We developed a simple method of estimating the freezing resistance of tea plants by measuring electrolyte leakage from low-temperature-treated overwintering buds and leaves. Overwintering buds and leaves were treated with subfreezing temperatures (−2°C to −15°C) in a controlled freezer for 1 hr and incubated for one hour at 15°C in a growth chamber. Each overwintering bud and leaf was then immersed in distilled water adjusted to 20 times (bud) or 40 times (leaf) the volume of the plant tissue’s weight. Electric conductivity (EC) of the water in which tissue was immersed was measured by a conductivity meter at 0, 60 and 120 minutes after addition of water. Freezing damage to tissues was confirmed by 0.1% (w/v) Evans blue staining after EC measurement. The increase of EC of tissue immersed in water from 0 to 120 minutes indicated the degree of freezing damage to buds and leaves. The freezing resistance of buds and leaves could be estimated from the variation in increase of EC value among the tissues treated at different temperatures, to an accuracy of 1°C. This method is an easy, precise method of evaluating the freezing resistance of tea plants and would be useful for monitoring changes in the freezing resistance of tea plants from autumn to spring to avoid frost damage.
Catechins, one of the main components in green tea extract, have antioxidative activity and immunomodulating activities, and play an important role in reducing the risk of disease. The most abundant catechins in a green tea extract are epigallocatechin gallate (EGCG) and epigallocatechin (EGC), and the EGCG/EGC ratio in a green tea extract was affected by the extraction temperature. We found that the cold water extract or the catechin mixture with a high EGC ratio induced greater immunoglobulin A (IgA) production by murine Peyer's patch (PP) cells. Here, we investigated the effect of cold water extract of green tea on salivaly sIgA levels in habitual green tea (hot water extract) drinker.