Sang-Uk Chon

Physiological Assessment and Path Coefficient Analysis to Improve Evaluation of Alfalfa Autotoxicity

Reseeding of alfalfa is affected until autotoxic chemicals break down or are dispersed, often requiring a year or more. Bioassays of seed germination and early seedling growth, on agar medium in petri dishes, were conducted to evaluate autotoxic responses of 20 alfalfa germplasms to water-soluble extracts of alfalfa leaf tissue. Root length, 120 hr after placing imbibed seed on agar, was more sensitive to the autotoxin(s) than was hypocotyl length, germination speed, and final germination percentage. Path coefficient analyses showed variation in root length had 7–17 times more effect than variation in hypocotyl length in determining autotoxic effects on total seedling length. Although variations in seed size and germination rate were negatively associated (P < 0.05) with final root length, the autotoxin had little effect on these factors relative to that on root length. Germplasms in the control differed (P < 0.05) in root length, requiring tolerance to be evaluated as percent of control. Germplasms, as percent of control, differed significantly (P<0.05) at extract concentrations of 1.0 and 4.0 g l−1, but the range and LSD were more favorable for selection at 1.0 g l−1. Root length is appropriate for genetic assessments of tolerance to the autotoxin when expressed as percent of control.

Either Soluble or Plastidic Expression of Recombinant Protoporphyrinogen Oxidase Modulates Tetrapyrrole Biosynthesis and Photosynthetic Efficiency in Transgenic Rice

Protoporphyrinogen oxidase (Protox) is the last shared enzyme of the porphyrin pathway. As a continuation of our previous work in which the transgenic rice plants expressing the Bacillus subtilis Protox in the cytoplasm or the plastid showed resistance to diphenyl ether herbicide, this study was undertaken to identify the effects of tertapyrrole biosynthesis in these transgenic rice plants. The transgenic plants either targeted into plastids or expressed in cytoplasm showed higher Protox activity than wild-type plants did. Photosynthetic activity, measured as a quantum yield of photosystem II, was slightly higher in transgenic plants than in wild-type plants, but chlorophyll contents were not significantly different between transgenic and wild-type plants. As for porphyrin biosynthesis, both cytoplasm-expressed and plastid-targeted transgenic plants showed increased synthesis of aminolevulinic acid, Mg-Proto IX, and protoheme in comparison to wild-type plants whereas synthesis of protoporphyrin IX was similar for wild-type and transgenic plants. These results indicate that either cytoplasm or plastid expression of B. subtilis Protox in rice can upregulate the porphyrin pathway leading to increase in photosynthetic efficiency in plants.

Effects of temperature and plant growth regulators on anthocyanin synthesis and phenylalanine ammonia-lyase activity in chicory (Cichorium intybus L.)

Summary This study addresses the effects of air temperature and plant growth regulators on anthocyanin synthesis, sugar content and phenylalanine ammonia-lyase (PAL) activity in chicory (Cichorium intybus L.). Anthocyanin in chicory was synthesised at the highest level under 15°/10°C (day/night) temperatures, followed by 20°/15°C, and 25°/20°C; while synthesis was inhibited > 90% at 30°/25°C, resulting in an almost green colour. Sugar contents paralleled anthocyanin development under the same temperatures. The plant growth regulators, abscisic acid (ABA), ethephon and uniconazole all stimulated anthocyanin synthesis, with uniconazole treatment showing the greatest effect. Gibberellic acid (GA3) inhibited anthocyanin development, while GA3 in combination with uniconazole alleviated this inhibition. PAL activity was higher at 15°/10°C or 20°/15°C (day/night) temperatures when plants were treated with ABA, ethephon or GA3, than at 25°/20°C and 30°/25°C (day/night) temperatures. These results suggest that, under lower temperatures, plant growth regulators may play an important role in anthocyanin synthesis and PAL activity in chicory.

Expression of recombinant protoporphyrinogen oxidase influences growth and morphological characteristics in transgenic rice

Transgenic rice plants expressing a Bacillus subtilis protoporphyrinogen oxidase (Protox), the last shared enzyme of the porphyrin pathway, in the cytoplasm (C89) or the plastids (P72) were compared with wild-type rice plants in their growth characteristics. Production of tiller buds 18 d after seeding was more profuse in transgenic plants than in wild-type plants, especially in plastid-targeted plants. Transgenic plants had 12–27% increase in tiller number and 17–33% increase in above-ground biomass compared with wild-type plants 4 and 8 weeks after transplanting of 2-week-old rice seedlings, demonstrating that tiller production and above-ground biomass correlate with each other. Cytoplasm-expressed and plastid-targeted transgenic plants also had a distinct phenotypic characteristic of narrower and more horizontal leaves than wild-type plants. Phenotypic and anatomical characteristics of the transgenic plants were clearly different from wild-type plants, indicating that regulation of porphyrin biosynthesis by expression of B. subtilis Protox in rice influences morphological characteristics of plant growth as well as biomass.

Physiological Characteristics and Yield of Onion Affected by Rapid Temperature Changes

Physiological Characteristics and Yield of Onion Affected by Rapid Temperature Changes Hyeong-Jin Lee, Hyo-Shim Han, Sang-Uk Chon, Dong-Kwan Kim , Hyun Sook Kwon and Kyung Dong Lee (Dept. of Oriental Medicine Materials, Dongshin University, Naju 520-714, Korea, Dept. of Biology, Sunchon National University, Suncheon 540-742, Korea, Future Agro-Food Research Institute, EFARINET Co. Ltd, Gwangju 500-895, Korea, Jeonnam ARES, Naju 520-715, Korea, Swine Science and Technology Center, Gyeongnam National University of Science and Technology, Jinju, 660-758, Korea)