Figure 1.
Carotenoid biosynthesis pathway.
Enzymes are indicated in bold and correspond to the Arabidopsis genes PSY (At5g17230), BCH2/CHY2 (At5g52570), ZEP/ABA1/NPQ2 (At5g67030), NCED3/SIS7 (At3g14440), ABA2/GIN1/XD (At1g52340), and AAO3/ABAO (At2g27150). The block of phytoene desaturation by norflurazon (NFZ) is indicated. Dashed arrows represent several steps. GGPP, geranylgeranyldiphosphate.
Figure 2.
Effect of salt stress on ABA and carotenoid accumulation.
(A) ABA quantification by LC-MS of root and shoot tissues from plants either treated (+) or not (−) with 200 mMNaCl for 5 h. The indicated samples were incubated with 20 µM norflurazon (NFZ) 48 h before and during the salt treatment. (B) Levels of β,βxanthophylls (β,β-x: neoxanthin and violaxanthin), β,β carotenes (β,β-c: β-carotene), and β,ε xanthophylls (β,ε-x: lutein) in root and shoot tissues separated from plants either treated (+) or not (−) with NaCl for 5 h. Data correspond to the mean and standard deviation of n = 3 independent samples. Asterisks mark statistically significant differences (p<0.01) relative to mock-treated controls.
Figure 3.
Analysis of Arabidopsis PSY promoter activity in roots.
Representative images from transgenic PSY:GUS-GFP (A, C, D, G–J) and control 35S:GUS-GFP (B, E, F) seedlings are shown. (A) GUS staining of PSY:GUS-GFP seedlings. (B) GUS staining of 35S:GUS-GFP seedlings. (C) Bright field image of the region boxed in blue in A. (D) GFP fluorescence of the root shown in C. (E) Bright field image of the region boxed in blue in B. (F) GFP fluorescence of the root shown in E. (G) GUS staining of the upper region of the root shown in C. (H) Cross-section of the root region shown in G. (I) Magnification of the region boxed in G. (J) Close up of the stele area in a GUS-stained and resin-embedded section. ep, epidermis; c, cortex; s, stele; en, endodermis; pe, pericycle; p, phloem; pc, phloem companion cells; x, xylem.
Figure 4.
Transcript levels of carotenoid and ABA biosynthetic genes in salt-treated seedlings.
After transferring plants to plates containing 200 mMNaCl for the indicated times, total RNA was separately extracted from shoot and root tissues and used for qPCR analysis of PSY expression (A). Transcript levels were normalized using the UBC gene and represented relative to those before treatment (0 h). Similarly, root samples from plants either treated (+) or not (−) with NaCl for 2 h were used to estimate the levels of transcripts from the carotenoid biosynthetic genes BCH2 and ZEP (B) or ABA biosynthetic genes NCED3 and AAO3 (C). Data correspond to the mean and standard deviation of n = 3 (A), n = 4 (B) and n = 2 (C) independent samples. Asterisks mark statistically significant differences (p<0.01) relative to mock-treated controls.
Figure 5.
(A) Levels of PSY transcripts in root and shoot tissues from plants treated with 50 µM ABA for the indicated times. (B) ABA levels of wild-type (WT) and ABA-deficient (aba2/gin1-3) plants either treated (+) or not (−) with 200 mMNaCl for 5 h. Shoot and root samples were collected separately and used for ABA quantification right after salt treatment. (C) Levels of PSY transcripts in root and shoot tissues from WT or aba2/gin1-3 plants after exposure to 200 mMNaCl for the indicated times. Transcript levels were normalized using the UBC gene and represented relative to those in samples from mock-treated plants. Data correspond to the mean and standard deviation of n = 3 (A,C) or n = 2 (B) experiments. Asterisks mark statistically significant differences (p<0.01) relative to mock-treated controls.