Ethephon-Induced Ethylene Enhances Starch Degradation and Sucrose Transport with an Interactive Abscisic Acid-Mediated Manner in Mature Leaves of Oilseed rape (Brassica napus L.)

Abstract

The leaf senescence process is characterized by the degradation of macromolecules in mature leaves and the remobilization of degradation products via phloem transport. The phytohormone ethylene mediates leaf senescence. This study aimed to investigate the ethephon-induced ethylene effects on starch degradation and sucrose remobilization through their interactive regulation with other hormones. Ethephon (2-chloroethylphosphonic acid) was used as an ethylene-generating agent. Endogenous hormonal status, carbohydrate compounds, starch degradation-related gene expression, sucrose transporter gene expression, and phloem sucrose loading were compared between the ethephon-treated plants and controls. Foliar ethephon spray enhanced the endogenous ethylene concentration and accelerated leaf senescence, as evidenced by reduced chlorophyll content and enhanced expression of the senescence-related gene SAG12. Ethephon-enhanced ethylene prominently enhanced the endogenous abscisic acid (ABA) level. accompanied with upregulation of ABA synthesis gene 9-cis-epoxycarotenoid dioxygenase (NCED3), ABA receptor gene pyrabactin resistance 1 (PYR1), and ABA signaling genes sucrose non-fermenting 1 (Snf1)-related protein kinase 2 (SnRK2), ABA-responsive element binding 2 (AREB2), and basic-helix-loop-helix (bHLH) transcription factor (MYC2).) Ethephon treatment decreased starch content by enhancing expression of the starch degradation-related genes α-amylase 3 (AMY3) and β-amylase 1 (BAM1), resulting in an increase in sucrose content in phloem exudates with enhanced expression of sucrose transporters, SUT1, SUT4, and SWEET11. These results suggest that a synergistic interaction between ethylene and ABA might account for sucrose accumulation, mainly due to starch degradation in mature leaves and sucrose phloem loading in the ethephon-induced senescent leaves.

Ethylene Acts as a Negative Regulator of the Stem-Bending Mechanism of Different Cut Snapdragon Cultivars

“…Recently, Wang et al (2020) and Wongjunta et al (2021) observed that STS inhibited ET production in lotus leaves and orchid flowers by suppressing the expression of ACS and the activities of ACS and ACO enzymes. Moreover, ethephon-enhanced ET production, ACS and ACO expression, and ACS and ACO activities have also been reported in previous studies (Imsabai et al, 2010;Lee et al, 2021;Nascimento et al, 2021;Wongjunta et al, 2021). Taken together, these findings showed that ethephon completely prevented stem bending in the three different cultivars of snapdragon cut flowers and that STS significantly stimulated stem bending.…”

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

“…The remobilization of N assimilates from source leaves is a crucial determinant for the production of the reproductive organs (sink), especially in B. napus, which has low nitrogen remobilization capacity, with less than 50% of nitrogen stored in source leaves used for seed filling [25,26]. Ethylene is the active signal compound involved in the senescence process of source leaves and in the sink development [2,11,12,14]. In this context, the present study emphasized the regulatory role of ethylene in protein degradation and amino acid transport in mature leaves (source) in relation to pod (sink) development in response to ethephon treatment at the early regenerative stage of B. napus.…”

“…In the present study, the depression of chlorophyll a/b-binding protein (CAB) gene was remarked in 50 and 75 ppm ethephon-treated mature leaves (Figure 1C), leading to a decrease in total chlorophyll content (−37.9% compared with the control) at day 30 (Figure 3E). Numerous studies have shown that exogenous application of ethylene or ethylene releaser accelerates the leaf senescence process [3,12,13]. Ethylene has been shown to be involved in the organized cell dismantling process, which includes nucleic acid reduction, protein degradation [36,37], lipid degradation, peroxidation [38,39], and the activation of nutrients recycling from senescing leaves to the other organs [17,19].…”

“…Ethylene promotes leaf senescence [3,[11][12][13] and inhibits regenerative development [2,14,15]. The production of reproductive organs (sink) is closely associated with a massive, coordinated degradation of macromolecules stored in source leaves and their remobilization to sink organs.…”

“…A large portion of remobilized N from senescent leaves is derived from the degradation of leaf proteins (mainly Rubisco) [17,18], and the amino acids released after protein degradation are transported via phloem to meet the N demand for grain filling [19,20]. Although the role of ethylene in developmentally regulated senescence has been extensively studied [3,[11][12][13], its role in the regulation of N remobilization from mature leaves (source) for pod (sink) development is still not clearly established.…”