Changes in the levels of plant metabolites in response to nutrient deficiency is indicative of how plants utilize scarce resources. In this study, changes in the metabolite profile of roots and shoots of wheat genotypes differing in phosphorus use efficiency (PUE) was investigated. Under low P supply and at 28 days after sowing (DAS), the wheat breeding line, RAC875 (P efficient) produced 42% more shoot biomass than the wheat variety, and Wyalkatchem (P inefficient). Significant changes in the metabolite profile in leaves and roots were observed under low P supply and significant genotypic variation was evident. Under low P supply, an increase in raffinose and 1-kestose was evident in roots of both wheat genotypes, with RAC875 accumulating more when compared to Wyalkatchem. There was no significant increase in raffinose and 1-kestose in leaves when plants were grown under P deficiency. P deficiency had no significant impact on the levels of sucrose, maltose, glucose and fructose in both genotypes, and while phosphorylated sugars (glucose-6-P and fructose-6-P) remained unchanged in RAC875, in Wyalkatchem, glucose-6-P significantly decreased in roots, and fructose-6-P significantly decreased in both leaves and roots. Glycerol-3-P decreased twofold in roots of both wheat genotypes in response to low P. In roots, RAC875 exhibited significantly lower levels of fumarate, malate, maleate and itaconate than Wyalkatchem, while low P enhanced organic acid exudation in RAC875 but not in Wyalkatchem. RAC875 showed greater accumulation of aspartate, glutamine and β-alanine in leaves than Wyalkatchem under low P supply. Greater accumulation of raffinose and 1-kestose in roots and aspartate, glutamine and β-alanine in leaves appears to be associated with enhanced PUE in RAC875. Glucose-6-P and fructose-6-P are important for glycolysis, thus maintaining these metabolites would enable RAC875 to maintain carbohydrate metabolism and shoot biomass under P deficiency. The work presented here provides evidence that differences in metabolite profiles can be observed between wheat varieties that differ in PUE and key metabolic pathways are maintained in the efficient genotype to ensure carbon supply under P deficiency.
Variation in root system architecture (RSA) and morphology are important for improving phosphorus use efficiency (PUE) in wheat. This work aims to analyze the root system architecture and morphology of wheat genotypes to explain their variation in PUE. Two genotypes differing in PUE, RAC875 (P efficient) and Wyalkatchem (P inefficient) were grown in a sandy soil amended with adequate basal nutrients and two P rates (10 and 30 mg P kg −1). RSA traits were measured by freely available software, GiA roots and DIRT, and root hair features were measured using a microscope with an attached camera and LAS v3.6 software. Under low P supply, RAC875 produced greater shoot dry matter (DM) at 24, 27 and 48 days after sowing (DAS), and at maturity, RAC875 also had a higher grain yield at maturity. Enhanced P efficiency (biomass and seed yield at inadequate P supply relative to adequate P supply) was observed more so in RAC875 at all harvest times. P supply affected most RSA traits, with low P leading to reductions in convex hull area (CHA), root surface area, root volume, total root length and root tip number. RAC875 produced significantly greater CHA than Wyalkatchem at low P supply while Wyalkatchem had significantly larger CHA than RAC875 when P was non-limiting. RAC875 also had greater root hair density (RHD) than Wyalkatchem at low P level, but no difference was observed at adequate P. When grown under low P supply, a greater CHA and RHD in RAC875 were likely to contribute to improved P uptake, resulting in its higher shoot biomass and grain yield. Keywords Convex hull area (CHA) • Phosphorus use efficiency (PUE) • Rhizoboxes • Root hair density (RHD) • Root system architecture (RSA)
Maintaining carbohydrate biosynthesis and C assimilation is critical under phosphorus (P) deficiency as inorganic P (Pi) is essential for ATP synthesis. Low available P in agricultural soils occurs worldwide and fertilizer P sources are being depleted. Thus, identifying biosynthetic traits that are favorable for P use efficiency (PUE) in crops is crucial. This study characterized agronomic traits, gas exchange, and chlorophyll traits of two wheat genotypes that differ in PUE. RAC875 was a P efficient genotype and Wyalkatchem was a P inefficient genotype. The plants were grown in pots under growth room conditions at two P levels; 10 mg P kg–1 soil (low P) and 30 mg P kg–1 soil (adequate P) and gas exchange and chlorophyll fluorescence were measured at the vegetative and booting stages using a portable photosynthesis system (LI-6800, LI-COR, United States). Results showed significant differences in some agronomic traits between the two wheat genotypes, i.e., greater leaf size and area, and a higher ratio of productive tillers to total tillers in RC875 when compared with Wyalkatchem. The CO2 response curve showed Wyalkatchem was more severely affected by low P than RAC875 at the booting stage. The relative ratio of the photosynthetic rate at low P to adequate P was also higher in RAC875 at the booting stage. Photochemical quenching (qP) in RAC875 was significantly higher when compared with Wyalkatchem at the booting stage. Maintaining CO2 fixation capacity under low P and higher qP would be associated with P efficiency in RAC875 and measuring qP could be a potential method to screen for P efficient wheat.
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