Metabolic Changes and Susceptibility to Chilling Stress in Capsicum annuum Plants Grown at Suboptimal Temperature

Abstract

Pepper plants (Capsicum annuum L.; hybrid Latino) were grown at temperature regimes of 29/20 and 25/14 (˚C, day/night) and the variables previously related to the cold acclimation process in temperate plants were studied. After 60 days of treatment, plants cultivated at the low temperature regime showed a 50–70% reduction in shoot length, leaf number and shoot dry weight in comparison with the high temperature regime. Root dry weight was not different between the two sets of plants, and the plants grown in the cold regime showed an increased number of axillary shoots. Analysis of the leaves at four different positions in the canopy (below the first bifurcation of the plant and in the first, second and third bifurcation) showed that chlorophyll and soluble protein content decreased with plant age at both temperature treatments, but absolute values were higher in the leaves of plants grown at low temperature, especially in the two upper leaves. The difference in 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 the nitrate form was lower in this condition. In relation to carbohydrates, the sucrose content was lower in the leaves of the cold regime plants, except in the youngest one, whereas the starch was higher in the leaves of these plants, specially in the two upper leaves. Finally, plants grown at the lower night temperature showed an improved chilling resistance when exposed for 4 nights at 6˚C, as estimated by visual rating and measurement of leaf electrolyte leakage. The level of cold tolerance observed was similar to the level obtained in plants grown at optimal temperature treated with paclobutrazol, a plant growth regulator that ameliorates chilling stress symptoms. Differences in carbon and nitrogen metabolism are discussed in relation to the cold acclimation process of pepper plants.