Melatonin and KNO3 Application Improves Growth, Physiological and Biochemical Characteristics of Maize Seedlings under Waterlogging Stress Conditions

Abstract

Waterlogging is one of the serious abiotic stresses that inhibits crop growth and reduces productivity. Therefore, investigating efficient waterlogging mitigation measures has both theoretical and practical significance. The objectives of the present research were to examine the efficiency of melatonin and KNO₃ seed soaking and foliar application on alleviating the waterlogging inhibited growth performance of maize seedlings. In this study, 100 µM melatonin and different levels (0.25, 0.50 and 0.75 g) of potassium nitrate (KNO₃) were used in seed soaking and foliar applications. For foliar application, treatments were applied at the 7th leaf stage one week after the imposition of waterlogging stress. The results showed that melatonin with KNO₃ significantly improved the plant growth and biochemical parameters of maize seedlings under waterlogging stress conditions. However, the application of melatonin with KNO₃ treatments increased plant growth characteristics, chlorophyll content, and the net photosynthetic rate at a variable rate under waterlogging stress. Furthermore, melatonin with KNO₃ treatments significantly reduced the accumulation of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA), and it decreased the activity of pyruvate decarboxylase and alcohol dehydrogenase, while increasing enzymatic activities and soluble protein content of maize seedlings under waterlogging stress conditions. Overall, our results indicated that seed soaking with 100 µM melatonin and 0.50 g KNO₃ was the most effective treatment that significantly improved the plant growth characteristics, chlorophyll content, photosynthetic rate, and enzymatic activity of maize seedling under waterlogging conditions.

Keywords: KNO3; enzymes; maize; melatonin; photosynthesis; plant growth; waterlogging stress.

Figure 1

Effect of melatonin with KNO₃ on plant height and leaf area per plant (cm²) of maize seedlings under waterlogging stress conditions. Data are presented as mean ± SD (n = 3, biological replicates). Different small letters (a–e) in each column indicate significant differences at p ≤ 0.05 (least significant difference (LSD) test).The abbreviations of treatment names are the same as those described in Table 2.

Figure 2

The photosynthetic rate and chlorophyll content of maize seedlings under waterlogging stress conditions. Data are presented as mean ± SD (n = 3, biological replicates). Different small letters (a–e) in each column indicate significant differences at p ≤ 0.05 (least significant difference (LSD) test). The abbreviations of treatment names are the same as those described in Table 2.

Figure 3

Antioxidant enzyme (SOD, POD, CAT and APX) activities of maize seedlings under waterlogging stress conditions. Data are presented as mean ± SD (n = 3, biological replicates). Different small letters (a–e) in each column indicate significant differences at p ≤ 0.05 (least significant difference (LSD) test).The abbreviations of treatment names are the same as those described in Table 2.

Figure 4

H₂O₂, MDA, soluble and soluble sugar content of maize seedlings under waterlogging stress conditions. Data are presented as mean ± SD (n = 3, biological replicates). Different small letters (a–e) in each column indicate significant differences at p ≤ 0.05 (least significant difference (LSD) test). The abbreviations of treatment names are the same as those described in Table 2.

Figure 5

Nitrogen metabolism enzyme activities of maize seedlings under waterlogging stress conditions. Data are presented as mean ± SD (n = 3, biological replicates). Different small letters (a–e) in each column indicate significant differences at p ≤ 0.05 (least significant difference (LSD) test).The abbreviations of treatment names are the same as those described in Table 2.

Figure 6

ADH and PDC activities of maize seedlings under waterlogging stress conditions. Data are presented as mean ± SD (n = 3, biological replicates). Different small letters (a–e) in each column indicate significant differences at p ≤ 0.05 (least significant difference (LSD) test).The abbreviations of treatment names are the same as those described in Table 2.