Transcriptomic Analysis of Banana in Response to Phosphorus Starvation Stress

Bananas are an important part of the diets of millions of people around the globe. Low P absorption and use efficiency significantly restrict banana yields. To further explore the molecular mechanisms of P regulation in banana plants, we used RNA sequencing-based transcriptomic analysis for banana plants subjected to Pi deficit stress for 60 days. We detected 1900 significantly differentially expressed genes (DEGs) in aboveground plant parts and 7398 DEGs in root parts under low P stress. Gene ontology (GO) classification analysis showed that 156,291 GO terms belonging to molecular functions, 53,114 GO terms belonging to cellular components, and 228,544 GO terms belonging to biological processes were enriched in the aboveground and root components. A number of DEGs involved in energy metabolism-related processes, signal transduction, control of rhizosphere P activation, and Pi mobilization were found, which were confirmed by quantitative reverse-transcription Polymerase Chain Reaction (qRT-PCR) analysis. At the transcriptomic level, we detected 13 DEGs from different organs and with different functions in the time-course response to phosphorus deficiency stress. These DEGs may include some key genes that regulate the phosphorus network, increasing our understanding of the molecular mechanism of Pi homeostasis in banana. These findings will also help develop biotechnologies to create a variant of banana with more effective Pi absorption and utilization.

Acid Phosphatases Activity and Growth of Barley, Oat, Rye and Wheat Plants as Affected by Pi Deficiency

Objective: The influence of phosphorus deficit on the growth of plants and acid phosphatases activity in leaves and roots of barley seedlings (Hordeum vulgare L.), as well as oat (Avena sativa L.), rye (Secale cereale L.) and wheat plants (Triticum vulgare L.) was studied. Method: Plants were cultured three weeks in a nutrient media: complete (control, +P) or without phosphorus (-P). The growth on -P medium significantly affected the inorganic phosphate (Pi) content in plants tissues. Pi deficit decreased shoots growth but ratio of root/shoot was higher for -P plants when compared to control. The root elongation was enhanced under Pi deficiency - in -P oat and barley more intensive elongation was observed than in other plants. On the other hand, inhibition of shoot growth was more pronounced for -P rye and wheat. Pi-deficient plants showed higher activity of acid phosphatases in tissue extracts and in exudates from roots than +P plants. Result: Extracellular acid phosphatases activity increased the most for -P rye and wheat plants. Acid phosphatases secretion was intensive in growing parts of Pi-deficient roots. The activity of enzymes secreted by -P roots of all studied plants was higher than intracellular acid phosphatases. Conclusion: Our results indicated that wheat is more sensitive to the Pi deficiency at the early stage of growth than other plants, whereas oat is rather resistant to Pi deficit. The results suggested that acid phosphatases played an important role in acclimation of studied crop plants to moderate Pi deficiency.

Acute phosphate depletion inhibits the Na+/H+ antiporter in a cultured renal cell line

We studied the effect of acute Pi depletion on the regulation of intracellular pH (pHi) in the OK opossum kidney cell line by using the pH-sensitive dye 2'7'-bis(carboxyethyl)-5(6)-carboxyfluorescein (BCECF). Cell recovery from an NH4Cl acid load in HCO3-free buffer disclosed an Na(+)-dependent component blocked by amiloride and a smaller Na(+)-independent component that increased on exposure of the cells to a high-K+ buffer. After 24-h incubation of the cells in phosphate-free medium, pHi recovery by the Na+/H+ exchanger was markedly inhibited, whereas the Na(+)-independent pHi recovery was not affected. The inhibition of Na+/H+ exchange was reversible on correction of cellular Pi deficit. A similar phenomenon was observed when cellular Pi depletion was induced by acute exposure (min) to fructose. Pi depletion shifted the pHi dependence of the exchanger and also reduced its maximal activity. Time-course studies revealed that the effect of Pi depletion could not be attributed to attenuation of Na(+)-K(+)-adenosinetriphosphatase activity and resultant diminution of the transmembrane gradient for the Na+ influx. We conclude that acute Pi depletion in cultured proximal tubular cells leads to reversible inhibition of the Na+/H+ exchanger. This in vitro finding may relate to the in vivo observation of impaired HCO3 reabsorption and bicarbonaturia in acute Pi depletion.