Short-term effects of fumigation with gaseous methanol on photosynthesis in horticultural plants

Short-term fumigation with 1% methanol in air was carried out to investigate effects on the photosynthetic apparatus of horticultural species characterized by leaves with different stomatal distribution. Methanol decreased the photosynthetic capacity of all species. The hypostomatous cherry (Prunus avium L,) was the most sensitive species. Between the two amphistomatous species, the effect was smaller in pepper (Capsicum annuum L, var, annuum) than in melon (Cucumis melo L.). A 4-minute fumigation caused a stronger inhibition of photosynthesis than a 90-second fumigation. The time course of the inhibition of the photosynthetic: electron transport following a methanol fumigation of cherry leaves suggests that methanol starts inhibiting photosynthesis and photorespiration after approximate to 60 seconds and that the effect is complete after 180 seconds. This inhibition is not permanent, however, since gas-exchange properties recovered within 24 hours, Methanol vapor effects were greatest when leaves were fumigated on the surfaces with stomata, However, fumigation with methanol does not affect stomatal conductance, Therefore, inhibition of photosynthesis following methanol fumigation can be attributed to a temporary inhibition of biochemical reactions.