Nanosilver as a novel biocide for control of senescence in garden cosmos

The genomes of Dahlia pinnata, Cosmos bipinnatus, and Bidens alba in tribe Coreopsideae provide insights into polyploid evolution and inulin biosynthesis

BACKGROUND

The Coreopsideae tribe, a subset of the Asteraceae family, encompasses economically vital genera like Dahlia, Cosmos, and Bidens, which are widely employed in medicine, horticulture, ecology, and food applications. Nevertheless, the lack of reference genomes hinders evolutionary and biological investigations in this tribe.

RESULTS

Here, we present 3 haplotype-resolved chromosome-level reference genomes of the tribe Coreopsideae, including 2 popular flowering plants (Dahlia pinnata and Cosmos bipinnatus) and 1 invasive weed plant (Bidens alba), with assembled genome sizes 3.93 G, 1.02 G, and 1.87 G, respectively. We found that Gypsy transposable elements contribute mostly to the larger genome size of D. pinnata, and multiple chromosome rearrangements have occurred in tribe Coreopsideae. Besides the shared whole-genome duplication (WGD-2) in the Heliantheae alliance, our analyses showed that D. pinnata and B. alba each underwent an independent recent WGD-3 event: in D. pinnata, it is more likely to be a self-WGD, while in B. alba, it is from the hybridization of 2 ancestor species. Further, we identified key genes in the inulin metabolic pathway and found that the pseudogenization of 1-FEH1 and 1-FEH2 genes in D. pinnata and the deletion of 3 key residues of 1-FFT proteins in C. bipinnatus and B. alba may probably explain why D. pinnata produces much more inulin than the other 2 plants.

CONCLUSIONS

Collectively, the genomic resources for the Coreopsideae tribe will promote phylogenomics in Asteraceae plants, facilitate ornamental molecular breeding improvements and inulin production, and help prevent invasive weeds.

Jasmonates and salicylic acid as enigmatic orchestrators of capitula senescence in Cosmos sulphureus Cav

The fine-tuning of the intricate network of plant growth hormones empowers the balanced responses of plants to environmental and developmental signals. Salicylic acid and jasmonates are emerging as advanced hormones that provide plants with resistance to environmental stresses. Senescence is characterized by coordinated and systematic crosstalk between phytohormones that remodels the biochemical and physiological mechanisms in plants, resulting in cell death. The present investigation examines the role of jasmonates (methyl jasmonate and jasmonic acid) and salicylic acid (SA) in regulating the petal senescence of detached stalks of Cosmos sulphureus. Based on our results, it was revealed that SA and jasmonic acid (JA) at 40 μM and methyl jasmonate (MJ) at 0.75 μM concentration delayed the senescence of detached flowers of C. sulphureus considerably. These growth regulators improved the membrane stability, reinforced the antioxidant enzyme activities and averted the upsurge of hydrogen peroxide (H2O2) content in the petals. Additionally, SA and jasmonates preserved higher content of total phenols, reducing sugars and soluble proteins in the petals, besides impeding the bacterial growth in testing solutions which corroborated with the maximum solution uptake. The elevated soluble protein content was found to be associated with low specific protease activity (SPA) and α-amino acid content in the petal tissues. Our study concluded that SA and jasmonates delayed flower senescence by averting oxidative stress and maintaining the nutritional status of the petals.

Green synthesis of silver nanoparticles using Eucommia ulmoides leaf extract for inhibiting stem end bacteria in cut tree peony flowers

Tree peony ( Paeonia suffruticosa Andr.) is a popular cut flower among ornamental plants. However, its short vase life severely hinders the production and application of cut tree peony flowers. To extend the postharvest longevity and improve the horticultural value, silver nanoparticles (Ag-NPs) was applied for reducing bacterial proliferation and xylem blockage in cut tree peony flowers in vitro and in vivo. Ag-NPs was synthesized with the leaf extract of Eucommia ulmoides and characterized. The Ag-NPs aqueous solution showed inhibitory activity against bacterial populations isolated from stem ends of cut tree peony 'Luoyang Hong' in vitro. The minimum inhibitory concentration (MIC) was 10 mg L^-1. Compared with the control, pretreatments with Ag-NPs aqueous solution at 5 and 10 mg L^-1 for 24 h increased flower diameter, relative fresh weight (RFW), and water balance of tree peony 'Luoyang Hong' flowers. Additionally, malondialdehyde (MDA) and H₂O₂ content in pretreated petals were lower than the control during the vase life. The activities of superoxide dismutase (SOD) and catalase (CAT) in pretreated petals were lower than that of the control at the early vase stage and higher at the late vase life. Furthermore, pretreatments with Ag-NPs aqueous solution at 10 mg L^-1 for 24 h could reduce bacterial proliferation in the xylem vessels on the stem ends by confocal laser scanning microscope (CLSM) and scanning electron microscope (SEM). Overall, pretreatments with green synthesized Ag-NPs aqueous solution effectively reduced bacteria-induced xylem blockage of cut tree peony, resulting in improved water uptake, extended vase life, and enhanced postharvest quality. Therefore, this technique can be used as a promising postharvest technology in the cut flower industry.

Combined Nano Silver, α-Aminoisobutyric Acid, and 1-Methylcyclopropene Treatment Delays the Senescence of Cut Roses with Different Ethylene Sensitivities

Flower senescence varies among cut roses (Rosa hybrida L.), and it is known that the postharvest life of ethylene-sensitive flowers is strongly related to the transcriptional accumulation of ethylene biosynthesis genes, whereas that of ethylene-insensitive flowers is shortened by water stress. These different responses of flowers to hormone and water stresses limit the action of preservatives in inhibiting the postharvest deterioration of cut rose flowers. This study was conducted to investigate the effects of the combined application of antibacterial agents and ethylene biosynthesis and binding inhibitors on the postharvest life and quality of the cut rose cultivars ‘Matador’ (ethylene-sensitive) and ‘Dolcetto’ (ethylene-insensitive). Cut flowers were treated with nano silver (NS), a combination of NS and α-aminoisobutyric acid (NS+A), or a combination of NS+A and 1-methylcyclopropene (NS+AM), and they were subsequently exposed to ethylene for 24 h. Treatment effectiveness was compared with that of control (CON) flowers, which were kept in distilled water and exposed only to ethylene. The results showed that all treatments significantly improved the postharvest quality and vase life of both rose cultivars. However, NS+AM most markedly delayed senescence and prolonged the vase life of cut flowers by 217% in ‘Matador’ and 168.4% in ‘Dolcetto’, compared with those of CON flowers. NS+AM also effectively increased the flower diameter and maintenance time of positive water balance and initial fresh weight by enhancing solution absorption as well as suppressing bacterial growth at the cut stem ends of the cut roses. Furthermore, NS+AM greatly suppressed the ethylene-inducible increase of ethylene biosynthesis genes and the reduction of ethylene receptor genes in petals, which resulted in a reduced flower response to exogenous ethylene in both rose cultivars. These findings show that NS+AM effectively delays flower senescence in both ethylene sensitive and insensitive cultivars by synergistically preventing ethylene response and water stress in cut flowers.