Season specificity in the cold-induced calcium signal and the volatile chemicals in the atmosphere.

Cold-induced Ca signals in plants are widely accepted to be involved in cold acclimation. Surprisingly, despite using Arabidopsis plants grown in a growth chamber, we observed a clear seasonal change in cold-induced Ca signals only in roots. Ca signals were captured using Arabidopsis expressing Yellow Cameleon 3.60. In winter, two Ca signal peaks were observed during a cooling treatment from 20 to 0°C, but in summer only one small peak was observed under the same cooling condition. In the spring and autumn seasons, an intermediate type of Ca signal, which had a delayed first peak and smaller second peaks compared with the those of the winter type, was observed. Volatile chemicals and/or particles in the air from the outside may affect plants in the growth chamber. This idea is supported by the fact that incubation of plants with activated carbon changed the intermediate-type Ca signal to the summer-type. The seasonality was also observed in the freezing tolerance of plants cold-acclimated in a low-temperature chamber. The solar radiation intensity was weakly correlated, not only with the seasonal characteristics of the Ca signal but also with freezing tolerance. It has been reported that the ethylene concentration in the atmosphere seasonally changes depending on the solar radiation intensity. Ethylene gas and 1-aminocyclopropane-1-carboxylic acid treatment affected the Ca signals, the shape of which became a shape close to, but not the same as, the winter type from the other types, indicating that ethylene may be one of several factors influencing the cold-induced Ca signal.