Identification and Transcriptional Regulation of CAMTA Genes in Liriodendron chinense

This study explores CAMTA genes in the rare and endangered Chinese plant species,Liriodendron chinense.Despite the completion of whole-genome sequencing,the roles of CAMTA genes in calcium regulation and stress responses in this species remain largely unexplored.Within the L.chinense genome,we identified two CAMTA genes,Lchi09764 and Lchi222536,characterized by four functional domains:CG-1,TIG,ANK repeats,and IQ motifs.Our analyses,including phylogenetic investigations,cis-regulatory element analyses,and chromosomal location studies,aim to elucidate the defining features of CAMTA genes in L.chinense.Applying Weighted Gene Co-Expression Network Analysis(WGCNA),we explored the impact of CAMTA genes on different organs and their regulation under abiotic stress conditions.The identification of significant gene modules and the prediction of promoter binding sites revealed co-expressed genes associated with CAMTA transcription factors.In summary,this study provides initial insights into CAMTA genes in L.chinense,laying the groundwork for future research on their evolution and biological roles.This knowledge enhancement contributes to a better understanding of plant responses to environmental stress—an essential aspect of plant biology.

鹅掌楸属(Liriodendron)杂交育种回顾与展望

对我国鹅掌楸杂交育种工作进行了回顾与总结。自已故叶培忠教授开创该树种杂交育种工作以来40a的历程,概括地分为3个阶段:杂交可配性与杂种优势探索阶段,杂交后代试种及其生长适应性测定阶段,杂交育种工作全面发展阶段。关于杂交育种工作的主要进展则包括了解和掌握了鹅掌楸属种间杂交可配性、杂交胚胎学、杂交授粉生物学与杂交技术;揭示了杂交种生长优势的形成原因;选出一批优良杂交后代家系与无性系;总结出无性繁殖的技术;初步建立了推广示范点,探索了科研与开发的途径。最后对今后的工作进行了展望性的讨论。

鹅掌楸属(Liriodendron L.)种质‘优酉’的遗传背景研究

应用光学显微镜和扫描电子显微镜,以鹅掌楸〔Liriodendron chinense(Hemsl.)Sarg.〕、北美鹅掌楸(L. tulipiferaL.)及杂种鹅掌楸(L. chinense×L. tulipifera)为对照,对重庆酉阳鹅掌楸(Liriodendron sp.)种源‘优酉’(‘Youyou’)的外部形态特征、叶表皮微形态结构特征和花粉形态特征进行观察比较,并利用RAPD标记技术对‘优酉’的遗传关系进行了分析。结果表明,鹅掌楸属各树种在外部形态上存在差别,但在叶表皮和花粉形态特征上表现出明显的一致性,‘优酉’的各形态特征与鹅掌楸有较多相似性。RAPD标记分析结果表明,‘优酉’的遗传距离与鹅掌楸和北美鹅掌楸较远,但与鹅掌楸的遗传关系相对较近。推测‘优酉’可能是由较原始的鹅掌楸向较进化的北美鹅掌楸过渡的1个中间类型。‘优酉’生长速度快、观赏价值高,可直接用于园林绿化及林木种植。

Fossil-Winged Fruits of Fraxinus(Oleaceae) and Liriodendron(Magnoliaceae) from the Duho Formation,Pohang Basin,Korea

A total of 16 specimens of fossil-winged fruits were found from the Middle Miocene marine deposits, Duho Formation, Pohang Basin, Korea. They were identified into two structurally different groups： 15 specimens into a winged fruit of Fraxinus, and one specimen of Liriodendron. The most samaras （13 specimens） were identified as Fraxinus oishii, which is characterized by narrowly ovate or ovate-elliptic shapes that are 2.7-3.6 cm in length and 0.7-1 cm in width （i/w ratio=3.4-4）. The apexes of the Fraxinus oishii samara are round or slightly emarginated, and a seed of the samara is always located at the base, of which the general shape is narrow rhombic-ellipsoidal. The seed is 1.2-2 cm long and 0.5-0.7 cm wide. Two specimens are different from the samara of Fraxinus oishii. They have a 6.6 length/width ratio （3.3 cm long and 0.5 cm wide）, and thus, are temporarily classified into the Fraxinus sp. One specimen was recognized as a winged seed of Liriodendron meisenense. The wing is broadly lanceolate to elliptic in shape, has a smooth, acute apex, and is approximately 3 cm long and 0.7 cm wide. Samaras of Fraxinus oishii and Liriodendron meisenense were early reported from the Middle Miocene deposits from North Korea, but these specimens are the first discovery in South Korea. Further study of the Duho Formation may connect flora relationships between North and South Korea.

Genome-wide identification and cold stress-induced expression analysis of the CBF gene family in Liriodendron chinense

Cold-resistance pathways that operate in model plants such as Arabidopsis thaliana and Oryza sativa have been studied extensively.It has been found that CBF genes play an important role in plant cold resistance.Liriodendron chinense,a tree known for its graceful tree shape and widely spread in south China,has weak cold tolerance.However,little is known about its response to cold.To further study the function of L.chinense CBF gene family,we started by characterizing all members of this gene family in the L.chinense genome and their expression profiling.Phylogenetic analysis found that 14 CBF genes in L.chinense are more closely related to their homologues in woody plants and A.thaliana than those in O.sativa.Cis-acting elements and GO analysis showed that some LcCBF genes participated in the biological process of cold stress response.The transcriptomic and RT-qPCR data showed that most of LcCBF genes displayed an initially increasing and subsequently decreasing trend during cold stress course and the expression profile of each member was different.Some LcCBF genes exhibited a different abundance in callus,root,stem and leaf tissues.The structure and expression characteristics of LcCBF genes imply that they may have similar and different functions in response to cold stress conditions.The identification and analysis of LcCBF gene family have laid the foundation for future studies into L.chinense cold stress mechanisms and for the cultivation of cold-resistance cultivars.

庐山鹅掌楸(Liriodendron chinense)幼苗蒸腾特性研究

庐山山地上的鹅掌揪幼苗，在夏季晴天土壤供水充足的条件下，其叶片蒸腾速率的日变化为午后高峰型，日蒸腾量为70．92molH2Om-2d-1，最大蒸腾速率达3.9mmolH2Om-21s-1,叶／气温度差、气孔导度、相对湿度等因素对蒸腾速率的影响最显著；鹅掌揪幼苗的水分利用率日平均为4．142mmolCO2mol-1H2o，最高可达11.8mmolCO2mo1-1H2O。

Changes in soil organic carbon and aggregate stability following a chronosequence of Liriodendron chinense plantations

The objectives for this study were to determine changes in soil organic carbon(SOC)components and water-stable aggregates for soil profi les from diff erent ages of plantations of Liriodendron chinense and to clarify which organic carbon component is more closely associated with the formation and stability of soil aggregates.Three layers of soil(depths 0–20 cm,20–40 cm,40–60 cm)were collected from young,half-mature and mature stages of L.chinense.SOC,readily oxidizable organic carbon,chemically stable organic carbon and aggregate composition were determined.Intermediate stable organic carbon,the microbial quotient and aggregate stability(mean weight diameter)were calculated.SOC and aggregate stability in the L.chinense plantation did not increase linearly with an increase in L.chinense age;rather,they fi rst decreased,then increased with increasing age of L.chinense.The microbial quotient had a negative eff ect on the level of organic carbon and the stability of aggregates,while chemically stable organic carbon had a positive eff ect,which explained 55.0%and 19.3%of the total variation,respectively(P<0.01).Therefore,more attention should be paid of these two indicators in the future.

The Regulatory Roles of microRNAs and Associated Target Genes during Early Somatic Embryogenesis in Liriodendron Sino-Americanum

Somatic cells respond to considerable stress,and go through a series of phytohormone pathways,then forming an embryo.The developmental process is recorded as somatic embryogenesis(SE).One of the key components regulating SE are the microRNAs(miRNAs).Despite previous studies,it is still not clear exactly how miRNAs exert their function of regulating targets during conditionally activated early SE.Here,we use Liriodendron sino-americanum as a model system and perform a combined analysis of microfluidic chips and degradome sequencing to study this process.We identified a total of 386 conserved miRNAs and 153 novel miRNAs during early SE.According to the ANOVA test,239 miRNAs showed 12 distinct expression patterns.Through degradome sequencing,419 targets and 198 targets were identified for 136 known miRNAs and 37 novel miRNAs,respectively.Gene Ontology(GO)and metabolism pathway enrichment analysis revealed that these targets were significantly involved in oxidation-reduction processes,calmodulin-mediated signal transduction pathways and carbohydrate metabolism.The genes that were related to stress responses,phytohormone pathways and plant metabolism were identified within the targets of miR319,miR395,miR408,miR472,miR482,miR390,miR2055,miR156,miR157,miR171,miR396,miR397,miR529,miR535 and miR159.According to promoter analysis,various cis-acting elements related to plant growth and development,phytohormones response and stress response were present in the promoter of the miRNAs.The differential expression patterns of 11 miRNA-target modules were confirmed by real-time quantitative PCR.The study demonstrated that the miRNA plays an important role in the early SE process by regulating its target and then participating in carbohydrate metabolism and stress response.It also provided a valuable resource for further research in determining the genetic mechanism of SE,and then facilitating breeding programs on plants.

Optimization on Ultrasonic Extraction Method of Total Flavonoids for Liriodendron chinense Sarg.×L.tulipifera L. by Response Surface Methodology (RSM)

With the leaves,bark and roots of Liriodendron chinense Sarg.× L.tulipifera L.as experiment materials,the ultrasonic-assisted extraction conditions of total flavonoids were optimized by response surface Box-Behnken test design.Ultrasonic time and liquid-to-solid ratio had significant effects on the extraction amount of flavonoids from the leaves of L.chinense Sarg.× L.tulipifera L.;ultrasonic temperature and liquid-to-solid ratio had an interaction on the extraction amount of flavonoids;and the optimum ultrasonic time,temperature and liquid-to-solid ratio for the extraction of flavonoids from leaves of L.chinense Sarg.× L.tulipifera L.were 19.82 min,28.60 ℃ and 9.48 ml/g,respectively.Ultrasonic time,temperature and liquid-to-solid ratio had significant effects on the extraction amount of flavonoids from L.chinense Sarg.× L.tulipifera L.;there was a significant interaction between any two of the factors,which had a significant effect on the extraction of flavonoids;and the optimum extraction parameters for flavonoids in the bark were the ultrasonic time of 33.66 min,the ultrasonic temperature at 32.85 ℃ and the liquid-to-solid ratio of 11.39 ml/g.Ultrasonic time and liquid-to-solid ratio had significant effects on the extraction of flavonoids from roots;there was a significant interaction between ultrasonic time and liquid-to-solid ratio and between ultrasonic temperature and liquid-to-solid ratio;and the optimum extraction parameters for flavonoids from the roots of L.chinense Sarg.× L.tulipifera L.were the ultrasonic time of 32.38 min,the ultrasonic temperature at 25.0 ℃ and the liquid-to-solid ratio of 8.00 ml/g.The results of the three models were stable.The models are feasible and have good application value.

Research on the Effects of Light Intensity and Seeding Density on the Seed Germination and Seedling Growth of Liriodendron chinense

It provides a theoretical basis for the artificial promotion of the reproduction and regeneration of Liriodendron chinense through exploring the effects of light intensity and seeding density on the seed germination and seedling growth of this rare plant. Controlled experiments were conducted by setting different seeding densities and shading intensities to observe and detect the seed germination and seedling growth under different experimental conditions. The data were analyzed by SPSS and the model was fitted to calculate the seed germination rate, seedling emergence rate and seedling growth parameters of Liriodendron chinense, which were used to analyze the effects of seeding density and light intensity on the seed germination and seedling growth of Liriodendron chinense. Light has a significant impact on the seed germination and seedling growth of Liriodendron chinense (P P > 0.05). High density promotes the seedling height (the seedling height showed a rising trend with the increase of seeding density, reaching the highest at 500 seeds/m2. “3-stitch + 300 seeds/m2” combination is an appropriate condition for Liriodendron chinense reproduction since it can realize higher germination rate and better seedling growth potential. The seedling height and basal diameter growth curve of Liriodendron chinense fits well to the Logistic equation (R2 ≥ 0.977). Light has a significant impact on the seed germination and seedling growth of Liriodendron chinense, and appropriate shading treatment can increase the seed germination rate and seedling emergence rate of Liriodendron chinense. Seeding density has little influence on the seed germination rate of Liriodendron chinense, but high density will promote seedling height.

Fossil Winged Fruits of Fraxinus and Liriodendron from the Duho Formation,Pohang Basin,Korea

The Middle Miocene Duho Formation of the Yeonil Group,Pohang Basin,Korea is one of the best recognized formations for the Cenozoic plant fossils, including various leaves,reproductive organs,and fossil woods.We,in this paper,first report winged fruits(10 specimens) from the Duho Formation.They were identified into two structurally different groups:

Optimization of Germinated Conditions for Somatic Embryos in Liriodendron Hybrids

The development of somatic embryos is a key technology in plant breeding. To gain the best cultural conditions,the factors influencing on germination and transplanting survival rate of the somatic embryos in Liriodendron hybrids were optimized,including the development period of somatic embryos,macro-element,Vitamin C,genotypes,plant hormones and transplant medium in this study. The results showed that the optimal development phase of germination was torpedo-shaped embryo,and the base cultural medium of 3/4 MS with vitamin C can keep normal form from somatic embryos. The germination rate of somatic embryo had obvious genotype difference,among which the hybrid 1 × 5002 was the most sensitive( 82. 46%),and the hybrid 1 × 4088 was the most insensitive( 13. 24%). The medium with 0. 1 mg/L of KT + 0. 1 mg/L of IBA can help promote the germination of somatic embryogenesis. In addition,the yellow soil was more suitable than mixed peat soil for transplanting Liriodendron hybrids seedlings. Therefore,the obtainment of the optimal conditions has important guidance for production practices of Liriodendron hybrids.

鹅掌楸（Liriodendron chinense）遗传多样性的等位酶论证

选择５个具有地理代表性的鹅掌楸（Ｌｉｒｉｏｄｅｎｄｒｏｎｃｈｉｎｅｎｓｅ（Ｈｅｍｓｌ．）Ｓａｒｇ．）种群，分析６种酶系统９个位点上２７个等位基因的遗传变异。结果表明，鹅掌楸种内保存较高的等位酶变异。遗传多样性的分布特点与种群地理分布型式一致，鹅掌楸的种内分化主要表现为东、西部种群之间的差异，东部亚区的总的基因丰富程度低于西部亚区。同时，东部亚区内“岛”状隔离分布使其中的种群分化加深，种群间差异大于西部亚区中呈“带”状地理连续分布的种群间的分化。

湘西石漠化区湿地松-马褂木人工混交林林分结构及土壤理化性质研究

为探究湘西石漠化区湿地松-马褂木人工混交林林分结构及土壤理化性质,该研究以湘西石漠化地区湿地松-马褂木人工针阔混交林为对象,利用植物群落学分析和野外取样检测的方法,分析林分结构和土壤理化性质,运用Winklemass 1.0计算林分空间结构参数,并用三维离散随机变量分析了优势种的空间分布格局。结果表明:(1)林分内胸径(DBH)≥2 cm的林木株数为897 plants·hm^(-2),隶属于15科16属。主林层为湿地松,平均DBH为32.3 cm,重要值为44.2%;次林层为阔叶树,中幼龄林木居多,其中樟树、马褂木为优势树种,重要值分别为17.1%和13.2%。此外,还存在较多处于劣势生态位的天然更新种。(2)林木的水平分布格局偏向于随机分布(W=0.503);林分整体趋向于中庸偏劣势过渡的态势(U=0.505);种间隔离程度较高(M=0.689),林木混交状况良好。空间结构参数的三维离散随机变量表明,湿地松87.3%为优势和亚优势,马褂木41.7%为亚优势、26.9%为中庸态势,樟树23.5%为中庸态势、56.8%为劣势和绝对劣势。(3)林分土壤pH值趋于中性;与撂荒地相比,林分土壤的容重、持水量、孔隙度、有机碳、全钾、全氮、全磷等因子均明显改善,但整体而言,林分土壤仍然较为贫瘠,局部土壤紧实,保水能力差。综上表明,湿地松、马褂木作为先锋树种生长43年后,林分有向异龄林、强度混交林演替的趋势;林分内中幼龄阔叶树株数占比较大,近熟林出现断层,老龄针叶树占据优势生态区位,需抽针补阔、间针育阔,择伐劣势木,促使林分向阳生性阔叶树为主、中生性和耐阴性阔叶树为次的林分结构演替。该研究结果为湘西石漠化区的植被恢复、人工林结构优化和土壤改良提供了理论依据。

Immunological Activities of Components from Leaves of Liriodendron chinensis

Objectives To investigate the anti-inflammatory components from the leaves of Liriodendron chinensis. Methods The 95% alcohol extract from the leaves of L. chinensis was subjected to column chromatography, and the structures of purified compounds were determined by spectral methods. The bioassay was performed through the inhibitory effects on the inflammatory cells activated by lipopolysaccharide （LPS）. Results Nine compounds were isolated, including octacosanoic acid （1）, stearic acid （2）, （2R-2-hydroxy-N-[（2S,3S,4R,8E- l ,3,4-tri-hydroxyicos-8-en- 2-yl]tetracosanamide （3）, （2 R）- 2- hyd roxy- N- [（2 S, 3 S,4 R,8 E）- 1 - O-β- D-glucopyranosyloxy-3,4-dihydroxy- octadec-8-en-2-yl]eicosanamide （4）, （2R）-2-hydroxy-N-[（2S,3S,4R,8E）-l-O-β-D- glucopyranosyloxy-3,4-dihydroxyoctadec-8-en-2-yl]hexadecanamide （5）, dicentrinone （6）, liriodenine （7）, daucosterol （8）, and liriodendritol （9） and among which five compounds could significantly lower the content of nitric oxide （NO） from peritoneal macrophages of rats induced by LPS and reduce the splenic lymphocyte proliferation in mice. This is the first report on the occurrence of ceramides and dicentrinone in the plants of Liriodendron Linn. Conclusion The five compounds are likely to be anti-inflammatory compounds concerning to their pronounced inhibitory action on the activated inflammatory cells. This assessment might provide a basis for searching the potent active compounds used for the treatment of inflammation.

北美鹅掌楸LtMYB305基因的克隆及功能分析

【目的】MYB305作为MYB家族R2R3亚族成员,对植物花蜜腺发育、花蜜蛋白表达、淀粉积累和水解、类黄酮合成发挥重要作用。因此,研究MYB305的表达模式及功能对于北美鹅掌楸花蜜腺调控分子机理研究具有重要意义。【方法】本文以蜜源植物北美鹅掌楸的花蜜腺为材料,通过分光光度计法测定5个时期花蜜腺的花青素含量,采用RACE技术克隆LtMYB305基因,利用RT-qPCR技术检测了该基因在北美鹅掌楸不同组织间相对表达量,以烟草叶片为材料验证LtMYB305蛋白定位,并以野生型拟南芥为材料进行遗传转化实验,研究LtMYB305基因功能。【结果】北美鹅掌楸花蜜腺的花青素从膨大后期开始积累,初放期含量急剧增加,败花期含量最高,达27.14μg/g,与花蜜分泌、着色过程相一致。LtMYB305基因全长为931 bp,编码了198个氨基酸,其蛋白为亲水性蛋白和非跨膜蛋白;LtMYB305仅在北美鹅掌楸盛花期花蜜腺中高水平表达,在其他组织中几乎不表达。LtMYB305蛋白定位于细胞核。过表达LtMYB305基因的拟南芥出现侧蜜腺的“蜜腺沟”消失和加深表型,与花蜜腺相关基因AtMYB305、AtPIN6和AtSWEET9表达量上调,AtCRC、AtBOP1/2、AtMYB21、AtSWEET3/4/7基因表达量下调。【结论】LtMYB305具有典型转录因子特征,并且参与调控拟南芥花蜜腺的发育。

龙山县中海拔山区鹅掌楸人工林单木生长规律与模型研究

以龙山县砂子坡国有林场36年生鹅掌楸人工林为研究对象,采用样地调查分析法、平均解析木法等方法分析了鹅掌楸人工林的胸径、树高和材积生长特征,并对胸径、树高和材积的生长过程进行了拟合,结果表明:(1)36年生鹅掌楸胸径总生长量和树高总生长量均持续平缓增长,第36年时分别达到20.1cm和20.7m;材积总生长量前期增长较慢,第24年后快速增长,第36年达到0.32745m^(3)。(2)胸径和树高的连年生长量上下波动较大;胸径平均生长量前15a快速增长,后期保持在0.54cm左右;树高平均生长量持续下降,第36年降至0.57m;材积连年生长量和平均生长量均持续增长,第36年分别达0.02136m^(3)和0.00850m^(3);36年生鹅掌楸未达到数量成熟,还不能确定主伐年龄;建议在第14~15年进行一次透光伐、第28~30年进行一次生长疏伐为宜。(3)通过分析得出胸径、树高和材积最优生长模型分别为Korf方程、Roляcp方程和Logistic方程;筛选出的各生长模型可用于预测龙山县中海拔山区鹅掌楸人工林幼龄林、中龄林和近熟林的生长情况,指导鹅掌楸人工林的经营与管理。

截顶和施肥对亚美马褂木采穗圃产量和质量的影响

为探究截顶及施肥措施对亚美马褂木采穗圃母株产量与质量的影响,筛选可供生产上推广的亚美马褂木采穗圃经营措施,于2022年在福建省漳平五一国有林场后福采穗圃开展亚美马褂木采穗圃母株不同截顶和施肥(截顶+施肥、未截顶+施肥、截顶+未施肥、未截顶+未施肥)试验。结果表明:不同截顶和施肥处理母株的生长、萌条产量和质量均存在极显著差异,其中以截顶+施肥处理效果最好,其母株地径生长和有效萌条量分别比未截顶+施肥、截顶+未施肥、未截顶+未施肥处理提高23.08%和70.83%、18.52%和74.47%、88.24%和110.26%,总萌条量分别比未截顶+施肥、未截顶+未施肥处理母株提高56.06%、53.73%,有效萌条率、有效萌条枝长、有效萌条枝径分别比截顶+未施肥、未截顶+未施肥处理提高72.80%和36.76%、80.77%和46.88%、100.00%和60.00%。亚美马褂木母株地径与萌条产量、质量指标之间存在显著或极显著正相关关系,截顶处理萌条数量与质量指标之间相关性不显著,截顶+施肥处理的总萌条量和萌条质量指标之间呈极显著正相关关系。综合结果表明,单独采取截顶或施肥不能兼顾母株萌条产量和质量,截顶+施肥组合处理可作为亚美马褂木采穗圃经营的有效措施。

Primary measurement of pollen flow in Liriodendron chinense using RAPD markers

Techniques of tracking movements of pollen grains are essential for many topics in pollination biology. Pollen transfer of Liriodendron chinense(Hemsl.) Sarg., a hermaphroditic plant, may be both interfloral and intrafloral pollination. Observations on pollinator movements and flower emasculated experiments in natural populations showed that most of pollen grains deposited on stigmas in a flower are foreign. But it is not certain whether cross pollination or long distance pollen transfer occurs in this insect-pollinated plant. The authors attempt to use random amplified polymorphic DNA (RAPD) loci for paternity analysis to mark pollen dispersal. The results indicated pollen via gene transportation reached at least 100 m away from the pollen source in a selected population. The primary study suggests a larger effective population size in this endangered plant. With its rapid and simple characters, RAPD methods can be a suitable technique for marking pollen flow and able to be widely used in various taxa.

Overexpression of the LcPIN2 and LtPIN2 Gene in Arabidopsis thaliana Promotes Root Elongation

The auxin polar transporter,PIN-FORMED 2(PIN2)plays an important role in root development.However,it remains unclear whether PIN2 genes form two Liriodendron species,L.chinense(LcPIN2)and L.tulipifera(LtPIN2),are both involved in root development and whether and to what extent these two genes diverge in function.Here,we cloned and overexpressed LcPIN2 and LtPIN2 in Arabidopsis thaliana wild-type(WT)and Atpin2 mutant.Phylogenetic and sequence analysis showed a small degree of differentiation between these two Liriodendron PIN2 genes.Tissue-specific gene expression analysis indicated that both Liriodendron PIN2 genes were highly expressed in roots,implying a potential role in root development.Finally,heterologous overexpression of LcPIN2 and LtPIN2 in Arabidopsis both significantly increased the root length compared to wild-type and empty vector.Furthermore,the root length defect in Atpin2 was complemented both by LcPIN2 and LtPIN2.However,heterologous overexpression of LcPIN2 and LtPIN2 cannot rescue the defect in root gravitropism of Atpin2 mutants.Taken together,ourfindings unravel PIN2 genes from the magnoliids plant Liriodendron were functionally conserved with AtPIN2 in the dicotyledonous plant Arabidopsis in regard to the regulation of root length,but not root gravitropism.This study also provides a potential target for genetic improvement of the root system in these valuable forest trees Liriodendron.