Tryptophan Seed Treatment Improves Morphological, Biochemical, and Photosynthetic Attributes of the Sunflower under Cadmium Stress

Abstract

Tryptophan, as a signal molecule, mediates many biotic and environmental stress-induced physiological responses in plants. Therefore, an experiment was conducted to evaluate the effect of tryptophan seed treatment in response to cadmium stress (0, 0.15, and 0.25 mM) in sunflower plants. Different growth and biochemical parameters were determined to compare the efficiency of the treatment agent. The results showed that cadmium stress reduced the growth attributes, including root and shoot length, dry and fresh weight, rate of seed germination, and the number of leaves. Cadmium stress also significantly reduced the contents of chlorophyll a, b, and total chlorophyll, carotenoid contents, phenolics, flavonoids, anthocyanin, and ascorbic acid. Whereas cadmium stress (0.15 and 0.25 mM) enhanced the concentrations of malondialdehyde (45.24% and 53.06%), hydrogen peroxide (-11.07% and 5.86%), and soluble sugars (28.05% and 50.34%) compared to the control. Tryptophan treatment decreased the effect of Cd stress by minimizing lipid peroxidation. Seed treatment with tryptophan under cadmium stress improved the root (19.40%) and shoot length (38.14%), root (41.90%) and shoot fresh weight (13.58%), seed germination ability (13.79%), average leaf area (24.07%), chlorophyll b (51.35%), total chlorophyll (20.04%), carotenoids (43.37%), total phenolic (1.47%), flavonoids (19.02%), anthocyanin (26.57%), ascorbic acid (4%), and total soluble proteins (12.32%) compared with control conditions. Overall, the tryptophan seed treatment showed positive effects on sunflower plants' growth and stress tolerance, highlighting its potential as a sustainable approach to improve crop performance.

Keywords: heavy metal stress; metabolites; photosynthetic pigments; seed treatment; sunflower; tryptophan.

Figure 1

Comparative change in sunflower root and shoot morphology under cadmium levels (0, 0.15, 0.25 mM) with tryptophan (1%) seed treatment (A–F). Error bars indicate standard deviation, and the different letters indicate significant differences at p < 0.05 using the LSD test.

Figure 2

Comparative change in photosynthetic pigments under cadmium levels (0, 0.15, 0.25 mM) with tryptophan (1%) tryptophan seed treatment (A–E). Error bars indicate standard deviation, and the different letters indicate significant differences at p < 0.05 using the LSD test.

Figure 3

Comparative change in germination and leaf various parameters under cadmium stress levels (0, 0.15, 0.25 mM) with tryptophan (1%) seed treatment (A–F). Error bars indicate standard deviation, and the different letters indicate significant differences at p < 0.05 using the LSD test.

Figure 4

Comparative change in malondialdehyde (MDA) and hydrogen peroxide (H₂O₂) under cadmium stress levels (0, 0.15, 0.25 mM) with tryptophan (1%) seed treatment (A,B). Error bars indicate standard deviation, and the different letters indicate significant differences at p < 0.05 using the LSD test.

Figure 5

Comparative change in biochemical parameters under cadmium stress levels (0, 0.15, 0.25 mM) with tryptophan (1%) seed treatment (A–F). Error bars indicate standard deviation, and different letters indicate significant difference at p < 0.05 by LSD test.