Alleviation of water deficit effects on photosynthesis by phosphate foliar fertilization

Title : Alleviation of water deficit effects on photosynthesis by phosphate foliar fertilization

Abstract:

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 (g_s) 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 g_s were not affected by Pi supply during dehydration. However, after rehydration A and g_s 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.

Biography:

Prof. Pimentel graduated in Agronomy at the Federal Rural University of Rio de Janeiro, Brazil, in 1977. He then joined the research group of Prof. Vieira da Silva at the University of Paris 7 (Jussieu), Paris, France. He received his Ph.D. degree in 1985 at the same institution. In 1988, he was approved in a concurs of Associate Professor at the Federal Rural University of Rio de Janeiro. In 1994, he passed another Concurs and obtained the position of Full Professor at the same University. He did one year of sabbatical leave (1999-2000) supervised by Dr. Long at the University of Illinois, U.S., working on the FACE programs with the GHG effects on soybean and corn. He has published more than 60 research articles, with more than 3000 citations in Web of Science, two books for graduated programs on agriculture in Brazil, and created two new varieties of pearl millet for agriculture.