Environmental stresses caused by climate change, such as high temperature, drought and salinity severely impact plant growth and productivity. Among these factors, high temperature stress will become more severe during summer. In this study, we examined physiological and molecular responses of maize plants to high temperature stress during summer. Highest level of H2O2 was observed in maize leaves collected July 26 compared with June 25 and July 12. Results indicated that high temperature stress triggers production of reactive oxygen species (ROS) in maize leaves. In addition, photosynthetic efficiency (Fv/Fm) sharply decreased in leaves with increasing air temperatures during the day in the field. RT-PCR analysis of maize plants exposed to high temperatures of during the day in field revealed increased accumulation of mitochondrial and chloroplastic small heat shock protein (HSP) transcripts. Results demonstrate that Fv/Fm values and organelle-localized small HSP gene could be used as physiological and molecular indicators of plants impacted by environmental stresses.

ABSTRACT
 Ⅰ. INTRODUCTION
 Ⅱ. MATERIALS AND METHODS
  1. Plant Material and Growth Condition
  2. Heat Stress Treatment
  3. Measurement of Climate Parameters
  4. Measurement of Photosynthetic Efficiency
  5. Determination of H2O2 Content
  6. Total RNA extraction and RT-PCR
  7. Statistical analysis
 Ⅲ. RESULTS AND DISCUSSION
  1. Effect of High Temperature on Reactive Oxygen Species
  2. Effect of High Temperature on Photosynthesis Efficiency
  3. Expression of Heat-responsive Genes in the Field-grown Maize Plants
 Ⅳ. CONCLUSIONS
 Ⅴ. ACKNOWLEDGEMENTS
 Ⅵ. REFERENCES

• Joon-Woo Lee(Division of Applied Life Science (BK21Plus), and IALS, Gyeongsang National University)
• Chang-Woo Min(Division of Applied Life Science (BK21Plus), and IALS, Gyeongsang National University)
• Byung-Hyun Lee(Division of Applied Life Science (BK21Plus), and IALS, Gyeongsang National University) Corresponding author