Title : Alleviation of water deficit effects on photosynthesis by phosphate foliar fertilization
Phosphorus is also an essential element for photosynthetic energy production and carbohydrate transport because there is an anti-port system with inorganic phosphorus (Pi) and triose-P in chloroplast membranes. Therefore, even under mild water deficit, a decrease in sink demand for sucrose due to paralyzation of plant growth causes either an increase in starch synthesis inside the chloroplast or a reduction in CO2 assimilation. Both processes can result from low Pi recycling from the cytoplasm to the chloroplast due to sucrose, especially fructose-1,6-bisphosphate accumulation, which regulates anti-port (PT systems), and sustains photophosphorylation and the Calvin cycle by controlling incoming Pi and carbon exporting in chloroplasts. An inadequate Pi supply to the chloroplast can limit ATP synthesis, even if the leaf phosphorus content is high, but in an organic form. Pi supply to the chloroplast is crucial for maintaining phosphorylation reactions during CO2 assimilation. One Pi is released from fructose-1,6-bisphosphate in the cytosol because of sucrose synthesis and export for other tissues, which will be used in the anti-port system. However, even under a mild water deficit, these soluble sugars are not exported and accumulate in the cytoplasm with the growth paralyzation, keeping phosphorus in an organic form. Some experiments were done to evaluate the effect of a foliar Pi spray before water deficit imposition. In a first experiment, carbohydrate content, net CO2 assimilation rate (A), and stomatal conductance (gs) were evaluated after an extra inorganic phosphate (Pi) supply at the pollination stage of the genotypes Carioca and Ouro negro. The treatments consisted of a foliar spray (12.5 mL of 10 g Pi L-1 solution, as ammonium dihydrogen phosphate (MAP: (NH4)H2PO4). In contrast, the other half of the plants were sprayed with 2.64 g N L-1, as urea ((NH2)2CO), to compensate for N added in the Pi treatment. In Phaseolus vulgaris L., different genotypes, grown in pots. The foliar spray was applied two days before the water deficit was imposed at the pollination stage. Under foliar Pi spray, the leaf starch content showed an increase for both genotypes. It enhanced A for water-stressed Ouro negro plants but not for Carioca plants, and among yield components, pod number per plant of Ouro negro showed an increase when using Pi supply. In another experiment with the genotypes A 320 and Ouro Negro, A and gs were not affected by Pi supply during dehydration. However, after rehydration A and gs for A320 and A for Ouro Negro, both supplied with Pi, were higher than for non Pi-supplied plants. In addition, the O2 evolution (Ac) of rehydrated A320 with foliar Pi supply was also higher than for non Pi-supplied plants, and the non-photochemical quenching (NPQ) was higher for rehydrated A320 without foliar Pi. The results revealed an up-regulation of the recovery of photosynthesis after water deficit induced by the foliar Pi supply, which was genotype-specific.
Audience Take Away Notes:
The results shows the beneficial effect of a foliar Pi spray before the pollination stage.
- The use of monoamonium phosphate (MAP) spray can alleviate the effect of environmental stresses.
- The results presented will help researchers working on agriculture to expand their research or teaching.
- The foliar Pi spray can improve yield in an agriculture rain-fed.