Vectors for RNAi technology in poplar

Abstract: The potential of double-stranded RNA interference (RNAi) technology was studied for down-regulation of gene expression in poplar. A set of vectors was constructed generating RNAs capable of duplex formation of sequences specific for the β-glucuronidase (GUS) reporter gene system. These gene cassettes are driven by the CaMV-35S promoter. To address the question of gene silencing, we tested the functionality of these vectors, both in transient assays by transforming protoplasts with the RNAi constructs, and in stably transformed GUSexpressing poplar plants. Agrobacterium -mediated transformation of those GUS-expressing plants with a GUS-specific RNAi construct showed a strong down-regulation of the reporter gene. From these results we conclude that RNAi is also functional in poplar.     

白杨不同倍性花粉的辐射敏感性及其应用

通过对白杨二倍性未减数花粉和单倍性花粉萌发率和萌发进程的观察统计,证明不同 倍性花粉对（６０）ＣＯγ射线辐射的敏感性不同,其中单倍性花粉的敏感性约为二倍性花粉的 ２倍。 为克服二倍性花粉在参与受精过程中萌发迟缓、竞争能力较差的问题,可利用这种花粉倍性 对辐射的敏感性差异,施加一定剂量的辐射以刺激二倍性花粉萌发,同时抑制或杀死部分单 倍性花粉,从而在一定程度上相对提高柱头上萌发和萌发较快的二倍性花粉比率。三倍体育 种结果亦证明了花粉辐射在提高三倍体得率方面应用的有效性,其中在银腺杨×毛新杨组 合中,以 １４７０ｒａｄ处理最佳,三倍体得率达３．８％,对照未检出三倍体;而在施加 １６８０ｒａｄ的银 腺杨×毛新杨杂交组合中,则获得了高达 １２．９％的三倍体。     

The relationship between rooting of poplar shoots and ATPase activity of their crude microsomal vesicles

Poplar shoots raised in vitro were induced to root by a 7 h passage on an auxin (1-naphthaleneacetic acid) medium. The percentage of rooting was reduced from ± 97% to ± 47% when vanadate (200 µM) was included in the auxin medium. Introduction of vanadate in the medium without auxin after the 7 h induction on auxin medium, did not inhibit rooting but affected only the development of the roots produced. The Mg²⁺-dependent ATPase activity of the microsomal vesicles of poplar shoots was increased after 7 h induction on rooting medium and corresponded to an increase in the Vmax of the enzyme. Results from experiments using some inhibitors of the polyamine metabolism suggested that this pathway was not involved in the increase of this activity. The auxin had no effect on the in vitro ATPase activity at any concentration tested except at about 2 mM where it was inhibitory, probably due to a change in the conformation of the enzyme. The transient increase of indole-3-acetic acid during rooting induction could be responsible for the increase in the level of the enzyme. The inhibition of root formation and growth by vanadate indicates strongly that the ATPase activity may be necessary for the induction and expression of rooting.     

No general soil carbon sequestration under Central European short rotation coppices

Wood from short rotation coppices (SRCs) is discussed as bioenergy feedstock with good climate mitigation potential inter alia because soil organic carbon (SOC) might be sequestered by a land-use change (LUC) from cropland to SRC. To test if SOC is generally enhanced by SRC over the long term, we selected the oldest Central European SRC plantations for this study. Following the paired plot approach soils of the 21 SRCs were sampled to 80 cm depth and SOC stocks, C/N ratios, pH and bulk densities were compared to those of adjacent croplands or grasslands. There was no general trend to SOC stock change by SRC establishment on cropland or grassland, but differences were very site specific. The depth distribution of SOC did change. Compared to cropland soils, the SOC density in 0–10 cm was significantly higher under SRC (17 ± 2 in cropland and 21 ± 2 kg C m⁻³ in SRC). Under SRC established on grassland SOC density in 0–10 cm was significantly lower than under grassland. The change rates of total SOC stocks by LUC from cropland to SRC ranged from −1.3 to 1.4 Mg C ha⁻¹ yr⁻¹ and −0.6 Mg C ha⁻¹ yr⁻¹ to +0.1 Mg C ha⁻¹ yr⁻¹ for LUC from grassland to SRC, respectively. The accumulation of organic carbon in the litter layer was low (0.14 ± 0.08 Mg C ha⁻¹ yr⁻¹). SOC stocks of both cropland and SRC soils were correlated with the clay content. No correlation could be detected between SOC stock change and soil texture or other abiotic factors. In summary, we found no evidence of any general SOC stock change when cropland is converted to SRC and the identification of the factors determining whether carbon may be sequestered under SRC remains a major challenge.     

Overexpression of the PtSOS2 gene improves tolerance to salt stress in transgenic poplar plants

In higher plants, the salt overly sensitive (SOS) signalling pathway plays a crucial role in maintaining ion homoeostasis and conferring salt tolerance under salinity condition. Previously, we functionally characterized the conserved SOS pathway in the woody plant Populus trichocarpa. In this study, we demonstrate that overexpression of the constitutively active form of PtSOS2 (PtSOS2TD), one of the key components of this pathway, significantly increased salt tolerance in aspen hybrid clone Shanxin Yang (Populus davidiana × Populus bolleana). Compared to the wild‐type control, transgenic plants constitutively expressing PtSOS2TD exhibited more vigorous growth and produced greater biomass in the presence of high concentrations of NaCl. The improved salt tolerance was associated with a decreased Na⁺ accumulation in the leaves of transgenic plants. Further analyses revealed that plasma membrane Na⁺/H⁺ exchange activity and Na⁺ efflux in transgenic plants were significantly higher than those in the wild‐type plants. Moreover, transgenic plants showed improved capacity in scavenging reactive oxygen species (ROS) generated by salt stress. Taken together, our results suggest that PtSOS2 could serve as an ideal target gene to genetically engineer salt‐tolerant trees.     

The Potential of the Ni-Resistant TCE-Degrading Pseudomonas putida W619-TCE to Reduce Phytotoxicity and Improve Phytoremediation Efficiency of Poplar Cuttings on A Ni-TCE Co-Contamination

To examine the potential of Pseudomonas putida W619-TCE to improve phytoremediation of Ni-TCE co-contamination, the effects of inoculation of a Ni-resistant, TCE-degrading root endophyte on Ni-TCE phytotoxicity, Ni uptake and trichloroethylene (TCE) degradation of Ni-TCE-exposed poplar cuttings are evaluated.

After inoculation with P. putida W619-TCE, root weight of non-exposed poplar cuttings significantly increased. Further, inoculation induced a mitigation of the Ni-TCE phytotoxicity, which was illustrated by a diminished exposure-induced increase in activity of antioxidative enzymes. Considering phytoremediation efficiency, inoculation with P. putida W619-TCE resulted in a 45% increased Ni uptake in roots as well as a slightly significant reduction in TCE concentration in leaves and TCE evapotranspiration to the atmosphere.

These results indicate that endophytes equipped with the appropriate characteristics can assist their host plant to deal with co-contamination of toxic metals and organic contaminants during phytoremediation. Furthermore, as poplar is an excellent plant for biomass production as well as for phytoremediation, the obtained results can be exploited to produce biomass for energy and industrial feedstock applications in a highly productive manner on contaminated land that is not suited for normal agriculture. Exploiting this land for biomass production could contribute to diminish the conflict between food and bioenergy production.     

Performance of hybrid poplar clones in short rotation coppice in Mediterranean environments: analysis of genotypic stability

Improving production in short rotation coppice (SRC) plantations requires, among other elements, a proper understanding of clonal performance. Genotypic stability over a range of environments is a factor of concern for breeding and recommendation purposes. Most common stability measures can be embedded in a mixed‐model framework accounting for interaction and heterocedasticity in genotype‐by‐environment tables. Data from nine hybrid poplars of different taxonomic background were tested in four Mediterranean sites under three agronomic practices (control, herbicide application, and supplementary fertilization) for total biomass (TB), stem biomass (SB), and branch biomass (BB) at the end of the first rotation. Stability models (stability variance, Finlay–Wilkinson and Eberhart–Russell) were compared, also allowing for the definition of groups of genotypes with distinct taxonomic backgrounds and a priori different variabilities. Results showed that genotype‐by‐environment (GE) interactions were associated with factors inherent to evaluation sites rather than to the agronomic practices tested. Depending on biomass fraction, regression models provided appropriate stability measures. Highly reactive clones to improving environmental conditions (e.g., ‘AF2’) tended to show the largest mean TB. However, this was not always the case, as clone ‘Monviso’ showed both intermediate reactivity (i.e., stable sensu Eberhart–Russell) and enhanced overall performance. The taxonomic group was relevant for explaining stability patterns for SB. The stability assessment for BB indicated different patterns in biomass allocation. Present findings point to the feasibility of either exploiting specific adaptation (in which case hybrid type may play a relevant role) or searching for broadly adapted, stable material exhibiting good performance in Mediterranean conditions.     

How deep must we dig? Sampling depth effects on root biomass assessments in Mediterranean riparian buffers

Abstract

Root turnover is a relevant process controlling carbon and nutrient cycles. Furthermore, root biomass could influence the effectiveness of riparian buffer systems with regard to immobilizing and processing soil water pollutants and improving soil quality. However, sampling root biomass presents many technical problems, because there is as yet no well-established method for assessment thereof. In the present study, we evaluated the effects of limited sampling depth on biomass assessment in four riparian buffers and on two different dates (January and June): a poplar forest, two mixed deciduous afforestations of different ages, and a grassy area. Although, for all systems, most root biomass was limited to the first 30 cm, detection of differences in root biomass among vegetation types depended strongly on sampling depth for both sampling dates. Furthermore, although the poplar forest presented one of the most stable root systems in terms of total biomass between the sampling dates, it was one of the most seasonally dynamic in terms of the amount and distribution with depth of root biomass. The results of this study suggest that a minimum sampling depth should be established for each study according to seasonal variation in vertical distribution of root biomass.     

Selectivity and delignification kinetics for oxidative short‐term lime pretreatment of poplar wood,part I: Constant‐pressure

Kinetic models applied to oxygen bleaching of paper pulp focus on the degradation of polymers, either lignin or carbohydrates. Traditionally, they separately model different moieties that degrade at three different rates: rapid, medium, and slow. These models were successfully applied to lignin and carbohydrate degradation of poplar wood submitted to oxidative pretreatment with lime at the following conditions: temperature 110–180°C, total pressure 7.9–21.7 bar, and excess lime loading of 0.5 g Ca(OH)₂ per gram dry biomass. These conditions were held constant for 1–6 h. The models properly fit experimental data and were used to determine pretreatment selectivity in two fashions: differential and integral. By assessing selectivity, the detrimental effect of pretreatment on carbohydrates at high temperatures and at low lignin content was determined. The models can be used to identify pretreatment conditions that selectively remove lignin while preserving carbohydrates. Lignin removal ≥50% with glucan preservation ≥90% was observed for differential glucan selectivities between ～10 and ～30 g lignin degraded per gram glucan degraded. Pretreatment conditions complying with these reference values were preferably observed at 140°C, total pressure ≥14.7 bars, and for pretreatment times between 2 and 6 h depending on the total pressure (the higher the pressure, the less time). They were also observed at 160°C, total pressure of 14.7 and 21.7 bars, and pretreatment time of 2 h. Generally, at 110°C lignin removal is insufficient and at 180°C carbohydrates do not preserve well. © 2011 American Institute of Chemical Engineers Biotechnol. Prog., 2011