Cold sensitivity oscillations of young soybean plants.

Every 4 hr, a different group of soybean seedlings (Glycine max [L.] Merr. cv. Corsoy), maintained in a controlled environment chamber (LD 16:8), were briefly subjected to cold (-10 degrees C for 4 min). Ten days after the beginning of the cold treatment, plants were harvested, weighed, and their cotyledons assayed for chlorophyll. In other experiments, potassium levels of the foliage were monitored. Both the sensitivity of plants to cold and the potassium content of unifoliolate leaves not subjected to cold displayed a significant 24-hr oscillation. Less injury and the lowest level of potassium occurred near the end of the light span. Cotyledon chlorophyll levels again were shown to be a good indicator of injury, with the highest levels in the most severely injured plants.