Trehalose Outperforms Chitosan, Humic Acid and Gamma-Aminobutyric Acid in Promoting the Growth of Field Maize

Abstract

Despite the fact that there are many distinct types of plant growth regulators (PGRs), the diverse ways in which they regulate plant development are rarely compared. In this study, four PGRs (trehalose, chitosan, humic acid and gamma-aminobutyric acid) were selected and sprayed folially, and plant samples were collected while maize was at vegetative leaf stages 6, 10, and 14 (V6, V10, and V14, respectively) to reveal the effects of different PGRs on photosynthesis, dry matter accumulation, oxidative stress, carbon and nitrogen metabolism, hormone levels, and gene expression of maize. Results showed that 100 mg/L PGRs did not induce oxidative damage or repair activities in maize. Trehalose significantly increased chlorophyll content at V6 and promoted dry matter (roots and shoots) accumulation at V6 and V10. The activities of carbon and nitrogen metabolizing enzymes were significantly enhanced by trehalose treatment, which promoted the accumulation of sucrose and soluble sugar, but did not affect the biosynthesis of auxin and gibberellin at V6. Changes in carbon and nitrogen metabolism enzymes are regulated by transcription of related synthetic genes. Lower starch content and higher sucrose content in trehalose-treated maize leaves are important biological characteristics. Further analysis revealed that the effect of trehalose on the metabolic activity of maize was a short-term promoting effect (0-12 days), while the effect on maize growth was a long-term cumulative effect (13-28 days). Overall, exogenous trehalose induced stronger carbon and nitrogen metabolic activity, higher photosynthetic capacity and more dry matter accumulation than chitosan, humic acid and gamma-aminobutyric acid.

Keywords: carbon assimilation; endogenous hormones; maize; nitrogen metabolism; plant growth regulator.

FIGURE 1

Effects of PGRs on maize growth at different growth stages. Comparisons were made between PGRs treatments with different colors in the same growth period; significant differences are indicated by different lowercase letters in the same figure panel, and no letter indicates no significant difference (P < 0.05, n = 5). V6, V10, and V14 represent the 6-, 10-, and 14-leaf stages of vegetative growth, respectively. DW, dry weight of the plant. (A) Root. (B) Shoot. (C) Root/shoot ratio. (D) Dry weight.

FIGURE 2

Effects of PGRs on carbon metabolite accumulation in maize at different growth stages. Statistical analysis was used to compare differences in the mean among the PGR treatments shown in different colors. Treatments labeled with different lowercase letters were significantly different (P < 0.05; n = 3), and the lack of such letters indicate no significant difference among treatments at each stage. V6, V10, and V14 represent the 6-, 10-, and 14-leaf stages of vegetative growth, respectively. FW, fresh weight. (A) Sucrose. (B) Starch. (C) Soluble sugar. (D) Sucrose/starch ratio.

FIGURE 3

Effects of plant growth regulators (PGRs) on nitrogen metabolite accumulation in maize at different growth stages. Statistical analysis was used to compare means of PGR treatments shown in different colors; significantly different treatments within each stage are labeled with different lowercase letters (P < 0.05; n = 3), and the lack of such letters indicates there was no significant difference. V6, V10, and V14 represent the 6-, 10-, and 14-leaf stages of vegetative growth, respectively. FW, fresh weight.

FIGURE 4

Correlation analysis of maize leaf oxidative stress (MDA, T-AOC), carbon assimilation (Chl, sucrose, starch, sucrose/starch ratio, soluble sugar, PEPC, Rubisco, SPS, AGPase, and SS), organic acid metabolism (IDH), nitrogen metabolism (NO₃^–, free amino acid, NR, GOGAT, GS, and GDH) and endogenous hormones (IAA and GA). The color of the ellipse in each small square represents the degree of correlation between the two indicators, and the orientation of the ellipse indicates a correlation is positive or negative. *P < 0.05 indicates statistically significant correlations.

FIGURE 5

Heat map of differentially expressed genes in maize leaves treated with plant growth regulators (PGRs) at the six-leaf stage of vegetative growth (V6) stage. Columns and rows in the heatmap represent genes and samples, respectively. The sample names are displayed to the left of the heatmap. The color scale indicates fold changes in gene expression. Blue and red indicate decreases and increases in transcript abundance, respectively. A cluster analysis of differentially expressed genes is shown above the figure. Heat maps were drawn with Origin software (2021b) based on normalized Z-scores.