Exposing pepper plants to high day temperatures prevents the adverse low night temperature symptoms

Exposing pepper ( Capsicum annuum ) plants to extremely high day temperatures (HDT) (day/night temperatures of 36 ± 2/10 ± 2°C), obtained by keeping the greenhouse closed during the day to exploit solar heating, prevented the development of low night temperature (LNT) symptoms. Plants of cultivars Fiesta and Selica grown under LNTs (10 ± 2°C) and moderate day temperatures (25 ± 2°C) during winter exhibited retarded growth, reduced leaf numbers, and deformed fruits with few or no seeds. LNT caused a reduction in the number and quality of pollen grains: the reduction in pollen quality was associated with reduced starch accumulation in pollen grains at 3 days before anthesis (DBA) and a decrease of more than two-fold in total soluble sugars in the mature pollen grains. This inhibitory effect was associated with more than 50% reduction in the enzymatic activities of the cell wall-bound and soluble acid invertases that catalyze the hydrolysis of incoming sucrose molecules. All these symptoms were prevented by HDT treatment which matched the vegetative and reproductive performance of the plants to those of plants grown under optimal night temperature (ONT) conditions (day/night temperatures of 23 ± 2/18 ± 2°C). HDT also prevented the inhibitory effect of LNT on enzymatic activities of both invertases in pollen at 5 DBA and brought about the accumulation of high levels of starch in pollen at 3 DBA. The results presented could support the development of a novel procedure for producing greenhouse crops with minimum or even with no fuel consumption for heating during the winter nights in regions with bright and sunny days.