Article Figures & Data
Figures
- Figure 1.
Effects of N form and nutrient solution pH on Fe deficiency chlorosis occurrence in sunflower plants after 2 weeks of growth in nutrient solution supplied with 1 μm Fe. Top (left to right): 2 mm NH4NO3 (pH ≅ 4.5, unbuffered) and NH4NO3 (pH 7.5, HEPES). Middle (left to right): 4 mm NH4+ (pH 5.0, MES) and 4 mm NH4+ (pH 7.5, HEPES). Bottom (left to right): 4 mm NO3– (pH 5.0, MES), 4 mm NO3– (pH ≅ 6.8, unbuffered), and 40 mm NO3– (pH 5.0, MES).
- Figure 2.
Effect of N form and pH of the nutrient solution on Fe concentration in xylem sap. Plants were grown for 2 weeks in nutrient solutions at 4 mm N supplied with either NO3– or NH4NO3. Black bars, Green (NO3–, pH 5.0; NH4NO3, unbuffered); white bars, chlorotic (NO3–, unbuffered; NH4NO3, pH 7.5). Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
- Figure 3.
Concentration of NO3– in xylem sap (A) and leaf apoplastic fluid (B) as affected by N forms and external pH. Plants were grown for 2 weeks in nutrient solutions supplied with NO3– (4 or 40 mm N) or NH4NO3 (4 mm N). Black bars, Green (NO3–, pH 5.0; NH4NO3, unbuffered); white bars, chlorotic (NO3–, unbuffered; NH4NO3, pH 7.5). Data are means ± sd of four replications. Significant differences between treatments (P < 5%) are indicated by different letters.
- Figure 4.
Effects of N forms and external pH on relative amount of Fe fractions (symplastic and apoplastic) and apoplastic Fe binding forms of sunflower leaves. Light gray, Symplastic Fe; gray, apoplastic Fe, weakly bound (cell walls); dark gray, strongly bound (cell walls); black, soluble (AWF).
- Figure 5.
Cell wall Fe concentration in relation to chlorophyll content (A) and NO3– concentration in leaf apoplastic fluid (B) in young, fully expanded leaves of sunflower. Plants were grown for 2 weeks in nutrient solutions supplied with NO3– (4–40 mm N) or NH4NO3 (4 mm N).
- Figure 6.
Uptake of 59Fe by the leaf symplast of sunflower, as depending of apoplastic NO3–. –NO3–, Plants were precultured in NO3–-free nutrient solution for 48 h, and less than 0.5 mm NO3– was measured in the apoplastic fluid obtained by centrifugation of intact leaves; no NO3– was added in 59Fe-labeled solution. +NO3–, Plants were grown in NO3–-supplied nutrient solution (4 mm), resulting in up to 5 mm NO3– in the leaf apoplastic fluid; 6 mm NO3– was added to the 59Fe-labeled solution. After perfusion of radioactive labeled ± NO3– solution into the leaf apoplast of excised leaves via the petiole (2 h) by the transpiration stream, leaves were further incubated in darkness or under light (500 μmol m–2 s–1) for 2 h. Black bars, Dark; white bars, light. Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
- Figure 7.
Effect of apoplastic pH on 59Fe uptake by the symplast of intact sunflower leaves. 59Fe-labeled solution (10 μm Fe citrate, 1:100 molar ratio) without or with various pH buffers (50 mm MES [pH 5.0 and 6.0] and 50 mm HEPES [pH 7.0]) was infiltrated into the leaf apoplast of excised leaves (2 h) via the petiole by the transpiration stream. Leaves were further incubated in darkness or under light (500 μmol m–2 s–1) for 2 h. Black bars, Dark; white bars, light. Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
Tables
- Table I.
Chlorophyll content and growth characteristics of sunflower as affected by N form and external pH
Plants were grown for 2 weeks in nutrient solutions supplied with 4 or 40 mm N as NO3- or with 4 mm N as either NH4+ or NH4NO3. In all treatments, Fe was applied as FeIIIEDDHA at 1 μm. Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
Treatments Chlorophyll Biomass Leaf Area Roots Shoot Spectral plant analysis diagnostic units mg cm-2 NO3-; pH 5.0 (green) 34.3 ± 0.7a 147 ± 17a 647 ± 49a 211 ± 8a NO3-, 40 mm; pH 5.0 (green) 31.7 ± 0.7a 153 ± 25a 760 ± 58a 228 ± 16a NO3-; unbuffered (chlorotic) 16.8 ± 4.2b 128 ± 9a 580 ± 42ab 183 ± 25b NH4+; pH 5.0 (green) 35.0 ± 2.2a 90 ± 12b 356 ± 5b 128 ± 8c NH4+; pH 7.5 (chlorotic) 3.9 ± 0.6c 56 ± 21b 345 ± 3b 110 ± 12c NH4NO3; unbuffered (green) 35.6 ± 1.1a 157 ± 26a 724 ± 54a 266 ± 33a NH4NO3; pH 7.5 (chlorotic) 4.2 ± 0.5c 42 ± 5c 335 ± 17b 123 ± 9c - Table II.
Effects of N form and nutrient solution pH on concentration, amount, and total Fe uptake of sunflower
Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
Treatments Fe concentration Fe Amount Fe Uptake Roots Leaves Roots Leaves μg g-1 dry wt μg organ-1 μg plant-1 NO3-; pH 5.0 (green) 266 ± 20a 81 ± 11a 39 ± 3a 34 ± 4a 81 ± 7a NO3-, 40 mm; pH 5.0 (green) 245 ± 34a 78 ± 8a 35 ± 12a 38 ± 5a 79 ± 8a NO3-; unbuffered (chlorotic) 175 ± 30b 49 ± 4b 22 ± 4b 19 ± 2b 45 ± 2b NH4+; pH 5.0 (green) 318 ± 28a 100 ± 14a 26 ± 5a 25 ± 3ab 58 ± 5ab NH4+; pH 7.5 (chlorotic) 207 ± 36b 34 ± 3c 10 ± 2c 9 ± 1c 23 ± 4 c NH4NO3; unbuffered (green) 239 ± 44ab 85 ± 10a 33 ± 2a 42 ± 6a 83 ± 6a NH4NO3; pH 7.5 (chlorotic) 229 ± 51b 35 ± 4c 9 ± 1c 8 ± 1c 21 ± 2c - Table III.
The pH of xylem sap and leaf apoplastic fluid of young fully expanded sunflower leaves as affected of N form and nutrient solution pH
Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
Treatments Xylem sap Leaf apoplastic fluid NO3-; pH 5.0 (green) 5.6 ± 0.1a 6.7 ± 0.1a NO3-, 40 mm; pH 5.0 (green) 5.8 ± 0.2a 6.6 ± 0.0a NO3-; unbuffered (chlorotic) 5.8 ± 0.1a 6.7 ± 0.0a NH4+; pH 5.0 (green) 5.7 ± 0.2a 6.4 ± 0.1a NH4+; pH 7.5 (chlorotic) 5.6 ± 0.1a 6.5 ± 0.1a NH4NO3; unbuffered (green) 5.8 ± 0.1a 6.5 ± 0.1a NH4NO3; pH 7.5 (chlorotic) 5.7 ± 0.2a 6.4 ± 0.1a - Table IV.
Effects of N form and nutrient solution pH on absolute and relative (share of total Fe) concentrations of symplastic and apoplastic Fe fractions in sunflower leaves
Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
Treatments Symplastic Fe Apoplastic Fe Absolute Relative Absolute Relative μg g-1 dry wt % μg g-1 dry wt % NO3-; pH 5.0 (green) 67.4 ± 3.2a 73 24.7 ± 2.7a 27 NO3-,40 mm; pH 5.0 (green) 54.1 ± 3.2a 72 21.5 ± 3.2a 28 NO3-; unbuffered (chlorotic) 42.1 ± 5.0b 76 12.9 ± 2.0b 24 NH4+; pH 5.0 (green) 58.3 ± 14.4a 75 18.3 ± 1.8a 25 NH4+; pH 7.5 (chlorotic) 29.0 ± 2.8c 72 11.4 ± 1.3b 28 NH4NO3; unbuffered (green) 63.8 ± 5.0a 72 24.1 ± 5.6a 28 NH4NO3; pH 7.5 (chlorotic) 35.3 ± 3.3c 74 12.2 ± 1.0b 26 - Table V.
Effects of N forms and nutrient solution pH on Fe-binding forms in cell walls of sunflower leaves
Total cell wall Fe was calculated as the sum of strongly bound and weakly bound fractions. Data are means ± sd of four replications. Significant differences (P < 5%) between treatments are indicated by different letters.
Treatments Total Fe Weakly Bound Fe Strongly Bound Fe μmol g-1 dry wt NO3-; pH 5.0 (green) 3.4 ± 0.9a 2.2 ± 0.7a 1.2 ± 0.1a NO3-, 40 mm; pH 5.0 (green) 3.9 ± 1.3a 2.6 ± 0.8a 1.3 ± 0.5a NO3-; unbuffered (chlorotic) 1.7 ± 0.4b 1.2 ± 0.4b 0.5 ± 0.1b NH4+; pH 5.0 (green) 4.2 ± 2.1a 2.8 ± 1.5c 1.4 ± 0.6a NH4+; pH 7.5 (chlorotic) 2.4 ± 0.3c 1.2 ± 0.3b 1.2 ± 0.1a NH4NO3; unbuffered (green) 3.8 ± 0.9a 2.5 ± 0.6a 1.3 ± 0.5a NH4NO3; pH 7.5 (chlorotic) 1.9 ± 1.0b 1.5 ± 0.5b 0.4 ± 0.2b
