Effect of heat stress on the photosynthetic apparatus in maize (Zea mays L.) grown at control or high temperature

The effects of short exposure to heat stress in the dark on maize seedlings grown at 25 degreesC or 41 degreesC were investigated by means of chlorophyll fluorescence and oxygen evolution. Exposure of plants grown at 25 degreesC to 35 degreesC for 20 min in the dark led to a transient inhibition (by about 50%) of the rate of photosynthesis, which recovered within 4 h. Treatments at temperatures above 45 degreesC led to permanent damage; the plants did not recover within 96 It. In contrast, no damage occurred to plants grown at 41 degreesC after exposure to temperatures up to 50 degreesC. Improved thermo-tolerance as a result of high growth temperature was not related to the presence of zeaxanthin. since it did not accumulate in heat-stressed leaves in the dark. In plants grown at 25 degreesC, measurements of the quantum yield of electron transport at PSH in leaves infiltrated with methylviologen (MV) indicated the presence of a heat-sensitive component of the photosynthetic apparatus, located downstream of photosystem II (PSII) and before the carbon cycle. (C) 2004 Elsevier B.V. All rights reserved.