Phosphorus Alters Starch Morphology and Gene Expression Related to Starch Biosynthesis and Degradation in Wheat Grain

From field to food: Impact of nitrogen and phosphorus fertilizers on mung bean starch synthesis, structure, and functional properties

Nitrogen (N) and phosphorus (P) are essential nutrients that play a critical role in mung bean growth and grain quality. This study aimed to evaluate the combined effects of four N and four P fertilizer levels on the synthesis, structure, and functional properties of mung bean starch. The combined application of N and P fertilizers significantly increased starch accumulation by enhancing key enzyme activities. These treatments also caused notable structural changes, resulting in better functional properties, such as increased light transmittance, water solubility, gelatinization enthalpy, and reduced pasting temperature and chewiness, which are crucial for optimizing the quality of starch-based products. In conclusion, the combined application of N and P fertilizers boosted starch synthesis and improved the functional properties of mung bean starch by altering its consists and structure. These findings enhance our understanding of nutrient-mediated starch biosynthesis and structural regulation in legumes providing a basis for increasing the industrial and commercial value of mung bean starch.

Physiological and molecular investigations on a high-yielding variety and near-isogenic line of rice under continuous phosphorus stress reveal major regulatory function of Pup1 QTL

Phosphorous (P) plays crucial roles in cellular functioning including respiration, photosynthesis, and membranes. P deficiency in the soil causes stunted growth, smaller/erect leaves, lesser tillers, and a considerable decrease in yield. To decipher the functions of Pup1 QTL and delineate the potential effects of continuous P stress on plant growth, yield/quality, physio-biochemical and molecular analyses of rice [Pusa-44 (P deficiency sensitive) and a near-isogenic line-23 (NIL-23), (harbouring Pup1 QTL, tolerant genotype)] were hydroponically grown under P continuous stress [deficiency (4 ppm) or extravagance (≥32 ppm)] till maturity. Decrease in the number of tillers and panicles under stress led to poor agronomic performance of rice. P concentration in roots, leaves, and seeds raised significantly with increasing concentration of P in hydroponic culture. Higher P concentration in the medium led to elevated phytate concentration in seeds; however, it was comparatively more in seeds of the tolerant (NIL-23) genotype. Comparative transcriptome analysis indicated differential expression of genes for P transporters and those implicated in P mobilization/homeostasis, carbohydrate/lipid metabolism, etc. on P deficiency. Moreover, the regulatory function of Pup1 in reprograming the gene expression involved in chromatin assembly, histone/DNA methylation, cell wall organization, etc. was detected in the panicle of tolerant genotype on P deficiency. This study confirms a major regulatory function of Pup1 and outlines the potential effects of excessive P on plant development, productivity, and quality of seeds. These findings would be useful in improving P uptake/use efficiency in rice and prudent/sustainable usage of phosphatic fertilizers.

Metabolic engineering of lipids for crop resilience and nutritional improvements towards sustainable agriculture

Metabolic engineering of lipids in crops presents a promising strategy to enhance resilience against environmental stressors while improving nutritional quality. By manipulating key enzymes in lipid metabolism, introducing novel genes, and utilizing genome editing technologies, researchers have improved crop tolerance to abiotic stresses such as drought, salinity, and extreme temperatures. Additionally, modified lipid pathways contribute to resistance against biotic stresses, including pathogen attacks and pest infestations. Engineering multiple stress-resistance traits through lipid metabolism offers a holistic approach to strengthening crop resilience amid changing environmental conditions. Beyond stress tolerance, lipid engineering enhances the nutritional profile of crops by increasing beneficial lipids such as omega-3 fatty acids, vitamins, and antioxidants. This dual approach not only improves crop yield and quality but also supports global food security by ensuring sustainable agricultural production. Integrating advanced biotechnological tools with a deeper understanding of lipid biology paves the way for developing resilient, nutrient-rich crops capable of withstanding climate change and feeding a growing population.

High-light and nutrient interactions drive carbohydrate and proton pump dynamics in Agastache rugosa (Fisch. & C.A.Mey.) Kuntze

Agastache rugosa, a perennial herb native to temperate and subtropical regions, shows remarkable adaptive strategies when exposed to varying light and nutrient conditions in tropical environments. Our study reveals new insights into the crosstalk mechanisms involving carbohydrate homeostasis, biomass allocation, and nutrient acquisition in A. rugosa under different environmental conditions. Treatments were two light levels; HL (high-light, 0% shade) and LL (low-light, 50% shade), and four nutrient rates; NPK1 (40 mg kg-1), NPK2 (80 mg kg-1), NPK3 (120 mg kg-1) and NPK4 (160 mg kg-1). High-light coupled with increasing nutrient levels (HL-NPK3 and HL-NPK4) promoted biomass production via increased carbon assimilation, associated with higher soluble sugar levels and higher phosphorus and potassium uptake mediated by the upregulation of plasma membrane H+-ATPase. Maximum carbohydrate accumulation occurred at high-light and the lowest nutrient levels (HL-NPK1), coinciding with increased nitrogen uptake and the drastically high leaf nitrogen concentration. This response was preceded by the upregulation of acid phosphatase and sucrose phosphate synthase, suggesting a compensatory mechanism to maintain nutrient and carbohydrate reserves for critical metabolic processes. Starch increase was more apparent under low-light and higher nutrient levels (LL-NPK3 and LL-NPK4), relative to invertase downregulation, indicating a shift towards carbohydrate storage rather than utilization. These findings underscore the complex interplay between sugar signaling, nutrient sensing, enzymatic actions, and proton pump activity in modulating plant adaptation to varying environmental conditions. This study also highlights the importance of understanding how non-model medicinal species like A. rugosa reprogram their metabolism and resource allocation in response to environmental changes.

Effects of Deep Tillage on Rhizosphere Soil and Microorganisms During Wheat Cultivation

The production of wheat is fundamentally interconnected with worldwide food security. The practice of deep tillage (DT) cultivation has shown advantages in terms of soil enhancement and the mitigation of diseases and weed abundance. Nevertheless, the specific mechanisms behind these advantages are unclear. Accordingly, we aimed to clarify the influence of DT on rhizosphere soil (RS) microbial communities and its possible contribution to the improvement of soil quality. Soil fertility was evaluated by analyzing several soil characteristics. High-throughput sequencing techniques were utilized to explore the structure and function of rhizosphere microbial communities. Despite lowered fertility levels in the 0-20 cm DT soil layer, significant variations were noted in the microbial composition of the DT wheat rhizosphere, with Acidobacteria and Proteobacteria being the most prominent. Furthermore, the abundance of Bradyrhizobacteria, a nitrogen-fixing bacteria within the Proteobacteria phylum, was significantly increased. A significant increase in glycoside hydrolases within the DT group was observed, in addition to higher abundances of amino acid and carbohydrate metabolism genes in the COG and KEGG databases. Moreover, DT can enhance soil quality and boost crop productivity by modulating soil microorganisms' carbon and nitrogen fixation capacities.

Effects of Deep Tillage on Wheat Regarding Soil Fertility and Rhizosphere Microbial Community

Wheat production is intrinsically linked to global food security. However, wheat cultivation is constrained by the progressive degradation of soil conditions resulting from the continuous application of fertilizers. This study aimed to examine the effects of deep tillage on rhizosphere soil microbial communities and their potential role in improving soil quality, given that the specific mechanisms driving these observed benefits remain unclear. Soil fertility in this research was evaluated through the analysis of various soil parameters, including total nitrogen, total phosphorus, total potassium, available phosphorus, and available potassium, among others. The high-throughput sequencing technique was utilized to examine the rhizosphere microbial community associated with deep tillage wheat. The findings indicated that deep tillage cultivation of wheat led to reduced fertility levels in the 0-20 cm soil layer in comparison with non-deep tillage cultivation. A sequencing analysis indicated that Acidobacteria and Proteobacteria are the dominant bacterial phyla, with Proteobacteria being significantly more abundant in the deep tillage group. The dominant fungal phyla identified were Ascomycota, Mortierellomycota, and Basidiomycota. Among bacterial genera, Arthrobacter, Bacillus, and Nocardioides were predominant, with Arthrobacter showing a significantly higher presence in the deep tillage group. The predominant fungal genera included Mortierella, Alternaria, Schizothecium, and Cladosporium. Deep tillage cultivation has the potential to enhance soil quality and boost crop productivity through the modulation of soil microbial community structure.

Insights into starch synthesis and amino acid composition of common buckwheat in response to phosphate fertilizer management strategies

To investigate the response and the regulatory mechanism of common buckwheat starch, amylose, and amylopectin biosynthesis to P management strategies, field experiments were conducted in 2021 and 2022 using three phosphorus (P) levels. Results revealed that the application of 75 kg hm-2 phosphate fertilizer significantly enhanced amylopectin and total starch content in common buckwheat, leading to improved grain weight and starch yield, and decreased starch granule size. The number of upregulated differentially expressed proteins induced by phosphate fertilizer increased with the application rate, with 56 proteins identified as shared differential proteins between different P levels, primarily associated with carbohydrate and amino acid metabolism. Phosphate fertilizer inhibited amylose synthesis by downregulating granule-bound starch synthase protein expression and promoted amylopectin accumulation by upregulating 1,4-alpha-glucan branching enzyme and starch synthase proteins expression. Additionally, Phosphate fertilizer primarily promoted the accumulation of hydrophobic and essential amino acids. These findings elucidate the mechanism of P-induced starch accumulation and offer insights into phosphate fertilizer management and high-quality cultivation of common buckwheat.

Effect of Different Fertilizer Types on Quality of Foxtail Millet under Low Nitrogen Conditions

In order to clarify the effect of different fertilizers on foxtail millet quality under low nitrogen conditions, we used JGNo.21 and LZGNo.2 as experimental materials and set up five treatments, including non-fertilization, nitrogen, phosphorus, compound, and organic fertilizers, to study the regulation of different fertilizer types on agronomic traits, nutrient fractions, and pasting characteristics of foxtail millet under low nitrogen conditions. Compared with the control, all of the fertilizers improved the agronomic traits of JGNo.21 to a certain extent. Nitrogen and compound fertilizer treatments reduced the starch content of JGNo.21; the starch content was reduced by 0.55% and 0.07% under nitrogen and compound fertilizers treatments. Phosphorus and organic fertilizers increased starch content, and starch content increased by 0.50% and 0.56% under phosphorus and organic fertilizer treatments. The effect of each fertilizer treatment on protein content was completely opposite to that of starch; different fertilizer treatments reduced the fat content of JGNo.21 and increased the fiber content. Among them, nitrogen and phosphorus fertilizers increased the yellow pigment content; the yellow pigment content increased by 1.21% and 2.64% under nitrogen and phosphorus fertilizer treatments. Organic and compound fertilizers reduced the content of yellow pigment; the yellow pigment content was reduced by 3.36% and 2.79% under organic and compound fertilizer treatments. Nitrogen and organic fertilizers increased the fat content of LZGNo.2; the fat content increased by 2.62% and 1.98% under nitrogen, organic fertilizer treatment. Compound and phosphorus fertilizer decreased the fat content; the fat content decreased by 2.16% and 2.90% under compound and phosphorus fertilizer treatment. Different fertilizer treatments reduced the cellulose and yellow pigment content of LZGNo.2. The content of essential, non-essential, and total amino acids of JGNo.21 was increased under compound and nitrogen fertilizer treatments and decreased under organic and phosphorus fertilizer treatments. The content of essential, non-essential, and total amino acids of LZGNo.2 was significantly higher under compound, nitrogen, and organic fertilizer treatments compared with control and significantly decreased under phosphorus fertilizer treatments. Nitrogen and compound fertilizer treatments significantly reduced the values of peak viscosity, trough viscosity, breakdown viscosity, final viscosity, setback viscosity, and pasting time of each index of JGNo.21; phosphorus and organic fertilizer treatments improved the values of each index. In contrast, the pasting viscosity of LZGNo.2 increased under phosphorus fertilizer treatment and decreased under nitrogen fertilizer treatment. Reasonable fertilization can improve the quality of foxtail millet, which provides a scientific theoretical basis for improving the quality of foxtail millet.

Speciation analysis and formation mechanism of iron-phosphorus compounds during chemical phosphorus removal process

Iron (Fe) salt was applied extensively to remove phosphorus (P) in wastewater treatment plants (WWTPs). Exploring the formation mechanism of iron-phosphorus compounds (FePs) during the chemical P removal (CPR) process is beneficial to P recovery. In this study, the performance of P removal, FePs speciation analysis and the kinetics of P removal under different conditions (pH, Fe/P molar ratio (Fe/P_mol), type of Fe salt, dissolved organic matters) were comprehensively investigated. More than 95% of P was removed under the optimal conditions with pH = 4.7, Fe/P_mol = 2, FeCl₃ or polymeric ferric sulfate (PFS) as the coagulant. The FePs formation mechanism was considerably influenced by reaction conditions. Iron-phosphate compounds were the dominant FePs species (>76%) at pH < 6.2, while more iron oxides were formed at pH ≥ 6.2 with decreased P removal efficiency. When the initial Fe/P_mol was 2, iron-phosphate compound was the only product that was formed by the reaction between PO₄^3- and Fe(III) or Fe(II) ions directly. More iron oxides were generated when the initial Fe/P_mol was 1 or 3. At Fe/P_mol = 1, the Fe(III) was hydrolyzed to form iron oxides and trapped PO₄^3-, while at Fe/P_mol = 3, iron-phosphate compounds were produced firstly and the remaining Fe(III) was hydrolyzed to form iron oxides. The pseudo-second-order kinetic model simulated the chemical P removal process well. The reaction rate of P with Fe(II) was slower than that with Fe(III), but complete removal was still achieved when the reaction time was more than 30 min. Poly-Fe salt exhibited a fast P removal rate, while the removal efficiency depended on its iron content. Organic matters in wastewater with large molecular weight and multiple functional groups (such as humic acids) inhibited P removal rate but hardly affect the removal amount. This study provides an insight into CPR by Fe salts and is beneficial for P recovery in WWTPs.

Heat Stress Tolerance 2 confers basal heat stress tolerance in allohexaploid wheat (Triticum aestivum L.)

Heat stress substantially reduces the yield potential of wheat (Triticum aestivum L.), one of the most widely cultivated staple crops, and greatly threatens global food security in the context of global warming. However, few studies have explored the heat stress tolerance (HST)-related genetic resources in wheat. Here, we identified and fine-mapped a wheat HST locus, TaHST2, which is indispensable for HST in both the vegetative and reproductive stages of the wheat life cycle. The studied pair of near isogenic lines (NILs) exhibited diverse morphologies under heat stress, based on which we mapped TaHST2 to a 485 kb interval on chromosome arm 4DS. Under heat stress, TaHST2 confers a superior conversion rate from soluble sugars to starch in wheat grains, resulting in faster grain filling and a higher yield potential. A further exploration of genetic resources indicated that TaHST2 underwent strong artificial selection during wheat domestication, suggesting it is an essential locus for basal HST in wheat. Our findings provide deeper insights into the genetic basis of wheat HST and might be useful for global efforts to breed heat-stress-tolerant cultivars.

Double zero tillage and foliar phosphorus fertilization coupled with microbial inoculants enhance maize productivity and quality in a maize-wheat rotation

Maize is an important industrial crop where yield and quality enhancement both assume greater importance. Clean production technologies like conservation agriculture and integrated nutrient management hold the key to enhance productivity and quality besides improving soil health and environment. Hence, maize productivity and quality were assessed under a maize-wheat cropping system (MWCS) using four crop-establishment and tillage management practices [FBCT-FBCT (Flat bed-conventional tillage both in maize and wheat); RBCT-RBZT (Raised bed-CT in maize and raised bed-zero tillage in wheat); FBZT-FBZT (FBZT both in maize and wheat); PRBZT-PRBZT (Permanent raised bed-ZT both in maize and wheat], and five P-fertilization practices [P100 (100% soil applied-P); P50 + 2FSP (50% soil applied-P + 2 foliar-sprays of P through 2% DAP both in maize and wheat); P50 + PSB + AM-fungi; P50 + PSB + AMF + 2FSP; and P0 (100% NK with no-P)] in split-plot design replicated-thrice. Double zero-tilled PRBZT-PRBZT system significantly enhanced the maize grain, starch, protein and oil yield by 13.1-19% over conventional FBCT-FBCT. P50 + PSB + AMF + 2FSP, integrating soil applied-P, microbial-inoculants and foliar-P, had significantly higher grain, starch, protein and oil yield by 12.5-17.2% over P100 besides saving 34.7% fertilizer-P both in maize and on cropping-system basis. P50 + PSB + AMF + 2FSP again had significantly higher starch, lysine and tryptophan content by 4.6-10.4% over P100 due to sustained and synchronized P-bioavailability. Higher amylose content (24.1%) was observed in grains under P50 + PSB + AMF + 2FSP, a beneficial trait due to its lower glycemic-index highly required for diabetic patients, where current COVID-19 pandemic further necessitated the use of such dietary ingredients. Double zero-tilled PRBZT-PRBZT reported greater MUFA (oleic acid, 37.1%), MUFA: PUFA ratio and P/S index with 6.9% higher P/S index in corn-oil (an oil quality parameter highly required for heart-health) over RBCT-RBCT. MUFA, MUFA: PUFA ratio and P/S index were also higher under P50 + PSB + AMF + 2FSP; avowing the obvious role of foliar-P and microbial-inoculants in influencing maize fatty acid composition. Overall, double zero-tilled PRBZT-PRBZT with crop residue retention at 6 t/ha per year along with P50 + PSB + AMF + 2FSP while saving 34.7% fertilizer-P in MWCS, may prove beneficial in enhancing maize productivity and quality so as to reinforce the food and nutritional security besides boosting food, corn-oil and starch industry in south-Asia and collateral arid agro-ecologies across the globe.

Nitrogen and potassium synergism influences the yield and quality of Dioscorea cayennensis

Abstract This study aimed to evaluate yield, quality, nematode incidence, chlorophyll content, and primary foliar macronutrients of yam in response to nitrogen and potassium fertilization. A complete randomized block design was used in a factorial scheme (5 x 5), with five nitrogen (0; 60; 120; 180 and 240 kg ha-1 of N) and five potassium doses (0; 60; 120; 180 and 240 kg ha-1 of K2O), with four replicates. The mass, total and commercial productivity of tubers, starch content, ash, leaf N, P, and K content, chlorophyll, and nematode incidence were evaluated. The average mass of tubers obtained was 1.935 kg with doses of 133 kg ha-1 of N and 105 kg ha-1 of K2O. The dose of 178 kg ha-1 of N promoted maximum total tuber productivity (22.56 t ha-1). The doses of 132 kg ha-1 of N and 118 kg ha-1 of K2O resulted in maximum productivity of commercial tubers with 20.35 t ha-1. Leaf N and K, starch, and ash contents were within the standards for yam. The incidence of Meloidogyne, Scutellonema, and Pratylenchus reduced with the increasing simple effect doses of N and K2O. The maximum chlorophyll content was obtained at the dose of 240 kg ha-1 of N. The nitrogen and potassium interaction, despite the antagonistic effects on the accumulation of foliar P and starch, increased the productivity and average mass of commercial tubers, consequently ensuring the profitability of yam cultivation.

Unmodified cassava starches with high phosphorus content

Our study was based on the fact that physiological changes in the plant resulting from the growth conditions alter the properties of the starch. An experimental trial was installed with cassava plants in poor phosphorus soil. A part of plants received phosphate fertilization at a level three times higher than the recommended dose, in order to provide high availability of phosphorus in the soil. The plants grew for two years and the starches were isolated at three times in the second vegetative cycle. The starches had A-type X-ray pattern. Starches isolated from cassava plants grown in soils with high phosphorus had increases of more than 100% in the content of bound phosphorus, which caused changes in the size of the granules, amylose, swelling power, solubility, pasting and thermal properties. These results indicate possibilities of increasing the commercial value of native cassava starch due to the expansion of use, considering the range of uses of phosphate starches for food and non-food purposes.

Use of Meat Industry Waste in the Form of Meat-and-Bone Meal in Fertilising Maize (Zea mays L.) for Grain

The processing of meat industry waste into meat-and-bone meal (MBM) provides the opportunity to use it as fertiliser in the cultivation of agricultural crops. This study was conducted in the years 2014–2017 at the Experimental Station in Tomaszkowo, Poland to assess MBM effects on yield and quality of maize cultivated for grain. An example of the effective use of nutrients contained in MBM applied at doses of 2.0 and 3.0 t ha is the cultivation of maize in 2016, which was affected by favourable weather conditions. The effect of the accumulation of MBM doses and, consequently, the provision of a greater amount of nutrients ensure sufficient amounts to obtain yields, greater than those provided by mineral fertilisation only. The macronutrient concentration in the maize grains following the application of MBM was similar to the composition of the grains of maize fertilised with mineral N, P and K fertilisers. With the MBM, micronutrients are introduced in amounts that are able to satisfy plants with these components, yet this study failed to demonstrate any effect of increased MBM doses on the concentration of the analysed elements in the maize grains.

Metabolite alteration in response to low phosphorus stress in developing tomato fruits

Alteration of fruit quality caused by environmental stress is a common but largely unresolved issue for plant cultivation and breeding practices. Phosphorus (P) deficiency may interfere with a variety of metabolic processes whose intermediate products are correlated with important fruit quality traits. However, how low P stress affects fruit quality has not been investigated in detail. In this study, we assessed the contents of major metabolites associated with tomato fruit quality under two low P treatments that started at the seedling or flowering stage. The major pigments and the key organic acids related to fruit sourness were differentially over-accumulated as fruit ripened under two low P treatments compared to those under the control treatment, while the total content of soluble sugars contributing to fruit sweetness was substantially reduced under both treatments. These changes were largely attributed to the alteration of enzyme activities in the relevant metabolic pathways. In particular, we found that low P stress from different developmental stages had differential effects on the activation of γ-aminobutyric acid shunt that were likely responsible for the preferential accumulation of different organic acids in tomato fruits. Our study suggested that low P stress strongly affected tomato fruit quality and the effects appeared to be variable under different regimes of low P conditions.

Late-maturity α-amylase expression in wheat is influenced by genotype, temperature and stage of grain development

Late-maturity α-amylase (LMA) expression in wheat grains can be induced by either a cool temperature shock close to physiological maturity or continuous cool maximum temperatures during grain development. Late-maturity α-amylase (LMA) is a genetic trait in wheat (Triticum aestivum L.) involving the production of α-amylase during grain development, which can result in an unacceptably low Falling Number (FN) in mature grain and consequent grain downgrading. Comparison of the FN test, an α-amylase activity assay and a high pI α-amylase-specific ELISA on the same meal samples gave equivalent results; ELISA was used for further experiments because of its isoform specificity. A cool temperature shock during the middle stages of grain development is known to induce LMA and is used for phenotypic screening. It was determined that a cool temperature treatment of seven days was required to reliably induce LMA. Glasshouse studies performed in summer and winter demonstrated that temperature affected the timing of sensitivity to cool-shock by altering the rate and duration of grain development, but that the sensitive grain developmental stage was unchanged at 35-45% moisture content. Wheat varieties with Rht-B1b or Rht-D1b dwarfing genes responded to a cool-shock only from mid grain filling until physiological maturity, whilst genotypes with Rht8c or without a dwarfing gene expressed LMA in response to a cool-shock during a wider developmental range. A continuous cool maximum temperature regimen (23 °C/15 °C day/night) during grain development also resulted in LMA expression and showed a stronger association with field expression than the cool-shock treatment. These results clarify how genotype, temperature and grain developmental stage determine LMA expression, and allow for the improvement of LMA phenotypic screening methods.

Key factors identified by proteomic analysis in maize (Zea mays L.) seedlings' response to long-term exposure to different phosphate levels

Background

Maize seedlings are constantly exposed to inorganic phosphate (Pi)-limited environments. To understand how maize cope with low Pi (LP) and high Pi (HP) conditions, physiological and global proteomic analysis of QXN233 genotype were performed under the long-term Pi starvation and supplementation.

Methods

We investigated the physiological response of QXN233 genotype to LP and HP conditions and detected the changes in ion fluxes by non-invasive micro-test technology and gene expression by quantitative real-time polymerase chain reaction. QXN233 was further assessed using vermiculite assay, and then proteins were isolated and identified by nano-liquid chromatography-mass spectrometry.

Results

A negative relationship was observed between Na⁺ and Pi, and Na⁺ efflux was enhanced under HP condition. Furthermore, a total of 681 and 1374 were identified in the leaves and roots, respectively, which were mostly involved in metabolism, ion transport, and stress response. Importantly, several key Pi transporters were identified for breeding potential. Several ion transporters demonstrated an elaborate interplay between Pi and other ions, together contributing to the growth of QXN233 seedlings.

Conclusion

The results from this study provide insights into the response of maize seedlings to long-term Pi exposure.

Electronic supplementary material

The online version of this article (10.1186/s12953-018-0147-3) contains supplementary material, which is available to authorized users.

Phosphorus Enhances Photosynthetic Storage Starch Production in a Green Microalga (Chlorophyta) Tetraselmis subcordiformis in Nitrogen Starvation Conditions

Microalgae are potential starch producers as alternatives to agricultural crops. This study disclosed the effects and mechanism of phosphorus availability exerted on storage starch production in a starch-producing microalga Tetraselmis subcordiformis in nitrogen starvation conditions. Excessive phosphorus supply facilitated starch production, which differed from the conventional cognition that phosphorus would inhibit transitory starch biosynthesis in plants. Phosphorus enhanced energy utilization efficiency for biomass and storage starch production. ADP-glucose pyrophosphorylase (AGPase), conventionally known to be critical for starch biosynthesis, was negatively correlated to storage starch biosynthesis. Excessive phosphorus supply maintained large cell volumes, enhanced activities of starch phosphorylases (SPs) along with branching enzymes and isoamylases, and increased phosphoenolpyruvate and trehalose-6-phosphate levels to alleviate the inhibition of high phosphate availability to AGPase, all of which improved starch production. This work highlighted the importance of phosphorus in the production of microalgal starch and provided further evidence for the SP-based storage starch biosynthesis pathway.