Abstract
This study was carried out to clarify the relation between occurrence of leaf injury, so-called “leaf spot”, and amount of electrolytes leaked from leaf tissue of Saintpaulia ionantha Wendl cv. Beth Elen. Leaves were dipped in water at a temperature lower than leaf (rapid fall of leaf temperature) for the development of leaf spot, and the leakage of electrolytes from leaf discs to water at different temperatures was determined.
1. Leaves were dipped in water at 40, 45 and 50°C for 60sec, followed by a dipping in water at 25°C for 60sec. The degree of leaf injury increased with the increasing differences between water and leaf temperatures.
2. The degree of leaf injury due to rapid fall of leaf temperature was influenced by temperature conditions during plant growth and pre-treatment.
3. Electrolyte leakage from leaf discs was minimum by soaking in 20-25°C water and increased above and below these temperatures. In this case, the amount of leakage in darkness was larger than that in exposure to light.
4. Exposure of leaf discs to a rapid fall of leaf temperature considerably increased the amounts of K+ and Mg++ leakage.
5. Leaf discs were divided transversely into two portions, adaxial and abaxial, and they were exposed to rapid fall of leaf temperature. The adaxial half containing palisade tissue had a greater amount of K+ leakage than the abaxial half.
6. Shrinkage of palisade cells was microscopically observed in injured leaf portions one day after rapid fall of leaf temperature, and then breakdown of chloroplasts was observed.
7. Electrolyte leakage from old leaves was greater than that from young leaves.
8. Exposure of leaves to high light intensity before rapid fall of leaf temperature increased leaf injury and electrolyte leakage.
