Effect of drought on safflower natural dyes and their biological activities

Abstract

Drought is the main abiotic constraint that affects crop species behaviour regarding bio-chemical responses. The current study was conducted to examine the effect of water deficit on growth, phenolic and carotenoid contents as well as the antioxidant and antimicrobial activities of two Carthamus tinctorius varieties (Jawhara and 104) flowers. Hence, plants were treated with different levels of water deficit: control (100 %), moderate water deficit (50 %) and severe water deficit (25 %). Obtained results showed that plant growth was significantly (p < 0.05) reduced under 50 %. Drought increased flower phenolic acids contents especially gallic acid where they increased significantly (p < 0.05) by 2.73 fold (104) and by 2.87 fold (Jawhara) with respect to controls under 50 %. However, the amounts of this major compound were reduced at 25 % by 9.66 % (104) and 3.83 % (Jawhara). Similar to phenolic compounds, total carotenoid content was at its highest level especially for Jawhara with an increase by 35.19 % at 50 %. On the other hands, C. tinctorius flowers extracts exhibited high antiradical activity as compared to BHT. A gradual increase by 35.29 % (Jawhara) and 33.33 % (104) especially under 25 % was observed. Moreover, under 50 %, the antimicrobial activity increased significantly (p < 0.05) by 30 % and 10.05 % against Aspergillus carbonarus and Pseudomonas aerogenosa, respectively. Taken together, our findings suggest that C. tinctorius could be a raw material for production of natural dyes under moderate salinity conditions.

Keywords: Carthamus tinctorius flower; antimicrobial activity; antioxidant activity; carotenoids; drought; phenolic composition.

Table 1. Drought effect on C. tinctorius plant growth

Table 2. Contents of individual phenolic compounds (mg/g DW) of C. tinctorius flowers under water deficit

Table 3. Contents of individual carotenoids (µg/100 g DW) of C. tinctorius flowers under water deficit^a

Table 4. Table 4: Antioxidant properties against ABTS^.+, DPPH^. radicals as well as chelating, lipid peroxidation inhibition (IC₅₀ in µg/mL) and reducing power (EC₅₀ mg/mL) of C. tinctorius flower extracts under water deficit.

Table 5. Antibacterial and antifungal activities of C. tinctorius flower extracts^A against human

pathogenic bacteria and fungi strains under water deficit.

Figure 1. Effect of water stress on polyphenol, flavonoid, proanthocyanidin contents of Carthamus tinctorius varieties (a; Jawhara, b; 104). (100 %) Control, (50 %) moderate water deficit, (25 %) Severe water deficit.

Figure 2. HPLC profile of carotenoids in the flower extract of C. tinctorius (1 = neoxanthin, 2 = violaxanthin, 3 = lutein, 4 = zeaxanthin, 5 = lycopene, 6 = ß-carotene) at full flowering stage.