Cytokinin Levels Research Articles

Growth, phytochemical, and phytohormonal responses of basil to different light durations and intensities under constant daily light integral

Horticulture in controlled environments has been increasingly used to tackle limitations on crop production. As a crucial environmental factor, light regulate plant growth and metabolism. In the present study, basil plants were subjected to different light durations and intensities considering constant daily light integral (DLI). The lighting environment included 200, 300, and 400 µmol m− 2 s− 1 intensities for 18, 12, and 9 h, respectively. DLI amounted to 12.96 mol m− 2 d− 1 among all light treatments (LI200 for 18 h, LI300 for 12 h, and LI400 for 9 h). Half of the plants under each light treatment were exposed to 30 µmol m− 2 s− 1 of far-red light. The results indicated the general negative impact of LI400/9 on the growth of basils. Exposure to far-red light hurt the growth of the shoot, while it enhanced stem and petiole elongation. This effect was due to higher gibberellin accumulation, which resulted in shade avoidance responses. Exposure to far-red light also reduced anthocyanin and flavonoid contents, as two important nutritional components. Soluble carbohydrates increased, while storage carbohydrates decreased by increasing lighting duration/decreasing light intensity or by far-red light inclusion. The lowest antioxidant activity was detected in LI400/9. In the LI200/18, the highest level of auxin and the lowest level of cytokinin were detected, while the LI300/12 exhibited the highest level of gibberellin hormone. Low light intensity and long photoperiod enhanced plant biomass and phytochemical production and are recommended for basil production in controlled environments.

Functional characterisation of BnaA02.TOP1α and BnaC02.TOP1α involved in true leaf biomass accumulation in Brassica napus L.

Leaves, as primary photosynthetic organs essential for high crop yield and quality, have attracted significant attention. The functions of DNA topoisomerase 1α (TOP1α) in various biological processes, including leaf development, in Brassica napus remain unknown. Here, four paralogs of BnaTOP1α, namely BnaA01.TOP1α, BnaA02.TOP1α, BnaC01.TOP1α and BnaC02.TOP1α, were identified and cloned in the B. napus inbred line 'K407'. Expression pattern analysis revealed that BnaA02.TOP1α and BnaC02.TOP1α, but not BnaA01.TOP1α and BnaC01.TOP1α, were persistently and highly expressed in B. napus true leaves. Preliminary analysis in Arabidopsis thaliana revealed that BnaA02.TOP1α and BnaC02.TOP1α paralogs, but not BnaA01.TOP1α and BnaC01.TOP1α, performed biological functions. Targeted mutations of four BnaTOP1α paralogs in B. napus using the CRISPR-Cas9 system revealed that BnaA02.TOP1α and BnaC02.TOP1α served as functional paralogs and redundantly promoted true leaf number and size, thereby promoting true leaf biomass accumulation. Moreover, BnaA02.TOP1α modulated the levels of endogenous gibberellins, cytokinins and auxins by indirectly regulating several genes related to their metabolism processes. BnaA02.TOP1α directly activated BnaA03.CCS52A2 and BnaC09.AN3 by facilitating the recruitment of RNA polymerase II and modulating H3K27me3, H3K36me2 and H3K36me3 levels at these loci and indirectly activated the BnaA08.PARL1 expression, thereby positively controlling the true leaf size in B. napus. Additionally, BnaA02.TOP1α indirectly activated the BnaA07.PIN1 expression to positively regulate the true leaf number. These results reveal the important functions of BnaTOP1α and provide insights into the regulatory network controlling true leaf biomass accumulation in B. napus.

Morphological, histological and transcriptomic mechanisms underlying different fruit shapes in Capsicum spp.

Pepper (Capsicum spp.) has a long domestication history and has accumulated diverse fruit shape variations. The illustration of the mechanisms underlying different fruit shape is not only important for clarifying the regulation of pepper fruit development but also critical for fully understanding the plant organ morphogenesis. Thus, in this study, morphological, histological and transcriptional investigations have been performed on pepper accessions bearing fruits with five types of shapes. From the results it can be presumed that pepper fruit shape was determined during the developmental processes before and after anthesis, and the anthesis was a critical developmental stage for fruit shape determination. Ovary shape index variations of the studied accessions were mainly due to cell number alterations, while, fruit shape index variations were mainly attributed to the cell division and cell expansion variations. As to the ovary wall thickness and pericarp thickness, they were regulated by both cell division in the abaxial-adaxial direction and cell expansion in the proximal-distal and medio-lateral directions. Transcriptional analysis discovered that the OFP-TRM and IQD-CaM pathways may be involved in the regulation of the slender fruit shape and the largest ovary wall cell number in the blocky-shaped accession can be attributed to the higher expression of CYP735A1, which may lead to an increased cytokinin level. Genes related to development, cell proliferation/division, cytoskeleton, and cell wall may also contribute to the regulation of helical growth in pepper. The insights gained from this study are valuable for further investigations into pepper fruit shape development.

Comparative analysis of element and hormone content in zygotic embryos of Pinus elliottii and P. elliottii × P. caribaea

Somatic embryogenesis is a crucial method for achieving clonal forestry in conifers. Understanding the development of zygotic embryos is essential not only for enhancing the efficiency and quality of somatic embryogenesis, but also for advancing forestry breeding programs. This study investigated dynamic changes of element and hormone contents during ZE development of Pinus elliottii and its hybrid P. elliottii × P. caribaea. Significant differences in embryo development speed among different clones were observed. Elemental analysis was conducted using inductively coupled plasma mass spectrometry (ICP-MS) and identified 68 elements, including major, minor, and beneficial elements. In both species, the contents of potassium (K), calcium (Ca), iron (Fe), boron (B) and five beneficial elements decreased during early ZE development, while phosphorus (P) and copper (Cu) increased. Significantly higher levels of K, Ca and Fe at the initial stage, and sulfur (S) and nickel (Ni) decreased at later stages were detected in P. elliottii than in the hybrid. For the other elements, except for very few significant differences at certain stages, most differences between the two species did not reach a significant level. The contents of endogenous hormones were determined and different accumulation patterns were detected in most hormones between the two species, except abscisic acid (ABA) which simultaneously decreased with developments by stage 8. Significant differences were found in indole-3-acetic acid (IAA) contents at most stages between species, while higher levels of total cytokinin (CK) at each stage were detected in the hybrid in comparison with those in P. elliottii. As a result, lower IAA to CK ratios in the hybrid than in P. elliottii. Methyl jasmonate (JA-me) and gibberellin A3 (GA3) contents showed a similar pattern and exhibited an M-shaped fluctuation in the hybrid. Furthermore, JA-me, GA3, gibberellin A4 (GA4) and brassinolide (BR) showed significantly higher levels in the hybrid than in P. elliottii. K-means clustering and correlation analyses were used to explore relationships between elements and hormones during embryo development, revealing complex interplay in both species. These data indicate different requirement in element and hormone contents for embryogenesis and suggest species-specific media composition for each step in somatic embryogenesis. The findings provide insights into their developmental processes and informing future research and applications in somatic embryogenesis and forestry breeding.

A nitrogen-responsive cytokinin oxidase/dehydrogenase regulates root response to high ammonium in rice.

Plant root system is significantly influenced by high soil levels of ammonium nitrogen, leading to reduced root elongation and enhanced lateral root branching. In Arabidopsis, these processes have been reported to be mediated by phytohormones and their downstream signaling pathways, while the controlling mechanisms remain elusive in crops. Through a transcriptome analysis of roots subjected to high/low ammonium treatments, we identified a cytokinin oxidase/dehydrogenase encoding gene, CKX3, whose expression is induced by high ammonium. Knocking out CKX3 and its homologue CKX8 results in shorter seminal roots, fewer lateral roots, and reduced sensitivity to high ammonium. Endogenous cytokinin levels are elevated by high ammonium or in ckx3 mutants. Cytokinin application results in shorter seminal roots and fewer lateral roots in wild-type, mimicking the root responses of ckx3 mutants to high ammonium. Furthermore, CKX3 is transcriptionally activated by type-B RR25 and RR26, and ckx3 mutants have reduced auxin content and signaling in roots under low ammonium. This study identified RR25/26-CKX3-cytokinin as a signal module that mediates root responses to external ammonium by modulating of auxin signaling in the root meristem and lateral root primordium. This highlights the critical role of cytokinin metabolism in regulating rice root development in response to ammonium.

RST31 controls salt tolerance in rice (Oryza sativa) by regulating the cytokinin pathway

Salt stress affects the growth of rice, which reduces grain yield. However, the mechanism of the rice response to salt stress is not fully understood. The rice salt tolerance 31 (rst31) mutant exhibits longer shoots and greater dry weight than wild type (WT) plants under salt stress conditions. Through map-based cloning and genetic complementation methods, we determined that RST31 encodes a half-size ABCG transporter protein, ABCG18. We showed that mutation of RST31 reduces DNA damage under salt stress, with less accumulation of reactive oxygen species (ROS). The deficiency of RST31 suppressed the root-to-shoot transport of cytokinin, which resulted in a decrease in cytokinin content in the shoot and an increase in cytokinin content in the root. ROS accumulated abundantly in WT and rst31 mutant plants after exogenous treatment with trans-zeatin, reducing rst31 tolerance of salt stress. Collectively, our results suggest that high cytokinin level in shoots leads to an increase in ROS content and severe DNA damage under salt stress, which lead to sensitivity to salt stress. These findings enhance our understanding of plant responses to salt stress through cytokinin pathways.

Deciphering the behind blackspot exocarp disorder in avocado cv. Hass through a hormonal, transcriptional and metabolic integration approach

Avocado cv. Hass is an important sub-tropical crop with an increasing global demand. However, the avocado supply chain experiences significant fruit losses, particularly during the postharvest stage due to diseases and disorders that manifest after prolonged cold storage or the ready-to-eat stage. The blackspot exocarp disorder, which appears as brown or black blotches only after extended cold storage conditions, leads to substantial commercial losses for exported avocados. This research aimed to identify transcriptomic, metabolomic, and hormonal changes in avocado fruits affected by blackspot disorder, differentiating between the green and black exocarp tissues directly impacted by this physiological disorder. The results showed a correlation between the black-colored exocarp of blackspot affected fruits with high levels of gibberellins, cytokinins, jasmonic acid and salicylic acid hormones. Metabolically, these changes were accompanied by a high fatty acid content of oleate, palmitate and linoleate. Using a metabolic pathway reconstruction analysis, we integrated hormonal and metabolic data with transcriptomic information. This approach identified several genes involved in central carbon metabolism, long-chain fatty acid elongation, and jasmonate/salicylate biosynthesis pathways, as well as a possible accumulation of lignins due to a high expression of genes associated with the phenylpropanoid pathway in the black exocarp of blackspot-affected fruits. These findings suggest that blackspot disorder results from a combination of plant defense mechanisms triggered to strengthen the fruit exocarp tissue.

Shade signals activate distinct molecular mechanisms that induce dormancy and inhibit flowering in vegetative axillary buds of sorghum.

Shoot branches grow from axillary buds and play a crucial role in shaping shoot architecture and determining crop yield. Shade signals inactivate phytochrome B (phyB) and induce bud dormancy, thereby inhibiting shoot branching. Prior transcriptome profiling of axillary bud dormancy in a phyB-deficient mutant (58M, phyB-1) and bud outgrowth in wild-type (100M, PHYB) sorghum genotypes identified differential expression of genes associated with flowering, plant hormones, and sugars, including SbCN2, SbNCED3, SbCKX1, SbACO1, SbGA2ox1, and SbCwINVs. This study examined the expression of these genes during bud dormancy induced by shade and defoliation in 100M sorghum. The aim was to elucidate the molecular mechanisms activated by shade in axillary buds by comparing them with those activated by defoliation. The expression of marker genes for sugar levels suggests shade and defoliation reduce the sugar supply to the buds and induce bud dormancy. Intriguingly, both shade signals and defoliation downregulated SbNCED3, suggesting that ABA might not play a role in promoting axillary bud dormancy in sorghum. Whereas the cytokinin (CK) degrading gene SbCKX1 was upregulated solely by shade signals in the buds, the CK inducible genes SbCGA1 and SbCwINVs were downregulated during both shade- and defoliation-induced bud dormancy. This indicates a decrease in CK levels in the dormant buds. Shade signals dramatically upregulated SbCN2, an ortholog of the Arabidopsis TFL1 known for inhibiting flowering, whereas defoliation did not increase SbCN2 expression in the buds. Removing shade temporarily downregulated SbCN2 in dormant buds, further indicating its expression is not always correlated with bud dormancy. Because shade signals also trigger a systemic early flowering signal, SbCN2 might be activated to protect the buds from transitioning to flowering before growing into branches. In conclusion, this study demonstrates that shade signals activate two distinct molecular mechanisms in sorghum buds: one induces dormancy by reducing CK and sugars, whereas the other inhibits flowering by activating SbCN2. Given the agricultural significance of TFL1-like genes, the rapid regulation of SbCN2 by light signals in axillary buds revealed in this study warrants further investigation to explore its potential in crop improvement strategies.

Identification of CKX gene family in Morusindica cv K2 and functional characterization of MiCKX4 during abiotic stress

Cytokinin oxidase/dehydrogenase (CKX) is the key enzyme that has been observed to catalyze irreversible inactivation of cytokinins and thus modulate cytokinin levels in plants. CKX gene family is known to have few members which are, expanded in the genome mainly due to duplication events. A total of nine MiCKXs were identified in Morus indica cv K2 with almost similar gene structures and conserved motifs and domains. The cis-elements along with expression analysis of these MiCKXs revealed their contrasting and specific role in plant development across different developmental stages. The localization of these enzymes in ER and Golgi bodies signifies their functional specification and property of getting modified post-translationally to carry out their activities. The overexpression of MiCKX4, an ortholog of AtCKX4, displayed longer primary root and higher number of lateral roots. Under ABA stress also the transgenic lines showed higher number of lateral roots and tolerance against drought stress as compared to wild-type plants. In this study, the CKX gene family members were analyzed bioinformatically for their roles under abiotic stresses.

Functional characterization of WsPR-1 reveals its interplay with cytokinin and gibberellin signaling pathways

Pathogenesis-related protein 1 (PR-1) is an antimicrobial protein involved in systemic acquired resistance (SAR) in plants, but its regulatory role and interactions with other pathways remain unclear. In this study, we functionally characterize WsPR-1 gene of Withania somnifera in Nicotiana tabacum to elucidate its role in plant defense, growth, and development. Interestingly, transgenic tobacco plants with increased levels of cytokinin (CK) and decreased gibberellins (GAs) exhibited stunted shoot growth, an underdeveloped root system, modified leaf morphology, reduced seed pod production, and delayed leaf senescence. Transcriptional analysis revealed that WsPR-1 overexpression downregulated the GA 20-oxidase (GA20ox) gene involved in GA biosynthesis while upregulating GA 2-oxidase (GA2ox), a GA catabolic enzyme. Moreover, transcript levels of FRUITFULL (FUL) and LEAFY (NFL2) flowering genes exhibited a decrease in WsPR-1 plants, which could explain the delayed flowering and reduced seed pod development in transgenic plants. Confocal microscopy confirmed increased lignin deposition in stem cross-sections of WsPR-1 transgenic plants, supported by gene expression analysis and lignin content quantification. Additionally, our findings also suggest the involvement of Knotted1-like homeobox (KNOX) gene in enhancing cytokinin levels. This study highlights PR-1's regulatory role in plant growth and development, with potential to boost crop yields and enhance resilience.

Genomic insights into cytokinin oxidase/dehydrogenase (CKX) gene family, identification, phylogeny and synteny analysis for its possible role in regulating seed number in Pigeonpea (Cajanus cajan (L.) Millsp.)

Cytokinin oxidase/dehydrogenase (CKX) regulates cytokinin levels in plants which are vital for plant growth and development. However, there is a paucity of evidence regarding their role in controlling embryo/seed development in pigeonpea. This comprehensive study provides information on the identification and characterization of CKX genes in pigeonpea. A genome-wide analysis identified 18 CKX genes, each with distinct structure, expression patterns, and possible diverse functions. Domain analysis revealed the presence of the sequences including FAD and CK-Binding domain, and subcellular localization analysis showed that almost 50 % of them reside within the nucleus. They were observed to be located unevenly on chromosome numbers 2, 4, 6, 7, and 11 with a majority of them present on the scaffolds. The 8 homologous pairs and various orthologous gene pairs provided further insights into their evolution pattern. Further, SNP/Indels variation in CKX genes and haplotype groups among contrasting genotypes for SNPP (seed number per pod) were analyzed. Spatiotemporal expression analysis revealed the significant expression pattern of CcCKX15, CcCKX17, and CcCKX2 in genotypes carrying low SNPP reiterating their possible role as negative regulators. These genes can be potential targets to undertake seed and biomass improvement in pigeonpea.

PagJAZ5 regulates cambium activity through coordinately modulating cytokinin concentration and signaling in poplar.

Wood is resulted from the radial growth paced by the division and differentiation of vascular cambium cells in woody plants, and phytohormones play important roles in cambium activity. Here, we identified that PagJAZ5, a key negative regulator of jasmonate (JA) signaling, plays important roles in enhancing cambium cell division and differentiation by mediating cytokinin signaling in poplar 84K (Populus alba × Populus glandulosa). PagJAZ5 is preferentially expressed in developing phloem and cambium, weakly in developing xylem cells. Overexpression (OE) of PagJAZ5m (insensitive to JA) increased cambium activity and xylem differentiation, while jaz mutants showed opposite results. Transcriptome analyses revealed that cytokinin oxidase/dehydrogenase (CKXs) and type-A response regulators (RRs) were downregulated in PagJAZ5m OE plants. The bioactive cytokinins were significantly increased in PagJAZ5m overexpressing plants and decreased in jaz5 mutants, compared with that in 84K plants. The PagJAZ5 directly interact with PagMYC2a/b and PagWOX4b. Further, we found that the PagRR5 is regulated by PagMYC2a and PagWOX4b and involved in the regulation of xylem development. Our results showed that PagJAZ5 can increase cambium activity and promote xylem differentiation through modulating cytokinin level and type-A RR during wood formation in poplar.

Cytokinin and reproductive shoot architecture: bigger and better?

Cytokinin (CK) is a key plant hormone, but one whose effects are often misunderstood, partly due to reliance on older data from before the molecular genetic age of plant science. In this mini-review, we examine the role of CK in controlling the reproductive shoot architecture of flowering plants. We begin with a long overdue re-examination of the role of CK in shoot branching, and discuss the relatively paucity of genetic evidence that CK does play a major role in this process. We then examine the role of CK in determining the number of inflorescences, flowers, fruit and seed that plants initiate during reproductive development, and how these are arranged in space and time. The genetic evidence for a major role of CK in controlling these processes is much clearer, and CK has profound effects in boosting the size and number of most reproductive structures. Conversely, the attenuation of CK levels during the reproductive phase likely contributes to reduced organ size seen later in flowering, and the ultimate arrest of inflorescence meristems during end-of-flowering. We finish by discussing how this information can potentially be used to improve crop yields.

Cytokinin catabolism and transport are involved in strigolactone-modulated rice tiller bud elongation fueled by phosphate and nitrogen supply

Phosphate (P) and nitrogen (N) fertilization affect rice tillering, indicating that P- and N-regulated tiller growth has a crucial effect on grain yield. Cytokinins and strigolactones (SLs) promote and inhibit tiller bud outgrowth, respectively; however, the underlying mechanisms are unclear. In this study, tiller bud outgrowth and cytokinin fractions were evaluated in rice plants fertilized at different levels of P and N. Low phosphate or nitrogen (LP or LN) reduced rice tiller numbers and bud elongation, in line with low cytokinin levels in tiller buds and xylem sap as well as low TCSn:GUS expression, a sensitive cytokinin signal reporter, in the stem base. Furthermore, exogenous cytokinin (6-benzylaminopurin, 6-BA) administration restored bud length and TCSn:GUS activity in LP- and LN-treated plants to similar levels as control plants. The TCSn:GUS activity and tiller bud outgrowth were less affected by LP and LN supplies in SL-synthetic and SL-signaling mutants (d17 and d53) compared to LP- and LN-treated wild-type (WT) plants, indicating that SL modulate tiller bud elongation under LP and LN supplies by reducing the cytokinin levels in tiller buds. OsCKX9 (a cytokinin catabolism gene) transcription in buds and roots was induced by LP, LN supplies and by adding the SL analog GR24. A reduced response of cytokinin fractions to LP and LN supplies was observed in tiller buds and xylem sap of the d53 mutant compared to WT plants. These results suggest that cytokinin catabolism and transport are involved in SL-modulated rice tillering fueled by P and N fertilization.

Karrikinolide1 (KAR1), a Bioactive Compound from Smoke, Improves the Germination of Morphologically Dormant Apium graveolens L. Seeds by Reducing Indole-3-Acetic Acid (IAA) Levels.

Smoke-water (SW) and Karrikinolide1 (KAR1) release dormancy and improve seed germination in many plant species. Therefore, we tested SW (1:2500 v/v) and KAR1 (10-7 M) to break the morphological dormancy of celery cultivar (Apium graveolens L.). In the first trial, seeds were subjected to a 21-day incubation period at 20 °C with SW and KAR1 applied as single treatments. KAR1 showed significantly improved germination (30.7%) as compared to SW (17.2%) and a water control (14.7%). In seed soaking experiments, SW, KAR1, and gibberellic acid (GA3) treatments showed higher germination percentages than the water control after 3 and 6 h of soaking. However, prolonged soaking (12 h) reduced germination percentages for all treatments, indicating a detrimental effect. Analysis of KAR1 content dynamics in 7-day- and 21-day-old celery seeds indicated its prolonged effects on germination and dormancy alleviation. Phytohormones, including auxins in 7-day-old and cytokinins in 7-day- and 21-day-old celery seedlings, along with their precursors and metabolites, were analyzed using ultra-high-performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) after treatment with KAR1 and SW. The analysis of auxin levels in 7-day-old seeds revealed a negative correlation between seed germination and auxin (indole-3-acetic acid, IAA) content. Notably, it was found that KAR1-treated seeds significantly reduced IAA levels in all treatments. SW and KAR1 did not significantly affect cytokinin levels during celery germination except for N6-Isopentenyladenine. Hence, further research is needed to understand their precise role in celery seed germination. This work will improve our understanding of the role of bioactive compounds from plant-derived smoke and how they regulate hormonal responses and improve germination efficiency in celery.

Morphological characterization and transcriptome analysis of rolled and narrow leaf mutant in soybean

BackgroundIn plants, the leaf functions as a solar panel, where photosynthesis converts carbon dioxide and water into carbohydrates and oxygen. In soybean, leaf type traits, including leaf shape, leaf area, leaf width, and leaf width so on, are considered to be associated with yield. In this study, we performed morphological characterization, transcriptome analysis, and endogenous hormone analysis of a rolled and narrow leaf mutant line (rl) in soybean.ResultsCompared with wild type HX3, mutant line rl showed rolled and narrower leaflet, and smaller leaf, meanwhile rl also performed narrower pod and narrower seed. Anatomical analysis of leaflet demonstrated that cell area of upper epidermis was bigger than the cell area of lower epidermis in rl, which may lead rolled and narrow leaf. Transcriptome analysis revealed that several cytokinin oxidase/dehydrogenase (CKX) genes (Glyma.06G028900, Glyma.09G225400, Glyma.13G104700, Glyma.14G099000, and Glyma.17G054500) were up-regulation dramatically, which may cause lower cytokinin level in rl. Endogenous hormone analysis verified that cytokinin content of rl was lower. Hormone treatment results indicated that 6-BA rescued rolled leaf enough, rescued partly narrow leaf. And after 6-BA treatment, the cell area was similar between upper epidermis and lower epidermis in rl. Although IAA content and ABA content were reduced in rl, but exogenous IAA and ABA didn’t affect leaf type of HX3 and rl.ConclusionsOur results suggest abnormal cytokinin metabolism caused rolled and narrow leaf in rl, and provide valuable clues for further understanding the mechanisms underlying leaf development in soybean.

Metabolism of Fluorinated Topolin Cytokinins in Micropropagated Phalaenopsis amabilis

Fluorinated cytokinins have emerged as promising alternatives to traditional cytokinins in Phalaenopsis plant tissue culture, offering enhanced stability and bioactivity. However, their metabolic fate and impact on endogenous cytokinin profiles remain largely unexplored. This study builds upon previous research to investigate the comparative metabolism of the traditional cytokinin 6-Benzylaminopurine (BA) with the successful alternatives 6-(3-fluorobenzylamino)purine (FmT) and 6-(3-fluorobenzylamino)purine 9-riboside (FmTR). Additionally, this study examines the impact of another crucial factor, the use of ventilated versus closed containers, on metabolic processes. The results revealed the distinct metabolic profiles associated with each treatment, highlighting the complex interplay between exogenous and endogenous cytokinin levels. This study is the first to investigate the effects of these stable, synthetic, and exogenous cytokinins on the naturally occurring cytokinin levels and their metabolites in micropropagated Phalaenopsis. Additionally, we proposed an alternative inactivation pathway involving the conversion of FmTR and BA to pT and pTR. These findings provide valuable insights into the intricate relationship between cytokinin metabolism and plant growth under in vitro conditions.

Overexpression of Sly-miR172a improved quality of tomato fruit by regulating MADS-box family

Fruit development is the key link in the reproductive cycle of plants, which determines the quality, yield and economic value of fruit. The present study investigated the effect of Sly-miR172a on the quality of the tomato fruit. The research results showed that overexpression of Sly-miR172a (OE-miR172a) in tomato fruit efficaciously increased the transverse and longitudinal diameter, weight, pericarp thickness, cell number and cell area. Compared with the wild-type (WT) fruit and the silencing miR172a by short tandem target mimic (STTM-miR172a), the relative expression levels of the MADS-box and the flavonoid biosynthesis synthesis pathway genes were higher in OE-miR172a. The expression level of AP2 and Cytokinin oxidase/dehydrogenase (CKX) family genes in OE-miR172a fruit was decreased, and accumulated more content of soluble sugars, lycopene, carotenoid, total phenol, anthocyanin and total flavonoid. The present study showed that overexpression of Sly-miR172 promoted the development and improved quality of tomato fruit.

Integrating histology and phytohormone/metabolite profiling to understand rooting in yellow camellia cuttings

Vegetative propagation through cutting is a widely used clonal approach for maintaining desired genotypes. However, some woody species have difficulty forming adventitious roots (ARs) with this approach, including yellow camellia (YC) C. nitidissima. Yellow camellias, prized for their ornamental value and potential health benefits in tea, remain difficult to propagate clonally due to this rooting recalcitrance. As part of the efforts to understand YC cuttings’ recalcitrance, we conducted a detailed investigation into AR formation in yellow camellia cuttings via histology and endogenous phytohormone dynamics during this process. We also compared YC endogenous phytohormone and metabolite phytohormone profiles with those of easy-to-root poplar and willow cuttings. Our results indicate that the induction of ARs in YC cuttings is achievable through auxin treatment, and YC ARs are initiated from cambial derivatives and develop a vascular system connected with that of the stem. During AR induction, endogenous hormones showed a dynamic profile, with IAA continuing to increase starting 9 days after auxin induction. JA, JA-Ile, and OPDA showed a similar trend as IAA but decreased by the 45th day. Cytokinin first decreased to its lowest level by the 18th day and then increased. SA largely exhibited an increasing trend with a drop on the 36th day, while ABA first increased to its peak level by the 18th day and then decreased. Compared to poplar, YC cuttings had a low level of IAA, IAA-Asp, and OPDA, and a high level of cytokinin and SA. Metabolite profiling highlighted significant down-accumulation of compounds associated with AR formation in yellow camellias, such as citric and ascorbic acid, fructose, sucrose, flavonoids, and phenolic acid derivatives. Our study reveals the unfavorable endogenous hormone and metabolite profiles underlying the rooting recalcitrance of YC cuttings, providing valuable knowledge for addressing this challenge in clonal propagation.

Over-accumulation of chloroplast-nucleus located WHIRLY1 in barley leads to a decrease in growth and an enhanced stress resistance.

WHIRLY1 is a chloroplast-nucleus located DNA/RNA-binding protein with functions in development and stress tolerance. By overexpression of HvWHIRLY1 in barley, one line with a 10-fold and two lines with a 50-fold accumulation of the protein were obtained. In these lines, the relative abundance of the nuclear form exceeded that of the chloroplast form. Growth of the plants was shown to be compromised in a WHIRLY1 abundance-dependent manner. Over-accumulation of WHIRLY1 in chloroplasts had neither an evident impact on nucleoid morphology nor on the composition of the photosynthetic apparatus. Nevertheless, oeW1 plants were found to be compromised in the light reactions of photosynthesis as well as in carbon fixation. The reduction in growth and photosynthesis was shown to be accompanied by a decrease in the levels of cytokinins and an increase in the level of jasmonic acid. Gene expression analyses revealed that in nonstress conditions the oeW1 plants had enhanced levels of pathogen response (PR) gene expression indicating activation of constitutive defense. During growth in continuous light of high irradiance PR gene expression increased indicating that under stress conditions oeW1 are capable to further enhance defense.