Time course of physiological responses in kiwifruit induced by bicarbonate

Direct and Bicarbonate-Induced Iron Deficiency Differently Affect Iron Translocation in Kiwifruit Roots

“…Inorganic nitrogen forms are mainly present as NH 4 + and NO 3 - , which represent over 70% of the total cations and anions in plants [ 40 ], and can influence Fe uptake and translocation within plants through the regulation of cellular pH homeostasis [ 23 , 41 , 42 ]. Bicarbonate treatment resulted in NH 4 + accumulation in kiwifruit roots ( Figure 4 a), which was in agreement with our previous study [ 27 ]. However, -Fe treatment did not affect NH 4 + concentration in roots ( Figure 4 a), which is inconsistent with the results obtained in Arabidopsis thaliana [ 20 ], likely because NH 4 + accumulation is dependent on species/cultivar and treatment duration.…”

“…Next, we analyzed Fe uptake-related indicators in kiwifruit plants. In +Bic and -Fe+Bic treatments, H + extrusion in roots decreased and correspondingly the pH of nutrient solution increased from 7.51 to 8.45 during each solution cultivation ( Figure 2 and Figure 3 a), coinciding well with previous works [ 27 , 34 ]. Interestingly, bicarbonate increased the H + -ATPase activity and HA1 expression in kiwifruit [ 25 ], citrus [ 11 ], Pisum sativum [ 33 ], and Medicago ciliaris [ 35 ], especially for bicarbonate-tolerant cultivars.…”

“…The pH in root tissues is much lower than that in bicarbonate-added solution ( Figure 2 and Figure 3 a) [ 36 ], and thus bicarbonate-treated roots must release much more OH - than H + into growth medium to maintain the normal physiological pH in root tissues. Our results also showed that the solution pH declined but no difference was found between the control and -Fe treatment ( Figure 2 ), probably due to high susceptibility of kiwifruit to Fe deficiency with low reaction of H + extrusion in roots [ 1 , 27 ]. The FCR activity decreased in both -Fe and +Bic treatments ( Figure 3 b), likely because FCR activity is dependent on Fe supply, solution pH, treatment duration and plant species/cultivar [ 27 ].…”

“…The FCR activity decreased in both -Fe and +Bic treatments ( Figure 3 b), likely because FCR activity is dependent on Fe supply, solution pH, treatment duration and plant species/cultivar [ 27 ]. In addition, Fe deposition on root surface did not differ between the control and +Bic treatments for 35-day cultivation in hydroponics ( Figure 3 c), which is inconsistent with the results that Fe deposition increased in short-term bicarbonate treatment in kiwifruit (7 days) [ 27 ], cucumber (30 min) [ 37 ], and rice (15 days) [ 23 ], indicating that Fe deposition on root surface is duration-specific.…”

“…In kiwifruit plants, -Fe treatment increased H + extrusion, FCR and phosphoenolpyruvate carboxylase (PEPC) activities in roots but lowered the pH of nutrient solution [ 24 , 25 , 26 ]. Our recent works indicated that +Bic treatment disrupted ionic balance in both kiwifruit leaves and roots, and resulted in the accumulation of NH 4 + and succinic acid in roots [ 27 , 28 ]. Additionally, amino acid metabolism is crucial for the resistance of various abiotic stresses in plants [ 29 , 30 ].…”