Delaying early leaf senescence is important for improving photosynthetic efficiency and crop productivity. Melatonin, a multitasking bio-stimulator, participates widely in plant development and str...

Melatonin: A Potential Agent in Delaying Leaf Senescence

Petal senescence involves numerous programmed changes in biological and biochemical processes. Ubiquitination plays a critical role in protein degradation, a hallmark of organ senescence. Therefore, we investigated changes in the proteome and ubiquitome of senescing rose (Rosa hybrida) petals to better understand their involvement in petal senescence. Of 3859 proteins quantified in senescing petals, 1198 were upregulated, and 726 were downregulated during senescence. We identified 2208 ubiquitinated sites, including 384 with increased ubiquitination in 298 proteins and 1035 with decreased ubiquitination in 674 proteins. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that proteins related to peptidases in proteolysis and autophagy pathways were enriched in the proteome, suggesting that protein degradation and autophagy play important roles in petal senescence. In addition, many transporter proteins accumulated in senescing petals, and several transport processes were enriched in the ubiquitome, indicating that transport of substances is associated with petal senescence and regulated by ubiquitination. Moreover, several components of the brassinosteroid (BR) biosynthesis and signaling pathways were significantly altered at the protein and ubiquitination levels, implying that BR plays an important role in petal senescence. Our data provide a comprehensive view of rose petal senescence at the posttranslational level.

https://www.mdpi.com/1422-0067/20/24/6108/pdf

Proteome and Ubiquitome Changes during Rose Petal Senescence

Aging and senescence in plants has a major impact on agriculture, such as in crop yield, the value of ornamental crops, and the shelf life of vegetables and fruits. Senescence represents the final developmental phase of the leaf and inevitably results in the death of the organ. Still, the process is completely under the control of the plant. Plants use their protein degradation systems to maintain proteostasis and transport or salvage nutrients from senescing organs to develop reproductive parts. Herein, we present an overview of current knowledge about the main protein degradation pathways in plants during senescence: The proteasome and autophagy. Although both pathways degrade proteins, autophagy appears to prevent aging, while the proteasome functions as a positive regulator of senescence.

https://www.mdpi.com/2073-4425/10/4/267/pdf

The Role and Regulation of Autophagy and the Proteasome During Aging and Senescence in Plants

Brassinosteroids (BR) play diverse roles in the regulation of plant growth and development BR promotes plant growth by triggering cell division and expansion However, the effect of exogenous BR application on the leaf size and expansion of tobacco is unknown Tobacco seedlings are treated with different concentrations of exogenous 2,4-epibrassinolide (EBL) [control (CK, 0 mol L−1), T1 (05 × 10−7 mol L−1), and T2 (05 × 10−4 mol L−1)] The results show that T1 has 1729% and T2 has 2599% more leaf area than control The epidermal cell area is increased by 2440% and 1713% while the number of epidermal cells is 706% and 2106% higher in T1 and T2, respectively, relative to control So the exogenous EBL application improves the leaf area by increasing cell numbers and cell area The endogenous BR (75 times and 684 times), auxin (IAA) (403% and 2529%), and gibberellin (GA3) contents (8442% and 9176%) are higher in T1 and T2, respectively, in comparison with control Additionally, NtBRI1, NtBIN2, and NtBES1 are upregulated showing that the brassinosteroid signaling pathway is activated Furthermore, the expression of the key biosynthesis-related genes of BR (NtDWF4), IAA (NtYUCCA6), and GA3 (NtGA3ox-2) are all upregulated under EBL application Finally, the exogenous EBL application also upregulated the expression of cell growth-related genes (NtCYCD3;1, NtARGOS, NtGRF5, NtGRF8, and NtXTH) The results reveal that the EBL application increases the leaf size and expansion by promoting the cell expansion and division through higher BR, IAA, and GA3 contents along with the upregulation of cell growth-related genes The results of the study provide a scientific basis for the effect of EBL on tobacco leaf growth at morphological, anatomical, biochemical, and molecular levels

Exogenous application of brassinosteroids regulates tobacco leaf size and expansion via modulation of endogenous hormones content and gene expression.

The synthesis and characterisation of novel polyphosphazene nanocarriers, based on hydrophilic polyalkylene oxide Jeffamine M1000 and hydrophobic steroids with a glycinate linker for pH-controlled release of diosgenin and two brassinosteroids (DI31 and S7) with agrochemical and potential anticancer activity, is hereby described. Polyphosphazenes carrying approximately 17 wt% of DI31 or S7 self-assembled in water to form 120–150 nm nanoaggregates, which showed an excellent plant growth effect on radish cotyledons due to sustained delivery of approximately 30% of the agrochemicals after 4 days. Cytotoxic evaluation showed that all polymers carrying steroids and Jeffamine M1000 resulted in strong to moderate toxicity to MCF-7 cancer cells and were non-toxic to primary human lung fibroblast cells at 0.1 to 0.025 mg mL−1. Thus, DI31 and S7 bearing polymers applied at 10−4 to 10−6 mg mL−1 for delivery of recommended DI31 or S7 quantities to crops should be harmless to humans. Particularly, DI31 and S7 bearing polymers with strong cytotoxicity on MCF-7 and non-toxicity on primary human lung fibroblasts, good cell uptake after 6 hours, proper hydrodynamic sizes between 100 and 200 nm, and slow sustained release of cytotoxic drugs (DI31, S7) in acidic conditions might potentiate their accumulation in cancer tissues with good antitumour effects and minor side effects. These results demonstrated that preparation of brassinosteroid bearing polymers is a promising strategy for the preparation of better agrochemicals with reduced pollutant impact on sustainable agriculture and potential anticancer formulations based on analogues of brassinosteroids.

/pdf/polyphosphazene-based-nanocarriers-for-the-release-of-2l2dxcf07w.pdf

Polyphosphazene-based nanocarriers for the release of agrochemicals and potential anticancer drugs.

The application of brassinosteroids (BR) is associated with increased tolerance to various stresses such as those induced by pathogens, temperature, salinity and drought. Here, we studied the influence of BRs analogues on the leaf senescence of papaya juvenile plants. The objective was to determine whether BRs affect plant growth and leaf senescence by promoting or inhibiting the degradation of chlorophyll and/or leaf abscission. Two-month-old plants were divided into five treatments: C (control without BR application); BRWC (BR applied in the whole canopy); BRL1 (BR applied in the youngest fully expanded leaf, L1); BRL2 (BR applied in L2 which is the secondly more mature leaf in relation to L1) and BRL3 (BR applied in L3 which is the third more mature leaf in relation to L2). We concluded that BRs do not interfere with the senescence of the youngest leaf (L1) but in older leaves (L3) BRWC maintains the leaves greener and attached to the plant for a longer time when compared to the leaves from the other treatments. BR application in whole-canopy increased the plant height, and it caused a delay in leaf senescence and, consequently, in leaf abscission. In addition, hyponastic leaves developed after BR-application in the whole-canopy. The senescence process and leaf abscission in papaya, stimulated by exogenous BRs, were directly related to leaf age.

Daniel Teixeira Pinheiro

Papers

Exogenous brassinosteroid application delays senescence and promotes hyponasty in Carica papaya L. leaves