Masami Ogawa

Effect of Gamma Radiation on Peroxidase Development in Sweet Potato Disks

OGAWA, MV., AND URITANI, I. Effect of Gamma Radiation on Peroxidase Development in Sweet Potato Disks. Radiation Res. 41, 342-351 (1970). Following irradiation with 90 krads of gamma rays from a 60Co source, roots of sweet potato were cut into thin disks, which were incubated aerobically at 300C under high humidity. Gamma radiation significantly stimulated the peroxidase development during incubation of disks. The peroxidase development was strongly inhibited by low concentration of cycloheximide in the nonirradiated and irradiated disk tissues. Exposure to exogenous ethylene alone similarly stimulated the peroxidase development. Evidence indicated that the stimulation of peroxidase development by gamma radiation may be partly mediated through the enhanced amounts of ethylene produced in disks by gamma radiation, but it is mainly mediated by an other unknown mechanism. Neither treatment by gamma radiation nor exogenous ethylene stimulated all components of peroxidase isoenzymes in a similar manner as appeared in response to cut injury, but did stimulate 2-3 individual components among them.

Metabolic Changes in Sweet Potato Roots Induced by Gamma Radiation in Response to Cutting

Sweet potato roots were irradiated with 5 to 120 krads of cobalt-60 gamma rays, and then cut into disks, which were incubated under aerobic conditions. The effects of gamma radiation on metabolic changes in the tissue in response to cutting were investigated. The polyphenol content and activities of o-diphenol oxidase, peroxidase, and phenyalanine ammonialyase increased greatly in both nonirradiated and irradiated samples after cutting. Following irradiation with 60 krads or more the polyphenol content and peroxidase activity in response to cutting was significantly stimulated over the nonirradiated sample. On the contrary, formation of lignin-like substance was inhibited. No significant effect on o-diphenol oxidase was observed at any dose tested. In samples irradiated with 90 krads an increase in phenylalanine ammonia-lyase was correlated with the increase in polyphenol content.

TISSUE BROWNING OF POTATO TUBERS INDUCED BY GAMMA IRRADIATION.

A considerable browning was observed especially in cortex tissue and along xylem of potato tubers harvested at Sakai in Osaka Prefecture, after irradiation with 10, 20 and 50 krad doses of cobalt-60 gamma rays. This phenomenon was accompanied by the marked increase in polyphenol content and peroxidase activity, and the transient increase in o-diphenol oxidase activity. Total reducing compounds in the tissue were also increased by gamma irradiation.The browning phenomenon depended on the storage period from the harvest to gamma irradiation treatment. The browning and the transient increase in o-diphenol oxidase activity were completely suppressed in the case of tubers irradiated 3 months after harvest.There was no significant change in α-amylase activity in all tubers tested.

Promotion of mesocotyl growth in etiolated rice seedlings by 4-ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione

Abstract4-Ethoxy-1-(p-tolyl)-s-triazine-2,6(1H,3H)-dione (TA) promoted mesocotyl growth in dark-grown rice (Oryza sativa L.) seedlings. In cultivars of the japonica type TA alone showed a small promotive effect and TA+gibberellic acid(GA3) had a marked synergistic effect, while in other cultivars, mostly of the indica type, TA alone showed a great promotive effect and TA+GA3 had only an additive effect. In cv. Nato, a typical representative of cultivars showing the second type of response, the concentration of TA giving the greatest growth promotion was around 0.1–0.2 mM. In Nato seedlings treated with TA at 0.1 mM, the mesocotyls continued to elongate for 6 days and reached about 75 mm in length, while the mesocotyls of control seedlings grew to a maximum of about 10 mm and growth was limited to the first 3 days after planting. The TA-induced mesocotyl elongation was mainly the consequence of increased cell multiplication in the meristematic area immediately below the coleoptilar node. GA3, abscisic acid (ABA) and ethylene also stimulated mesocotyl growth in dark-grown Nato seedlings but their effects were much smaller than those of TA. ABA, like GA3, had an additive effect with TA, but ethylene suppressed the effect of TA and resulted in increased lateral expansion in the upper region of the mesocotyls of TA-treated seedlings.

Synthetic gibberellin synergists in elongation of shoot growth ofOryza sativa L.

Previous studies showed that 2-ethyl-3-methoxycarbonyl-1-(p-tolylcarbamoyl) isourea acts as a potent GA3-synergist in stimulating shoot growth of rice seedlings. Studies with several structurally related compounds show that the alkoxycarbonylcarbamoyl-isourea or -isothiourea skeleton is required for biological activity. Any chemical deletion from this skeleton causes complete loss of activity. From present and previous data it seems that alkoxycarbonylcarbamoyl-isourea or -isothiourea is converted by intramolecular cyclization in the rice seedlings into the corresponding triazinone that serves as the active form.