Summary• White lupin (Lupinus albus) forms specialized cluster roots characterized by exudation of organic anions under phosphorus (P) deficiency. Here, the role of nitric oxide (NO) in P deficiency-induced cluster-root formation and citrate exudation was evaluated.• White lupin plants were treated with the NO donor sodium nitroprusside (SNP) and scavenger or inhibitor of NO synthase under conditions of P deficiency (0 lM) or P sufficiency (50 lM).• Phosphorus deficiency enhanced NO production in primary and lateral root tips, with a greater increase in cluster roots than in noncluster roots. NO concentrations decreased with cluster root development from the pre-emergent stage, through the juvenile stage, to the mature stage. The P deficiency-induced increase in NO production was inhibited by antagonists of NO synthase and xanthine oxidoreductase, suggesting the involvement of these enzymes in NO production. SNP markedly increased the number of cluster roots. Citrate exudation from different root segments in P-deficient roots was positively correlated with endogenous root NO concentrations.• These findings demonstrate differential patterns of NO production in white lupin, depending on root zone, developmental stage and P nutritional status. NO appears to play a regulatory role in the formation of cluster roots and citrate exudation in white lupin under conditions of P deficiency.

Over the past five decades, Chinese grain production has increased 4-fold, from 110 Mt in 1961 to 557 Mt in 2014, with less than 9% of the world's arable land feeding 22% of the world's population, indicating a substantial contribution to global food security. However, compared with developed economies, such as the USA and the European Union, more than half of the increased crop production in China can be attributed to a rapid increase in the consumption of chemicals, particularly fertilizers. Excessive fertilization has caused low nutrient use efficiency and high environmental costs in grain production. We analysed the key requirements underpinning increased sustainability of crop production in China, as follows: (i) enhance nutrient use efficiency and reduce nutrient losses by fertilizing roots not soil to maximize root/rhizosphere efficiency with innovative root zone nutrient management; (ii) improve crop productivity and resource use efficiency by matching the best agronomic management practices with crop improvement; and (iii) promote technology transfer of the root zone nutrient management to achieve the target of high yields and high efficiency with low environmental risks on a broad scale. Coordinating grain production and environmental protection by increasing the sustainability of nutrient use will be a key step in achieving sustainable crop production in Chinese agriculture.

White lupin (Lupinus albus) is a legume that is very efficient in accessing unavailable phosphorus (Pi). It develops short, densely clustered tertiary lateral roots (cluster/proteoid roots) in response to Pi limitation. In this report, we characterize two glycerophosphodiester phosphodiesterase (GPX-PDE) genes (GPX-PDE1 and GPX-PDE2) from white lupin and propose a role for these two GPX-PDEs in root hair growth and development and in a Pi stress-induced phospholipid degradation pathway in cluster roots. Both GPX-PDE1 and GPX-PDE2 are highly expressed in Pi-deficient cluster roots, particularly in root hairs, epidermal cells, and vascular bundles. Expression of both genes is a function of both Pi availability and photosynthate. GPX-PDE1 Pi deficiency-induced expression is attenuated as photosynthate is deprived, while that of GPX-PDE2 is strikingly enhanced. Yeast complementation assays and in vitro enzyme assays revealed that GPX-PDE1 shows catalytic activity with glycerophosphocholine while GPX-PDE2 shows highest activity with glycerophosphoinositol. Cell-free protein extracts from Pi-deficient cluster roots display GPX-PDE enzyme activity for both glycerophosphocholine and glycerophosphoinositol. Knockdown of expression of GPX-PDE through RNA interference resulted in impaired root hair development and density. We propose that white lupin GPX-PDE1 and GPX-PDE2 are involved in the acclimation to Pi limitation by enhancing glycerophosphodiester degradation and mediating root hair development.

SummaryIncreasing light intensity enhances cluster-root formation, citrate exudation, and phosphate-uptake capacity in white lupin under phosphate-deficient conditions by affecting the coordination between P and sucrose signals.

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Background Limitation of plant productivity by phosphorus (P) supply is widespread and will probably increase in the future. Relatively large amounts of P fertilizer are applied to sustain crop growth and development and to achieve high yields. However, with increasing P application, plant P efficiency generally declines, which results in greater losses of P to the environment with detrimental consequences for ecosystems. Scope strategy for reducing P input and environmental losses while maintaining or increasing plant performance is the development of crops that take up P effectively from the soil (P acquisition efficiency) or promote productivity per unit of P taken up (P utilization efficiency). In this review, we describe current research on P metabolism and transport and its relevance for improving P utilization efficiency. Conclusions Enhanced P utilization efficiency can be achieved by optimal partitioning of cellular P and distributing P effectively between tissues, allowing maximum growth and biomass of harvestable plant parts. Knowledge of the mechanisms involved could help design and breed crops with greater P utilization efficiency.

Micronutrient deficiency commonly occurs in calcareous soils. We hypothesized that localized application of ammonium in the P-banding zone could improve micronutrient uptake and thus grain yield through inducing rhizosphere acidification and stimulating root proliferation. A 2-year field experimentation with maize growing on a calcareous soil was conducted with localized application of P (superphosphate) only (P), P plus ammonium as ammonium sulfate (NH 4-N+P) or urea plus P (Urea+P) at sowing and jointing. Compared with localized Urea+P, localized NH 4-N+P significantly improved root dry weight, whole root length and first-order lateral root density/length at the seedling stage, as well as chlorophyll content and net photosynthetic rate at flowering. Shoot Zn content was 30-50% greater at the seedling stage and 22-36% higher at grain maturity in localized NH 4-N+P compared with localized P and Urea+P in 2012 and 2013. The Fe content at the seedling, flowering and harvest stages in localized NH 4-N+P was higher than that in localized P, and also exhibited an increasing trend relative to localized Urea+P. Compared with localized Urea+P, grain Zn concentration in the NH 4-N+P treatment increased by 17% in 2012, and exhibited an increasing trend in 2013. Grain Fe concentration in the NH 4-N+P treatment increased in 2013 in comparison with the P and Urea+P treatments. Maize grain yield in localized NH 4-N+P increased by 10-14% in 2012 and 13-25% in 2013 compared with localized P and Urea+P. The results indicate that localized application of NH 4-N+P may be an efficient approach to improving maize growth, grain Zn and Fe accumulation and yield via modifying root traits (such as root length, lateral root 2 proliferation and root length density), and intensifying rhizosphere acidification by ammonium uptake.

Root system architecture (RSA) plays an important role in the acquisition of mineral nutrients. Nevertheless, RSA has seldom been selected as an important agricultural trait in conventional breeding programs. Little is known about the response of RSA and phosphorus use efficiency (PUE) in regards to phosphorus (P) availability between parental inbred lines and their F1. In this study, 6 maize inbred lines and their 15 F1 generated by a diallel mating system, were used to analyze the genetic associations between RSA and PUE. Heterosis for PUE-related traits were comparatively greater under high P condition and reduced significantly under low P condition. Relative mid-parent heterosis for root traits were expressed more under the low P condition. Low P supply had a significant effect on heterosis, GCA and SCA of RSA- and PUE- related traits. The hybrid C3 (7922 × 8703-2), which had the highest PUE, showed an average yield with a lower P uptake under the both P conditions. Results from this study suggested breeding for a relatively high grain yield with reducing aboveground P demand and grain P concentration should be sufficient to reduce P fertilizer input and improve P efficiency.