Low Phosphorus Conditions Research Articles

Inoculation of arbuscular mycorrhizal fungi and phosphorus addition increase coarse mint (Plectranthus amboinicus Lour.) plant growth and essential oil content

The coarse mint (Plectranthus amboinicus Lour.) is a medicinal plant that produces essential oil; however, it is still little studied the effects of effects of arbuscular mycorrhizal fungi species on growth and essential oil content and its composition in P. amboinicus. Therefore, this study aimed to evaluate Rhizophagus clarus and Claroideoglomus etunicatum under low and high phosphorus conditions and its effects in plant growth and the essential oil content and chemical composition in coarse mint. The experimental design was completely randomized with 8 replicates per treatment in a 3 × 2 factorial (without and with two arbuscular mycorrhizal fungi, two levels of phosphorus (at 20 or 200 mg dm−3 of substrate). We evaluated spore density in the substrate and root colonization by arbuscular mycorrhizal fungi, an also shoot and root phosphorus content and nitrogen in the shoots, plant growth, essential oil content and its chemical composition. Spore density and root colonization by arbuscular mycorrhizal fungi were higher in the inoculated treatments. The shoot dry matter, root dry matter and total dry matter increased with arbuscular mycorrhizal fungi inoculation, mainly with the inoculation of R. clarus and high addition of phosphorus to the substrate. Inoculation of arbuscular mycorrhizal fungi and/or the addition of phosphorus in the substrate increased phosphorus and nitrogen content in the plant. The essential oil content was higher with R. clarus and with low phosphorus addition (0.61%) and 18 compounds were identified in essential oil, being carvacrol (38.48–51.07%), followed by trans-Caryophyllene, α-Bergamotene and α-Humulene the major constituents. It was concluded that plant growth increased with R. clarus inoculation and high phosphorus condition and R. clarus inoculation increased essential oil content.

Effect of pH and prior treatment with phosphate on the rate and amount of reaction of soils with phosphate

AbstractThe rate at which phosphate continues to react with soil is an important determinant of its effectiveness as a fertiliser. Yet it has seldom been measured and we do not know which soil properties affect its value. Here, the effects of electric charge are investigated. The charge of a low phosphorus status soil was changed both by changing the soil pH by incubation with acid or alkali for 2 days at 60°C, and also by adding phosphate and incubating for 30 days at 80°C. The amount and rate of reaction of further additions of phosphate were then measured after periods of 1, 3, 10 and 30 days of incubation at 25°C. Prior reaction with phosphate greatly decreased both the amount and the rate of sorption of subsequent additions. We think this is one factor causing differences between soils in the rate of reaction. Changing the pH had smaller effects on the amount and rate of reaction. We think the effects on rate of reaction were caused by changing the pH rather than the pH itself. The effects of changed pH and of phosphate treatment were closely described by a mechanistic model, with the effects on amount of sorption described by varying the electric potential and the effects on rate of reaction described by varying the rate of diffusion. The two methods of changing the charge have differing effects on both the amount and rate of reaction and we discuss the reasons for these differences.Highlights The rate at which phosphate continues to react with soil is an important determinant of its effectiveness as a fertiliser. Loading with phosphate greatly decreased both the amount and the rate of sorption of subsequent additions. Changing the pH had smaller effects. Results were closely described by a mechanistic model. Phosphate status is an important cause of differences between soils in the rate of reaction.

GmPAP12 Is Required for Nodule Development and Nitrogen Fixation Under Phosphorus Starvation in Soybean.

Nodulation process in legume plants is essential for biological nitrogen fixation during which process a large amount of phosphorus (P) is required. Under P deficiency, nodule formation is greatly affected, and induction of purple acid phosphatases (PAPs) is an adaptive strategy for nodules to acquire more P. However, regulation roles of PAPs in nodules remain largely understood. In this study, by transcriptome sequencing technology, five PAP genes were found to be differentially expressed, which led to the greatly increased acid phosphatase (APase) and phytase activities in soybean mature nodules under P starvation conditions; and among the five PAP genes, GmPAP12 had the highest transcript level, and RT-PCR indicated expression of GmPAP12 was gradually increasing during nodule development. GUS activity driven by GmPAP12 promoter was also significantly induced in low phosphorus conditions. Further functional analysis showed that under low phosphorus stress, overexpression of GmPAP12 resulted in higher nodule number, fresh weight, and nitrogenase activity as well as the APase activity than those of control plant nodules, whereas the growth performance and APase activity of nodules on hairy roots were greatly lower when GmPAP12 was suppressed, indicating that GmPAP12 may promote P utilization in soybean nodules under low P stress, which thus played an important role in nodulation and biological nitrogen fixation. Moreover, P1BS elements were found in the promoter of GmPAP12, and yeast one-hybrid experiment further proved the binding of P1BS by transcription factor GmPHR1 in the promoter of GmPAP12. At last, overexpression and suppression of GmPHR1 in nodules indeed caused highly increased and decreased expression of GmPAP12, respectively, indicating that GmPAP12 is regulated by GmPHR1 in soybean nodules. Taken together, these data suggested that GmPAP12 was a novel soybean PAP involved in the P utilization and metabolism in soybean root nodules and played an important role in the growth and development of root nodules and biological nitrogen fixation.

Relationship between Adaptability of Rice to Low Phosphorus Conditions and Arbuscular Mycorrhizal Fungi Colonization in Kenya

Relationship between Adaptability of Rice to Low Phosphorus Conditions and Arbuscular Mycorrhizal Fungi Colonization in Kenya

Characterisation of genes involved in galactolipids and sulfolipids metabolism in maize and Arabidopsis and their differential responses to phosphate deficiency.

Galactolipids (MGDG and DGDG) and sulfolipids (SQDG) are key components of plastidic membranes, and play important roles in plant development and photosynthesis. In this study, the whole families of MGD, DGD and SQD were identified in maize genome, and were designated as ZmMGD1-3, ZmDGD1-5 and ZmSQD1-5 respectively. Based on the phylogenetic analyses, maize and Arabidopsis MGDs, DGDs and SQDs were clearly divided into two major categories (Type A and Type B) along with their orthologous genes from other plant species. Under low-phosphorus condition, the expression of Type B MGD, DGD and SQD genes of maize and Arabidopsis were significantly elevated in both leaf and root tissues. The lipid analysis was also conducted, and an overall increase in non-phosphorus lipids (MGDG, DGDG and SQDG), and a decrease in phosphorus lipids (PC, PE and PA) were observed in maize leaves and roots under phosphate deficiency. Several maize MGD and SQD genes were found involved in various abiotic stress responses. These findings will help for better understanding the specific functions of MGDs, DGDs and SQDs in 18:3 plants and for the generation of improved crops adapted to phosphate starvation and other abiotic stresses.

Genetic Diversification and Selection Strategies for Improving Sorghum Grain Yield Under Phosphorous-Deficient Conditions in West Africa

Sorghum, a major crop for income generation and food security in West and Central Africa, is predominantly grown in low-input farming systems with serious soil phosphorus (P) deficiencies. This study (a) estimates genetic parameters needed to design selection protocols that optimize genetic gains for yield under low-phosphorus conditions and (b) examines the utility of introgressed backcross nested association mapping (BCNAM) populations for diversifying Malian breeding materials. A total of 1083 BC1F5 progenies derived from an elite hybrid restorer “Lata-3” and 13 diverse donor accessions were evaluated for yield and agronomic traits under contrasting soil P conditions in Mali in 2013. A subset of 298 progenies were further tested under low-P (LP) and high-P (HP) conditions in 2014 and 2015. Significant genetic variation for grain yield was observed under LP and HP conditions. Selection for grain yield under LP conditions was feasible and more efficient than the indirect selection under HP in all three years of testing. Several of the BCNAM populations exhibited yields under LP conditions that were superior to the elite restorer line used as a recurrent parent. The BCNAM approach appears promising for diversifying the male parent pool with introgression of diverse materials using both adapted Malian breed and unadapted landrace material from distant geographic origins as donors.

PHOSPHORUS SORPTION KINETIC ON ACID UPLAND SMECTITIC SOIL AMENDED WITH CALCIUM CARBONATE AND CALCIUM SILICATE

Acid upland smectitic soil is identified by high amount of exchangeable Al due to the weathering of aluminum (Al) octahedral layer by H+ saturation and by very low phosphorus (P) status. Calcium carbonate (CaCO3) and calcium silicate (CaSiO3) were commonly used to decrease exchangeable Al and increase soil pH. Laboratory experiments were conducted with clayey smectitic Typic Paleudults from Gajrug region, West Java. The CaCO3 and CaSiO3 were added at rates to replace 0, 1.5 or 3 times of exchangeable Al. After one month of incubation, P sorption kinetic experiments were conducted. The changes in some chemical properties after one month incubation showed that both CaCO3 and CaSiO3 increased the soil pH, exchangeable Ca, and base saturation but did not increase the cation exchange capacity. The results of the experiment showed that both CaCO3 and CaSiO3 decreased the rate constant value of first order kinetic equation (k) and the P sorbed maximum (a) at given amount of added P compared to Control.The CaCO3 was better than CaSiO3 in decreasing k values and on the contrary for a values. The decrease in P maximum sorption and the rate constant of the soil amended with CaSiO3 and CaCO3 due to occupation of P sorption sites by silicates and hydroxyl ions. The CaCO3with the rate to replace 1.5 x exchangeable Al was recommended to decrease the rate constant of P sorption. However, the CaSiO3 at the rate to replace 3 x exchangeable Al was recommended to decrease the maximum P sorption.

Formation mechanism of the Microcystis aeruginosa bloom in the water with low dissolved phosphorus.

The utilization of phosphorus by algae in the low-phosphorus state has drawn wide concerns due to the high risk of forming algal blooms. The cyanobacteria Microcystis aeruginosa (M. aeruginosa) grew well under low-phosphorus condition by hydrolyzing dissolved organic phosphorus (DOP) to dissolved inorganic phosphorus (DIP) through alkaline phosphatase (AP). There was a negative correlation between DIP concentration and AP activity of algae. AP activity significantly increased at 0-3 d (p < 0.05), and reached the peak values of 43.06 and 49.11 King unit/gprot on day 5 for DIP (0.1 mg/L) and DOP (4.0 mg/L), respectively. The relative expression of phosphate transporter gene increased with decreasing phosphorus concentrations. The catalase activity under low-phosphorus condition increased significantly (p < 0.05) after one week, and was generally higher than 0.15 U/mgprot on day 14. Understanding the utilization efficiency and mechanism of DIP and DOP in the low-phosphorus state would help to inhibit the formation of algal blooms.

Impacts of soil nitrogen and phosphorus levels on cytotype performance of the circumboreal herb Chamerion angustifolium: implications for polyploid establishment.

Although polyploidy commonly occurs in angiosperms, not all polyploidization events lead to successful lineages, and environmental conditions could influence cytotype dynamics and polyploid success. Low soil nitrogen and/or phosphorus concentrations often limit ecosystem primary productivity, and changes in these nutrients might differentially favor some cytotypes over others, thereby influencing polyploid establishment. We grew diploid, established tetraploid, and neotetraploid Chamerion angustifolium (fireweed) in a greenhouse under low and high soil nitrogen and phosphorus conditions and different competition treatments and measured plant performance (height, biomass, flower production, and root bud production) and insect damage responses. By comparing neotetraploids to established tetraploids, we were able to examine traits and responses that might directly arise from polyploidization before they are modified by natural selection and/or genetic drift. We found that (1) neopolyploids were the least likely to survive and flower and experienced the most herbivore damage, regardless of nutrient conditions; (2) both neo- and established tetraploids had greater biomass and root bud production under nutrient-enriched conditions, whereas diploid biomass and root bud production was not significantly affected by nutrients; and (3) intra-cytotype competition more negatively affected diploids and established tetraploids than it did neotetraploids. Following polyploidization, biomass and clonal growth might be more immediately affected by environmental nutrient availabilities than plant survival, flowering, and/or responses to herbivory, which could influence competitive dynamics. Specifically, polyploids might have competitive and colonizing advantages over diploids under nutrient-enriched conditions favoring their establishment, although establishment may also depend upon the density and occurrences of other related cytotypes in a population.

Reaction of popcorn lines (s7) cultivated in distinct phosphorus levels to Bipolaris maydis infection

ABSTRACT Popcorn culture is highly susceptible to helminthosporiosis (Bipolaris maydis) (h-Bm). The genetic breeding of this culture should prioritize resistance to h-Bm and develop cultivars that offer greater crop sustainability, especially in soils with phosphorus (P) scarcity. P-mineral is usually supplied to maize culture by the application of phosphate fertilizers, which are produced from mineral sources rich in P, the natural reserves of which will be depleted in the medium term. With the aim of selecting popcorn genotypes resistant to h-Bm and with higher P utilization capacity, the present study evaluated h-Bm incidence and severity for 25 popcorn lines (S7) cultivated under high and low phosphorus conditions. There was a significant interaction between genotype (lines) and P fertilization for h-Bm resistance, expressed as disease severity values in the first ear leaf. There was genetic variability for disease resistance. The incidence analysis identifies the lines L-65 L-69, L-70 and L-76 as potentially resistant genotypes, presenting low mean values of h-Bm. The severity analysis, however, presents L-69, L-76, P-3 and P-7 genotypes as potentially resistant in environments with fertilization and without fertilization. The obtained data show that the lines L-69 and L-76 had the best resistance performance in both environments. The genetic resistance to h-Bm can somehow correlate with the response to P fertilization at planting in soils with low natural fertility.

Estimating the importance of maize root hairs in low phosphorus conditions and under drought.

Root hairs are single-cell extensions of the epidermis that face into the soil and increase the root-soil contact surface. Root hairs enlarge the rhizosphere radially and are very important for taking up water and sparingly soluble nutrients, such as the poorly soil-mobile phosphate. In order to quantify the importance of root hairs for maize, a mutant and the corresponding wild type were compared. The rth2 maize mutant with very short root hairs was assayed for growth and phosphorus (P) acquisition in a slightly alkaline soil with low P and limited water supply in the absence of mycorrhization and with ample P supply. Root and shoot growth was additively impaired under P deficiency and drought. Internal P concentrations declined with reduced water and P supply, whereas micronutrients (iron, zinc) were little affected. The very short root hairs in rth2 did not affect internal P concentrations, but the P content of juvenile plants was halved under combined stress. The rth2 plants had more fine roots and increased specific root length, but P mobilization traits (root organic carbon and phosphatase exudation) differed little. The results confirm the importance of root hairs for maize P uptake and content, but not for internal P concentrations. Furthermore, the performance of root hair mutants may be biased by secondary effects, such as altered root growth.

Relationship between volatile organic compounds released and growth of Cunninghamia lanceolata roots under low-phosphorus conditions

To understand whether Chinese fir (Cunninghamia lanceolata) can conserve energy by reducing root volatiles to maintain growth under low phosphorus (P) conditions, we cultivated two half-sib families of Chinese fir that display high and low P use efficiency under conditions of normal P supply and total P deficiency. Gas chromatography-mass spectrometry analysis was used to determine the content of root volatiles, and the relationships among root volatiles and root growth index, P content, and distribution were analyzed. There were significantly fewer volatile organic compounds (VOCs) in the rhizosphere of these two fir families, No. 25 and No. 32, under P deficiency. Low P supply significantly promoted root growth in No. 25, increasing both average diameter and volume. A negative correlation was found between the volatiles and the increment of root average diameter and surface area. The belowground P distribution and the root to shoot P concentration (Pr/Ps) were higher in No. 25 than in No. 32. The total amount of VOCs, as well as the amount of 18 individual volatiles were positively correlated with P accumulation, aboveground P distribution, and belowground P distribution, but the opposite pattern was seen in Pr/Ps for family No. 25 seedlings. We conclude that the content and types of VOCs differ among the Chinese fir genotypes. Under low-P stress, the roots of Chinese fir reduce the release of VOCs to maintain seedling growth.

Interactions between Microcystis aeruginosa and coexisting bisphenol A at different phosphorus levels

Microcystis aeruginosa is known as the main contributor to cyanobacterial bloom, which is prevalent globally and degrades freshwater systems worldwide. The argument that the introduction of anthropogenic contaminants in fresh water stimulates cyanobacterial growth and microcystin production has attracted widespread attention. Bisphenol A (BPA), one of the most abundant endocrine-disrupting compounds, is often detected in various water bodies due to its notably high annual levels of production and use. Research on the combined effects of endocrine-disrupting compounds and environmental factors on cyanobacteria remains limited. To investigate the mechanism of interactions between contaminants and cyanobacteria at the cellular and proteomic levels, the growth rate, chlorophyll-a content, photosynthetic activities, microcystin-LR (MC-LR) production and release, reactive oxygen species (ROS) content, superoxide dismutase (SOD) activities, malondialdehyde (MDA) content, and proteome expression of M. aeruginosa under 1 μM BPA stress at a standard phosphorus level were investigated. The results showed that stress responses to BPA included increases in the growth rate, chlorophyll-a content, and Fv/Fm and rETRmax values under the low phosphorus condition. Responses involving ROS, SOD, and MDA indicated that phosphorus sufficiency and BPA caused oxidative stress in M. aeruginosa. Moreover, phosphorus sufficiency and BPA stimulated the production and release of MCs. Compared to levels in the non-BPA-treated group, exposure of M. aeruginosa to BPA caused 72 up-regulated proteins, which were primarily associated with photosynthesis, ribosome, fatty acid biosynthesis, glycolysis/glyconeogenesis, and carbon fixation in photosynthetic organisms. The 105 down-regulated proteins were related to quorum sensing, base excision repair, ABC transporters, longevity regulating and cell cycle-caulobacter, suggesting that the cytotoxicity of cyanobacterial cells induced by BPA was significantly increased. These findings provide insights into the molecular mechanism of the effects of BPA and phosphorus on M. aeruginosa, suggesting that coexisting pollutants may cause greater harm to and health risks in the environment.

Expression analysis of three phosphate transporter genes in the fast-growing mutants of Gracilariopsis lemaneiformis (Rhodophyta) under low phosphorus condition

Three phosphate transporter (PHT) genes of Gracilariopsis lemaneiformis were cloned, and the expression patterns under different phosphate concentrations were analyzed. The phylogenetic analysis indicated that the amino acid sequence of GlPHT2 shared high identity with high-affinity PHT in many species. Meanwhile, GlPHT1 and GlPHT3 showed significant similarity to the low-affinity PHT sequences of other species. The results of expression patterns analysis showed that glpht2 was significantly upregulated when glpht1 remained expression stable under low-phosphorus treatment. The expression of glpht3 is positively correlated with the concentration of environmental phosphorus. Therefore, these results provided important evidence of the mechanism of Pi uptake and use in G. lemaneiformis. In addition, the low-phosphorus fast-growing mutant WLP-22 showed traits superiority in both growth and photosynthetic activity.

Genome-wide analysis of purple acid phosphatase (PAP) family proteins in Jatropha curcas L

Purple acid phosphatase (PAP) family genes play a crucial role in the phosphorus (P) foraging and recycling. There are 25 putative Jatropha curcas PAP genes (JcrPAP) were identified and classified into three groups based on their molecular weights. Subcellular localization prediction indicated that most of the JcrPAPs were localized to secretory pathway. Several PAPs possess signal peptide motifs and varied numbers of N-glycosylation and transmembrane helix motifs. JcrPAP proteins have 3–5 active pocket sites comprising 1 to 11 binding residues which interact with different ligands such as iron (Fe), N-acetyl l-d-Glucosamine (NAG), zinc (Zn) and manganese (Mn). The core structure of the predicted JcrPap28 was similar to the Ipomoea batatas Pap protein. Most of the JcrPAP genes showed higher expression in the root tissues compared to stem and leaf tissues. Several JcrPAP genes were upregulated under low phosphorus conditions. JcrPAP genes such as JcrPap26b, JcrPap27b, and JcrPap28 have shown multifold induction in low phosphorus treated plants which suggest that these genes might be involved in phosphorus metabolism. The present study provided the structural variations and expression regulation of JcrPAP genes in the economically viable biodiesel crop and it would be helpful for the crop improvement under phosphorus limiting conditions.

Greater lateral root branching density in maize improves phosphorus acquisition from low phosphorus soil.

The development of crops with better growth under suboptimal phosphorus availability would improve food security in developing countries while reducing environmental pollution in developed countries. We tested the hypothesis that maize (Zea mays) phenotypes with greater lateral root branching density have greater phosphorus acquisition from low phosphorus soils. Recombinant inbred lines with either 'many short' (MS) or 'few long' (FL) lateral root phenotypes were grown under high and low phosphorus conditions in greenhouse mesocosms and in the field. Under low phosphorus in mesocosms, lines with the MS phenotype had 89% greater phosphorus acquisition and 48% more shoot biomass than FL lines. Under low phosphorus in the field, MS lines had 16% shallower rooting depth (D95), 81% greater root length density in the top 20 cm of the soil, 49% greater shoot phosphorus content, 12% greater leaf photosynthesis, 19% greater shoot biomass, and 14% greater grain yield than FL lines. These results are consistent with the hypothesis that the phenotype of many, shorter lateral roots improves phosphorus acquisition under low phosphorus availability and merits consideration for genetic improvement of phosphorus efficiency in maize and other crops.

Acid phosphatase gene GmHAD1 linked to low phosphorus tolerance in soybean, through fine mapping.

Map-based cloning identified GmHAD1, a gene which encodes a HAD-like acid phosphatase, associated with soybean tolerance to low phosphorus stress. Phosphorus (P) deficiency in soils is a major limiting factor for crop growth worldwide. Plants may adapt to low phosphorus (LP) conditions via changes to root morphology, including the number, length, orientation, and branching of the principal root classes. To elucidate the genetic mechanisms for LP tolerance in soybean, quantitative trait loci (QTL) related to root morphology responses to LP were identified via hydroponic experiments. In total, we identified 14 major loci associated with these traits in a RIL population. The log-likelihood scores ranged from 2.81 to 7.43, explaining 4.23-13.98% of phenotypic variance. A major locus on chromosome 08, named qP8-2, was co-localized with an important P efficiency QTL (qPE8), containing phosphatase genes GmACP1 and GmACP2. Another major locus on chromosome 10 named qP10-2 explained 4.80-13.98% of the total phenotypic variance in root morphology. The qP10-2 contains GmHAD1, a gene which encodes an acid phosphatase. In the transgenic soybean hairy roots, GmHAD1 overexpression increased P efficiency by 8.4-16.5% relative to the control. Transgenic Arabidopsis plants had higher biomass than wild-type plants across both short- and long-term P reduction. These results suggest that GmHAD1, an acid phosphatase gene, improved the utilization of organic phosphate by soybean and Arabidopsis plants.

Sensitivity of different Lupinus species to calcium under a low phosphorus supply.

To study mechanism underpinning the calcifuge habit of some Lupinus species, especially under low-phosphorus (P) conditions, Lupinus species that were likely to respond differently to calcium (Ca) availability were assembled, and the sensitivity to Ca under a low-P supply was assessed. Seven Lupinus species (9 genotypes, L.albus L. cv Kiev, L.albus L. P26766, L.angustifolius L. cv Mandelup, L.angustifolius L. P26723, L.luteus L. cv Pootalong, L.hispanicus ssp. bicolor Boiss. and Reut. P22999, L.pilosus Murr. P27440, L.cosentinii Guss. P27225, and L.atlanticus Gladst. P27219) were grown hydroponically at 10 or 6000μM Ca. Leaf symptoms, gas exchange and biomass were recorded; leaf and root nutrient concentrations were analysed, and the leaf cell types in which Ca and P accumulated were determined using elemental X-ray microanalyses. Calcium toxicity was demonstrated for L.angustifolius P26723, L.hispanicus ssp. bicolor. P22999, and L.cosentinii P27225, whereas the other species were tolerant of a high Ca supply under low-P conditions. In addition, genotypic differences in Ca toxicity were found within L.angustifolius. Most Ca accumulated in the mesophyll cells in all species, whereas most P was located in epidermal cells.

Evaluation of the Relationship Between the 18S rRNA/rDNA Ratio and Population Growth in the Marine Diatom Skeletonema tropicum via the Application of an Exogenous Nucleic Acid Standard.

Ribosomal RNA (rRNA) has been regarded as a proxy for metabolic activity and population growth in microbes, but the limitations and assumptions of this approach should be better defined, particularly in eukaryotic microalgae. In this study, the 18S rRNA/rDNA ratio of a marine diatom, Skeletonema tropicum, was examined in batch and semi-continuous cultures subjected to low nitrogen and phosphorus treatments at a temperature of 20°C. In the semi-continuous cultures, the measured 18S rRNA/rDNA ratio ranged from 4.0×102 to 5.0×103 , and the logarithmic form of this ratio increased linearly with the population growth rate under both low nitrogen and low phosphorus conditions. In batch cultures grown under low nitrogen or low phosphorus conditions, log (rRNA/rDNA) also increased linearly with growth rate when the latter ranged between -0.4 and 1.5day-1 . The 18S rRNA/rDNA ratios of Skeletonema sampled from in the southern East China Sea were substantially lower than measured from laboratory cultures. Among the field samples, ratios obtained at a coastal station were higher than those obtained farther offshore. These results imply higher growth rate at the coastal station, but the influences of other factors, such as cell size and temperature, cannot be ruled out.

Molecular Mechanisms of Acclimatization to Phosphorus Starvation and Recovery Underlying Full-Length Transcriptome Profiling in Barley (Hordeum vulgare L.).

A lack of phosphorus (P) in plants can severely constrain growth and development. Barley, one of the earliest domesticated crops, is extensively planted in poor soil around the world. To date, the molecular mechanisms of enduring low phosphorus, at the transcriptional level, in barley are still unclear. In the present study, two different barley genotypes (GN121 and GN42)—with contrasting phosphorus efficiency—were used to reveal adaptations to low phosphorus stress, at three time points, at the morphological, physiological, biochemical, and transcriptome level. GN121 growth was less affected by phosphorus starvation and recovery than that of GN42. The biomass and inorganic phosphorus concentration of GN121 and GN42 declined under the low phosphorus-induced stress and increased after recovery with normal phosphorus. However, the range of these parameters was higher in GN42 than in GN121. Subsequently, a more complete genome annotation was obtained by correcting with the data sequenced on Illumina HiSeq X 10 and PacBio RSII SMRT platform. A total of 6,182 and 5,270 differentially expressed genes (DEGs) were identified in GN121 and GN42, respectively. The majority of these DEGs were involved in phosphorus metabolism such as phospholipid degradation, hydrolysis of phosphoric enzymes, sucrose synthesis, phosphorylation/dephosphorylation and post-transcriptional regulation; expression of these genes was significantly different between GN121 and GN42. Specifically, six and seven DEGs were annotated as phosphorus transporters in roots and leaves, respectively. Furthermore, a putative model was constructed relying on key metabolic pathways related to phosphorus to illustrate the higher phosphorus efficiency of GN121 compared to GN42 under low phosphorus conditions. Results from this study provide a multi-transcriptome database and candidate genes for further study on phosphorus use efficiency (PUE).