Intraspecific Variations of Phosphorus Absorption and Remobilization, P Forms, and Their Internal Buffering in Brassica Cultivars Exposed to a P‐Stressed Environment

Abstract

Translocation of absorbed phosphorus (P) from metabolically inactive sites to active sites in plants growing under P deprivation may increase its P utilization efficiency (PUE). Acclimation to phosphate (Pi) starvation may be caused by a differential storage pool of vacuolar P, its release, and the intensity of re-translocation of absorbed P as P starvation inducible environmental cues (PSIEC) from ambient environment. Biomass assay and three P forms, namely inorganic (Pi), organic (Po), and acid-soluble total (Ptas) were estimated in Brassica cultivars exposed to 10 d P deprivation in the culture media. Considering that -delta Pi/delta t denotes the rate of Pi release, Pi release velocity (RSPi) was determined as the tangent to the equations obtained for Pi f(t) at the mean point in the period of greatest Pi decrease, whereas the inverse of the RSPi was an estimate of the internal Pi buffering capacity (IBCPi). Inter cultivar variations in size of the non-metabolic Pi pool, RSPi, re-translocation of Pi from less to more active metabolic sites, and preferential Pi source and sink compartments were evaluated under P starvation. The cultivar 'Brown Raya' showed the highest Pi storage ability under adequate external P supply, and a more intensive release than 'Rain Bow' and 'Dunkled' under P stress. Cultivar 'B.S.A' was inferior to 'Con-1' in its ability to store and use Pi. Roots and upper leaves were the main sink of Pi stored in the lower and middle leaves of all cultivars and showed lower IBCPi and larger RSPi values than lower and middle leaves. In another trial, six cultivars were exposed to P-free nutrition for 29 d after initial feeding on optimum nutrition for 15 d. With variable magnitude, all of the cultivars re-translocated P from the above ground parts to their roots under P starvation, and [P] at 44 d after transplanting was higher in developing leaves compared with developed leaves. Under P deprivation, translocation of absorbed P from metabolically inactive to active sites may have helped the tolerant cultivars to establish a better rooting system, which provided a basis for tolerance against P starvation and increased PUE. A better understanding of the extent to which changes in the flux of P absorption and re-translocation under PSIEC will help to scavenge Pi from bound P reserves and will bring more sparingly soluble P into cropping systems and obtain capitalization of P reserves.

Functional properties and expression quantitative trait loci for phosphate transporter GmPT1 in soybean

“…). Pi remobilization occurs not only in old leaves but also in young, immature tissues (Akhtar, Oki & Adachi ). The remobilization of Pi in leaves is an important source of grain P that may ultimately affect crop production (Grabau et al .…”

“…Under the conditions of Pi deficiency, the translocation of absorbed P from metabolically inactive sites to active sites in plants could increase the PUE (Akhtar et al . ), and a high PUE was found to be associated with high root/shoot ratios (Huang et al . ).…”

Improving phosphorus use efficiency in agriculture: opportunities for breeding

“…recycling P from mature/senescing plant parts to actively growing tissue and re-use of phosphate from vacuoles that have a buffering function in storing P when in excess of metabolic needs in the cytoplasm. Brassica cultivars with high PUE were shown to have efficient internal phosphate mobilization to active non-mature plant parts (Akhtar et al 2008). At high P, up to 75 % of P in leaves can be present as orthophosphate, most of which in the vacuoles (up to 85-95 % of cellular P, Akhtar et al 2008).…”

“…Brassica cultivars with high PUE were shown to have efficient internal phosphate mobilization to active non-mature plant parts (Akhtar et al 2008). At high P, up to 75 % of P in leaves can be present as orthophosphate, most of which in the vacuoles (up to 85-95 % of cellular P, Akhtar et al 2008). Nevertheless, upon P limitation photosynthesis is quickly affected, so there are apparently limitations to mobilization of this stored P (Richardson et al 2011, also see below the effects of cytokinin signalling from the roots upon P limitation).…”

“…An indication for mobilization efficiency may come from the observation by Ozturk et al (2005) that wheat genotypes with relatively strong senescence symptoms in older leaves were producing higher biomass under P stress; these genotypes may have been mobilizing P more quickly from the older leaves. Akhtar et al (2008) studied internal PUE on a number of Brassica cultivars by following the distribution of Pi and Po (organically bound P) among plant parts after P deprivation in hydroponics. They showed an association of higher biomass production with large Pi reserves at high P availability and fast Pi internal remobilization at low P to sustain Po homeostasis; at P stress, roots and young leaves were the most important sinks for Pi.…”