Intraspecific Variation in Physiological Responses to Freeze Stress in Brassica rapa and Arabidopsis thaliana
Low-temperature stress limits plant survival, growth, species distribution, and agricultural output in northern regions. The identification of freeze-tolerant variants is essential for crop improvement in a changing climate. In this study, we evaluated the freeze stress response of several ecotypes of Arabidopsis thaliana and diverse morphotypes of the agricultural crop Brassica rapa to examine intraspecific variation in cold tolerance. We evaluated the effect of freezing temperatures on reactive oxygen species (ROS) levels in plants exposed to freezing conditions to those in a control group. ROS are metabolic products that accumulate during periods of stress, such as drought or extreme temperatures, and can also serve as important signaling molecules during stress. Preliminary results from this experiment suggest that plants exposed to freezing conditions had higher levels of ROS in leaf tissue. We also used image analysis using Plant CV, an open-source imaging software, prior to the freeze stress and after recovery, to evaluate the effects on plant growth. Shape analysis was conducted on images containing multiple plants by grouping contour objects and generating binary images. This analysis facilitated the extraction of growth attributes, such as area, convex hull area, center of mass, among others. Area analysis was performed by graphing plant area by day (before, recovery, and one week after freeze) for both control and freeze treatments based on the total area pixels. Together, these results enable us to combine physiological and morphological measures of plant responses to a freezing stress. This work will facilitate future research into uncovering the genomic mechanisms of cold tolerance to enable precision crop improvement techniques.