Effects of Climate Temperature and Water Stress on Plant Growth and Accumulation of Antioxidant Compounds in Sweet Basil (Ocimum basilicum L.) Leafy Vegetable

Abstract

The effects of climate temperature and water stress on growth and several stress markers were investigated in sweet basil plants. Some growth parameters (shoot length and number of leaves) and photosynthetic chlorophyll contents were determined every two days during plant growth, and foliage leaf material was collected after 15 and 21 days of treatment. Both climate temperature and water stress inhibited sweet basil plant growth; especially, total chlorophyll levels were decreased significantly in response to high-temperature treatments. Under strong stresses, basil plants induced the synthesis and accumulation of glycine betaine (GB) as a secondary osmolyte, although at less content when compared with the proline content under the same stress conditions. Proline concentrations particularly increased in leaves of both basil stressed plants, accomplishing levels high enough to play a crucial role in cellular osmoregulation adjustment. Stress-induced accumulation of these antioxidant compounds was detected in sweet basil. Therefore, it appears that sweet basil-treated plants are able to synthesize antioxidant compounds under strong stress conditions. On the other hand, total sugar concentrations decreased in stress-treated basil plants. Both temperature and water stress treatments caused oxidative stress in the treated plants, as indicated by a significant increment in malondialdehyde (MDA) concentrations. An increase in total phenolic and flavonoid concentrations in response to water stress and a highly significant decrease in carotenoid concentrations in basil leaves were observed; flavonoids also increased under high climate temperature conditions.

Figure 1

(a, b) Effect of different climate temperatures (C, 25°C; T₁, 35°C; T₂, 45°C; and T₃, 55°C) and water stress (WS) treatments on the electric conductivity (dS/m), measured in soil:water (1 : 5) extracts after two sampling periods (S1, 14 days and S2, 21 days) in basil plants (mean ± SD, n = 5). Asterisks indicate significant differences between sampling periods of each treatment and differences between treatments for the same sampling periods according to the Tukey test (α = 0.05).

Figure 2

Effect of different climate temperatures (C, 25°C; T₁, 35°C; T₂, 45°C; and T₃, 55°C) and water stress (WS) treatments on the shoot length (a, b) and number of leaves (c, d) after two sampling periods (S1, 14 days and S2, 21 days) in basil plants (mean ± SD, n = 10). Asterisks indicate significant differences between sampling periods of each treatment and differences between treatments for the same sampling period according to the Tukey test (α = 0.05).

Figure 3

Effect of different climate temperatures (C, 25°C; T₁, 35°C; T₂, 45°C; and T₃, 55°C) and water stress (WS) treatments on fresh weight, FW (a, b); dry weight, DW (c, d); and water content (e, f) after two sampling periods (S1, 14 days and S2, 21 days) in basil plants (mean ± SD, n = 10). Asterisks indicate significant differences between sampling periods of each treatment and differences between treatments for the same sampling period according to the Tukey test (α = 0.05).

Figure 4

Effect of different climate temperatures (C, 25°C; T₁, 35°C; T₂, 45°C; and T₃, 55°C) and water stress (WS) treatments on total chlorophyll (a, b) and total carotenoids (c, d) after two sampling periods (S1, 14 days and S2, 21 days) in basil plants (mean ± SD, n = 10). Asterisks indicate significant differences between sampling periods of each treatment and differences between treatments for the same sampling period according to the Tukey test (α = 0.05).

Figure 5

Effect of different climate temperatures (C, 25°C; T₁, 35°C; T₂, 45°C; and T₃, 55°C) and water stress (WS) treatments on glycine betaine (GB) (a, b), proline (c, d), and total sugar contents after two sampling periods (S1, 14 days and S2, 21 days) in basil plants (mean ± SD, n = 10). Asterisks indicate significant differences between sampling periods of each treatment and differences between treatments for the same sampling period according to the Tukey test (α = 0.05).