植物根构型特性与磷吸收效率

植物根构型,即根系在生长介质中的空间造型和分布,与磷吸收效率密切相关;认识植物根构型,可为植物磷效率的遗传改良提供依据。长期以来,人们试图定量描述植物根构型,确立一个能客观全面地描述根系三维立体构型的综合指标。试验指出,植物主要通过向地性变化和根冠之间的碳源分配来改变根构型,从而影响磷吸收效率;根系向地性变化可由缺磷等因素所诱导,且存在着一定的遗传变异性。有证据表明,根构型对低磷胁迫的适应性变化是     

植物根系向地性感应的分子机理与养分吸收

植物根系向地性是决定根系空间生长趋势的主要因素之一,对于养分吸收具有重要影响.认识根系向地性感应和根系生长变化的分子机理及其与养分吸收的关系,可为遗传改良根系性状、提高植物养分吸收效率提供理论依据.本文从重力感应、信号转导和生长素非对称分布等方面总结了植物根系向地性感应的分子机理,探讨了根系在养分胁迫下(特别是磷胁迫下)向地性变化的生理基础及其与养分吸收(特别是磷吸收)的关系,最后对根系向地性研究的若干问题进行了展望.     

植物根系向地性感应的分子机理与养分吸收

植物根系向地性是决定根系空间生长趋势的主要因素之一, 对于养分吸收具有重要影响。认识根系向地性感应和根系生长变化的分子机理及其与养分吸收的关系, 可为遗传改良根系性状、提高植物养分吸收效率提供理论依据。本文从重力感应、信号转导和生长素非对称分布等方面总结了植物根系向地性感应的分子机理, 探讨了根系在养分胁迫下(特别是磷胁迫下)向地性变化的生理基础及其与养分吸收(特别是磷吸收)的关系, 最后对根系向地性研究的若干问题进行了展望。     

植物根系响应低磷胁迫的机理研究

磷是植物生长的必需营养元素之一。但大部分土壤中有效磷含量较低,难以满足植物生长的需求。作物磷效率遗传改良是解决土壤磷供应不足的有效途径。根系是植物吸收矿质营养元素的主要器官,其性状决定了植物对土壤磷的吸收利用效率。解析根系对低磷胁迫的响应机制是进行作物磷效率遗传改良的基础。主要介绍了近年来关于植物根系响应低磷胁迫机理的重要研究成果。     

植物根毛的发生、发育及养分吸收

根毛是植物吸收养分的重要器官,认识根毛的发生、发育规律及其与养分吸收的关系,可为植物养分吸收效率的遗传改良提供依据。介绍了植物根毛的形态特性、发生和发育过程及其调控机制,并结合本实验室的工作,讨论了根毛对养分吸收的贡献、根毛受养分有效性的调节及其与其他根系形态构型性状间的关系,阐述了根毛中养分转运等植物营养过程及其生理和分子生物学基础。最后提出了关于根毛研究中的一些问题和研究前景。     

植物根毛的发生、发育及养分吸收

根毛是植物吸收养分的重要器官,认识根毛的发生、发育规律及其与养分吸收的关系,可为植物养分吸收效率的遗传改良提供依据.介绍了植物根毛的形态特性、发生和发育过程及其调控机制,并结合本实验室的工作,讨论了根毛对养分吸收的贡献、根毛受养分有效性的调节及其与其他根系形态构型性状间的关系,阐述了根毛中养分转运等植物营养过程及其生理和分子生物学基础.最后提出了关于根毛研究中的一些问题和研究前景.     

植物磷营养高效的分子生物学研究进展

挖掘利用植物自身的磷高效营养遗传资源是农业可持续发展的关键。磷高效营养性状涉及根形态、根分泌物、膜与体内磷转运以及菌根等许多方面,表现为数量遗传性状及受多基因控制。近年来,许多高亲和磷转运子基因已被克隆, 磷向地上部转运和磷吸收负反馈调节的控制基因也被发现, 对于根系分泌有机酸和酸性磷酸酶的基因的控制也有了一定的了解, 但目前对于根毛、排根、根构型以及菌根的营养学意义性状的分子生物学研究进展缓慢。     

植物磷营养高效的分子生物学研究进展

挖掘利用植物自身的磷高效营养遗传资源是农业可持续发展的关键.磷高效营养性状涉及根形态、根分泌物、膜与体内磷转运以及菌根等许多方面,表现为数量遗传性状及受多基因控制.近年来,许多高亲和磷转运子基因已被克隆,磷向地上部转运和磷吸收负反馈调节的控制基因也被发现,对于根系分泌有机酸和酸性磷酸酶的基因的控制也有了一定的了解,但目前对于根毛、排根、根构型以及菌根的营养学意义性状的分子生物学研究进展缓慢.     

遮阴和磷限制下胡桃楸1级根养分吸收策略选择

本研究探讨了1年生胡桃楸在不同光照环境和不同剂量磷肥下根系功能性状的变化，以了解胡桃楸根系资源获取策略与光环境和磷养分限制之间的关系。设置了4种遮阴处理(全光、65%全光、35%全光和20%全光),以及3种磷肥处理(对照、200%和500%土壤本底有效磷),并测定了1级根形态、构型特征和菌根侵染率的变化。结果表明：随着遮阴程度的增加，胡桃楸1级根的平均直径、平均根长和菌根侵染率逐渐减小，比根长、比表面积、分支比和分支强度则呈现先增加后减小的趋势。随着磷含量的减少，1级根直径逐渐变细，而菌根侵染率则逐渐升高。在遮阴环境下，胡桃楸的根系形态和构型会发生适应性变化，通过增加比根长、比表面积、分支比和分支强度等来适应遮阴环境；而在磷限制条件下，胡桃楸的根系更倾向于与菌根真菌共生以促进对磷的吸收。胡桃楸在透光度为35%的林地人工更新时，根系形态、构型会做出改变以适应遮阴环境；在磷受限的情况下，胡桃楸与菌根真菌共生能力增强，可以适当接种菌根来帮助根系吸收磷。     

菜豆根构型对低磷胁迫的适应性变化及基因型差异

利用特殊设计的营养袋纸培养和分层式磷控释砂培等根系生长系统结合计算机图像分析技术,以基根根长在生长介质各层的相对分布和基根平均生长角度为指标,定量测定菜豆（Ｐｈａｓｅｏｌｕｓ ｖｕｌｇａｒｉｓ Ｌ．）根构型在低磷胁迫下的适应性变化及其与磷效率的关系。结果表明,菜豆根构型对低磷胁迫具有适应性反应,在缺磷条件下基根向地性减弱,基根在生长介质表层相对分布增多、基根平均生长角度（与水平线夹角）变小,从而导     

Adaptive Changes and Genotypic Variation for Root Architecture of Common Bean in Response to Phosphorus Deficiency

Root architectural responses to phosphorus (p) availability may be an important trait for P acquisition efficiency. In the present study, The authors examined the effects of P availability on root architectural responses of different common bean genotypes. Five common bean (Phaseolus vulgaris L.) genotypes representing different origins and ecotypic races were compared both in a specially designed paper pouch system and a stratified P buffer sand culture system with computer image analysis. The results showed that root architecture was regulated by P availability. P deficiency led to form a shallower root system, as indicated by increased relative distribution of basal root length in the upper layers and decreased the growth angle of basal roots. There was significant genetic variation in root architecture in response to P deficiency both in the paper pouch system and the stratified sand culture system. Under low P conditions some genotypes were more gravitropically sensitive to low P availability, resulting in producing a shallower root system and enhanced root exploration into the surface soil, where soil available P is more concentrated. G19833 and DOR364, which were most contrasting in P efficiency, were also very different in root architectural response to P availability. The results from this study suggest that P availability regulates root architecture and P deficiency leads to shallower root architecture in beans. The genetic potential of root architecture provides the possibility of selecting this trait for improving P acquisition efficiency in common bean.     

Genotypic Variation in Root Morphological Characteristics of Common Bean in Relation to Phosphorus Efficiency (in English)

Root morphology in plants may be related to phosphorus (P) efficiency by affecting the absorption characteristics of the root system. However, genotypic variation in root morphological characteristics of common bean (Phaseolus vulgaris L.) as affected by P availability has not been well clarified. In the present study, systematic studies were conducted in a P-buffered sand culture system using three pairs of common bean parental materials with contrasting root traits in response to P deficiency. The results indicate that P availability significantly affects bean root morphology. Common bean tends to have smaller root system, shorter and coarser roots at low P availability. Genotypic variation in root morphology was observed among different genotypes in response to P availability. The P efficient genotypes appear to have larger, finer and longer root systems than the P inefficient genotypes, and such a variation was particularly obvious in the basal roots. From allomeric analysis, we found that morphological characteristics of the basal roots contribute more to P efficiency than those of the tap roots. Further studies with the F9 recombinant inbred lines derived from one of the most contrasting parental pairs, DOR364 and G19833, confirmed the above findings, indicating that those morphological characteristics are inheritable hence provide potential for genetic improvement. Root morphology in plants may be related to phosphorus (P) efficiency by affecting the absorption characteristics of the root system. However, genotypic variation in root morphological characteristics of common bean (Phaseolus vulgaris L.) as affected by P availability has not been well clarified. In the present study, systematic studies were conducted in a P-buffered sand culture system using three pairs of common bean parental materials with contrasting root traits in response to P deficiency. The results indicate that P availability significantly affects bean root morphology. Common bean tends to have smaller root system, shorter and coarser roots at low P availability. Genotypic variation in root morphology was observed among different genotypes in response to P availability. The P efficient genotypes appear to have larger, finer and longer root systems than the P inefficient genotypes, and such a variation was particularly obvious in the basal roots. From allomeric analysis, we found that morphological characteristics of the basal roots contribute more to P efficiency than those of the tap roots. Further studies with the F9 recombinant inbred lines derived from one of the most contrasting parental pairs, DOR364 and G19833, confirmed the above findings, indicating that those morphological characteristics are inheritable hence provide potential for genetic improvement.     

菜豆根形态特性的基因型差异与磷效率

应用磷控释砂培以及计算机图象分析技术,研究了磷效率差异显的菜豆（Phaseolus vulgaris L.)亲本及其重组自交系后代的根形态特性及其与磷效率的关系。试验结果表明,供磷状况显影响菜豆根系形态学特性。在低磷胁迫下,菜豆根系总根长变短、根部生物量减少,根直径增大。菜豆根形态特性对低磷有效性的适应性反应具有显的基因型差异。在低磷条件下磷高效率基因型的根系比磷低效率基因型相对根部生物量较大、总根长较长,根表面积较大。异计分析表明,菜豆基根根形态特性在低磷条件下的适应性变化对磷效率的贡献远远大于主根,并且这些适应性变化是可以遗传的,表明通过对菜豆根形态特性进行遗传改良来提高磷效率有一定的可行性。     

The importance of root gravitropism for inter-root competition and phosphorus acquisition efficiency: results from a geometric simulation model

We have observed that low soil phosphorus availability alters the gravitropic response of basal roots in common bean (Phaseolus vulgaris L.), resulting in a shallower root system. In this study we use a geometric model to test the hypotheses that a shallower root system is a positive adaptive response to low soil P availability by (1) concentrating root foraging in surface soil horizons, which generally have the highest P availability, and (2) reducing spatial competition for P among roots of the same plant. The growth of nine root systems contrasting in gravitropic response over 320 h was simulated in SimRoot, a dynamic three-dimensional geometric model of root growth and architecture. Phosphorus acquisition and inter-root competition were estimated with Depzone, a program that dynamically models nutrient diffusion to roots. Shallower root systems had greater P acquisition per unit carbon cost than deeper root systems, especially in older root systems. This was due to greater inter-root competition in deeper root systems, as measured by the volume of overlapping P depletion zones. Inter-root competition for P was a significant fraction of total soil P depletion, and increased with increasing values of the P diffusion coefficient (De), with root age, and with increasing root gravitropism. In heterogenous soil having greater P availability in surface horizons, shallower root systems had greater P acquisition than deeper root systems, because of less inter-root competition as well as increased root foraging in the topsoil. Root P acquisition predicted by SimRoot was validated against values for bean P uptake in the field, with an r ² between observed and predicted values of 0.75. Our results support the hypothesis that altered gravitropic sensitivity in P-stressed roots, resulting in a shallower root system, is a positive adaptive response to low P availability by reducing inter-root competition within the same plant and by concentrating root activity in soil domains with the greatest P availability. This revised version was published online in August 2006 with corrections to the Cover Date.     

Topsoil foraging – an architectural adaptation of plants to low phosphorus availability

Low phosphorus availability is a primary constraint to plant productivity in many natural and agricultural ecosystems. Plants display a wide array of adaptive responses to low phosphorus availability that generally serve to enhance phosphorus mobility in the soil and increase its uptake. One set of adaptive responses is the alteration of root architecture to increase phosphorus acquisition from the soil at minimum metabolic cost. In a series of studies with the common bean, work in our laboratory has shown that architectural traits that enhance topsoil foraging appear to be particularly important for genotypic adaptation to low phosphorus soils (phosphorus efficiency). In particular, the gravitropic trajectory of basal roots, adventitious rooting, the dispersion of lateral roots, and the plasticity of these processes in response to phosphorus availability contribute to phosphorus efficiency in this species. These traits enhance the exploration and exploitation of shallow soil horizons, where phosphorus availability is greatest in many soils. Studies with computer models of root architecture show that root systems with enhanced topsoil foraging acquire phosphorus more efficiently than others of equivalent size. Comparisons of contrasting genotypes in controlled environments and in the field show that plants with better topsoil foraging have superior phosphorus acquisition and growth in low phosphorus soils. It appears that many architectural responses to phosphorus stress may be mediated by the plant hormone ethylene. Genetic mapping of these traits shows that they are quantitatively inherited but can be tagged with QTLs that can be used in plant breeding programs. New crop genotypes incorporating these traits have substantially improved yield in low phosphorus soils, and are being deployed in Africa and Latin America.     

QTL analysis of root traits as related to phosphorus efficiency in soybean

Background and Aims

Low phosphorus (P) availability is a major constraint to soybean growth and production, especially in tropical and subtropical areas. Root traits have been shown to play critical roles in P efficiency in crops. Identification of the quantitative trait loci (QTLs) conferring superior root systems could significantly enhance genetic improvement in soybean P efficiency.

Methods

A population of 106 F₉ recombinant inbred lines (RILs) derived from a cross between BD2 and BX10, which contrast in both P efficiency and root architecture, was used for mapping and QTL analysis. Twelve traits were examined in acid soils. A linkage map was constructed using 296 simple sequence repeat (SSR) markers with the Kosambi function, and the QTLs associated with these traits were detected by composite interval mapping and multiple-QTL mapping.

Key Results

The first soybean genetic map based on field data from parental genotypes contrasting both in P efficiency and root architecture was constructed. Thirty-one putative QTLs were detected on five linkage groups, with corresponding contribution ratios of 9·1–31·1 %. Thirteen putative QTLs were found for root traits, five for P content, five for biomass and five for yield traits. Three clusters of QTLs associated with the traits for root and P efficiency at low P were located on the B1 linkage group close to SSR markers Satt519 and Satt519-Sat_128, and on the D2 group close to Satt458; and one cluster was on the B1 linkage group close to Satt519 at high P.

Conclusions

Most root traits in soybean were conditioned by more than two minor QTLs. The region closer to Satt519 on the B1 linkage group might have great potential for future genetic improvement for soybean P efficiency through root selection.