Nutrient Deficiency Affects Root Architecture of Young Seedlings of Malus hupehensis (Pamp) Rehd. Under Conditions of Artificial Medium Cultivation

What the researchers go in for is to establish models between root architecture （RA） changes and nutrition, mold ideal root architecture of apple trees, improve the nutrient uptake efficiency, and further explore the functional mechanism of nutrient elements during the course of RA construction. The cultivation system of filter paper is utilized to research the effect of nutrient deficiency on the RA of Malus hupehensis （Pamp.） Rehd. There may be eight types of RA. In complete Hogland solution, the main type of RA is ＂lateral roots clustering in the upper and middle regions of primary root＂. With the lack of P, K or Ca, the main type of RA is ＂lateral roots clustering in the upper region primary root＂, and the ＂lateral roots clustering in the upper and middle regions of primary root＂ types of RA decrease. But with shortage of P, the type of lateral roots clustering in the upper and lower regions of primary root increases, and the type of lateral roots clustering in the middle region of primary root decreases, with the types of RA diversified. Under the condition of K deficiency, the type of no lateral root increases and types of lateral roots clustering in the middle region of primary root decrease, and the percentage of such types as ＂no lateral root＂, ＂lateral roots clustering in the upper region of primary root＂, and ＂lateral roots clustering in the upper and middle regions of primary root＂ accounts for 97.9% in all, with the types of RA simplified. With lack of Fe, Mg or Zn, the main type of RA is ＂lateral roots clustering in the upper and middle regions of primary root＂, but the type of lateral roots evenly-distributed on primary root increases. The main type of RA is ＂lateral roots evenlydistributed on primary root＂, under the condition of N deficiency, and the types of RA turn out to be diversified. There exists a close relation between nutrient deficiency and RA changes. Owing to various forms of nutrient deficiency, correspondingly different types of RA have been produced.

Root architecture characteristics of plant inlay in live slope grating

In the experimental garden of the Department of Soil Bioengineering and Landscape Construction, University of Applied Life Sciences in Vienna, Austria, coarse root systems of three different brush species were completely excavated and semiutomatically digitized. The species were Lonicera xylosteum, Ligustrum vulgare and Euonymus europaeus. The 3-D root architectures reveal different growth strategies between species, which are related to ecological characteristics and physical soil properties. The root architecture of Lonicera xylosteum and Ligustrum vulgare, planted in the under layer of the live slope grading, where the soil is very tight and the soil water content and fertility are relatively low, is shallow. However, the root distribution of E. europaeus, planted in the middle layer, where environmental conditions are better, is deeper. Most of the root biomass of the three species is concentrated in the 0-30 cm soil layer. A quarter of the root biomass ofLigustrum vulgare is distributed in the upper layer of the plant inlay. E. europaeus has a relatively even distribution in the 30-0 cm and 60-90 cm soil layer.

Development of Root Phenotyping Platforms for Identification of Root Architecture Mutations in EMS-Induced and Low-Path-Sequenced Sorghum Mutant Population

Sorghum’s natural adaptation to a wide range of abiotic stresses provides diverse genetic reserves for potential improvement in crop stress tolerance. Growing interest in sorghum research has led to the expansion of genetic resources though establishment of the sorghum association panel (SAP), generation of mutagenized populations, and recombinant inbred line (RIL) populations, etc. Despite rapid improvement in biotechnological tools, lack of efficient phenotyping platforms remains one of the major obstacles in utilizing these genetic resources. Scarcity of efforts in root system phenotyping hinders identification and integration of the superior root traits advantageous to stress tolerance. Here, we explored multiple approaches in root phenotyping of an ethyl methanesulfonate (EMS)-mutagenized sorghum population. Paper-based growth pouches (PGP) and hydroponics were employed to analyze root system architecture (RSA) variations induced by mutations and to test root development flexibility in response to phosphorus deficiency in early growing stages. PGP method had improved capabilities compared to hydroponics providing inexpensive, space-saving, and high-throughput phenotyping of sorghum roots. Preliminary observation revealed distinct phenotypic variations which were qualitatively and quantitatively systemized for association analysis. Phenotypes/ideotypes with root architecture variations potentially correlated with Pi acquisition were selected to evaluate their contribution to P-efficiency (PE). Sand mixed with P-loaded activated alumina substrate (SAS) provided closely to natural but still controlled single-variable conditions with regulated Pi availability. Due to higher labor and cost input we propose SAS to be used for evaluating selected sorghum candidates for PE. The ability of rapidly screening root phenotypes holds great potential for discovering genes responsible for relevant root traits and utilizing mutations to improve nutrient efficiency and crop productivity.

Increasing root-lower characteristics improves drought tolerance in cotton cultivars at the seedling stage

Drought is an important abiotic stress factor in cotton production.The root system architecture(RSA)of cotton shows high plasticity which can alleviate drought-related stress under drought stress(DS)conditions;however,this alleviation is cultivar dependent.Therefore,this study estimated the genetic variability of RSA in cotton under DS.Using the paper-based growth system,we assessed the RSA variability in 80 cotton cultivars at the seedling stage,with 0 and10%polyethylene glycol 6000(PEG6000)as the control(CK)and DS treatment,respectively.An analysis of 23 aboveground and root traits in the 80 cotton cultivars revealed different responses to DS.On the 10th day after DS treatment,the degree of variation in the RSA traits under DS(5–55%)was greater than that of CK(5–49%).The 80 cultivars were divided into drought-tolerant cultivars(group 1),intermediate drought-tolerant cultivars(group 2),and drought-sensitive cultivars(group 3)based on their comprehensive evaluation values of drought resistance.Under DS,the root lengthlower,root area-lower,root volume-lower,and root length density-lower were significantly reduced by 63,71,76,and 4%in the drought-sensitive cultivars compared to CK.Notably,the drought-tolerant cultivars maintained their root lengthlower,root area-lower,root volume-lower,and root length density–lower attributes.Compared to CK,the root diameter(0–2 mm)-lower increased by 21%in group 1 but decreased by 3 and 64%in groups 2 and 3,respectively,under DS.Additionally,the drought-tolerant cultivars displayed a plastic response under DS that was characterized by an increase in the root-lower characteristics.Drought resistance was positively correlated with the root area-lower and root length density-lower.Overall,the RSA of the different cotton cultivars varied greatly under DS.Therefore,important root traits,such as the root-lower traits,provide great insights for exploring whether drought-tolerant cotton cultivars can effectively withstand adverse environments.

Ideotype root architecture for efficient nitrogen acquisition by maize in intensive cropping systems

The use of nitrogen(N) fertilizers has contributed to the production of a food supply sufficient for both animals and humans despite some negative environmental impact.Sustaining food production by increasing N use efficiency in intensive cropping systems has become a major concern for scientists,environmental groups,and agricultural policymakers worldwide.In high-yielding maize systems the major method of N loss is nitrate leaching.In this review paper,the characteristic of nitrate movement in the soil,N uptake by maize as well as the regulation of root growth by soil N availability are discussed.We suggest that an ideotype root architecture for efficient N acquisition in maize should include(i) deeper roots with high activity that are able to uptake nitrate before it moves downward into deep soil;(ii) vigorous lateral root growth under high N input conditions so as to increase spatial N availability in the soil;and(iii) strong response of lateral root growth to localized nitrogen supply so as to utilize unevenly distributed nitrate especially under limited N conditions.

An Arabidopsis ABC Transporter Mediates Phosphate Deficiency-Induced Remodeling of Root Architecture by Modulating Iron Homeostasis in Roots

The remodeling of root architecture is a major developmental response of plants to phosphate （Pi） deficiency and is thought to enhance a plant＇s ability to forage for the available Pi in topsoil. The underlying mechanism controlling this response, however, is poorly understood. In this study, we identified an Arabidopsis mutant, hps 10 （hypersensitive to Pi starvation 10）, which is morphologically normal under Pi sufficient condition but shows increased inhibition of primary root growth and enhanced production of lateral roots under Pi defi- ciency, hpslO is a previously identified allele （als3-3） of the ALUMINUM SENSITIVE3 （ALS3） gene, which is involved in plant tolerance to aluminum toxicity. Our results show that ALS3 and its interacting protein AtSTAR1 form an ABC transporter complex in the tonoplast. This protein complex mediates a highly electro- genic transport in Xenopus oocytes. Under Pi deficiency, als3 accumulates higher levels of Fe3＋ in its roots than the wild type does. In Arabidopsis, LPR1 （LOW PHOSPHATE ROOT1） and LPR2 encode ferroxidases, which when mutated, reduce Fe3＋ accumulation in roots and cause root growth to be insensitive to Pi defi- ciency. Here, we provide compelling evidence showing that ALS3 cooperates with LPR1/2 to regulate Pi deficiency-induced remodeling of root architecture by modulating Fe homeostasis in roots.

Phosphate Availability Alters Lateral Root Anatomy and Root Architecture of Fraxinus mandshurica Rupr. Seedlings

Abstract: Plants have evolved some mechanisms to maximize the efficiency of phosphorus acquisition. Changes in root architecture are one such mechanism. When Fraxinus mandshurica Rupr. seedlings were grown under conditions of low phosphorus availability, the length of cells in the meristem zone of the lateral roots was longer, but the length of cells in the elongation and mature zones of the lateral roots was shorter, compared with seedlings grown under conditions of high phosphorus availability. The elongation rates of primary roots increased as phosphorus availability increased, but the elongation rates of the branched zones of the primary roots decreased. The number of lateral root primordia and the length of the lateral roots decreased as phosphorus availability increased. The topological index (altitude slope) decreased as phosphorus availability increased, suggesting that root architecture tended to be herringbone-like when seedlings were grown under conditions of low phosphate availability. Herringbone-like root systems exploit nutrients more efficiently, but they have higher construction costs than root systems with a branching pattern.

Improving crop nutrient efficiency through root architecture modifications

Improving crop nutrient ef ficiency becomes an essential consideration for environmentally friendly and sustainable agriculture. Plant growth and development is dependent on 17 essential nutrient elements,among them,nitrogen（N） and phosphorus（P） are the two most important mineral nutrients. Hence it is not surprising that low N and/or low P availability in soils severely constrains crop growth and productivity,and thereby have become high priority targets for improving nutrient ef ficiency in crops. Root exploration largely determines the ability of plants to acquire mineral nutrients from soils. Therefore,root architecture,the 3-dimensional con figuration of the plant＇s root system in the soil,is of great importance for improving crop nutrient ef ficiency. Furthermore,the symbiotic associations between host plants and arbuscular mycorrhiza fungi/rhizobial bacteria,are additional important strategies to enhance nutrient acquisition. In this review,we summarize the recent advances in the current understanding of crop species control of root architecture alterations in response to nutrient availability and root/microbe symbioses,through gene or QTL regulation,which results in enhanced nutrient acquisition.

Natural variation of hormone levels in Arabidopsis roots and correlations with complex root architecture

Studies on natural variation are an important tool to unravel the genetic basis of quantitative traits in plants. Despite the significant roles of phytohormones in plant development, including root architecture, hardly any studies have been done to investigate natural variation in endogenous hormone levels in plants. Therefore, in the present study a range of hormones were quantified in root extracts of thirteen Arabidopsis thaliana accessions using a ultra performance liquid chromatography triple quadrupole mass spectrometer. Root system architecture of the set of accessions was quantified, using a new parameter （mature root unit） for complex root systems, and correlated with the phytohormone data. Significant variations in phytohormone levels among the accessions were detected, but were remarkably small, namely less than three-fold difference between extremes. For cytokinins, relatively larger variations were found for ribosides and glucosides, as compared to the free bases. For root phenotyping, length-related traits--lateral root length and total root length--showed larger variations than lateral root number-related ones. For root architecture, antagonistic interactions between hormones, for example, indole-3-acetic acid to trans-zeatin were detected in correlation analysis. These findings provide conclusive evidence for the presence of natural variation in phytohormone levels in Arabidopsis roots, suggesting that quantitative genetic analyses are feasible.

Ecological adaptation of Reaumuria soongorica root system architecture to arid environments

The architectural parameters of Reaumuria soongorica root system in different habitats of Gansu Province, China were analyzed to examine its ecological adaptability to arid environments. Results show that： （1） Topological indices of R. Soongorica root sys- tem are small in all habitats, and root branching pattem tends to be dichotomous. Also, the indices gradually increase in the Min- qin windblown sand region and the Zhangye Gobi region in Hexi Corridor, which indicates that drought tends to produce her- ringbone-like root branching pattems. （2） Fractal dimension values ofR. Soongorica root system are small and not obvious in the Minqin windblown sand region and the Zhangye Gobi region in Hexi Corridor, with values of 1.1778 and 1.1169, respectively. Fractal dimension values are relatively large in Jiuzhoutai semi-arid hilly and gully region of the Loess Plateau, which indicates that the R. Soongorica root system has better fractal characteristics in this region than in the other regions. （3） Total branching ra- tios of the R. Soongorica root system in arid regions of Hexi Corridor are smaller than that in the Jiuzhoutai semi-arid hilly and gully region of the Loess Plateau. This shows that root branching ability in the semi-arid region is stronger, and it decreases to some degree with increased drought. （4） The root connection lengths of R. soongorica root system are long in all habitats, but there are significant length differences between the different habitats. The root connection length at the Minqin windblown sand region is the longest. It is concluded that R. soongoriea adapts to arid environments by decreasing root branching, decreasing root overlap and increasing root connection length, which makes its root branching pattern tend to be herringbone-like to reduce com- petition in root internal environment for nutrients and to enhance root absorption rate of nutrients, and ensure effective nutrition space. Thus the roots can absorb enough water and nutrients in resource-poor settings to ensure normal physiological requirements.

Interacted Effect of Arbuscular Mycorrhizal Fungi and Polyamines on Root System Architecture of Citrus Seedlings

Either arbuscular mycorrhizal fungi （AMF） or polyamines （PAs） may change root system architecture （RSA） of plants, whereas the interaction of AMF and PAs on RSA remains unclear. In the present study, we studied the interaction between AMF （Paraglomus occultum） and exogenous PAs, including putrescine （Put）, spermidine （Spd） and spermine （Spin） on mycorrhizal development of different parts of root system, plant growth, RSA and carbohydrate concentrations of 6-m-old citrus （Citrus tangerine Hort. ex Tanaka） seedlings. After 14 wk of PAs application, PA-treated mycorrhizal seedlings exhibited better mycorrhizal colonization and numbers of vesicles, arbuscules, and entry points, and the best mycorrhizal status of taproot, first-, second-, and third-order lateral roots was respectively found in mycorrhizal seedlings supplied with Put, Spd and Spm, suggesting that PAs might act as a regulated factor of mycorrhizal development through transformation of root sucrose more into glucose for sustaining mycorrhizal development. AMF usually notably increases RSA traits （taproot length, total length, average diameter, projected area, surface area, volume, and number of first-, second-, and third-order lateral roots） of only PA-treated seedlings. Among the three PA species, greater positive effects on RSA change and plant biomass increment of the seedlings generally rank as Spd〉Spm〉Put, irrespective of whether or not AMF colonization. PAs significantly changed the RSA traits in mycorrhizal but not in non-mycorrhizal seedlings. It suggests that the application of PAs （especially Spd） to AMF plants would optimize RSA of citrus seedlings, thus increasing plant growth （shoot and root dry weight）.

Identification of QTL and underlying genes for root system architecture associated with nitrate nutrition in hexaploid wheat

The root system architecture(RSA) of a crop has a profound effect on the uptake of nutrients and consequently the potential yield. However, little is known about the genetic basis of RSA and resource adaptive responses in wheat(Triticum aestivum L.). Here, a high-throughput germination paper-based plant phenotyping system was used to identify seedling traits in a wheat doubled haploid mapping population, Savannah×Rialto. Significant genotypic and nitrate-N treatment variation was found across the population for seedling traits with distinct trait grouping for root size-related traits and root distribution-related traits. Quantitative trait locus(QTL) analysis identified a total of 59 seedling trait QTLs. Across two nitrate treatments, 27 root QTLs were specific to the nitrate treatment. Transcriptomic analyses for one of the QTLs on chromosome 2 D, which was found under low nitrate conditions, revealed gene enrichment in N-related biological processes and 28 differentially expressed genes with possible involvement in a root angle response. Together, these findings provide genetic insight into root system architecture and plant adaptive responses to nitrate, as well as targets that could help improve N capture in wheat.

Analysis of root fractal characteristics in remote areas of the Taklimakan desert,China

Fractal geometry is a potential new approach to analyze the root architecture, which may offer improved ways to quantify and summarize root system complexity as well as yield ecological and physiological insights into the functional relevance of specific architectural patterns. Fractal analysis is a sensitive measure of root branching intensity and fractal dimension expresses the ＂space filling＂ properties of a structure. The objective of this study was to find out the fractal characteristics of root systems in a remote area of the Taklimakan desert in China. The entire root system of two naturally occurring species were excavated and exposed with shov- els in 2007. The species were Tamarix taklamakanensis and Calligonum roborovskii. A one-factorial ANOVA with species as factor showed statistically a highly significant difference in fractal dimensions, indicating differences in their pattern of root branching. There was no relationship between root diameter and two parameters of fractal root models a and q, representing general characteris- tics of root systems, for either species （a： the ratio of the sum of root cross-sectional areas after a branching to the cross-sectional area before root division; q： the distribution of the cross-sectional areas after branching）. We have found significant linear relation- ships between the diameter after branching and root length and biomass respectively, because of the self-similarity of root branching. Branching rules are the same for roots of all sizes and lengths. Root biomass for the root systems of entire trees can be estimated by measuring the diameter of each root at the base of the trunk or the diameter after branching. We have shown that the diameter of each root at the base of the trunk and the diameter after branching are effective indices that can be measured easily in order to estimate the root lengths, biomass and other parameters of root architecture.

Tolerance to Iron-Deficiency Stress of Three Apple Rootstock Species in Hydroponic System

[Objective] Iron deficiency is one of the most important crop element deficiencies in the Loess Plateau of northwestern China. The selection for crop cultivars that are tolerant to low iron levels could be one of the approaches to solving the problem and improving crop production. [Method] Three major apple root stock species （Malus prunifolia, Malus sieversii and Malus baccata） were selected to evaluate their tolerance to iron defciency in hydroponic system. A 3×2 factorial pot experiment was conducted with three replicates in a greenhouse at Gansu Agricultural University, Lanzhou, China. [Result] The SOD, POD and CAT activities in roots and stems of the 3 root stock species in Fe-defcient Hoagland solution decreased, however Malus sieversii got the less reduction and had better root architecture and growth than the other species. The aboveground biomass, plant height, chlorophyll content, total root length and lateral root number were correlated positively with iron-defciency stress tolerance. The species’ tolerance to iron-defciency from high to low was M. sieversii’s〉M. baccata’s〉M. prunifolia’s. Moreover, the improvement of some morphological features such as root length, above-ground biomass, plant height and lateral root number in apple could be conducive to breeding cultivars with tolerance to iron-defciency stress. [Conclusion] Malus sieversii had better tolerance to iron-defciency stress than the others in this study.

Tanoak (Notholithocarpus densiflorus) Coarse Root Morphology: Prediction Models for Volume and Biomass of Individual Roots

Descriptions of tree root morphology inform design of belowground biomass and carbon inventories and sampling for research. We studied root morphology of tanoak (Notholithocarpus densiflorus), an important component in mixed evergreen forests of California and Oregon, USA. Tanoak re-sprouts from belowground lignotubers after disturbances, and stores an unknown amount of carbon in coarse roots underground. We sought to ascribe explanatory nomenclature to roots’ morphological features and to identify models describing tanoak root morphology. Twelve tanoak root systems were excavated, dissected, and measured. Roots tapered according to their circumference and location. Larger roots closer to the lignotuber (located at the base of the tree stem) tapered more rapidly per unit of length. Tanoak roots forked frequently. Root cross-sectional area was preserved after forking events (i.e., the sum of cross-sectional areas for smaller roots on one side of the fork correlated with the adjoining large root). Occurrence and quantity of root branches (small roots branching laterally from larger roots) was dependent upon length of the source root segment. Our models of tanoak root morphology are designed to be organized together to estimate biomass of any segment or collection of lateral roots (e.g., roots lost/missed during excavation, or in lieu of destructive sampling), given root diameter at a known distance from the lignotuber. The taper model gives distal- and proximal-end diameters for calculation of volume for segments of root tapering between forks. Frequency of forking and branching can also be predicted. Summing the predicted mass of each lateral root segment, branch, and forked segment would produce an estimate of mass for a contiguous network of lateral roots.

The influence of plant root system architectural properties upon the stability of loess hillslopes,Northeast Qinghai,China

To investigate the influence of root system architectural properties of three indigenous （cold- adapted） shrubs on the hillslope stability of loess deposits in the Xining Basin, northeast part of Qinghai-Tibet Plateau （QTP）, indoor direct shear tests have been conducted on the remolded rooted soil of three shrubs. Test results show that root system architectural indices （root area ratio （RAR）, root length density （RLD） and root density （RD）） of the shrubs decline with depth and the relationship between RAR, RD and depth is exponential, while a power relationship describes the relationship between RLD and depth. The cohesion force of remolded rooted soil for the shrubs initially increases with depth, but it then demonstrates a slightly decreasing trend, which can be described with a power relationship. Power relationships also describe relationships between cohesion force and RAR, RLD and RD for the shrubs. As the growth period increases from lO to 17 months, the incremental increase in RAR is 48.32% ~ 21o.25% for Caragana korshinskii Kom and 0.56% ~ 166.85% for ZygophyUum xanthoxylon （Bunge） Maxim. This proportional increase is notably larger than that for RLD and RD. The increment in RAR is marginally greater for C. korshinskff than it is for Z. xanthoxylon. Correspondingly, the cohesion force incremental rates of remolded rooted soil for C. korshinskii and Z. xanthoxylon are 12.41% ~ 25.22% and 3.45% ~ 17.33% respectively. Meanwhile, as root content increases, the contribution by roots to cohesion force increases markedly until a threshold condition is reached.

Phenotyping of Weedy Rice to Assess Root Characteristics Associated with Allelopathy

Weedy rice is a species of Oryza, and is a wild relative of cultivated rice. The weed possesses unique hardiness that allows them to thrive in dynamic and stressful environments. These characteristics suggest that weedy rice is a stored source of novel genes for competitive traits. One such trait is allelopathy, where a species releases secondary metabolites that suppress the growth and development of neighboring species. Weed competition is a limiting factor in rice production systems;therefore, it is critical to identify specific allelopathic weedy rice accessions to determine the genetic pathways and mechanisms associated with allelopathy to be used in breeding programs. Due to the complex nature of allelochemical production and the lack of knowledge of allelopathy mechanisms in weedy rice, phenotypic traits, particularly root traits, can be used to overcome this limitation and serve as target characteristics for breeding weed suppressive rice varieties. Five weedy rice accessions were chosen from preliminary screenings of larger sample sizes with the ability to suppress barnyardgrass weed seedling growth. Another five weedy rice with low barnyardgrass suppression was selected for the current root phenotypic study. Five cultivated rice lines were used as a comparison. All plants were propagated in a transparent germination pouch for four weeks. Roots were scanned and analyzed for root length and area covered. No differences were found in the seedling root area among weedy rice and rice accessions;however, allelopathic weedy rice plants exhibited a 14% increase in root length than non-allelopathic weedy rice plants. The allelopathic weedy rice accession B2 possessed the most extended root system (22.4 cm root length). The highly allelopathic weedy rice accessions (including B2) screened and phenotyped in this study are ideal candidates for identifying the genetic controls of early root length, a possible trait contributing to underground allelopathic production and competitive advantage.

Breeding maize of ideal plant architecture for high-density planting tolerance through modulating shade avoidance response and beyond

Maize is a major staple crop widely used as food,animal feed,and raw materials in industrial production.High-density planting is a major factor contributing to the continuous increase of maize yield.However,high planting density usually triggers a shade avoidance response and causes increased plant height and ear height,resulting in lodging and yield loss.Reduced plant height and ear height,more erect leaf angle,reduced tassel branch number,earlier flowering,and strong root system architecture are five key morphological traits required for maize adaption to high-density planting.In this review,we summarize recent advances in deciphering the genetic and molecular mechanisms of maize involved in response to high-density planting.We also discuss some strategies for breeding advanced maize cultivars with superior performance under high-density planting conditions.

Constitutive basis of root system architecture:uncovering a promising trait for breeding nutrient-and drought-resilient crops

Root system architecture(RSA)plays a pivotal role in efficient uptake of essential nutrients,such as phosphorous(P),nitrogen(N),and water In soils with heterogeneous nutrient distribution,root plasticity can optimize acquisition and plant growth.Here,we present evidence that a constitutive RSA can confer benefits for sorghum grown under both sufficient and limiting growth conditions.Our studies,using P efficient SC103 and inefficient BTx635 sorghum cultivars,identified significant differences in root traits,with SC103 developing a larger root system with more and longer lateral roots,and enhanced shoot biomass,under both nutrient sufficient and deficient conditions.In addition to this constitutive attribute,under P deficiency,both cultivars exhibited an initial increase in lateral root development;however,SC103 still maintained the larger root biomass.Although N deficiency and drought stress inhibited both root and shoot growth,for both sorghum cultivars,SC103 again maintained the better performance.These findings reveal that SC103,a P efficient sorghum cultivar,also exhibited enhanced growth performance under N deficiency and drought.Our results provide evidence that this constitutive nature of RSA can provide an avenue for breeding nutrient-and drought-resilient crops.

Brassinosteroids modulate nitrogen physiological response and promote nitrogen uptake in maize(Zea mays L.)

Brassinosteroids(BRs)are steroid hormones that function in plant growth and development and response to environmental stresses and nutrient supplies.However,few studies have investigated the effect of BRs in modulating the physiological response to nitrogen(N)supply in maize.In the present study,BR signalingdeficient mutant zmbri1-RNAi lines and exogenous application of 2,4-epibrassinolide(e BL)were used to study the role of BRs in the regulation of physiological response in maize seedlings supplied with N.Exogenous application of e BL increased primary root length and plant biomass,but zmbri1 plants showed shorter primary roots and less plant biomass than wild-type plants under low N(LN)and normal N(NN)conditions.LN induced the expression of the BR signaling-associated genes Zm DWF4,Zm CPD,Zm DET2,and Zm BZR1 and the production of longer primary roots than NN.Knockdown of Zm BRI1 weakened the biological effects of LN-induced primary root elongation.e BL treatment increased N accumulation in shoots and roots of maize seedlings exposed to LN or NN treatment.Correspondingly,zmbri1 plants showed lower N accumulation in shoots and roots than wild-type plants.Along with reduced N accumulation,zmbri1 plants showed lower NO3-fluxes and^(15)NO_(3)^(-)uptake.The expression of nitrate transporter(NRT)genes(Zm NPF6.4,Zm NPF6.6,Zm NRT2.1,Zm NRT2.2)was lower in zmbri1 than in wild-type roots,but e BL treatments up-regulated the transcript expression of NRT genes.Thus,BRs modulated N physiological response and regulated the transcript expression of NRT genes to promote N uptake in maize.