Dynamic analysis of water stress of sunflower leaves by means of a thermal image processing system

This paper describes a method for measuring the temperatures of all regions of an intact leaf by using an infrared scanning thermometer at wavelengths between 8 and 14 micrometers combined with a digital image processing system. Pictures obtained every 2 minutes from leaves of sunflower (Helianthus annuus L. cv Large Russian) plants subjected to increasing water stress showed that water deficit develops first at the margins of leaves, accompanied by stomatal closure and increase in temperature. Finally, the temperature of the entire leaf rises 3 to 5 degrees C above that of nonstressed leaves. When transpiration resumed, it did so first at the leaf margins and these proceeded nonuniformly inward.The results of these experiments indicate that there are significant differences in the temperature and water status of different parts of a leaf. This makes it important to determine causes of such behavior and decide in what part of a leaf the temperature and water status should be measured. The thermo-imaging method can be useful in monitoring short term temperature changes occurring in leaves undergoing water, chilling, and other stresses.