A study was carried out to investigate the biochemical effects on sprout-inhibition of potato tubers by $\gamma$ -ray irradiation. The tubers, which were treated at low temperature 4℃ for 4 weeks, were irradiated with a dose of 0.12 kGy from $^{60}Co$ sources and stored at 20±2℃ and 70-90% humidity for 5 weeks. Changes of several enzyme activities such as α-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 $\underline{in} \underline{vitro}$. $D_{37}$ values obtained were 0.36, 0.94 kGy for α-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 α-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 nonirradiated, irradiated, and irradiated and gibberellin or indole acetic acid treated potatoes were observed. In irradiated potatoes, deformed bud with necrosis in the meristmatic tissue are developed. It was not reversed in itself by treatment with gibberellin or indole acetic acid.
In conclusion, the roles of the metabolic pathway associated with the radiation-induced respiration accompanied by increased carbohydrate catabolism such as induction of α-amylase seems to supply chemical energy (ATP) and provide the cells with precursors for the biosynthesis of the materials which is related to the wound-healing process an defense reaction. And the depletion of indole acetic acid by the action of indole acetic acid oxidase induced and indole acetic acid synthesizing system damaged by radiation seems to be possible cause to radiation-induced dormancy.
방사선 조사에 의한 발아억제의 기작을 살펴보기 위하여 감자를 4℃ 에서 저온처리 하므로써 휴면기간을 제거하고 곧 $^{60}Co$ 조사 선원에서 감마선을 0.12 kGy 조사한 후 5주 동안 20±2℃ 에서 저장하였다. 이 저장기간 중 발아에 관여된다고 생각되는 α-amylase, peroxidase, IAA oxidase, IAA 합성 효소의 활성 변화를 추적하여 다음과 같은 결과를 얻었다.
1. 방사선 조사에 의해 호흡량이 이틀 후에 7배 정도로 급격히 증가 되어 최고에 달했고 그후로 줄어들어 2주후엔 정상으로 돌아왔다.
2. 시판 α-amylase 와 peroxidase 에 대한 방사선 감수성이 측정되어 0.94 와 0.36 kGy 의 $D_{37}$ 값을 얻었다.
3. α-amylase 역가가 일주일 내에 2배 정도 증가했다.
4. 페놀 대사에 관여된 peroxidase 역가가 뒤이어 저장 2주에 2배 정도 증가되었다.
5. IAA oxidase 역가가 조사 후 급격히 증가하였다.
6. IAA 합성 효소의 역가는 조사직 후 조금 증가하였으나 저장기간에 따라 크게 감소하였다.
7. 조사에 의해 억제되었던 발아가 IAA 나 GA의 처리에 의해 부분적으로 다시 촉진되었다.
8. 형태적인 측면에서는 조사된 감자에서는 성장점의 고사와 변형된 눈이 관찰되었다. 이들은 호르몬 처리에 의해 회복되지 않았다.
결론적으로, 방사선 조사에 의해 야기된 감자의 호흡은 탄수화물이 α-amylase 등의 효소에 의한 분해로 이루어져 ATP를 공급하며 뒤이은 peroxidase 역가의 증가 등 효소의 합성은 방사선에 의한 손상을 치유하려는 과정에 속한다 할 수 있다. 또한 눈의 생장점에서의 고사현상은 손상에 대한 방어작용의 일종으로 해석되며 이로 인한 발아억제 현상을 페놀 대사와 관련지어 추축할 수 있고 증가된 IAA oxidase 와 IAA 합성계의 손상에 의한 IAA 의 고갈 역시 방사선 조사에 의한 발아억제 현상의 원인이 됨을 알 수 있다.
