METABOLIC CHANGES AND SUSCEPTIBILITY TO CHILLING STRESS IN CAPSICUM-ANNUUM PLANTS GROWN AT SUBOPTIMAL TEMPERATURE

Pepper plants (Capsicum annuum L.; hybrid Latino) were grown at temper ature regimes of 29/20 and 25/14 (degrees C, day/night) and the variab les previously related to the cold acclimation process in temperate pl ants were studied. After 60 days of treatment, plants cultivated at th e low temperature regime showed a 50-70% reduction in shoot length, le af number and shoot dry weight in comparison with the high temperature regime. Root dry weight was not different between the two sets of pla nts, and the plants grown in the cold regime showed an increased numbe r of axillary shoots. Analysis of the leaves at four different positio ns in the canopy (below the first bifurcation of the plant and in the first, second and third bifurcation) showed that chlorophyll and solub le protein content decreased with plant age at both temperature treatm ents, but absolute values were higher in the leaves of plants grown at low temperature, especially in the two upper leaves. The difference i n the protein content could be explained by different leaf content of soluble Rubisco enzyme. Total nitrogen content was slightly higher in the leaves of plants grown at low temperature, but the percentage of t he nitrate form was lower in this condition. Tn relation to carbohydra tes, the sucrose content was lower in the leaves of the cold regime pl ants, except in the youngest one, whereas the starch was higher in the leaves of these plants, specially in the two upper leaves. Finally, p lants grown at the lower night temperature showed an improved chilling resistance when exposed for 4 nights at 6 degrees C, as estimated by visual rating and measurement of leaf electrolyte leakage. The level o f cold tolerance observed was similar to the level obtained in plants grown at optimal temperature treated with paclobutrazol, a plant growt h regulator that ameliorates chilling stress symptoms. Differences in carbon and nitrogen metabolism are discussed in relation to the cold a cclimation process of pepper plants.