Eun-Young Sohn

Gibberellin production and plant growth promotion from pure cultures of Cladosporium sp. MH-6 isolated from cucumber (Cucumis sativus L.)

Gibberellin (GA) production by soil fungi has received little attention, although substantial work has been carried out on other aspects of plant growth promoting fungi (PGPF). In our studies we investigated GA production and growth-promoting capacity of a novel fungal strain isolated from the roots of soil-grown cucumber. Pure cultures of 19 endophytic fungi were tested for shoot length promotion of Waito-C rice to identify the GA production capacity of these fungal isolates. Isolate MH-6 significantly increased shoot length (12.9 cm) of Waito-C, in comparison to control treatments. Bioassay with culture filtrate (CF) of MH-6 also significantly promoted growth attributes of cucumber plants. Analysis of MH-6 CF showed the presence of physiologically active (GA1, 1.97 ng/mL; GA3, 5.18 ng/mL; GA4, 13.35 ng/mL and GA7, 2.4 ng/ mL) in conjunction with physiologically inactive (GA9 [0.69 ng/mL], GA12 [0.24 ng/mL], GA15 [0.68 ng/mL, GA19 [1.94 ng/mL and GA20 [0.78 ng/mL]) gibberellins. The CF of MH-6 produced greater amounts of GA3, GA4, GA7 and GA19 than wild type Fusarium fujikuroi, a fungus known for high production of GA. The fungal isolate MH-6 was identified as a new strain of Cladosporium sp. on the basis of sequence homology (99%) and phylogenetic analysis of 18S rDNA sequence.

Effect of jasmonic acid on endogenous gibberellins and abscisic acid in rice under NaCl stress

Content of endogenous abscisic acid (ABA) increased in rice plants under salt stress. Pre- or post-treatment by jasmonic acid (JA) mostly further increased ABA content. In the presence of salt stress also content of gibberellins (GAs) mostly increased more after treatment by JA. Endogenous content of bioactive GA1 was higher in post-treatment by JA than in pre-treatment by JA.

Starch properties of native foxtail millet, Setaria italica Beauv.

Properties of foxtail millet (Setaria italica Beauv.) starches have been studied. Amylose content ranged between 3.3 and 11.4%. Starch content was from 67.5 to 68.7%. The onset temperature (To) of all samples ranged from 66.4 to 69.6°C, peak temperature (Tp) ranged 71.0 to 74.2°C, and their gelatinization enthalpy varied from 0.44 to 8.22 J/g, respectively. A highest gelatinization temperature was obtained for Bongseongjaerae (69.6°C). The enthalpy of the gelatinization (Δ Hgel) was highest in Andongjaerae. The highest peak, highest breakdown, very high final viscosity, and very low setback were noted in Jucheonjaerae. The starch granule sizes ranged 10.1–25.0 in length and 4.7–12.5μm in diameter. X-ray diffraction angles indicated that all starch samples possess a typical A-type crystallinity.

Quantification of endogenous gibberellins in two flax (Linum usitatissimum L.) cultivars during seed development

Eight gibberellins (GAs) were identified and quantified in extracts of seed of the flax, Linum usitatissimum L. cv. Hwanamama, Hwabaekama by GC-MS-SIM and Kovats retention indices. Four of these gibberellins are members of the early-C13-hydroxylation pathway (GA53, GA19, GA20, and GA1), and four are members of the non-C13-hydroxylation pathway (GA12, GA24, GA9, and GA4). Of these eight gibberellins, GA24 was more abundant in yellow-seeded flax (cv. Hwanamama) than in brown-seeded flax (cv. Hwabaekama), whereas GA9 was 8.3-fold more abundant in brown-seeded flax (cv. Hwabaekama) than in yellow-seeded flax (cv. Hwanamama). In both flax cultivars, non-C13-hydroxylation pathway was the main route leading to endogenous accumulation of GA4 in the seed.

Evaluation of Pollen Viability of Nakdongbyeo, Two Transgenic Rice Lines, ItsHybrids with Weedy Rice, and Subsequent Selfed Progenies : F₂ and F₃

This experiment was conducted to evaluate pollen viability of Nakdongbyeo, transgenic rice lines, an F1 hybrid from a cross between Milyang weedy rice and ABC-promoter transgenic rice line containing basta-resistant (bar) gene and subsequent selfed progenies, F₂ and F₃. The reaction of pollen with 3-{4,5 dimethylthiazolyl-2}-2,5-diphenyl monotetrazolium bromide (MTT) as a staining chemical immediately after pollen shedding showed maximum pollen viability of 86% in Nakdongbeyo, 75% in ABC-promoter transgenic rice line, 62% in ubiquitin-promoter transgenic line, 68% in F1, 79% in F₂ and 78% in F₃. Viability gradually declined during subsequent observations at 20-minute intervals. However, there was a drastic decline in pollen viability after 40 minutes of pollen shedding. The mean difference of pollen viability among rice lines and time was highly significant, indicating significantly different pollen viabilities at different time intervals. Maximum viability of 36.2% was observed in F₃ and minimum viability of 3.5% was found in F₂ at 90 min after pollen shedding. Results of this experiment on pollen viability and longevity elucidate potential risks of pollen-mediated flow of herbicide-resistant gene from transgenic rice lines and possible integration of it into the weedy rice population.