Myung-Hwa Baek

Alterations in the Photosynthetic Pigments and Antioxidant Machineries of Red Pepper (Capsicum annuum L.) Seedlings from Gamma-Irradiated Seeds

To characterize the stimulatory effects of low-dose gamma radiation on early plant growth, we investigated alterations in the photosynthesis and antioxidant capacity of red pepper (Capsicum annuum L.) seedlings produced from gamma-irradiated seeds. For two cultivars (Yeomyung and Joheung), three irradiation groups (2, 4, and 8 Gy, but not 16 Gy) showed enhanced development, although Fv/Fm, the maximum photochemical efficiency of Photosystem II (PSII), did not differ significantly among any of the four groups. In contrast, values for 1/Fo — 1/Fm, i.e., a measure of functional PSII content, decreased in the irradiated groups of ‘Yeomyung’ but increased in those of ‘Joheung’. Pigment analyses and enzyme activity assays revealed that irradiation altered the compositions of photosynthetic pigments (chlorophylls and carotenoids) as well as the activities of antioxidant enzymes (superoxide dismutase and glutathione reductase). However, these shifts were not directly related to the increase in early growth, although they were cultivar-and developmental stage-dependent In addition, the effects of irradiation on the enzymatic activities measured here were at opposition between the two cultivars.

Ultrastructural changes of cell organelles inArabidopsis stems after gamma irradation

We examined ultrastructural changes of the cell organelles ofArabidopsis stems in response to gamma irradiation. Seedlings treated with 0 to 5 Gy developed normally, while height growth in plants exposed to 50 Gy was significantly inhibited. Based on TEM observations, the chloroplasts were extremely sensitive to such irradiation. In particular, the thylakoids were heavily swollen, some portions of the mitochondria and endoplasmic reticulum were structurally altered, and the plasmalemma had pulled away from the cell wall in places. However, no ultrastructural changes in cell organelles occurred at doses of 0 to 5 Gy.

Cloning, characterization, and expression of two cDNA clones for a rice ferulate-5-hydroxylase gene, a cytochrome P450-dependent monooxygenase

Ferulate-5-hydroxylase (F5H) is a cytochrome P450-dependent monooxygenase that catalyses the hydroxylation of ferulic acid, coniferaldehyde, and coniferyl alcohol in the pathways leading to sinapic acid and the syringyl unit of lignin. We have isolated twoF5H genes,OsF5HL andOsF5HL2, from a japonica-type rice (Oryza sativa L. cv. llpoombyeo). They are the firstF5H genes experimentally identified in monocotyledonous plants. Phylogenetic analysis indicated that both genes are closely related to dicotF5H genes fromArabidopsis thaliana andBrassica napus. Southern blot analysis showed that these genes exist as single copies in the rice genome. Alignments of theOsF5HL andOsF5HL2 cDNAs to their genomic DNAs revealed thatOsF5HL has an open reading frame (ORF) of 1590 b from four exons, whileOsF5HL2 has an ORF of 1560 b from two exons. Expression ofOsFSHL is highest in young leaves, whereas that ofOsF5HL2 is greatest in mature leaves. In the roots and stems, transcription levels for both genes are markedly low. These data suggest that theOsF5HL andOsF5HL2 genes belong to theCYP84 subfamily and that their expressions are tissue-specific.

Effect of Low-Dose Gamma Radiation to Enhance Germination Rate in Bottle Gourd and Pumpkin Seeds

To establish the seed treatment method of the gamma radiation for germination enhancement of bottle gourd(Lagenaria siceraria Standl.) and pumpkin(Cucurbita ficifolia Bouche), seeds were irradiated with the dose of 120 Gy of the gamma radiation. The germination rate in irradiated group was higher than that of the control, depending on seed condition. In the case of bottle gourd, the germination rate of 7080% germinative seed was increased at 420 Gy irradiated groups. Especially, it was the highest at 4 Gy irradiated group. The germination rate of 8090% germinative seed was the highest at 4 Gy irradiated group. The germination rate of 7080% and 8090% germinative seed at 4 days after sowing was increased 66% and 26% at 4 Gy irradiated group, respectively. In the case of pumpkin, the germination rate of 7080% and 8090% germinative seed was increased at 2 Gy and 8 Gy irradiated group, respectively. Effect of the low-dose gamma radiation on the early growth was enhanced depending on their germination enhancement. Especially, it was the highest at 2 Gy irradiated group of 7080% germinative seed of pumpkin. Catalase activity of bottle gourd was increased at 4 Gy irradiated group. Catalase and peroxidase activity of pumpkin were increased at 2 Gy and 8 Gy irradiated group. These results suggest that the germination, early growth and physiological activity of bottle gourd and pumpkin seeds could be promoted by the low dose gamma radiation.

Gamma radiation and hormone treatment as tools to reduce salt stress in rice (Oryza sativa L.)

We investigated the effects of jasmonic acid (JA) and gamma irradiation on the growth and metabolic responses to salt stress in rice (Oryza sativa L.) plants. The relative growth rate (RGR), relative water content (RWC), and chlorophyll (Chl) content were lower in NaCI-treated plants than in the control, whereas the malondialdehyde content (MDA), electrolyte leakage (EL), and contents of proline and abscisic acid (ABA) were higher in the treated plants. When induced by the salt stress, those effects, however, were somewhat alleviated by the application of JA or gamma irradiation. The most significant response was manifested by the proline content, with relatively lower values for alleviation being recorded for the contents of RGR, RWC, Chl, and MDA, as well as EL. Moreover, although total Chl content was not significantly influenced by JA or gamma irradiation in plants under salt stress, an increase in the level of Chl a resulted in a markedly changed ratio of Chl a/b. The degree of alleviation, in terms of growth and metabolic responses, was more extensive for JA-treated plants than for those exposed to gamma irradiation.

Effects of Low Dose Gamma-irradiation on Alleviation of Salt Stress in Rice (Oryza sativa L.) Seedling

To investigate alleviation effects of salt stress by low dose gamma-irradiation on seedling growth of rice (Oryza shrive L), in plants of two rice cultivars (Ilpumbyeo and Gancheokbyeo), seeds were irradiated with the different doses of gamma-ray by irradiator (, ca.150 TBq of capacity, AECL). The salt stress caused a remarkable decrease of seedling growth, particularly for dry weight. In addition, relative growth rate was decreased over 50% by the salt stress. However, the salt stress-induced inhibition of growth was alleviated by gamma-irradiation. Especially, the relative growth rate of shoot showed the reduction effect over 30% at 4 Gy-irradiated groups as compared with that of control. Also, electrolyte leakage and relative water content were damaged, respectively 4 times and 30% by the salt stress but the damages were alleviated by the gamma-irradiation. These alleviation effects were observed similarly in both the cultivars tested. These results suggest that the low dose gamma-irradiation may have a better protection or the salt stress.

Effect of the Storage Temperature, Duration and Gamma Irradiation on the Respiration Rate and Sugar Content of Minituber 'Superior'

This study was to evaluate whether ionizing gamma radiation could be applied to break the dormancy of a potato minituber. The respiration rate of the minitubers was significantly affected by the storage temperature and a low dose gamma radiation. Ionizing radiation of 8 Gy enhanced the respiration rate of the potato tuber stored at for 20 days. The potato tuber subjected to 4 and 8 Gy after 40 days storage at 10 and exhibited higher respiration rates compared to the control (non-irradiated), but not at st. However, the ionizing radiation did not exhibit on significant effect on the respiration rate of the potato tuber stored for 60 days. It was observed that minitubers stored for 20 days had significant response to the storage temperature in terms of the total sugar content the higher the storage temperature, the lower the total sugar content. It was measured that the reducing sugar content was increased under the storage conditions both 5 and for 40 days, but not to . The total sugar contents in the minituber stored for 60 days were similar to those stored for 40 days. The data was discussed on the relationships among the storage duration, temperature and ionizing radiation.