Background and Aims Root proliferation is a response to heterogeneous nutrient distribution. However, the growth of root hairs in response to heterogeneous nutrients and the relationship between root hairs and lateral roots remain unclear. This study aims to understand the effects of heterogeneous nutrients on root hair growth and the trade-off between root hairs and lateral roots in phosphorus (P) acquisition. Methods Near-isogenic maize lines, the B73 wild type and the rth3 root hairless mutant were grown in rhizoboxes with uniform or localized supply of 40 (low) or 140 (high) mg P kg -1 soil. Results Both WT and rth3 had nearly 2 times greater shoot biomass and P content under local than uniform treatment at low P. Significant root proliferation was observed in both WT and rth3 in the nutrient patch, with the WT accompanied by an obvious increase (from 0.7 mm to 1.2 mm) in root hair length. The root response ratio of rth3 was greater than that of WT at low P level, but could not completely compensate for the loss of root hairs. This suggests that plants enhanced P acquisition through complementarity between lateral roots and root hairs, and thus regulated nutrient foraging and shoot growth. The disappearance of WT and rth3 root response differences at high P level indicated that the P application reduced the dependence of the plants on specific root traits to obtain nutrients. Conclusions In addition to root proliferation, the root response to nutrient-rich patch was also accompanied by root hair elongation. The genotypes without root hairs increased their investment in lateral roots in nutrient-rich patch to compensate for the absence of root hairs, suggesting that plants enhanced nutrient acquisition by regulating the tradeoff of complementary root traits.
Improved management and breeding increased maize (Zea mays L.) yields over the last century, but nutritional efficiency was usually not the focus. This study investigates whether old and recently released flint and dent maize seedlings vary in the phosphorus (P) acquisition and utilization. P use efficiency (PUE) and related traits were measured and compared at two P levels in a calcareous soil. PUE and P acquisition efficiency (PAE) from founder flints to elite flints declined over the last decades. This was associated with smaller root systems, reduced ability to exploit external P, decreased rhizosphere pH and shorter root hairs in low P. Comparing flints with doubled haploid landraces (DH_LR), old and elite dents and hybrids revealed that dents started to acquire exogenous P earlier and had improved PUE. Most DH_LRs had similar PUE as elite flints. When evaluating root traits associated with P efficiency, seed P was also critical, and it is important to stack different root traits to optimize PUE, P utilization efficiency (PUtE) and PAE in breeding programmes. The root hair length, the ability to acidify the rhizosphere and the root diameter in flint and dent pools may be utilized to improve P use in maize germplasm.
Aims: High maize yields in modern well‐managed agroecosystems depend on the use of elite varieties and hybrids. Unfortunately, because of repeated selection at high fertilizer rates, some beneficial traits, such as the interaction with arbuscular mycorrhizal fungi or the release of organic acid anions for phosphate mobilization and for attracting beneficial microorganisms, might be gradually declining in modern elite genotypes. However, old founder lines and landraces possibly carry genetic relicts that originate from pre‐green revolution times that are useful for breeding elite material for low input farming systems. Methods: Seedling colonization with arbuscular mycorrhizal fungi (AMF) and organic acid anion release were measured in flint lines that were released over more than five decades ago and in six preselected doubled haploid (DH) lines from landraces. P‐uptake‐related root traits were compared under P‐sufficient and P‐deficient conditions. Results: Weak trends for the loss of AMF colonization or changes in organic acid anion release at low P supply were detected in modern varieties. One DH line from a landrace was found with increased mycorrhization, whereas others were similar to modern elite lines. Overall, substantial genetic variance was encountered for these traits. Conclusions: The concern that modern elite maize varieties have lost beneficial traits for nutrient acquisition is not substantiated for the flint pool of maize, although weak trends exist. Lines associated with better P‐acquisition efficiency under limited P availability should be utilized for breeding more sustainable varieties.
Plants cope with low phosphorus availability by adjusting growth and metabolism through transcriptomic and proteomic adaptations. We hypothesize that selected genotypes with distinct phosphorous (P) use efficiency covering the breeding history of European Flint heterotic pool provide a tool to reveal general and genotype-specific molecular responses to P limitation. We reconstructed protein and gene co-expression networks by weighted correlation network analysis and related these to phosphate deficiency-induced traits. In roots, low phosphate supply resulted in a decreasing abundance of proteins in the oxidative pentose phosphate pathway and a negative correlation with root and shoot phosphate content. We observed an increase in abundance and positive correlation with root and shoot phosphate content for proteins in sucrose biosynthesis, lipid metabolism, respiration and RNA processing. Purple acid phosphatases, superoxide dismutase and phenylalanine ammonia lyase were identified as being upregulated under low phosphate in all genotypes. Overall, correlations between protein and mRNA abundance changes were limited, with ribosomal proteins and the ubiquitin protein degradation pathway exclusively responding with protein abundance changes. Carbohydrate, phospho-and sulfo-lipid metabolism showed abundance changes at the protein and mRNA levels. These partially non-overlapping proteomic and transcriptomic adjustments to low phosphate suggest sugar and lipid metabolism as metabolic processes associated with improved P use efficiency specifically in Founder Flint lines. We identified a mitogen-activated protein kinase-kinase as a potential genotype-specific regulator of sucrose metabolism at low phosphate in Founder Flint line EP1. We conclude that, during breedingt of Elite Flint lines, regulation of primary metabolism has changed to result in a distinct low phosphate response in Founder lines.
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