IAA Content Research Articles

Auxin plays a key role in nitrogen and plant density-modulated root growth and yield in different plant types of rapeseed

ContextWith the increasing global food and oil security problems, improvement in rapeseed (Brassica napus L.) yield become urgent. Moreover, previous studies rarely used the semi-dwarf and compact plant type of rapeseed to improve yield potential. ObjectiveHerein, we aimed to investigate the effects of different nitrogen application rates and plant density on root growth and yield-related traits using three genotypes with different plant types to clarify various regulatory mechanisms using semi-dwarf and compact plant type mutants to achieve high yield. MethodsSplit-split-plot experiments with three nitrogen application rates (N1: N2: N3, 120: 240: 360 kg ha−1) and three plant densities (D1: D2: D3, 15 × 104: 45 × 104: 75 × 104 plants·ha−1) were conducted during the three growing seasons (2019–2022) using semi-dwarf mutant HS5sca, and HS5 (wild type) as well as their F1 hybrid HS5+/sca. ResultsWith decreasing nitrogen application rate (N3 to N2), the expression level of IAA signal response genes BnaA07. GH3 and BnaA03. IAA13 was decreased in root, while increased in shoot at the early-flowering stage. Moreover, IAA content was decreased in roots and aboveground parts, whereas soluble sugar content of root bleeding sap was increased and volume of root bleeding sap was decreased in three genotypes at early-flowering stage. Additionally, nitrogen accumulation per plant and yield per plant was decreased, while population nitrogen accumulation and population yield were increased with decreasing nitrogen application rate in three studied genotypes. On the other side, with increasing plant density, the expression of BnaA07. GH3 and BnaA03. IAA13 genes were first increased and then decreased in root tissues. In addition, root surface area, the total volume of root bleeding sap, and nitrogen accumulation were decreased, which decreased dry matter and yield per plant. However, total root area, population nitrogen accumulation, and population yield in the three genotypes were increased, and yield was the highest at D2. The population yield of HS5sca, HS5+/sca, and HS5 achieved the largest increase of 26.0%, 10.3%, and 9.5% under N2D2 in 2019, 6.9%, 8.4%, and 4.7% under N3D2 in 2020, respectively, as compared to N3D1. Moreover, the morphological indices of HS5+/sca were greater than other genotypes, with the highest population yield. ConclusionsAppropriate nitrogen application rate with plant density optimized the root architecture and aboveground type of HS5+/sca that improved auxin level through affecting the downstream auxin-related genes, as well as improved dry matter accumulation and distribution, which increased yield potential. Compared with the two parents, F1 genotype HS5+/sca was suitable for nitrogen fertilizer (240 kg ha−1) and plant density (45–75 × 104 plants ha−1). Implications+ /sca heterozygous genotypes might promote root growth under low nitrogen application rate and high plant density. A strong root system is an important guarantee of high yield; thus, this heterozygous site could use to introduce excellent hybrids in rapeseed production to further improve root traits and optimize cultivation factors to increase seed yield.

Integrated transcriptomics and metabolomics analyses provide insights into the mechanisms of capitulum architecture in Argyranthemum frutescens (Asteraceae)

The capitulum is a crucial Asteraceae innovation; however, the molecular mechanisms of its development remain elusive. Here, we performed transcriptome and metabolome analyses to explore the molecular mechanisms underlying floret development of Argyranthemum frutescens, whose capitula produce ray (R), disk (D) and trans (T) florets. Up-regulated differentially expressed genes (DEGs) related to cutin, suberine and wax biosynthesis, fatty acid elongation and lipid accumulation were significantly enriched in T. DEGs in the tryptophan metabolism pathway were up-regulated in R, and DEGs in the abscisic acid synthesis pathway were up-regulated in D. Auxin and abscisic acid occurred as a reverse distribution gradient in the three floret types. TCP, WOX transcription factors and ABCE genes were identified and analyzed. Our results suggest that cutin, suberine and wax biosynthesis regulates the formation of petal cuticle by upregulating the content of lipids in T, thereby improving the reproductive efficiency of A. frutescens. Auxin and abscisic acid co-regulate floret development in a concentration dependent manner in A. frutescens, and expression of flower development genes was strongly correlated with the IAA content. These results enable a comprehensive understanding of the molecular mechanisms of capitulum formation in A. frutescens and increase our understanding of capitulum diversity in Asteraceae.

Content Patterns of Maize Endogenous Hormones and Grain Yield Influenced by Field Phosphorus Application

The content of plant endogenous hormones could be influenced by fertilization, which play an important regulatory role in plant growth and yield formation. However, the effects of phosphate (P) application rates on the dynamical changes in the exogenous hormone content in maize plants to support high-yield production are still unclear. An experiment with six P application rates was designed (P1, 0 kg ha−1; P2, 20 kg ha−1; P3, 40 kg ha−1; P4, 60 kg ha−1; P5, 80 kg ha−1; and P6, 100 kg ha−1), aimed at determining the distribution or biosynthesis of phytohormones in maize roots and leaves, and clarifying the role of P fertilization in the formation of phytohormones. The results showed that P fertilization significantly increased the content of IAA, by 51.57%, and significantly decreased the contents of ABA and GA3, by 18.92% and 19.13% on average compared to P1. The highest increase in IAA was 99.02%, and the highest decreases in ABA and GA3 were 32.30% and 26.85%, respectively, in the P6 treatment in maize roots. Meanwhile, an increase in the IAA (41.34%), SA (27.58%), and GA3 (37.36%) contents and a decrease in the ABA (19.18%) content in maize leaves were observed. The highest increases in IAA, GA3, and SA in the P6 treatment in maize leaves were 57.5%, 62.50%, and 48.57%, respectively, and the highest decrease in ABA was 28.05%. Meanwhile, different contents of endogenous hormones in maize roots and leaves were observed at various maize growth stages. The maize phenotypes and soil available P content were increased with P application as well. A Pearson’s correlation analysis showed that endogenous hormones were significantly correlated with maize phenotypes and yield. Our results confirmed that P fertilization could change the content of endogenous hormones in maize roots and leaves; P6 was the best treatment for improving the endogenous hormone contents in maize plants, P3 was the best for improving the maize grain yield. Overall, 40 kg ha−1 is recommended as the best P application rate under the experimental conditions, considering the economic cost and environmental effects.

FUSCA3-induced AINTEGUMENTA-like 6 manages seed dormancy and lipid metabolism.

FUSCA 3 (FUS3), a seed master regulator, plays critical role in seed dormancy and oil accumulation. However, its downstream regulation mechanisms remain poorly understood. Here, we explored the roles of AINTEGUMENTA-like 6 (AIL6), a seed transcription factor, in these processes. The activation of AIL6 by FUS3 was demonstrated by dual-LUC assay. Seeds of ail6 mutants showed alterations in fatty acid compositions, and both AtAIL6 (AIL6 from Arabidopsis thaliana) and BnaAIL6 (AIL6 from Brassica napus) rescued the phenotype. Over-expression (OE) of AIL6s reversed changes in seed fatty acid composition. Notably, OE lines showed low seed germination rates down to 12% compared to 100% of wild-type Col-0. Transcriptome analysis of the mutant and an OE line indicated widespread expression changes of genes involved in lipid metabolism and phytohormone pathways. In OE mature seeds, GA4 content decreased more than 15-fold, while abscisic acid and indole-3-acetic acid (IAA) contents clearly increased. Exogenous GA3 treatments did not effectively rescue the low germination rate. Nicking seed coats increased germination rates from 25% to nearly 80% while the wild-type rdr6-11 is 100% and 98% respectively, and elongation of storage time also improved seed germination. Furthermore, dormancy imposed by AIL6 was fully released in the della quintuple mutant. Together, our results indicate AIL6 acts as a manager downstream of FUS3 in seed dormancy and lipid metabolism.

Exogenous spraying of IAA improved the efficiency of microspore embryogenesis in Wucai (Brassica campestris L.) by affecting the balance of endogenous hormones, energy metabolism, and cell wall degradation

BackgroundMicrospore embryogenesis is an extraordinarily complicated process, comprehensively regulated by a composite network of physiological and molecular factors, among which hormone is one of the most crucial factors. Auxin is required for stress-induced microspore reprogramming, however, the mechanism of its regulation of microspore embryogenesis is still unclear.ResultsIn this study, we found exogenously spraying 100 mg·L− 1 IAA on the buds of Wucai significantly increased the rate of microspore embryogenesis, and moreover accelerated the process of embryogenesis. Physiological and biochemical tests showed that the contents of amino acids, soluble total sugar, soluble protein, and starch were significantly increased after IAA treatment. Furthermore, exogenously spraying 100 mg·L− 1 IAA significantly enhanced IAA, GA4, and GA9 content, increased catalase (CAT) and malondialdehyde (MDA) activity, and reduced abscisic acid (ABA), MDA and soluble protopectin content, H2O2 and O2·− production rate in the bud with the largest population of late-uninucleate-stage microspores. Transcriptome sequencing was performed on buds respectively treated with 100 mg·L− 1 IAA and fresh water. A total of 2004 DEGs were identified, of which 79 were involved in micropores development, embryonic development and cell wall formation and modification, most of which were upregulated. KEGG and GO analysis revealed that 9.52% of DEGs were enriched in plant hormone synthesis and signal transduction pathways, pentose and glucuronic acid exchange pathways, and oxidative phosphorylation pathways.ConclusionsThese findings indicated that exogenous IAA altered the contents of endogenous hormone content, total soluble sugar, amino acid, starch, soluble protein, MDA and protopectin, the activities of CAT and peroxidase (POD), and the production rate of H2O2 and O2·−. Combined with transcriptome analysis, it was found that most genes related to gibberellin (GA) and Auxin (IAA) synthesis and signal transduction, pectin methylase (PME) and polygalacturonase (PGs) genes and genes related to ATP synthesis and electron transport chain were upregulated, and genes related to ABA synthesis and signal transduction were downregulated. These results indicated that exogenous IAA treatment could change the balance of endogenous hormones, accelerate cell wall degradation, promote ATP synthesis and nutrient accumulation, inhibit ROS accumulation, which ultimately promote microspore embryogenesis.

Study on the Rooting Physiological Mechanism of Schisandra chinensis (Turcz.) Baill. Green-Branched Cuttings

Schisandra chinensis (Turcz.) Baill. is an important medicinal plant in northeast China. Cutting propagation is an effective method for the rapid propagation of many tree species. This research aimed to determine a suitable growing medium and appropriate root hormone type, concentration and treatment time through the utilization of different substrates and hormones to treat one-year-old branches of S. chinensis. The optimal treatment achieved a rooting rate of 60% with 225 ppm ABT and 75 ppm NAA for 2.5 h. The substrate of vermiculite/perlite = 1:1 (urea+potassium) was beneficial to the adventitious root formation, which reached 79%. The adventitious root primordium of S. chinensis originated from the junction of the xylem and cambium. ABT and NAA treatments altered the peak timing of POD, PPO and IAAO in S. chinensis cuttings. During the adventitious root formation of S. chinensis cuttings, the high endogenous IAA concentration promoted the occurrence of adventitious roots in the early stage and the lower endogenous IAA and GA3 concentrations promoted the elongation and growth of adventitious roots in the later period. Low ABA and ZR concentrations enabled adventitious root formation and elongation. An efficient cutting propagation system would enable the mass propagation of S. chinensis seedlings.

Optimization of Hormonal Compositions of Media in In Vitro Propagation of Orange Cultivars from Shoot Tip Nodal Segments

Orange is one of the most horticulturally important and widely cultivated Citrus species. Citrus cultivar improvement via conventional breeding strategies is normally impeded by factors related to its reproductive biology. The present study was undertaken to investigate the optimization of growth regulators’ composition of media in in vitro propagation of orange cultivar from nodal segment explants. The nodal segment explants were collected from sweet orange cultivars. The MS medium supplemented with sucrose and different concentrations of growth regulators were used for shoot proliferation and root induction. The optimum compositions of growth regulators in MS medium were assessed. The result indicated that the highest shoot response was recorded for Washington naval orange with maximum shoot proliferation rate (99.75%), shoot number per explant (3.10), shoot length (10.70 cm), leaf number per explants (12.50) after three weeks of culture. In all experiments, no growth was observed for the basal MS medium. Phytohormones combinations of indole-3-acetic acid, IAA (1.2 mg/L), and kinetin (2.0 mg/L) were found to be the best for shoot proliferation. Among the cultivars, significantly, the highest rooting rate (81.25%), root number (4.95), and root length (2.95 cm) were recorded for Washington naval orange cultivar. The least rooting rate (48.45%), root number (3.55), and root length (2.26 cm) were observed from the Valencia cultivar. Significantly, the highest rooting rate (84.90%), root number per microshoot (5.20), and root length (3.05 cm) for MS medium supplemented with 1.5 mg/L 1-naphthalene acetic acid (NAA). The comparison of different concentrations of IAA and NAA on root induction of microshoots from nodal segments of sweet orange cultivars demonstrated NAA as the more effective hormone than IAA.

Influence of nutrient media on the physiological parameters of grape microclones

Successful rooting of grape microclones in uncontrolled environmental conditions (in vivo) depends on the level of resistance, which is formed at the stage of their passage and growth in vitro. An important role in this case is played by indicators of the water regime of the vegetative mass. The purpose of this study was to get acquainted with the results of determining the water-holding capacity, the intensity of transpiration of grape microclones in vitro and to establish the share of their influence on the adaptation potential in vivo. Biotechnological, laboratory, vegetation, and mathematical and statistical research methods were used in this study. The obtained results showed that to optimize the physiological processes in the tissues of the leaves and shoots of grape microclones, to increase their viability under in vivo conditions, it is advisable to cultivate them in vitro on structured nutrient media (MS + agroperlite, MS + vermiculite, MS + agroperlite + vermiculite) with the content of phytohormones IAA – 0.2 mg/l, and 6-BAP – 0.3 mg/l. Structured nutrient media contributed to an increase in water retention capacity and a decrease in the intensity of transpiration of tissues of leaves and shoots of microclones of both technical and rootstock varieties. During 60 minutes of research, from 0.006 g to 0.034 g of water evaporated from microclones of technical varieties, from 0.003 g to 0.053 g from microclones of rootstock varieties, respectively. Transpiration intensity (after 10 min) decreased by 1.7-1.8 times. On the control Murashige and Skoog nutrient medium, plants evaporated a larger amount of water during the corresponding period of time: from 0.006 g to 0.079 g (technical varieties) and from 0.008 g to 0.086 g (rootstock varieties); the intensity of transpiration was higher. After cultivation of grape microclones on structured nutrient media, they were characterized by a higher content of dry matter in the tissues of leaves and shoots (14.6-15.0%) and better survival rates in vivo (76.3-98.5%, at 58.5-65.2% in control). The reliability of the results obtained is confirmed by the results of multivariate analysis of variance. The obtained results expand the understanding of dynamic changes in the indicators of the water regime of the vegetative mass of grape microclones in vitro, their influence on plant survival under in vivo conditions

Effects of exogenous GA3 and warm water on dormancy breaking germination characteristics of Eucommia ulmoides

Seeds of the plant Eucommia ulmoides Oliver, have prominent dormant characteristics. In the present study, seed dormancy and germination of E. ulmoides were investigated by treating them with exogenous GA3 and different water temperatures. The results revealed that exogenous GA3 and warm water soaking treatments were beneficial to the dormancy breaking and germination of seeds. The germination rate of seeds treated with 50℃ water was 84.67%. In comparison, the seeds treated with 300 mg·L-1 GA3 had only a germination rate of 45%. This low germination rate resulted probably due to the low temperature of the GA3 solution. Another important reason is the presence of eucommia gum in the seed coat of E. ulmoides which hinders the germination process. During germination, the SOD activity in the seeds treated with GA3 (300 mg·L-1) and warm water (50 °C) increased significantly. Increased SOD activity reduced the degree of oxidative damage of the plasma membrane and resulted a continuous decrease in TBARS content. Thereby, the seeds were prompted to develop in a direction conducive to germination. In addition, GA3 (300 mg·L-1) and warm water (50℃) treatments increased the content of endogenous GA3, IAA, and ZR in the seeds, and decreased the content of endogenous ABA. This had resulted significantly higher ratios of GA3/ABA, IAA/ABA and ZR/ABA than those ratios of distilled water (room temperature) treated plants. In short, 50 °C warm water treatment has a more marked germination promoting effect on E. ulmoides seeds.

Wheat type one protein phosphatase promotes salt and osmotic stress tolerance in arabidopsis via auxin-mediated remodelling of the root system

The control of optimal root growth and plant stress responses depends largely on a variety of phytohormones among which auxin and brassinosteroids (BRs) are the most influential. We have previously reported that the durum wheat type 1 protein phosphatase TdPP1 participates in the control of root growth by modulating BR signaling. In this study, we pursue our understanding of how TdPP1 fulfills this regulatory function on root growth by evaluating the physiological and molecular responses of Arabidopsis TdPP1 over-expressing lines to abiotic stresses. Our results showed that when exposed to 300 mM Mannitol or 100 mM NaCl, the seedlings of TdPP1 over-expressors exhibit modified root architecture with higher lateral root density, and longer root hairs concomitant with a lower inhibition of the primary root growth. These lines also exhibit faster gravitropic response and a decrease in primary root growth inhibition when exposed to high concentrations of exogenous IAA. On another hand, a cross between TdPP1 overexpressors and DR5:GUS marker line was performed to monitor auxin accumulation in roots. Remarkably, the TdPP1 overexpression resulted in an enhanced auxin gradient under salt stress with a higher accumulation in primary and lateral root tips. Moreover, TdPP1 transgenics exhibit a significant induction of a subset of auxin-responsive genes under salt stress conditions. Therefore, our results reveal a role of PP1 in enhancing auxin signaling to help shape greater root plasticity thus improving plant stress resilience.

ChIFNα regulates adventitious root development in Lotus japonicus via an auxin-mediated pathway

ABSTRACT Adventitious roots (ARs), developing from non-root tissue, play an important role in some plants. Here, the molecular mechanism of AR differentiation in Lotus japonicus L. (L. japonicus) with the transformed chicken interferon alpha gene (ChIFNα) encoding cytokine was studied. ChIFNα transgenic plants (TP) were identified by GUS staining, PCR, RT-PCR, and ELISA. Up to 0.175 μg/kg rChIFNα was detected in TP2 lines. Expressing rChIFNα promotes AR development by producing longer roots than controls. We found that the effect was enhanced with the auxin precursor IBA treatment in TP. IAA contents, POD, and PPO activities associated with auxin regulation were higher than wild type (WT) in TP and exogenous ChIFNα treatment plants. Transcriptome analysis revealed 48 auxin-related differentially expressed genes (DEGs) (FDR < 0.05), which expression levels were verified by RT-qPCR analysis. GO enrichment analysis of DEGs also highlighted the auxin pathway. Further analysis found that ChIFNα significantly enhanced auxin synthesis and signaling mainly with up-regulated genes of ALDH, and GH3. Our study reveals that ChIFNα can promote plant AR development by mediating auxin regulation. The findings help explore the role of ChIFNα cytokines and expand animal gene sources for the molecular breeding of growth regulation of forage plants.

Concentration-dependent mechanisms of fluoranthene uptake by ryegrass

Fluoranthene (Flu) uptake by plants is affected by plant growth and environmental concentration. Although plant growth processes, including substance synthesis and antioxidant enzyme activities, have been reported to regulate Flu uptake, their contributions have been poorly evaluated. Moreover, the effect of Flu concentration is little known. Here, low concentrations (0, 1, 5, and 10 mg/L) and high concentrations (20, 30, and 40 mg/L) of Flu were set to compare the changes in Flu uptake by ryegrass (Lolium multiflorum Lam.). Indices of plant growth (biomass, root length, root area, root tip number, and photosynthesis and transpiration rates), substance synthesis (indole acetic acid [IAA] content), and antioxidant enzyme activities (superoxide dismutase [SOD], peroxidase [POD], and catalase [CAT]) were recorded to unravel the mechanism of Flu uptake. Findings suggested that the Langmuir model fitted Flu uptake by ryegrass well. Flu absorption capacity in the root was stronger than that that in the leaf. Flu bioconcentration and translocation factors increased then reduced with the increase in Flu concentration and reached the maximum value under 5 mg/L Flu treatment. Plant growth and IAA content had the same pattern as before bioconcentration factor (BCF). SOD and POD activities increased then decreased with Flu concentration and reached their highest levels under 30 and 20 mg/L Flu treatments, respectively, whereas CAT activity decreased continuously and reached its lowest level under 40 mg/L Flu treatment. Variance partitioning analysis indicated that IAA content had the greatest significant effect on Flu uptake under low-concentration Flu treatments, whereas antioxidant enzyme activities had the greatest significant effect on Flu uptake under high-concentration Flu treatments. Revealing the concentration-dependent mechanisms of Flu uptake could provide a basis for regulating pollutant accumulation in plants.

Alternating temperature stratification breaks seed dormancy of Paeonia ostii

Paeonia ostii T. Hong & J. X. Zhang (Paeoniaceae), a traditional ornamental and medicinal plant, is used as a new oil tree crop in China, but its cultivation is greatly hindered by seed dormancy. By using an alternating temperature stratification assay, the present study investigated seed germination of P. ostii. Seeds of P. ostii did not germinate under low temperature, and produced the root but not the shoot under continuous warm conditions. Seedling emergence of P. ostii was dependent on a warm (I) - cold - warm (II) sequence of temperature regimes. During warm (I) stratification, the embryo developed fully and the radicle emerged and grew; the activity of peroxidase increased in the embryo, the contents of soluble protein, IAA and ABA in the embryo decreased before radicle emerged and increased after radicle emerged, the contents of GA3 and the GA3: ABA ratio in the embryo increased before radicle emerged and decreased after radicle emerged,and the content of starch decreased in the endosperm.Under cold stratification, the embryo and the root developed slowly, but the GA3: ABA ratio in embryo gradually increased. Subsequent warm (II) condition allowed the epicotyl to elongate and produce a shoot. These results indicate that seeds of P. ostii have morphophysiological dormancy. The radicle and shoot of the underdeveloped embryo have physiological dormancy (PD). Warm stratification breaks PD, allowing the embryo to grow and the radicle to emerge. Cold stratification is required to break dormancy of the epicotyl, but this treatment is not effective until after the radicle has emerged.

Transcriptomic analysis of Cucumis sativus uncovers putative genes related to hormone signaling under low temperature (LT) and high humidity (HH) stress

Climate change has caused changes in environmental conditions, leading to both low temperature (LT) and high humidity (HH) stress on crops worldwide. Therefore, there is a growing need to enhance our understanding of the physiological and molecular mechanisms underlying LT and HH stress tolerance in cucumbers, given the significance of climate change. The findings of this study offer a comprehensive understanding of how the transcriptome and hormone profiles of cucumbers respond to LT and HH stress. In this study, cucumber seedlings were subjected to LT and HH stress (9/5 °C day/night temperature, 95% humidity) as well as control (CK) conditions (25/18 °C day/night temperature, 80% humidity) for 24, 48, and 72 h. It was observed that the LT and HH stress caused severe damage to the morphometric traits of the plants compared to the control treatment. The concentrations of phytohormones IAA, ethylene, and GA were lower, while ABA and JA were higher during LT and HH stress at most time points. To gain insights into the molecular mechanisms underlying this stress response, RNA-sequencing was performed. The analysis revealed a total of 10,459 differentially expressed genes (DEGs) with annotated pathways. These pathways included plant hormone signal transduction, protein processing in the endoplasmic reticulum, MAPK signaling pathway, carbon fixation in photosynthetic organisms, and glycerolipid metabolism. Furthermore, 123 DEGs associated with hormone signaling pathways were identified, and their responses to LT and HH stress were thoroughly discussed. Overall, this study sheds light on the LT and HH tolerance mechanisms in cucumbers, particularly focusing on the genes involved in the LT and HH response and the signaling pathways of endogenous phytohormones.

Effect of Low Light Stress on Distribution of Auxin (Indole-3-acetic Acid) between Shoot and Roots and Development of Lateral Roots in Barley Plants.

Depending on their habitat conditions, plants can greatly change the growth rate of their roots. However, the mechanisms of such responses remain insufficiently clear. The influence of a low level of illumination on the content of endogenous auxins, their localization in leaves and transport from shoots to roots were studied and related to the lateral root branching of barley plants. Following two days' reduction in illumination, a 10-fold reduction in the emergence of lateral roots was found. Auxin (IAA, indole-3-acetic acid) content decreased by 84% in roots and by 30% in shoots, and immunolocalization revealed lowered IAA levels in phloem cells of leaf sections. The reduced content of IAA found in the plants under low light suggests an inhibition of production of this hormone under these conditions. At the same time, two-fold downregulation of the LAX3 gene expression, facilitating IAA influx into the cells, was detected in the roots, as well as a decline in auxin diffusion from shoots through the phloem by about 60%. It was suggested that the reduced emergence of lateral roots in barley under a low level of illumination was due to a disturbance of auxin transport through the phloem and down-regulation of the genes responsible for auxin transport in plant roots. The results confirm the importance of the long distance transport of auxins for the control of the growth of roots under conditions of low light. Further study of the mechanisms that control the transport of auxins from shoots to roots in other plant species is required.

The Chemical Capping Regulation Mechanism of Cotton Main Stem Growth

In China, due to labor shortages and increasing labor costs, manual topping is gradually being replaced by chemical capping with mepiquat chloride (DPC). External chemicals can adjust plant growth by affecting endogenous hormones. Based on the hormone changes combined with the development of the main stem of cotton plants, a comparative experiment was conducted in 2019 and 2020 to determine the regulatory mechanism of the growth of the cotton main stem after chemical capping. In the experiment, two treatment times (T1: 12 July, T2: 18 July) and two treatment agents (CA [chemical capping agent] and DPC) were set, the hormone (auxin IAA, abscisic acid ABA, Gibberellin GA3 and Zeatin ZR) concentrations at the top of main stem (0–5 and 5–10 cm) were continuously measured and the main stem development situation was observed and recorded. The results showed that after chemical capping, the IAA concentration decreased firstly and increased later, lower than that of CK. ABA concentration increased significantly and GA3 concentration decreased significantly compared with CK. ZR concentrations fluctuated obviously at T1 and gently at T2. In terms of main stem growth, the plant height, number of fruit branches and average length of upper internode (fifth and above) were decreased compared with CK, while the CA treatment was inhibited more strongly than the DPC treatment. To conclude, chemical capping operation affected the hormone concentration at the plant apex significantly and effectively regulated plant development. In comparison with DPC treatment, CA regulated hormones effectively, which is favorable for conducive reasonable plant shaping.

Comparative Microscopic, Transcriptome and IAA Content Analyses Reveal the Stem Growth Variations in Two Cultivars Ilex verticillata.

Ilex verticillata is not only an excellent ornamental tree species for courtyards, but it is also a popular bonsai tree. 'Oosterwijk' and 'Red sprite' are two varieties of Ilex verticillata. The former has a long stem with few branches, while the latter has a short stem. In order to explain the stem growth differences between the two cultivars 'Oosterwijk' and 'Red sprite', determination of the microstructure, transcriptome sequence and IAA content was carried out. The results showed that the xylem thickness, vessel area and vessel number of 'Oosterwijk' were larger than in 'Red sprite'. In addition, our analysis revealed that the differentially expressed genes which were enriched in phenylpropanoid biosynthesis; phenylalanine metabolism and phenylalanine, tyrosine and tryptophan biosynthesis in the black and tan modules of the two varieties. We found that AST, HCT and bHLH 94 may be key genes in the formation of shoot difference. Moreover, we found that the IAA content and auxin-related DEGs GH3.6, GH3, ATRP5, IAA27, SAUR36-like, GH3.6-like and AIP 10A5-like may play important roles in the formation of shoot differences. In summary, these results indicated that stem growth variations of 'Oosterwijk' and 'Red sprite' were associated with DEGs related to phenylpropanoid biosynthesis, phenylalanine metabolism and phenylalanine, tyrosine and tryptophan biosynthesis, as well as auxin content and DEGs related to the auxin signaling pathway.

Enhanced rice plant (BRRI-28) growth at lower doses of urea caused by diazinon mineralizing endophytic bacterial consortia and explorations of relevant regulatory genes in a Klebsiella sp. strain HSTU-F2D4R

Endophytic biostimulant with pesticide bioremediation activities may reduce agrochemicals application in rice cultivation. The present study evaluates diazinon-degrading endophytic bacteria, isolated from rice plants grown in the fields with pesticide amalgamation, leading to increased productivity in high-yielding rice plants. These endophytes showed capabilities of decomposing diazinon, confirmed by FT-IR spectra analysis. Growth promoting activities of these endophytes can be attributed to their abilities to produce an increased level of IAA content and to demonstrate high level ACC-deaminase activities. Furthermore, these endophytes demonstrated enhanced level of extracellular cellulase, xylanase, amylase, protease and lignin degrading activities. Five genera including Enterobacter, Pantoea, Shigella, Acinetobacter, and Serratia, are represented only by the leaves, while four genera such as Enterobacter, Escherichia, Kosakonia, and Pseudomonas are represented only by the shoots. Five genera including, Klebsiella, Enterobacter, Pseudomonas, Burkholderia, and Bacillus are represented only by the roots of rice plants. All these strains demonstrated cell wall hydrolytic enzyme activities, except pectinase. All treatments, either individual strains or consortia of strains, enhanced rice plant growth at germination, seedling, vegetative and reproductive stages. Among four (I-IV) consortia, consortium-III generated the maximum rice yield under 70% lower doses of urea compared to that of control (treated with only fertilizer). The decoded genome of Klebsiella sp. HSTU-F2D4R revealed nif-cluster, chemotaxis, phosphates, biofilm formation, and organophosphorus insecticide-degrading genes. Sufficient insecticide-degrading proteins belonging to strain HSTU-F2D4R had interacted with diazinon, confirmed in molecular docking and formed potential catalytic triads, suggesting the strains have bioremediation potential with biofertilizer applications in rice cultivation.

Effects of 5-HT on the cold resistance of mangrove Kandelia obovata seedlings.

5-hydroxytryptamine (5-HT) participates in plant growth and development, and can also delay senescence and cope with abiotic stress. To explore the role of 5-HT in regulating the abilities of mangrove in cold resis-tance, we examined the effects of cold acclimation and the spraying of p-chlorophenylalanine (p-CPA, 5-HT synthesis inhibitor) on leaf gas exchange parameters and CO2 response curves (A/Ca), as well as the endogenous phytohormone content levels in the mangrove species Kandelia obovata seedlings under low temperature stress. The results showed that low temperature stress significantly reduced the contents of 5-HT, chlorophyll, endogenous auxin (IAA), gibberellin (GA), and abscisic acid (ABA). It weakened the CO2 utilization abilities of plants and reduced net photosynthetic rate, which ultimately reduced carboxylation efficiency (CE). Under low temperature stress, exogenous p-CPA reduced the contents of photosynthetic pigments, endogenous hormones, and 5-HT in the leaves, which aggravated the damages caused by low temperature stress on photosynthesis. By enhancing cold acclimation abilities, the endogenous IAA content in the leaves could was reduced under low temperature stress, promoted the production of 5-HT, improved the contents of photosynthetic pigments, GA, and ABA, as well as enhanced photosynthetic carbon assimilation abilities, which would increase photosynthesis in the K. obovata seedlings. Under cold acclimation conditions, the spraying of p-CPA could significantly inhibit the synthesis of 5-HT, promote the production of IAA, and reduce the contents of photosynthetic pigments, GA, ABA, and CE, which would weaken the effects of cold acclimation by improving the cold resistance of mangroves. In conclusion, cold acclimation could improve the cold resistance abilities of K. obovata seedlings by regulating photosynthetic carbon assimilation capacity and the contents of endogenous phytohormone. 5-HT synthesis is one of the necessary conditions for improving the cold resistance abilities of mangroves.

The Mechanism of Manganese Ferrite Nanomaterials Promoting Drought Resistance in Rice.

Strategies to reduce the risk of drought damage are urgently needed as intensified climate change threatens agricultural production. One potential strategy was using nanomaterials (NMs) to enhance plant resistance by regulating various physiological and biochemical processes. In the present study, 10 mg kg-1 manganese ferrite (MnFe2O4) NMs had the optimal enhancement to elevate the levels of biomass, photosynthesis, nutrient elements, and polysaccharide in rice by 10.9-525.0%, respectively, under drought stress. The MnFe2O4 NMs were internalized by rice plants, which provided the possibility for rice to better cope with drought. Furthermore, as compared with drought control and equivalent ion control, the introduction of MnFe2O4 NMs into the roots significantly upregulated the drought-sensing gene CLE25 (29.4%) and the receptor gene NCED3 (59.9%). This activation stimulated downstream abscisic acid, proline, malondialdehyde, and wax biosynthesis by 23.3%, 38.9%, 7.2%, and 26.2%, respectively. In addition, 10 mg·kg-1 MnFe2O4 NMs significantly upregulated the relative expressions of OR1, AUX2, AUX3, PIN1a, and PIN2, and increased IAA content significantly, resulting in an enlarged root angle and a deeper and denser root to help the plant withstand drought stresses. The nutritional quality of rice grains was also improved. Our study provides crucial insight for developing nano-enabled strategies to improve crop productivity and resilience to climate change.