Salicylic acid deficiency in NahG transgenic lines and sid2 mutants increases seed yield in the annual plant Arabidopsis thaliana

Abstract

Salicylic acid-deficient NahG transgenic lines and sid2 mutants were used to evaluate the role of this compound in the development of the short-lived, annual plant Arabidopsis thaliana, with a particular focus on the interplay between salicylic acid and other phytohormones. Low salicylic acid levels led to increased growth, as well as to smaller abscisic acid levels and reduced damage to PSII (as indicated by F(v)/F(m) ratios) during the reproductive stages in rosette leaves of NahG transgenic lines and sid2 mutants, compared with wild-type plants. Furthermore, salicylic acid deficiency highly influenced seed yield and composition. Seed production increased by 4.4-fold and 3.5-fold in NahG transgenic lines and sid2 mutants, respectively, compared to the wild type. Salicylic acid deficiency also improved seed composition in terms of antioxidant vitamin concentrations, seeds of salicylic acid-deficient plants showing higher levels of alpha- and gamma-tocopherol (vitamin E) and beta-carotene (pro-vitamin A) than seeds of wild-type plants. Seeds of salicylic acid-deficient plants also showed higher nitrogen concentrations than seeds of wild-type plants. It is concluded that (i) the sid2 gene, which encodes for isochorismate synthase, plays a central role in salicylic acid biosynthesis during plant development in A. thaliana, (ii) salicylic acid plays a role in the regulation of growth, senescence, and seed production, (iii) there is a cross-talk between salicylic acid and other phytohormones during plant development, and (iv) the concentrations of antioxidant vitamins in seeds may be influenced by the endogenous levels of salicylic acid in plants.

Fig. 1.

Endogenous salicylic acid (SA) concentrations in leaves and seeds of wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Plants were transferred from short days to long days and leaf samples analysed at pre-reproductive (days 0, 6, and 11) and reproductive stages (days 21, 27, and 31). Data represent the mean ±SE of four measurements. Letters indicate statistically significant differences between seeds of different plant groups at a probability level of P ≤0.05.

Fig. 2.

Chlorophyll a+b levels, maximum efficiency of PSII photochemistry (F_v/F_m ratio, indicative of damage to PSII), malondialdehyde levels (MDA, an estimation of lipid peroxidation), relative leaf water content (RWC), nitrogen (N) concentration, and carbon/nitrogen (C/N) ratio in leaves of wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Plants were transferred from short days to long days and leaf samples analysed at pre-reproductive (days 0, 6, and 11) and reproductive stages (days 21, 27, and 31). Data represent the mean ±SE of four measurements. Significance of plant group-generated changes (NahG and sid2 versus the wild type) is depicted inside the panels (results of ANOVA). Differences were considered significant at a probability level of P ≤0.05. NS, not significant.

Fig. 3.

Time-course evolution of plant growth in wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Plants were transferred from short days to long days and leaf rosette biomass measured at pre-reproductive (day 0, 6, and 11) and reproductive stages (days 21, 27, and 31). Data represent the mean ±SE of five individuals. Significance of plant group-generated changes (NahG and sid2 versus the wild type) is depicted inside the panels (results of ANOVA). Differences were considered significant at a probability level of P ≤0.05.

Fig. 4.

Endogenous concentrations of abscisic acid (ABA), indole-3-acetic acid (IAA), jasmonic acid (JA), gibberellin 4 (GA₄), zeatin (Z), and zeatin riboside (ZR) in leaves of wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Plants were transferred from short days to long days and leaf samples analysed at pre-reproductive (days 0, 6, and 11) and reproductive stages (days 21, 27, and 31). Data represent the mean ±SE of four measurements. Significance of plant group-generated changes (NahG and sid2 versus the wild type) is depicted inside the panels (results of ANOVA). Differences were considered significant at a probability level of P ≤0.05. NS, not significant.

Fig. 5.

Endogenous concentrations of indole-3-acetic acid (IAA), jasmonic acid (JA), abscisic acid (ABA), gibberellin 4 (GA₄), zeatin (Z), and zeatin riboside (ZR) in seeds of wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Data represent the mean ±SE of four measurements. Letters indicate statistical significant differences between seeds of different plant groups at a probability level of P ≤0.05.

Fig. 6.

Endogenous concentrations of the carotenoids, lutein, and β-carotene (pro-vitamin A) and α- and γ-tocopherols (vitamin E) in seeds of wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Data represent the mean ±SE of four measurements. Letters indicate statistical significant differences between seeds of different plant groups at a probability level of P ≤0.05.

Fig. 7.

Total N concentration and C/N ratio in seeds of wild type and SA-deficient NahG transgenic lines and sid2 mutants of A. thaliana. Data represent the mean ±SE of four measurements. Letters indicate statistical significant differences between seeds of different plant groups at a probability level of P ≤0.05.