John S Choinski, Jr.

Professor of Biology

Department of Biology

University of Central Arkansas

Conway, AR 72035

Telephone: (501) 450-5918

Fax: (501) 450-5914

Email: or


Courses Taught:

Principles of Biology I (Biology 1440)

Principles of Biology II (Biology 1441)

Economic Botany (Biology 3390)

Plant Ecophysiology (Biology 4450/5450)

Organisms in Extreme Environments (Biology 4412/5412)



I am a plant physiologist interested in how photosynthesis rates change during leaf expansion. My students and I have discovered that young, immature leaves have higher midday temperatures than more mature leaves because of limited transpirational cooling capacity. Additionally, young leaves are more photosynthetically thermotolerant than mature leaves possibly because of differences in chloroplastic membrane fatty acid saturation levels. Although I have worked with many different species of trees, recently we have been focusing on the important crop plant, cotton. The image below is of 50-day-old field grown Gossypium hirsutum (Upland Cotton) showing leaves in various stages of expansion. In bright sun, the smallest leaves are sometimes 10C or more warmer with photosynthetic thermal optima 10-15C higher than larger, more mature leaves. Understanding the mechanisms behind changes in temperature tolerance in expanding leaves will be an important part of learning how cotton and other plants adapt to predicted rises in global temperature, increasing desertification and other environmental changes.


Cotton Leaf Stages.jpg


Personal Links:

The New Crop Home Page

Reason Foundation

Nature Conservancy


Return To:

UCA Home Page

UCA Biology Department Page