Plant hormones (PH) adjust plant growth to environmental conditions such as nutrient availability. Although responses of individual PHs to growth-determining nutrient supplies have been reported, ...little is known about simultaneous dynamics in the metabolism of different PH species.
Brassica napus seedlings were grown under increasing supply of B, and LC-MS/MS was used to characterize bioactive forms of different PH species together with several of their precursors, storage and inactivated forms.
Increasing shoot B concentrations in response to B supply were accompanied by decreasing concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA), which appeared to be synthesized under B deficiency mainly via indole-3-acetonitrile (IAN). By contrast, shoot B concentrations correlated closely with cytokinins, and the B-dependent growth response appeared to be triggered primarily by de-novo synthesis of cytokinins and by re-routing less active towards highly active forms of cytokinin. Also gibberellin biosynthesis strongly increased with B supply, in particular gibberellin species from the non-13-hydroxylation pathway. The brassinosteroid castasterone appeared to support shoot growth primarily at suboptimal B nutrition.
These results indicate that a variable B nutritional status causes coordinated changes in PH metabolism as prerequisite for an adjusted growth response.
Cereal crop yield comprises interrelated components, among which the number of tillers is highly responsive to nitrogen fertilization. We addressed the hypothesis of whether the supply of different ...nitrogen forms can be employed to manipulate the tiller number in cereal crops. Relative to urea or ammonium, exclusive supply of nitrate increased tiller number in hydroponically-grown barley plants. Thereby, tiller number correlated positively with the root-to-shoot translocation rate of endogenous cytokinins. External supply of a synthetic cytokinin analog further stimulated tillering in nitrate-containing but not in urea-containing nutrient solution. When the cytokinin analog 6-benzylaminopurine riboside was externally supplied to roots, its translocation to shoots was 2.5 times higher in presence of nitrate than in presence of urea or ammonium, suggesting that cytokinin loading into the xylem is affected by different nitrogen forms. We then translated this finding to field scale, cultivated winter wheat in four environments, and confirmed that nitrate fertilization significantly increased tiller number in a dose-dependent manner. As assessed in 22 winter wheat cultivars, nitrogen form-dependent tiller formation was subject to substantial genotypic variation. We conclude that cytokinin-mediated signaling effects of fertilizer nitrogen forms can be employed as a management tool to regulate the tiller number in cereal crops.
BACKGROUND AND AIMS: Seed vigour is of great importance for seedling establishment and plant productivity. Despite the high boron (B) demand of oilseed rape and the potential benefit of B for ...improved seed vigour, it is still unclear whether B fertilization to mother plants is effective to enrich B in seeds to an extent that improves seed vigour. We addressed this question and investigated first the dynamics of B enrichment in mother plants and their seeds and then the influence of B on seed vigour using seeds that either were B-enriched from their mother plants or received B from soil fertilization. METHODS: Oilseed rape was grown in a pot experiment and supplied with different B levels. Developing and mature seeds were analysed for biomass and mineral element profiles. In mature seeds, embryos and seed coats were analyzed separately. Seeds were subsequently germinated under no, low, sufficient or excessive B supplies to assess germination rates and seedling establishment. RESULTS: During seedling establishment external B supply strongly promoted water and nutrient uptake as well as biomass formation. When maternal plants were supplied with elevated levels of B, seeds became enriched with B mainly in the seed coat. Sowing these seeds in low B substrate did not provide any advantage for germination or seedling establishment. By contrast, nutrient uptake and especially tissue water content strongly increased with external B supply but irrespective of seed B levels, except when excess B was supplied. CONCLUSIONS: Additional B supply to mother plants allows for an increase in seed B levels. However, additional B is mainly the seed coat and ineffective in improving seed germination or seedling establishment. In contrast, B fertilization to the soil effectively improves seedling establishment. We conclude that adequate B supply via the soil is more effective to improve seed vigour than fertilization of mother plants for B enrichment in seeds.
Beneficial interactions between plant roots and rhizosphere microorganisms are pivotal for plant fitness. Nevertheless, the molecular mechanisms controlling the feedback between root architecture and ...microbial community structure remain elusive in maize. Here, we demonstrate that transcriptomic gradients along the longitudinal root axis associate with specific shifts in rhizosphere microbial diversity. Moreover, we have established that root-derived flavones predominantly promote the enrichment of bacteria of the taxa Oxalobacteraceae in the rhizosphere, which in turn promote maize growth and nitrogen acquisition. Genetic experiments demonstrate that LRT1-mediated lateral root development coordinates the interactions of the root system with flavone-dependent Oxalobacteraceae under nitrogen deprivation. In summary, these experiments reveal the genetic basis of the reciprocal interactions between root architecture and the composition and diversity of specific microbial taxa in the rhizosphere resulting in improved plant performance. These findings may open new avenues towards the breeding of high-yielding and nutrient-efficient crops by exploiting their interaction with beneficial soil microorganisms.
In plants, urea derives either from root uptake or protein degradation. Although large quantities of urea are released during senescence, urea is mainly seen as a short‐lived nitrogen (N) catabolite ...serving urease‐mediated hydrolysis to ammonium. Here, we investigated the roles of DUR3 and of urea in N remobilization. During natural leaf senescence urea concentrations and DUR3 transcript levels showed a parallel increase with senescence markers like ORE1 in a plant age‐ and leaf age‐dependent manner. Deletion of DUR3 decreased urea accumulation in leaves, whereas the fraction of urea lost to the leaf apoplast was enhanced. Under natural and N deficiency‐induced senescence DUR3 promoter activity was highest in the vasculature, but was also found in surrounding bundle sheath and mesophyll cells. An analysis of petiole exudates from wild‐type leaves revealed that N from urea accounted for >13% of amino acid N. Urea export from senescent leaves further increased in ureG‐2 deletion mutants lacking urease activity. In the dur3 ureG double insertion line the absence of DUR3 reduced urea export from leaf petioles. These results indicate that urea can serve as an early metabolic marker for leaf senescence, and that DUR3‐mediated urea retrieval contributes to the retranslocation of N from urea during leaf senescence.
The CLAVATA signaling pathway is essential for the regulation of meristem activities in plants. This signaling pathway consists of small signaling peptides of the CLE family interacting with CLAVATA1 ...and leucine-rich repeat receptor-like kinases (LRR-RLKs). The peptide-receptor relationships determine the specificities of CLE-dependent signals controlling stem cell fate and differentiation that are critical for the establishment and maintenance of shoot and root apical meristems. Plants root systems are highly organized into three-dimensional structures for successful anchoring and uptake of water and mineral nutrients from the soil environment. Recent studies have provided evidence that CLE peptides and CLAVATA signaling pathways play pivotal roles in the regulation of lateral root development and systemic autoregulation of nodulation (AON) integrated with nitrogen (N) signaling mechanisms. Integrations of CLE and N signaling pathways through shoot–root vascular connections suggest that N demand modulates morphological control mechanisms and optimize N uptake as well as symbiotic N fixation in roots.
SUMMARY
WHIRLY1 is a chloroplast‐nucleus located DNA/RNA‐binding protein with functions in development and stress tolerance. By overexpression of HvWHIRLY1 in barley, one line with a 10‐fold and two ...lines with a 50‐fold accumulation of the protein were obtained. In these lines, the relative abundance of the nuclear form exceeded that of the chloroplast form. Growth of the plants was shown to be compromised in a WHIRLY1 abundance‐dependent manner. Over‐accumulation of WHIRLY1 in chloroplasts had neither an evident impact on nucleoid morphology nor on the composition of the photosynthetic apparatus. Nevertheless, oeW1 plants were found to be compromised in the light reactions of photosynthesis as well as in carbon fixation. The reduction in growth and photosynthesis was shown to be accompanied by a decrease in the levels of cytokinins and an increase in the level of jasmonic acid. Gene expression analyses revealed that in nonstress conditions the oeW1 plants had enhanced levels of pathogen response (PR) gene expression indicating activation of constitutive defense. During growth in continuous light of high irradiance PR gene expression increased indicating that under stress conditions oeW1 are capable to further enhance defense.
Significance Statement
With regard to its dual localization in chloroplasts and nucleus WHIRLY1 is an excellent communicator in retrograde signaling. Previous studies with barley showed that a knockdown of WHIRLY1 compromises acclimation to environment. Here we show that overexpression of WHIRLY1 in barley, leading to an over‐accumulation of the protein in both chloroplasts and nucleus, improves stress resistance whereas it has a negative impact on photosynthesis and growth.
Ammonium is a major inorganic nitrogen source for plants. At low external supplies, ammonium promotes plant growth, while at high external supplies it causes toxicity. Ammonium triggers rapid changes ...in cytosolic pH, in gene expression, and in post-translational modifications of proteins, leading to apoplastic acidification, co-ordinated ammonium uptake, enhanced ammonium assimilation, altered oxidative and phytohormonal status, and reshaped root system architecture. Some of these responses are dependent on AMT-type ammonium transporters and are not linked to a nutritional effect, indicating that ammonium is perceived as a signaling molecule by plant cells. This review summarizes current knowledge of ammonium-triggered physiological and morphological responses and highlights existing and putative mechanisms mediating ammonium signaling and sensing events in plants. We put forward the hypothesis that sensing of ammonium takes place at multiple steps along its transport, storage, and assimilation pathways.
Abstract
NGATHA-Like 1 (NGAL1) transcription factor has been identified as a gene regulated through AUG-stop-mediated boron (B)-dependent translation stall; however, its function in B response ...remains unknown. Here, we show that NGAL1 plays an important role in the maintenance of B transport under both low- and high-B conditions in Arabidopsis thaliana. NGAL1 mRNA is accumulated predominantly in shoots in response to B stress. Independent ngal1 mutants carrying transferred DNA (T-DNA) and Ds-transposon insertions exhibit reduced B concentrations in aerial tissues and produce shortened and reduced number of siliques when B supply is limited. Furthermore, the expression of B transporter genes including nodulin 26-like intrinsic protein 6; 1 (NIP6;1), NIP5;1, NIP7;1 and borate exporter 1 (BOR1) is significantly decreased in ngal1 mutants under low-B condition, suggesting that NGAL1 is required for the transcript accumulation of B transporter genes to facilitate B transport and distribution under B limitation. Under high-B condition, ngal1 mutants exhibit reduced growth and increased B concentration in their shoots. The accumulation of BOR4 mRNA, a B transporter required for B efflux to soil, is significantly reduced in roots of ngal1 plants under high-B condition, suggesting that NGAL1 is involved in the upregulation of BOR4 in response to excess B. Together, our results indicate that NGAL1 is involved in the transcriptional regulation of B transporter genes to facilitate B transport and distribution under both low- and high-B conditions.
Plant root development is strongly affected by nutrient availability. Despite the importance of structure and function of roots in nutrient acquisition,statistical modeling approaches to evaluate ...dynamic and temporal modulations of root system architecture in response to nutrient availability have remained as widely open and exploratory areas in root biology. In this study,we developed a statistical modeling approach to investigate modulations of root system architecture in response to nitrogen availability. Mathematical models were designed for quantitative assessment of root growth and root branching phenotypes and their dynamic relationships based on hierarchical con figuration of primary and lateral roots formulating the fishbone-shaped root system architecture in Arabidopsis thaliana. Time-series datasets reporting dynamic changes in root developmental traits on different nitrate or ammonium concentrations were generated for statistical analyses. Regression analyses unraveled key parameters associated with：（i） inhibition of primary root growth under nitrogen limitation or on ammonium;（ii） rapid progression of lateral root emergence in response to ammonium; and（iii） inhibition of lateral root elongation in the presence of excess nitrate or ammonium. This study provides a statistical framework for interpreting dynamic modulation of root system architecture,supported by metaanalysis of datasets displaying morphological responses of roots to diverse nitrogen supplies.
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