Sulfur is an essential element in plants, including amino acids, vitamin synthesis, and acting as an antioxidant. However, the interaction between endogenous sulfur and proline synthesis has not been yet fully documented. White clover (Trifolium repens L.) is known as a species highly sensitive to sulfate supply. Therefore, this study aimed to elucidate the role of sulfur in regulating proline metabolism in relation to ammonia detoxification and hydrogen peroxide (H2O2) accumulation in white clover. The detached leaves of white clover were immersed in solution containing different concentration of sulfate (0, 10, 100, and 1000 mM MgSO4). As MgSO4 concentrations were increased, the concentration of H2O2 increased up to 2.5-fold compared to control, accompanied with H2O2 detection in leaves. Amino acid concentrations significantly increased only at higher levels (100 and 1000 mM MgSO4). No significant difference was observed in protein concentration. Proline and Δ1-pyrroline-5-carboxylate (P5C) concentrations slightly decreased at 10 and 100 mM MgSO4 treatments, whereas it rapidly increased over 1.9-fold at 1000 mM MgSO4 treatment. Ammonia concentrations gradually increased up to 8.6-fold. These results indicate that exogenous sulfur levels are closely related to H2O2 and ammonia synthesis but affect proline biosynthesis only at a higher level.

ABSTRACT
Ⅰ. INTRODUCTION
Ⅱ. MATERIALS AND METHODS
    1. Plant culture and treatments
    2. Determination of hydrogen peroxide (H2O2) contentsand visualization
    3. Measurement of Δ1-pyrroline-5-carboxylate (P5C) andproline
    4. Determination of amino acid and protein
    5. Determination of ammonia
    6. Statistical analysis
Ⅲ. RESULTS
    1. H2O2 visualization and contents in detached leavesof white clover
    2. Amino acid and protein concentrations in detachedleaves of white clover
    3. Δ1-pyrroline-5-carboxylate (P5C), proline and ammoniaconcentrations in detached leaves of white clover
Ⅳ. DISCUSSION
Ⅴ. ACKNOWLEDGMENTS
Ⅵ. REFERENCES

• Seon-Hye Baek(Department of Animal Science, College of Agriculture & Life Sciences, Chonnam National University)
• Muchlas Muchamad(Department of Animal Science, College of Agriculture & Life Sciences, Chonnam National University)
• Bok-Rye Lee(Department of Animal Science, College of Agriculture & Life Sciences, Chonnam National University)
• Tae-Hwan Kim(Department of Animal Science, College of Agriculture & Life Sciences, Chonnam National University) Corresponding author