Interactive effects of phosphorus deficiency and exogenous auxin on root morphological and physiological traits in white lupin (Lupinus albus L.)

White lupin (Lupinus albus) exhibits strong root morphological and physiological responses to phosphorus (P) deficiency and auxin treatments, but the interactive effects of P and auxin in regulating root morphological and physiological traits are not fully understood. This study aimed to assess white lupin root traits as influenced by P (0 or 250 μmol L^?1) and auxin (10^?8 mol L^?1 NAA) in nutrient solution. Both P deficiency and auxin treatments significantly altered root morphological traits, as evidenced by reduced taproot length, increased number and density of first-order lateral roots, and enhanced cluster-root formation. Changes in root physiological traits were also observed, i.e., increased proton, citrate, and acid phosphatase exudation. Exogenous auxin enhanced root responses and sensitivity to P deficiency. A significant interplay exists between P and auxin in the regulation of root morphological and physiological traits. Principal component analysis showed that P availability explained 64.8% and auxin addition 21.3% of the total variation in root trait parameters, indicating that P availability is much more important than auxin in modifying root responses of white lupin. This suggests that white lupin can coordinate root morphological and physiological responses to enhance acquisition of P resources, with an optimal trade-off between root morphological and physiological traits regulated by external stimuli such as P availability and auxin.     

Localized application of NH4 +-N plus P at the seedling and later growth stages enhances nutrient uptake and maize yield by inducing lateral root proliferation

Background and aims

Localized supply of P plus ammonium improves root-proliferation and nutrient-uptake by maize (Zea mays L.) at seedling stage, but it is largely unknown how localized supply of nutrients at both early and late stages influences maize-growth, nutrient-uptake and grain-yield.

Methods

A 2-year field experimentation with maize was conducted with localized application of P plus ammonium as diammonium phosphate (LDAP) or ammonium sulfate plus P (LASP) at sowing or jointing stage, with broadcast urea and P (BURP) or no nitrogen (F0) as controls.

Results

Localized supply of P plus ammonium significantly increased root-proliferation, shoot dry-weight and nutrient-uptake at seedling stage. The positive effect disappeared at 53 days after sowing. However, plant-growth and nutrient-uptake increased again after the second localized application of P plus ammonium at jointing. The density and average length of the first-order lateral roots in local patches increased by 50 % in LDAP and LASP compared with F0 and BURP. Maize-yield increased by 8–10 % compared with BURP. Agronomic N efficiency and N-use efficiency increased by 41–48 % and 25–57 % compared with the BURP.

Conclusions

It is suggested that enhanced root-proliferation in the nutrient-rich patches with localized supply of ammonium and P at sowing and jointing stages is essential for improving nutrient-uptake and ultimately grain-yield.     

Combined linkage and association mapping of flowering time in Sunflower (Helianthus annuus L.)

Association mapping and linkage mapping were used to identify quantitative trait loci (QTL) and/or causative mutations involved in the control of flowering time in cultivated sunflower Helianthus annuus. A panel of 384 inbred lines was phenotyped through testcrosses with two tester inbred lines across 15 location × year combinations. A recombinant inbred line (RIL) population comprising 273 lines was phenotyped both per se and through testcrosses with one or two testers in 16 location × year combinations. In the association mapping approach, kinship estimation using 5,923 single nucleotide polymorphisms was found to be the best covariate to correct for effects of panel structure. Linkage disequilibrium decay ranged from 0.08 to 0.26 cM for a threshold of 0.20, after correcting for structure effects, depending on the linkage group (LG) and the ancestry of inbred lines. A possible hitchhiking effect is hypothesized for LG10 and LG08. A total of 11 regions across 10 LGs were found to be associated with flowering time, and QTLs were mapped on 11 LGs in the RIL population. Whereas eight regions were demonstrated to be common between the two approaches, the linkage disequilibrium approach did not detect a documented QTL that was confirmed using the linkage mapping approach.     

Improved measurements of Na+ fluxes in plants using calixarene-based microelectrodes

Ion-selective microelectrodes are a powerful tool in studying adaptive responses of plant cells and tissues to various abiotic stresses. However, application of this technique in Na⁺ flux measurements was limited due to poor selectivity for Na⁺ ions of commercially available Na⁺ cocktails. Often, these cocktails cannot discriminate between Na⁺ and other interfering ions such as K⁺ and Ca²⁺, leading to inaccurate measurements of Na⁺ concentration and, consequently, inaccurate Na⁺ flux calculations. To overcome this problem, three Na⁺-selective cocktail mixtures were prepared using tetramethoxyethyl ester derivative of p-t-butyl calix[4]arene. These cocktail mixtures were compared with commercially available ETH 227-based Na⁺ cocktail for selectivity for Na⁺ ions over other ions (particularly K⁺ and Ca²⁺). Among the three calixarene-based Na⁺ cocktails tested, cocktail 2 [in % w/w: Na⁺ ionophore (4-tert-butylcalix[4]arene-tetra acetic acid tetraethyl ester) 3.5, the plasticizer (2-nitrophenyl octyl ether) 95.9 and lipophilic anion (potassium tetrakis (4-chlorophenyl) borate) 0.6] showed the best selectivity for Na⁺ ions over K⁺ and Ca²⁺ ions and was highly stable over time (up to 10 h). Na⁺ flux measurements under a wide range of NaCl concentrations (25-150 mM) using Na⁺ cocktail 2 established a clear dose-response relationship between severity of salt stress and magnitude of Na⁺ influx at the distal elongation and mature zones of Arabidopsis thaliana roots. Furthermore, Na⁺ cocktail 2 was compared with commercially available ETH 227-based Na⁺ cocktail by measuring Na⁺ fluxes at the two Arabidopsis root zones in response to 100 mM NaCl treatment. With calixarene-based Na⁺ cocktail 2, a large decreasing Na⁺ influx (0-15 min) followed by small Na⁺ influx (15-45 min) was measured, whereas with ETH-based Na⁺ cocktail Na⁺ influx was short-lived (1-3 min) and was followed by Na⁺ efflux (3-45 min) that might have been due to K⁺ and Ca²⁺ efflux measured together with Na⁺ influx. In conclusion, Na⁺-selective calixarene-based microelectrodes have excellent potential to be used in real-time Na⁺ flux measurements in plants.     

The possibility of respiratory distress syndrome prevention of premature born children

Pregnant women and premature born children were classified into four groups. In each group there were thirty of them. The first group included the pregnant women with premature rupture of membranes and amniotic fluid effluxed for 72 hours before the delivery. The second group included the pregnant women with amniotic fluid effluxing less then 72 hours before the delivery. The third group included the pregnant women who were given corticosteroids. The forth group was a control group formed by those pregnant women (and their premature born children) whose amniotic fluid did not efflux long and those who weren't given corticosteroids during pregnancy. In all groups of pregnant women we observed: median age of pregnant women, the duration of pregnancy and mode of delivery (vaginal or cesarean section). In groups of premature born children we also observed: newborn birth weight, Apgar score in the first minute after delivery, Apgar score in the fifth minute after delivery, pH of the blood of umbilical cord, L/S ratio of amniotic fluid (lecithin-sphingomyelin ratio), RDS (neonatologist valuation in any degree of RDS developed et newborn child). Symptoms of RDS include tachypnoea, chest wall retraction and cyanosis and a zground glass' appearance of the chest on X-ray. Histopatological examinations of placentas compared the frequency of inflammatory or noninflammatory changes, also in all groups. No significant difference was found among groups of pregnant women for the following factors: the age of pregnant women, the duration of pregnancy and mode of delivery. No significant difference was found among the groups of children for the following factors: newborn birth weight, Apgar score in the fifth minute after delivery, blood pH of umbilical cord, L/S ratio of amniotic fluid. Significant difference was found among groups for the following factors: Apgar score in the first minute after delivery, the frequency of RDS and hystology of placentas. The prevention of premature delivery is the most important. All the pregnant women with symptoms of the premature delivery must be transported to the centers with the well developed unites of intensive neonatal care ("transport in utero").     

Role of magnesium in alleviation of aluminium toxicity in plants

Magnesium is pivotal for activating a large number of enzymes; hence, magnesium plays an important role in numerous physiological and biochemical processes affecting plant growth and development. Magnesium can also ameliorate aluminium phytotoxicity, but literature reports on the dynamics of magnesium homeostasis upon exposure to aluminium are rare. Herein existing knowledge on the magnesium transport mechanisms and homeostasis maintenance in plant cells is critically reviewed. Even though overexpression of magnesium transporters can alleviate aluminium toxicity in plants, the mechanisms governing such alleviation remain obscure. Possible magnesium-dependent mechanisms include (i) better carbon partitioning from shoots to roots; (ii) increased synthesis and exudation of organic acid anions; (iii) enhanced acid phosphatase activity; (iv) maintenance of proton-ATPase activity and cytoplasmic pH regulation; (v) protection against an aluminium-induced cytosolic calcium increase; and (vi) protection against reactive oxygen species. Future research should concentrate on assessing aluminium toxicity and tolerance in plants with overexpressed or antisense magnesium transporters to increase understanding of the aluminium-magnesium interaction.     

PR-Set7-dependent lysine methylation ensures genome replication and stability through S phase

PR-Set7/SET8 is a histone H4–lysine 20 methyltransferase required for normal cell proliferation. However, the exact functions of this enzyme remain to be determined. In this study, we show that human PR-Set7 functions during S phase to regulate cellular proliferation. PR-Set7 associates with replication foci and maintains the bulk of H4-K20 mono- and trimethylation. Consistent with a function in chromosome dynamics during S phase, inhibition of PR-Set7 methyltransferase activity by small hairpin RNA causes a replicative stress characterized by alterations in replication fork velocity and origin firing. This stress is accompanied by massive induction of DNA strand breaks followed by a robust DNA damage response. The DNA damage response includes the activation of ataxia telangiectasia mutated and ataxia telangiectasia related kinase–mediated pathways, which, in turn, leads to p53-mediated growth arrest to avoid aberrant chromosome behavior after improper DNA replication. Collectively, these data indicate that PR-Set7–dependent lysine methylation during S phase is an essential posttranslational mechanism that ensures genome replication and stability.     

Nitrate supply affects ammonium transport in canola roots

Plants may suffer from ammonium (NH4+) toxicity when NH4+ is the sole nitrogen source. Nitrate (NO3-) is known to alleviate NH4+ toxicity, but the mechanisms are unknown. This study has evaluated possible mechanisms of NO3- alleviation of NH4+ toxicity in canola (Brassica napus L.). Dynamics of net fluxes of NH4+, H+, K+ and Ca2+ were assessed, using a non-invasive microelectrode (MIFE) technique, in plants having different NO3- supplies, after single or several subsequent increases in external NH4Cl concentration. After an increase in external NH4Cl without NO3-, NH4+ net fluxes demonstrated three distinct stages: release (tau1), return to uptake (tau2), and a decrease in uptake rate (tau3). The presence of NO3- in the bathing medium prevented the tau1 release and also resulted in slower activation of the tau3 stage. Net fluxes of Ca2+ were in the opposite direction to NH4+ net fluxes, regardless of NO3- supply. In contrast, H+ and K+ net fluxes and change in external pH were not correlated with NH4+ net fluxes. It is concluded that (i) NO3- primarily affects the NH4+ low-affinity influx system; and (ii) NH4+ transport is inversely linked to Ca2+ net flux.     

Ammonium and nitrate uptake by the floating plant Landoltia punctata

BACKGROUND AND AIMS: Plants from the family Lemnaceae are widely used in ecological engineering projects to purify wastewater and eutrophic water bodies. However, the biology of nutrient uptake mechanisms in plants of this family is still poorly understood. There is controversy over whether Lemnaceae roots are involved in nutrient uptake. No information is available on nitrogen (N) preferences and capacity of Landoltia punctata (dotted duckweed), one of the best prospective species in Lemnaceae for phytomelioration and biomass production. The aim of this study was to assess L. punctata plants for their ability to take up NH4+ and NO3- by both roots and fronds. METHODS: NO3- and NH4+ fluxes were estimated by a non-invasive ion-selective microelectrode technique. This technique allows direct measurements of ion fluxes across the root or frond surface of an intact plant. KEY RESULTS: Landoltia punctata plants took up NH4+ and NO3- by both fronds and roots. Spatial distribution of NH4+ and NO3- fluxes demonstrated that, although ion fluxes at the most distal parts of the root were uneven, the mature part of the root was involved in N uptake. Despite the absolute flux values for NH4+ and NO3- being lower in roots than at the frond surface, the overall capacity of roots to take up ions was similar to that of fronds because the surface area of roots was larger. L. punctata plants preferred to take up NH4+ over NO3- when both N sources were available. CONCLUSIONS: Landoltia punctata plants take up nitrogen by both roots and fronds. When both sources of N are available, plants prefer to take up NH4+, but will take up NO3- when it is the only N source.