Certified Professional Horticulturist (CPH) Practice Exam

Cold acclimation generally follows a two-stage pattern. Which of the following would stimulate the pattern?

1. Short days with high temperatures

2. Short days with low temperatures

3. Long days with low temperatures

4. Long days with high temperatures

The correct answer is: Short days with low temperatures

Cold acclimation is a physiological process that prepares plants for winter by enhancing their ability to withstand freezing temperatures. This process typically follows a two-stage pattern: an initial phase where the plant senses changes in day length and temperature, and a second phase that strengthens its cold hardiness. The stimulation of cold acclimation is significantly influenced by the length of daylight and the temperature. Short days associated with low temperatures create an environment that signals the plant to prepare for the impending cold. The shorter day lengths indicate the approach of winter, while the low temperatures serve to activate the biochemical pathways that promote changes in cell structure and function, enhancing cold tolerance. During this acclimation process, plants undergo various physiological changes, such as the accumulation of protective compounds, changes in membrane fluidity, and alterations in cell wall properties. These adaptations increase the plant’s ability to survive freezing temperatures and desiccation during winter. In contrast, long days or high temperatures do not provide the necessary cues for cold acclimation. Long days typically signal optimal growth conditions and do not induce the protective mechanisms needed for surviving cold stress. Similarly, high temperatures inhibit the cold acclimation pathways, as the plant perceives it is still in a growing season rather than preparing for dormancy or colder weather. Therefore