiation with 0.12 kGy dose of $\gamma$-ray inactivated easily the enzyme activities in vitro. $D_{37}$ values obtained were 0.36, 0.94 kGy for $\alpha$-amylase, and peroxidase, respectively. 2. Complete inhibition of the tuber sprouting was resulted by the irradiation of tubers with a dose of 0.12 kGy. 3. Respiration rate increased about 7 times on 2-day storage after irradiation, compared with control and normalized thereafter. It was followed by the induction of $\alpha$-amylase which was increased about 2 times within one week after storage and maintained for five weeks. 4. The peroxidase activity was significantly enhanced for 2-3 week storage. 5. The indole acetic acid oxidase activity was increased 2 times immediately after the irradiation. 6. The indole acetic acid synthesizing activity decreased about 50-75\% for 4-5 week storage in irradiated potatoes, whereas nonirradiated potatoes showed the enzyme activity increased about 3.5 times along with sprouting. 7. Treatment of gibberellin or indole acetic acid at the concentration of 100 or 20 ppm, respectively, on the irradiated tubers reversed the sprout inhibition partially. 8. The morphological changes in buds of...