Effect of Temperature Stress on Antioxidant Defenses in Brassica oleracea

Abstract

Brassica oleracea crops are exposed to seasonal changes in temperature because of their biennial life cycle. Extreme temperatures (cold and heat) affect the photosynthetic activity and the yield of cabbage (B. oleracea capitata group) and kale (B. oleracea acephala group). We studied the relationship among antioxidant defenses, photosynthesis, and yield under extreme temperatures in both crops. Under these conditions, the plants increase the antioxidant defenses, responding to an increment in reactive oxygen species (ROS). The accumulation of ROS in chloroplasts decreases the chlorophyll content and provokes photoinhibition that leads to a low fixation of CO₂ and loss of dry weight. Low temperatures especially increase the antioxidant defenses and decrease the chlorophyll content compared to the heat conditions. However, dry weight losses are higher when plants are grown under heat than under cold conditions, probably because of the inactivation of Rubisco and/or the associated enzymes. Both crops were more resilient to cold than to heat temperatures, the capitata group being more resistant.

Figure 1

Activities of (A) CAT, (B) SOD, and (C) GR enzymes in the seedlings of B. oleracea var. acephala and B. oleracea var. capitata grown under three temperatures: 12, 20, and 32 °C. The significant differences among temperatures (p ≤ 0.05) are indicated by different letters. The significant differences between the crops at a given temperature are indicated by an asterisk (p ≤ 0.05).

Figure 2

(A) Total phenolic content, (B) antioxidant potential (ABTS), and (C) glutathione content in the seedlings of B. oleracea var. acephala and B. oleracea var. capitata grown under three temperatures: 12, 20, and 32 °C. The significant differences among temperatures (p ≤ 0.05) are indicated by different letters. The significant differences between the crops at a given temperature are indicated by an asterisk (p ≤ 0.05).

Figure 3

(A) Total Chl concentration and (B) Chl a and Chl b concentrations in the seedlings of B. oleracea var. acephala and B. oleracea var. capitata grown under three temperatures: 12, 20, and 32 °C. The significant differences among temperatures (p ≤ 0.05) are indicated by different letters. The significant differences between the crops at a given temperature are indicated by an asterisk (p ≤ 0.05).

Figure 4

Loss of dry weight expressed as percentage with respect to control in the seedlings of B. oleracea var. acephala and B. oleracea var. capitata grown under 12 and 32 °C. The significant differences among temperatures (p ≤ 0.05) are indicated by different letters. The significant differences between the crops at a given temperature are indicated by an asterisk (p ≤ 0.05).