Abstract
The effects of coldness on Saintpaulia leaf vary depending on the modes of cooling. When cooled rapidly to 5C, Saintpaulia leaf lost variable chlorophyll fluorescence (Fv) and was led to irreversible injuries of chlorosis, but when cooled to 5C at the rate of 1C/min or slower, the leaf was free from this injury and showed normal photosynthetic oxygen evolution at room temperature. This slowly cooled leaf was readily injured if recovered to room temperature soon after cooled to 5C and exposed to sudden chilling, while if incubated at 5C for10 min or longer, the slowly chilled leaf was found to be tolerant to sudden cooling, indicating that this plant is not cold labile natively and that the conversion to cold hardy leaf was achieved within 10 min. It was assumed that the sudden cooling cause destabilization of cells, whereas this reaction was inactivated during the incubation at 5C.
