A synthetic cytokinin primes photosynthetic and growth response in grapevine under ion-independent salinity stress

Figures & data

Figure 1. (A) Lengths of the distal eight internodes (single boxes in each horizontal bar) measured on the last day of stress on the main shoot of a vine under salt stress [SALT], primed with 6-Benzylaminopurine [BAP + SALT], control [CTRL] conditions and primed with the BAP [BAP]. Error bars and statistics refer to the total lengths of the measured nodes. (B) Average height of vines (from ground to apex) measured on the initial (black filled columns) and final (gray filled columns) day of stress. Comparing treatments different letters indicate statistically significant differences (p < 0.05). On the right, a view of vines (×3 per treatment, excepting the [BAP]) pictured on the last day of the salt stress.

Figure 2. Fine/coarse root ratios in vines exposed to salt [SALT], vines primed with the synthetic cytokinin BAP then exposed to salt [BAP + SALT], in un-primed vines [CTRL] and vines primed with BAP [BAP] measured on the last day of exposure to salt (i.e. day 11 after priming was imposed). Data are the means (±SE) of 15 intersections of roots sampled from five pots per treatment. Different letters indicate statistically significant differences (p < 0.05).

Figure 3. Mean values (±SE) of (A) soil electrical conductivity (EC) and (B) stem water potential (SWP) measured during the experiment in vines under salt stress (o, [SALT]), under salt stress primed with the BAP (•, [BAP + SALT]), control (Δ, [CTRL]) and vines primed with BAP (▴, [BAP]). Comparing treatments at the same time different letters indicate statistically significant differences (p < 0.05). Note that when differences among treatments were not statistically significant letters are not reported. SE bars are visible only when larger than the symbol; in the inset the correlation between soil EC and stem water potential (SWP) of vines under salt stress, note that data from BAP-primed [BAP + SALT] and un-primed [SALT] vines were pooled before linear fitting. The gray filled area indicates the salt-stress period.

Figure 4. Variations in (A) stomatal conductance, (B) transpiration and (C) photosynthetic rate measured in vines under salt stress (o, [SALT]), under salt stress primed with the BAP (•, [BAP + SALT]), control (Δ, [CTRL]) and vines primed with BAP (▴, [BAP]) during the salt stress (gray filled area) and recovery periods. Comparing treatments at the same time different letters indicate statistically significant differences (p < 0.05). Note that when differences among treatments were not statistically significant letters are not reported. Bars are SE and are visible only when larger than the symbol.

Figure 5. Variation in chlorophyll fluorescence measured in vines under salt stress (o, [SALT]), under salt stress primed with BAP (•, [BAP + SALT]), control (Δ, [CTRL]) and vines primed with BAP (▴, [BAP]) during the application of salt (gray filled area) and recovery phases. Comparing treatments at the same time different letters indicate statistically significant differences (p < 0.05). Note that when differences among treatments were not statistically significant letters are not reported. Bars are SE and are visible only when larger than the symbol.

Figure 6. Concentrations (±SE) of chlorophyll a (left panels), chlorophyll b (center panels) and carotenoids (right panels) measured on the last day of salt stress (upper row) and on after recovery (bottom row) in vines irrigated with tap water ([CTRL]) and vines primed with BAP ([BAP]), receiving salt [SALT] and primed with the BAP ([BAP + SALT]). Gray filled bar = salt exposure, dashed bar = primed with BAP). Comparing treatments in each panel different letters indicate statistically significant differences (p < 0.05).

Figure 7. Relative expression (±SE) of the CAT and APX genes in Vitis vinifera leaves under salt stress ([SALT]), primed with the exogenous cytokinin application ([BAP + SALT]) and under control ([CTRL]) determined on day 5 and 8 after priming. Transcript levels of the genes analysed were measured by qRT-PCR and were normalized to the expression of the reference Actin gene. Comparing treatments in each panel different letters indicate statistically significant differences (p < 0.05).

Figure 8. Relative expressions (±SE) of (A) AHP1 and (B) AHK4 genes in leaves of Vitis vinifera irrigated with water (Δ, ▴) and subjected to cytokinin priming treatment (▴, [BAP]) measured at 3 h, 5 and 8 days after BAP spraying. Transcript levels of the genes analysed were measured by qRT-PCR and were normalized to the expression of the reference actin gene. * indicates statistically significant differences (**p  < 0.01, *** p  < 0.001; Student’s t-test).

Figure 9. Values (relative to that of control) of photosynthetic rate (upper panel) and transpiration rate (lower panel) in vines under salt stress primed with the cytokinin (•, [BAP + SALT]) and un-primed (o, [SALT]) plotted against soil electrical conductivity during the salt-stress and recovery periods. The horizontal gray filled band indicates the salt stress period and vertical dashed line the beginning of recovery.

Figure 10. Correlation between intrinsic water use efficiency (A/ g_s) and stomatal conductance (g_s) values detected in vines under salt stress (o, [SALT]), under salt stress primed with BAP (•, [BAP + SALT]) control (Δ, [CTRL]) and vines primed with BAP (▴, [BAP]). Note that the for the symbols • and ▴ a 70% transparency has been used.

Data availability

The data supporting the findings of this study are available from the corresponding author (G. Montanaro), upon request.