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Although the fates of microplastics (0.1–5 mm in size) and nanoplastics (<100 nm) in marine environments are being increasingly well studied1,2, little is known about the behaviour of nanoplastics in terrestrial environments3–6, especially agricultural soils7. Previous studies have evaluated the consequences of nanoplastic accumulation in aquatic plants, but there is no direct evidence for the internalization of nanoplastics in terrestrial plants. Here, we show that both positively and negatively charged nanoplastics can accumulate in Arabidopsis thaliana. The aggregation promoted by the growth medium and root exudates limited the uptake of amino-modified polystyrene nanoplastics with positive surface charges. Thus, positively charged nanoplastics accumulated at relatively low levels in the root tips, but these nanoplastics induced a higher accumulation of reactive oxygen species and inhibited plant growth and seedling development more strongly than negatively charged sulfonic-acid-modified nanoplastics. By contrast, the negatively charged nanoplastics were observed frequently in the apoplast and xylem. Our findings provide direct evidence that nanoplastics can accumulate in plants, depending on their surface charge. Plant accumulation of nanoplastics can have both direct ecological effects and implications for agricultural sustainability and food safety.The accumulation of nanoplastics in terrestrial plants is directly linked to the nanoparticles’ charge and can have ecological effects and implications for agricultural sustainability and food safety.

The efficacy and efficiency of submerged arc welding (SAW) are largely dictated by the physicochemical properties of the employed welding fluxes, including melting point, viscosity, and activity, etc., which are inherently rooted in the microstructure of the fluxes. SiO2–CaO–Al2O3-based fluxes are widely employed for welding high strength low alloy (HSLA) steels. In the present study, the structural roles of CaF2 on SiO2–CaO–Al2O3-based welding fluxes have been systematically investigated through Raman and magic angle spinning-nuclear magnetic resonance (MAS-NMR) techniques. The results showed that originally intact flux structures depolymerized upon increasing content of CaF2. Raman and 29Si NMR results demonstrated that Q2 (Qn, n is the number of bridging oxygens (O0) in one [SiO4]-tetrahedron) increased at the cost of Q3(1Al) (Qn(mAl), m means the number of neighboring aluminate groups), which could be well explained by the interruption of the Si-O-Al linkages. Moreover, as confirmed by 27Al and 19F NMR results, the proportion of AlF6 species increased from 9.9 to 34.2 pct, indicating the substitution of Al–F for Al–O bonds and the depolymerization of the flux structure. The unique behavior of F may offer a theoretical basis for fine-tuning structural unit mobility and element transfer behaviors during the actual welding process.

The brassinosteroids (BRs) represent a class of phytohormones, which regulate numerous aspects of growth and development. Here, a det2-9 mutant defective in BR synthesis was identified from an EMS mutant screening for defects in root length, and was used to investigate the role of BR in root development in Arabidopsis. The det2-9 mutant displays a short-root phenotype, which is result from the reduced cell number in root meristem and decreased cell size in root maturation zone. Ethylene synthesis is highly increased in the det2-9 mutant compared with the wild type, resulting in the hyper-accumulation of ethylene and the consequent inhibition of root growth. The short-root phenotype of det2-9 was partially recovered in the det2-9/acs9 double mutant and det2-9/ein3/eil1-1 triple mutant which have defects either in ethylene synthesis or ethylene signaling, respectively. Exogenous application of BR showed that BRs either positively or negatively regulate ethylene biosynthesis in a concentration-dependent manner. Different from the BR induced ethylene biosynthesis through stabilizing ACSs stability, we found that the BR signaling transcription factors BES1 and BZR1 directly interacted with the promoters of ACS7, ACS9 and ACS11 to repress their expression, indicating a native regulation mechanism under physiological levels of BR. In addition, the det2-9 mutant displayed over accumulated superoxide anions (O2-) compared with the wild-type control, and the increased O2- level was shown to contribute to the inhibition of root growth. The BR-modulated control over the accumulation of O2- acted via the peroxidase pathway rather than via the NADPH oxidase pathway. This study reveals an important mechanism by which the hormone cross-regulation between BRs and ethylene or/and ROS is involved in controlling root growth and development in Arabidopsis.

Plants develop a high flexibility to alter growth, development, and metabolism to adapt to the ever-changing environments. Multiple signaling pathways are involved in these processes and the molecular pathways to transduce various developmental signals are not linear but are interconnected by a complex network and even feedback mutually to achieve the final outcome. This review will focus on two important plant hormones, auxin and brassinosteroid (BR), based on the most recent progresses about these two hormone regulated plant growth and development in , and highlight the cross-talks between these two phytohormones.

Reactive oxygen species (ROS) are recognized as important regulators of cell division and differentiation. The Arabidopsis thaliana P-loop NTPase encoded by APP1 affects root stem cell niche identity through its control of local ROS homeostasis. The disruption of APP1 is accompanied by a reduction in ROS level, a rise in the rate of cell division in the quiescent center (QC) and the promotion of root distal stem cell (DSC) differentiation. Both the higher level of ROS induced in the app1 mutant by exposure to methyl viologen (MV), and treatment with hydrogen peroxide (H2O2) rescued the mutant phenotype, implying that both the increased rate of cell division in the QC and the enhancement in root DSC differentiation can be attributed to a low level of ROS. APP1 is expressed in the root apical meristem cell mitochondria, and its product is associated with ATP hydrolase activity. The key transcription factors, which are defining root distal stem niche, such as SCARECROW (SCR) and SHORT ROOT (SHR) are both significantly down-regulated at both the transcriptional and protein level in the app1 mutant, indicating that SHR and SCR are important downstream targets of APP1-regulated ROS signaling to control the identity of root QC and DSCs.

Auxin is necessary for the inhibition of root growth induced by aluminium (Al) stress, however the molecular mechanism controlling this is largely unknown. Here, we report that YUCCA (YUC), which encodes flavin monooxygenase-like proteins, regulates local auxin biosynthesis in the root apex transition zone (TZ) in response to Al stress. Al stress up-regulates YUC3/5/7/8/9 in the root-apex TZ, which we show results in the accumulation of auxin in the root-apex TZ and root-growth inhibition during the Al stress response. These Al-dependent changes in the regulation of YUCs in the root-apex TZ and YUC-regulated root growth inhibition are dependent on ethylene signalling. Increasing or disruption of ethylene signalling caused either enhanced or reduced up-regulation, respectively, of YUCs in root-apex TZ in response to Al stress. In addition, ethylene enhanced root growth inhibition under Al stress was strongly alleviated in yuc mutants or by co-treatment with yucasin, an inhibitor of YUC activity, suggesting a downstream role of YUCs in this process. Moreover, ethylene-insensitive 3 (EIN3) is involved into the direct regulation of YUC9 transcription in this process. Furthermore, we demonstrated that PHYTOCHROME INTERACTING FACTOR4 (PIF4) functions as a transcriptional activator for YUC5/8/9. PIF4 promotes Al-inhibited primary root growth by regulating the local expression of YUCs and auxin signal in the root-apex TZ. The Al-induced expression of PIF4 in root TZ acts downstream of ethylene signalling. Taken together, our results highlight a regulatory cascade for YUCs-regulated local auxin biosynthesis in the root-apex TZ mediating root growth inhibition in response to Al stress.

The development of lateral roots in Arabidopsis thaliana is strongly dependent on signaling directed by the AUXIN RESPONSE FACTOR7 (ARF7), which in turn activates LATERAL ORGAN BOUNDARIES DOMAIN (LBD) transcription factors (LBD16, LBD18 and LBD29). Here, the product of PRH1, a PR-1 homolog annotated previously as encoding a pathogen-responsive protein, was identified as a target of ARF7-mediated auxin signaling and also as participating in the development of lateral roots. PRH1 was shown to be strongly induced by auxin treatment, and plants lacking a functional copy of PRH1 formed fewer lateral roots. The transcription of PRH1 was controlled by the binding of both ARF7 and LBDs to its promoter region.

Aluminum (Al) stress is a major limiting factor for plant growth and crop production in acid soils. At present, only a few transcription factors involved in the regulation of Al resistance have been characterized. Here, we used reversed genetic approach through phenotype analysis of overexpressors and mutants to demonstrate that AtHB7 and AtHB12, two HD-Zip I transcription factors, participate in Al resistance. In response to Al stress, AtHB7 and AtHB12 displayed different dynamic expression patterns. Although both AtHB7 and AtHB12 positively regulate root growth in the absence of Al stress, our results showed that AtHB7 antagonizes with AtHB12 to control root growth in response to Al stress. The athb7/12 double mutant displayed a wild-type phenotype under Al stress. Consistently, our physiological analysis showed that AtHB7 and AtHB12 oppositely regulate the capacity of cell wall to bind Al. Yeast two hybrid assays showed that AtHB7 and AtHB12 could form homo-dimers and hetero-dimers in vitro, suggesting the interaction between AtHB7 and AtHB12 in the regulation of root growth. The conclusion was that AtHB7 and AtHB12 oppositely regulate Al resistance by affecting Al accumulation in root cell wall.

Dirigent proteins (DIR) are involved in lignan biosynthesis, stress responses, and disease resistance in plants. However, systematic characterization of the DIR gene family in watermelon (Citrullus lanatus) remains limited. Here, we identified 22 ClDIR genes in watermelon using bioinformatics methods, designated ClDIR1 to ClDIR22, which were unevenly distributed across eight chromosomes and classified into three subfamilies (DIR-a, DIR-b/d, DIR-e) based on phylogenetic analysis, with DIR-b/d being the largest. Synteny analysis revealed that tandem duplication primarily drove ClDIR family expansion, and collinear relationships with Arabidopsis, rice, and cucurbit species indicated evolutionary conservation. Cis-acting element analysis showed abundant stress- and hormone-responsive elements in ClDIR promoters, suggesting roles in stress regulation. Tissue-specific expression analysis demonstrated distinct patterns, with most genes highly expressed in roots. Expression profiling under 16 abiotic and biotic stresses showed 18 ClDIR genes responded to stress, with ClDIR8 differentially expressed across all conditions. qRT-PCR validation of six key genes (ClDIR5, ClDIR8, ClDIR9, ClDIR12, ClDIR16, ClDIR22) confirmed their expression patterns under high-temperature, drought, salt, and low-temperature stresses, showing a high degree of consistency with transcriptome data. Subcellular localization indicated ClDIR8 is peroxisome-localized. Yeast two-hybrid (Y2H) and bimolecular fluorescence complementation (BiFC) assays validated two ClDIR8-interacting proteins, Cla97C02G049920 (encoding peroxidase) and Cla97C08G152180 (encoding catalase). These findings provide insights into ClDIR genes in watermelon, highlighting ClDIR8 as a key stress-responsive candidate for further functional studies and breeding.

KEY MESSAGE : The core regulators which are required for primary root growth and development also function in lateral root development or lateral root stem cell niche maintenance. The primary root systems and the lateral root systems are the two important root systems which are vital to the survival of plants. Though the molecular mechanism of the growth and development of both the primary root systems and the lateral root systems have been extensively studied individually in Arabidopsis, there are not so much evidence to show that if both root systems share common regulatory mechanisms. AP2 family transcription factors such as PLT1 (PLETHORA1) and PLT2, GRAS family transcription factors such as SCR (SCARECROW) and SHR (SHORT ROOT) and WUSCHEL-RELATED HOMEOBOX transcription factor WOX5 have been extensively studied and found to be essential for primary root growth and development. In this study, through the expression pattern analysis and mutant examinations, we found that these core regulators also function in lateral root development or lateral root stem cell niche maintenance.