Comparative analysis of microRNAs and putative target genes in hybrid clone <Emphasis Type="Italic">Paulownia</Emphasis> ‘yuza 1’ under drought stress

Drought stress in plants often leads to reduced productivity and limited geographic distribution, which can affect human life and ecosystems. The responses of diploid and tetraploid Paulownia tomentosa × Paulownia fortunei to drought have been reported, but the effects of drought stress on the levels of microRNA (miRNA) expression have not been published so far. Here, we constructed four small RNA (sRNA) libraries and four corresponding degradome libraries of well-watered and severe drought-treated diploid and tetraploid plants to identify the miRNAs and their putative target genes in Paulownia ‘yuza 1’, a P. tomentosa × P. fortunei hybrid clone, by sRNA and degradome sequencing. The putative target genes of miRNAs were annotated with gene ontology terms and Kyoto Encyclopedia of Genes and Genomes pathways. Three conserved and 21 novel miRNAs responsive to drought stress were found, in which 15 were identified as the main drought responsive miRNAs that conferred higher resistance in tetraploid than in diploid of Paulownia ‘yuza 1’. Our results will lay the foundation for investigating the roles of miRNAs in Paulownia and other trees in response to drought.     

Non-native liana, <Emphasis Type="Italic">Euonymus fortunei</Emphasis>, associated with increased soil nutrients,unique bacterial communities,and faster decomposition rate

Invasive plants have wide-ranging impacts on native systems including reducing native plant richness and altering soil chemistry, microbes, and nutrient cycling. Increasingly, these effects are found to linger long after removal of the invader. We examined how soil chemistry, bacterial communities, and litter decomposition varied with cover of Euonymus fortunei, an invasive evergreen liana, in two central Kentucky deciduous forests. In one forest, E. fortunei invaded in the late 1990s but invasion remained patchy and we paired invaded and uninvaded plots to examine the associations between E. fortunei cover and our response variables. In the second forest, E. fortunei had completely invaded the forest by 2005; areas where it had been selectively removed by 2010 were paired with an adjacent invaded plot. Where E. fortunei had patchily invaded, E. fortunei patches had up to 3.5× nitrogen, 2.7× carbon, and 1.9× more labile glomalin in soils than uninvaded plots, whereas there were no differences in soil characteristics between invaded and removal plots. In the patchily invaded forest, bacterial community composition varied among invaded and non-invaded plots, whereas bacterial communities did not vary among invaded and removal plots. Finally, E. fortunei leaf litter decomposed faster (k = 4.91 year^?1) than the native liana (k = 3.77 year^?1), Vitis vulpina; decomposition of both E. fortunei and V. vulpina was faster in invaded (k = 7.10 year^?1) than removal plots (k = 4.77 year^?1). Our findings suggest that E. fortunei invasion increases the rate of leaf litter decomposition via high-quality litter, alters the decomposition environment, and shifts in the soil biotic communities associated with a dense mat of wintercreeper. Land managers with limited resources should target the densest mats for the greatest restoration potential and remove wintercreeper patches before they establish dense mats.     

Assessment of the preventive effect of vermicompost on salinity resistance in tomato (<Emphasis Type="Italic">Solanum lycopersicum</Emphasis> cv. Ailsa Craig)

To determine the effects of vermicompost leachate (VCL) on resistance to salt stress in plants, young tomato seedlings (Solanum lycopersicum, cv. Ailsa Craig) were exposed to salinity (150 mM NaCl addition to nutrient solution) for 7 days after or during 6 mL L^??1 VCL application. Salt stress significantly decreased leaf fresh and dry weights, reduced leaf water content, significantly increased root and leaf Na⁺ concentrations, and decreased K⁺ concentrations. Salt stress decreased stomatal conductance (g_s), net photosynthesis (A), instantaneous transpiration (E), maximal efficiency of PSII photochemistry in the dark-adapted state (F_v/F_m), photochemical quenching (qP), and actual PSII photochemical efficiency (ΦPSII). VCL applied during salt stress increased leaf fresh weight and g_s, but did not reduce leaf osmotic potential, despite increased proline content in salt-treated plants. VCL reduced Na⁺ concentrations in leaves (by 21.4%), but increased them in roots (by 16.9%). VCL pre-treatment followed by salt stress was more efficient than VCL concomitant to salt stress, since VCL pre-treatment provided the greatest osmotic adjustment recorded, with maintenance of net photosynthesis and K⁺/Na⁺ ratios following salt stress. VCL pre-treatment also led to the highest proline content in leaves (50 µmol g^??1 FW) and the highest sugar content in roots (9.2 µmol g^??1 FW). Fluorescence-related parameters confirmed that VCL pre-treatment of salt-stressed plants showed higher PSII stability and efficiency compared to plants under concomitant VCL and salt stress. Therefore, VCL represents an efficient protective agent for improvement of salt-stress resistance in tomato.     

Mapping of novel salt tolerance QTL in an Excalibur × Kukri doubled haploid wheat population

Key message

Novel QTL for salinity tolerance traits have been detected using non-destructive and destructive phenotyping in bread wheat and were shown to be linked to improvements in yield in saline fields.

Abstract

Soil salinity is a major limitation to cereal production. Breeding new salt-tolerant cultivars has the potential to improve cereal crop yields. In this study, a doubled haploid bread wheat mapping population, derived from the bi-parental cross of Excalibur?×?Kukri, was grown in a glasshouse under control and salinity treatments and evaluated using high-throughput non-destructive imaging technology. Quantitative trait locus (QTL) analysis of this population detected multiple QTL under salt and control treatments. Of these, six QTL were detected in the salt treatment including one for maintenance of shoot growth under salinity (QG_(1–5).asl-7A), one for leaf Na⁺ exclusion (QNa.asl-7A) and four for leaf K⁺ accumulation (QK.asl-2B.1, QK.asl-2B.2, QK.asl-5A and QK:Na.asl-6A). The beneficial allele for QG_(1–5).asl-7A (the maintenance of shoot growth under salinity) was present in six out of 44 mainly Australian bread and durum wheat cultivars. The effect of each QTL allele on grain yield was tested in a range of salinity concentrations at three field sites across 2 years. In six out of nine field trials with different levels of salinity stress, lines with alleles for Na⁺ exclusion and/or K⁺ maintenance at three QTL (QNa.asl-7A, QK.asl-2B.2 and QK:Na.asl-6A) excluded more Na⁺ or accumulated more K⁺ compared to lines without these alleles. Importantly, the QK.asl-2B.2 allele for higher K⁺ accumulation was found to be associated with higher grain yield at all field sites. Several alleles at other QTL were associated with higher grain yields at selected field sites.

     

How salinity stress influences the thermal time requirements of seed germination in <Emphasis Type="Italic">Silybum marianum</Emphasis> and <Emphasis Type="Italic">Calendula officinalis</Emphasis>

Salinity is a major problem of many agricultural lands that is usually associated with drought stress in arid and semi-arid regions. In this study we examine the role of salinity stress on temperature requirements of two herbaceous species and how it could be modeled to quantify alterations. We applied four non-linear regression models (segmented, beta, beta modified, and dent-like) to describe the germination rate–temperature relationships of Silybum marinum L. and Calendua officinalis L. over six constant temperatures exposed to different levels of salinity stress. Our results revealed that salinity could affect the cardinal temperatures in both plants and, as a result, it is not possible to suggest one model for all levels of salinity stress. The best model to fit data to predict cardinal temperatures of Silybum marianum and Calendula officinalis at the no-salinity condition were dent-like (AICc?=?4.03) and beta (AICc = ??2.30), respectively. Knowing the thermal time constant (f_o) value helps us predict the minimum number of hours required for completion of germination at the optimal temperature. All models in this study were estimated higher f_o due to higher salinity stress in both Silybum marianum and Calendula officinalis seeds. The highest estimated f_o for Silybum marianum (91.5?±?59.6) and Calendula officinalis (178.9?±?26.5) was obtained from the results of germination rate prediction using a dent-like model at 200 mM salinity.     

Exogenous Diethyl Aminoethyl Hexanoate,a Plant Growth Regulator,Highly Improved the Salinity Tolerance of Important Medicinal Plant <Emphasis Type="Italic">Cassia obtusifolia</Emphasis> L.

The purpose of the present study was to investigate the mechanism of DA-6 in alleviating the salinity inhibition of Cassia obtusifolia L. seeds and seedlings. NaCl (100 mM) was used to mimic salinity stress in a series of experiments. Varying combinations of DA-6 were added to seeds and seedlings under salinity stress. Seed germination indices and seedling parameters were investigated. Seed germination and seedling growth were significantly inhibited under salinity stress. NaCl-induced inhibitory effects on seed germination and seedling growth were ameliorated by DA-6 with different concentrations. Addition of DA-6 to seeds (50 µM) and seedlings (100 µM) significantly alleviated damage to the plant cells under salinity stress. DA-6 (regardless of the presence or absence of NaCl) enhanced chlorophyll concentration, total soluble sugars, free proline, and soluble protein, and improved photosystem II (PSII) photochemical efficiency levels (F _v/F _m), PSII actual photochemical efficiency (ΦPSII), and the photochemical quench coefficient. In contrast, the initial fluorescence (F _o) and the non-photochemical quenching coefficient decreased. Application of DA-6 also enhanced the activities of superoxide dismutase (SOD; EC 1.15.1.1), peroxidase (POD; EC 1.11.1.7), catalase (CAT; EC 1.11.1.6), ascorbate peroxidase (APX; EC 1.11.1.11), and glutathione reductase (GR; EC 1.6.4.2), thus alleviating oxidative damage, as indicated by decreases in thiobarbituric acid-reactive substances, hydrogen peroxide concentration (H₂O₂), relative conductivity, and lipoxygenase activity (LOX; EC 1.13.11.12). Based on the experimental results, we conclude that DA-6 induces advantageous effects on the attenuation of salt-stress inhibition of C. obtusifolia seeds and seedlings and alleviates oxidative damage by conferring beneficial cytoprotection and activating antioxidant enzymes. DA-6 can be used as an effective plant growth regulator to alleviate salinity stress.     

Dynamic changes in energy metabolism and electron transport of photosystem II in <Emphasis Type="Italic">Nicotiana tabacum</Emphasis> infested by nymphs of <Emphasis Type="Italic">Bemisia tabaci</Emphasis> (Middle East-Asia Minor 1)

Bemisia tabaci Middle East-Asia Minor 1 (MEAM1) infestation adversely affected photosynthesis of host plants. In the current study, chlorophyll a fluorescence was measured to determine the effects of MEAM1 nymph infestation of tobacco local and systemic leaves on energy metabolism and electron transport of photosystemII(PSII). The results showed that the density of PSII reaction centres per excited cross section (CS) (RC/CS) of infested and systemic leaves was reduced at 14 and 20 days. In systemic leaves, the number of PSII closed reaction centres (1-qP) increased significantly at 14 and 20 days. Absorption flux per Q_A^? reducing PSII reaction centre (RC) (ABS/RC), trapped energy flux per RC (TRo/RC), and electron transport per RC (ETo/RC) of infested and systemic leaves increased with MEAM1 nymph infestation. The most obvious increase in absorption flux per CS (ABS/CSo) and trapped energy flux per CS (TRo/CSo) of infested and systemic leaves occurred at 14 days. MEAM1 nymph infestation significantly reduced the energy required for PSII Q_A to be completely reduced (Sm) in tobacco leaves. These results suggested that MEAM1 nymph infestation caused changes in light-harvesting antenna system and deactivation of the reaction centre, resulting in the reduction of photons absorbed by reaction centres per unit area. MEAM1 nymph infestation, particularly the 3rd instar nymphs, decreased light utilization ability and increased excess excitation energy in tobacco leaves. With MEAM1 nymph infestation, the relative electron transport capacity of the entire electron transport chain decreased, and more light energy was used to reduce Q_A.     

Overexpression of <Emphasis Type="Italic">Populus tomentosa</Emphasis> cytosolic ascorbate peroxidase enhances abiotic stress tolerance in tobacco plants

Reactive oxygen species (ROS) play key roles in plants and are regulated by several ROS-scavenging enzymes. Ascorbate peroxidase (APX), which catalyzes the reduction of hydrogen peroxide to water, a vital part of ROS formation, plays a significant role in higher plants. In this study, a cytosolic APX gene from Populus tomentosa, named PcAPX, was identified and characterized. Recombinant PcAPX had a calculated mass of 33.24 kD and showed high activity towards ascorbic acid (ASA) and hydrogen peroxide (H₂O₂). Real-time PCR analysis showed that APX mRNA expression levels were higher in leaves than roots or stems of P. tomentosa. Compared with wild-type, transgenic tobacco plants overexpressing PcAPX showed no significant difference in morphology under normal conditions. However, the transgenic plants were more resistant to drought, salt and oxidative stress conditions, as shown by decreased levels of malondialdehyde and increased levels of chlorophyll. Moreover, decreased H₂O₂ levels, increased ASA consumption, an increase in the NADP to NADPH ratio, and higher APX activity in the transgenic plants suggested an increased ability to eliminate ROS. These data suggest that PcAPX overexpression in transgenic tobacco plants can enhance tolerance to drought, salt and oxidative stress. Therefore, APX has a crucial role in abiotic stress tolerance in plants.     

Potential of a halophyte-associated endophytic fungus for sustaining Chinese white poplar growth under salinity

Endophyte-mediated plant growth and stress tolerance have been increasingly acknowledged. Our knowledge of functions of endophytes from saline environments, however, is currently scant indeed. In this work, we found that an endophytic ascomycetous Curvularia sp. isolated from a halophytic plant Suaeda salsa was able to establish beneficial symbiosis with poplar (Populus tomentosa). Microscopic staining technique confirmed that the Curvularia sp. can penetrate the poplar roots after two week inoculation and readily form sclerotia-like structures and monilioid hyphal cells in root hair and/or cortex cells, both intercellularly and intracellularly. This implied that this fungus can be referred to as a dark septate endophyte. Pot experiments revealed that Curvularia sp. significantly promoted the poplar growth and resulted in increased production of the antioxidant enzymes, particularly the superoxide dismutase (SOD) and ascorbate peroxidase (APX) under salinity stress condition. The presence of Curvularia sp. also enhanced chlorophyll a, b and proline contents in leaves, although not all differences were significant. Compared to the non-inoculated plants, the photosystem II-based electron transport rate (ETR), actual quantum yield in the light-adapted steady state (?PSII) and photochemical quenching values (qP) was significantly higher in colonized plants, despite there were only slight differences in the values of the maximum quantum yield in the dark-adapted state (F_v/F_m) and in the light-adapted sate (F’_v/F’_m). Collectively, our data supports the evidence of the ability of Curvularia sp. to alleviate the adverse effects of salinity stress on poplar growth and highlights the potential use of endophytes from extreme conditions as novel probiotics in improving salt tolerance of tree seedlings.     

Overexpression of a <Emphasis Type="Italic">Populus euphratica CBF4</Emphasis> gene in poplar confers tolerance to multiple stresses

C-repeat binding factors (CBFs) play a key role in abiotic stresses. However, little is known about CBFs in Populus euphratica. Here, we isolated PeCBF4a, a member of CBF gene family from P. euphratica. Its expression was induced by dehydration, salinity and low temperature. We generated transgenic poplars (Populus tomentosa ‘YiXianCiZhu B385’) overexpressing PeCBF4a (OE-PeCBF4a) under the control of the CaMV 35S promoter or transformed with empty vector. The wild-type (WT) and empty vector lines were used as controls. Under abiotic stresses, the photosynthetic rate (Pn) of 60-day-old OE-PeCBF4a lines increased 34.7–165.7?% and the instantaneous water use efficiency (iWUE) increased 48.9–103.7?% over controls. The maximum quantum efficiency of PSII photochemistry (Fv/Fm) values in PeCBF4a-overexpressing lines did not change significantly and were 2.14–5.89?% higher. The non-photochemical quenching coefficient (NPQ) mean of OE-PeCBF4a lines decreased by 12.02–23.64?% while the photochemical quenching (qP) value was 8.75–22.31?% higher than controls. OE-PeCBF4a lines also displayed higher superoxide dismutase (SOD) activities and markedly lower malondialdehyde (MDA) levels compared to controls. Higher levels of proline and sugars accumulated in transgenic plants. Overexpression of PeCBF4a not only induced strong expression of the stress-responsive downstream target genes of PeCBF4a, PtRCI2A (rare-cold-inducible 2A) and PtDI21 (drought-induced 21), but also caused dwarfed phenotypes. Based on results from P-V curve measurements, the osmotic adjustment capability of OE-PeCBF4a plants was enhanced. These results confirmed that OE-PeCBF4a poplars exhibit greater tolerance to stress, indicating that PeCBF4a plays a positive role in stress tolerance.     

Effects of cycloheximide on photosynthetic abilities,reflectance spectra and fluorescence emission spectra in <Emphasis Type="Italic">Phyllostachys edulis</Emphasis>

Key message

CHX had remarkable inhibition on P. edulis photosynthesis, and the reflectance indexes and F ₆₈₅ / F ₇₃₅ had the potential value for quantifying the effects of antibiotics on trees.

Abstract

To reveal the effects of antibiotics on photosynthesis and provide help for remote sensing the influence of antibiotics on trees, we investigated the effects of cycloheximide (CHX) on Phyllostachys edulis. In CHX treatment, the photosynthetic pigment content in P. edulis was decreased markedly, which led to the increase in the reflectance spectra in visible region. CHX reduced the donor side and acceptor side of photosystem II (PSII), density of reaction centers, quantum production and electron transport in PSII, and raised the dissipation of absorbed light energy. Besides the dissipation, the absorbed light energy can be emitted as fluorescence with two main peaks in the red (685 nm) and far-red (735 nm) region, respectively. In 0.50 mM CHX treatment, a significant decline in the height and area of the peak at 685 nm might result from Chl loss reducing the light absorption and lower photochemical reaction in PSII. When fourth derivative analysis of fluorescence emission spectra was performed, the changes of the peaks at 718, 735 and 750 nm might result from the decline of absorbed solar radiation caused by the reduced pigment content and/or the damages to the PSI. In CHX treatment, a remarkable increase in intercellular CO₂ concentrations and light compensation point and decrease in light saturation point demonstrated that the CO₂ assimilation ability was decreased. Those results suggested that the photosynthesis in trees can be reduced after they were watered with wastewater containing CHX. The reflectance indexes and F ₆₈₅/F ₇₃₅ (H ₆₈₅/H ₇₃₅ and A ₆₈₅/A ₇₃₅) were markedly affected by CHX, demonstrating that they had the potential value for quantifying the effects of antibiotics on trees.

     

Changes in photosynthesis of alpine plant <Emphasis Type="Italic">Saussurea superba</Emphasis> during leaf expansion

The native alpine plant Saussurea superba is widely distributed in Qinghai–Tibetan Plateau regions. The leaves of S. superba grow in whorled rosettes, and are horizontally oriented to maximize sunlight exposure. Experiments were conducted in an alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station (37°29′–37°45′N, 101°12′–101°33′E; alt. 3200 m). Leaf growth, photosynthetic pigments and chlorophyll fluorescence parameters were measured in expanding leaves of S. superba. The results indicate that leaf area increased progressively from inner younger leaves to outside fully expanded ones, and then slightly decreased in nearly senescent leaves, due to early unfavorable environmental conditions, deviating from the ordinary growth pattern. The specific leaf area decreased before leaves were fully expanded, and the leaf thickness was largest in mature leaves. There were no significant changes in the content of chlorophylls (Chl) and carotenoids (Car), but the ratios of Chl a/b and Car/Chl declined after full expansion of the leaves. The variation of Chl a/b coincided well with changes in photochemical quenching (q _P) and the fraction of open PSII reaction centers (q _L). The maximum quantum efficiency of PSII photochemistry after 5 min dark relaxation (F _(v)/F _(m)) continuously increased from younger leaves to fully mature leaves, suggesting that mature leaves could recover more quickly from photoinhibition than younger leaves. The light-harvesting capacity was relatively steady during leaf expansion, as indicated by the maximum quantum efficiency of open PSII centers (\(F_{\text{v}}^{{\prime }}\)/\(F_{\text{m}}^{{\prime }}\)). UV-absorbing compounds could effectively screen harmful solar radiation, and are a main protection way on the photosynthetic apparatus. The decline of q _P and q _L during maturation, together with limitation of quantum efficiency of PSII reaction centers (L _(PFD)), shows a decrease of oxidation state of Q_A in PSII reaction centers under natural sunlight. Furthermore, light-induced (Φ _NPQ) and non-light-induced quenching (Φ _NO) were consistent with variation of L _(PFD). It is concluded that the leaves of S. superba could be classified into four functional groups: young, fully expanded, mature, and senescent. Quick recovery from photoinhibition was correlated with protection by screening pigments, and high level of light energy trapping was correlated with preservation of photosynthetic pigments. Increasing of Φ _NPQ and Φ _NO during leaves maturation indicates that both thermal dissipation of excessive excitation energy in safety and potential threat to photosynthetic apparatus were strengthened due to the declination of q _P and q _L, and enhancement of L _(PFD).