Enhancing Arabidopsis salt and drought stress tolerance by chemical priming for its abscisic acid responses

Abstract

Drought and salt stress tolerance of Arabidopsis (Arabidopsis thaliana) plants increased following treatment with the nonprotein amino acid beta-aminobutyric acid (BABA), known as an inducer of resistance against infection of plants by numerous pathogens. BABA-pretreated plants showed earlier and higher expression of the salicylic acid-dependent PR-1 and PR-5 and the abscisic acid (ABA)-dependent RAB-18 and RD-29A genes following salt and drought stress. However, non-expressor of pathogenesis-related genes 1 and constitutive expressor of pathogenesis-related genes 1 mutants as well as transgenic NahG plants, all affected in the salicylic acid signal transduction pathway, still showed increased salt and drought tolerance after BABA treatment. On the contrary, the ABA deficient 1 and ABA insensitive 4 mutants, both impaired in the ABA-signaling pathway, could not be protected by BABA application. Our data demonstrate that BABA-induced water stress tolerance is based on enhanced ABA accumulation resulting in accelerated stress gene expression and stomatal closure. Here, we show a possibility to increase plant tolerance for these abiotic stresses through effective priming of the preexisting defense pathways without resorting to genetic alterations.

Figure 1.

Protective effect of BABA against drought and salinity. A, Symptoms of drought stress in Arabidopsis (accession Col-0). One day prior to stress treatment, plants were pretreated with water (control) or 300 μm BABA. Six-week-old plants were subjected to dehydration. Pictures were taken after 6 d of dehydration. B, Quantification of drought stress in Col-0 plants. One day prior to stress treatment, plants were pretreated with water (control), 300 μm AABA, BABA, GABA, or 100 μm ABA, respectively. Six-week-old plants were subjected to dehydration. Values shown are means of water loss (μL/g fresh weight) in the leaves (10–12 leaves from five to six different plants) after different days of dehydration. Results shown come from a representative experiment that was repeated three times yielding comparable results. C, Symptoms of salt stress in Arabidopsis (accession Col-0). One day prior to stress treatment, plants were pretreated with water (control) or 300 μm BABA. Four-week-old plants were subjected to salt stress by drenching the soil with 3 m NaCl to a final concentration of 300 mm. Pictures were taken 3 d after NaCl application. D, Quantification of salt stress in Col-0 plants. One day prior to stress treatment, plants were pretreated with water (control), 300 μm AABA, BABA, GABA, or 100 μm ABA, respectively. Four-week-old plants were subjected to salt stress by drenching the soil with 3 m NaCl solution to a final concentration of 300 mm. Data shown are means (±sd, n = 50) of the percentage of wilted plants at different days after NaCl treatment.

Figure 2.

Effect of BABA on salt-inducible expression of ABA-inducible genes (RD29A and RAB18) and SA-inducible genes (PR-1 and PR-5) in Arabidopsis (Col-0) plants. One day prior to salt application, plants were treated with water (control) or 300 μm BABA. Hybridization with an 18S rRNA-specific probe was used as a loading control. The experiment was performed three times with similar results. A, Four-week-old plants were treated with 300 mm NaCl (final concentration in the soil), and samples were collect at the times indicated on the top of the figure. B, Four-week-old plants were treated with increasing concentrations of NaCl 3 d before harvesting the leaves.

Figure 3.

Quantification of drought and salt stress in Arabidopsis. A, Quantification of water loss in 6-week-old Arabidopsis (Col-0, cpr1-1, npr1-1, NahG, ein2-1, jar1-1, aba1-5, and abi4-1) plants after different periods of dehydration. One day prior to the start of dehydration, plants were treated with water (black circles) or 300 μm BABA (white circles). Data shown are the average amounts of water loss in 15 leaves (μL/g fresh weight) collected from five different plants. The experiment was repeated twice with similar results. B, Quantification of wilting in 4-week-old Arabidopsis (Col-0, cpr1-1, npr1-1, NahG, ein2-1, jar1-1, aba1-5, and abi4-1) plants at different days after application of 300 mm NaCl. One day prior to salt application, plants were treated with water (black circles) or 300 μm BABA (white circles). Data shown are means (±sd, n = 10) of the percentage wilted plants.

Figure 4.

Quantification of ABA accumulation in wild-type Arabidopsis (Col-0) upon exposure to salt stress (A) and decreased humidity (B) and determination of stomatal conductance during water stress (C). A, ABA was quantified in 3-week-old plants subjected to salt stress by drenching the soil with 3 m NaCl solution to a final concentration of 50, 75, 100, and 150 mm of NaCl. Two days prior to stress treatment, plants were treated with water (control, black circles) or 300 μm BABA (white circles), and 24 h after the stress application plants were collected and freeze dried for analysis. Data shown are means (±sd, n = 15) of the amount of isolated ABA (ng/g dry weight). B, ABA was quantified in plants subjected to low humidity. Five-week-old plants were kept at 100% relative air humidity for 5 d. Twenty-four hours after treatment with either BABA (300 μm, white circles) or water (control, black circles) plants were transferred to 60% relative air humidity (T = 0). Plants were collected at different time points as indicated and freeze dried for analysis. Data shown are means (±sd, n = 10) of the amount of isolated ABA (ng/g dry weight). C, Stomatal conductance of water-treated (black symbols) or BABA-treated (300 μm, white symbols) plants during adaptation to low humidity. Five-week-old plants were treated as in B. Stomatal conductance was determined by six consecutive measurements using three leaves per plant at different time points, as indicated. Values shown are means (±sd) of 10 plants per time points.