Ethephon-Induced Ethylene Enhances Protein Degradation in Source Leaves, but Its High Endogenous Level Inhibits the Development of Regenerative Organs in Brassica napus

Abstract

To investigate the regulatory role of ethylene in the source-sink relationship for nitrogen remobilization, short-term effects of treatment with different concentrations (0, 25, 50, and 75 ppm) of ethephon (2-chloroethylphosphonic acid, an ethylene inducing agent) for 10 days (EXP 1) and long-term effects at 20 days (Day 30) after treatment with 100 ppm for 10 days (EXP 2) on protein degradation and amino acid transport in foliar sprayed mature leaves of Brassica napus (cv. Mosa) were determined. In EXP 1, endogenous ethylene concentration gradually increased in response to the treated ethephon concentration, leading to the upregulation of senescence-associated gene 12 (SAG12) expression and downregulation of chlorophyll a/b-binding protein (CAB) expression. Further, the increase in ethylene concentration caused a reduction in protein, Rubisco, and amino acid contents in the mature leaves. However, the activity of protease and expression of amino acid transporter (AAP6), an amino acid transport gene, were not significantly affected or slightly suppressed between the treatments with 50 and 75 ppm. In EXP 2, the enhanced ethylene level reduced photosynthetic pigments, leading to an inhibition of flower development without any pod development. A significant increase in protease activity, confirmed using in-gel staining of protease, was also observed in the ethephon-treated mature leaves. Ethephon application enhanced the expression of four amino acid transporter genes (AAP1, AAP2, AAP4, and AAP6) and the phloem loading of amino acids. Significant correlations between ethylene level, induced by ethephon application, and the descriptive parameters of protein degradation and amino acid transport were revealed. These results indicated that an increase in ethylene upregulated nitrogen remobilization in the mature leaves (source), which was accompanied by an increase in proteolytic activity and amino acid transport, but had no benefit to pod (sink) development.

The Relationships among “STAY-GREEN” Trait, Post-Anthesis Assimilate Remobilization, and Grain Yield in Rice (Oryza sativa L.)

“…Leaf senescence is modulated by the application of ETH and AVG ( Figure 1 ). However, overproduction of ethylene is frequently related to fruit abortion and grain weight reduction [ 53 , 54 ], which is consistent with the lower weight of inferior grains following ETH treatment ( Figure 9 , Table 1 ). Cytokinins regulate the proliferation and differentiation of plant cells [ 21 ].…”

The Sink-Source Relationship in Cucumber (Cucumis sativus L.) Is Modulated by DNA Methylation

“…Therefore, four upregulated BRI1s and three upregulated BAK1 genes in FNLs might play a role in transporting signals between source and sink organs. Generally, higher levels of ethylene are a sign of leaf maturity [ 37 ]. The gene expression of most vital genes involved in ethylene biosynthesis and metabolism pathways increased in FNLs, indicating that higher sink activity may result in strengthened ethylene storage in cucumber leaves.…”

Two Hybrid Histidine Kinases Involved in the Ethylene Regulation of the Mycelial Growth and Postharvest Fruiting Body Maturation and Senescence of Agaricus bisporus

“…In this study, we used ethephon instead of ethylene to investigate the effect of exogenous ethylene on the expression of the button mushroom ethylene receptors and on the mycelial growth and postharvest mushroom maturation and senescence of the antisense ethylene receptor transformants because ethylene gas may not be conveniently available to nonethylene laboratories for occasional use ( 62 – 64 ). Ethephon is a widely used chemical replacement for ethylene that is expediently added to media at concentrations of 10 nM ( 65 ) or 100 μM ( 27 ), sprayed at 25 to 100 ppm (173 nM to 692 nM) ( 66 ) or 1,000 mg L −1 (6.9 mM) ( 67 ), or used as an immersion solution for several minutes at a strength of 0.05% (3.4 mM) ( 27 ) or 2 mg/mL (13.8 mM) ( 68 ). Ethephon (2,4-dichlorophenoxyacetic acid) decomposes slowly to produce ethylene and simultaneously produces phosphate and chloride at a pH above 4.0 ( 64 ).…”