The role of JrPPOs in the browning of walnut explants

Abstract

Background Tissue culture is an effective method for the rapid breeding of seedlings and improving production efficiency, but explant browning is a key limiting factor of walnut tissue culture. Specifically, the polymerization of PPO-derived quinones that cause explant browning of walnut is not well understood. This study investigated explants of ‘Zanmei’ walnut shoot apices cultured in agar (A) or vermiculite (V) media, and the survival percentage, changes in phenolic content, POD and PPO activity, and JrPPO expression in explants were studied to determine the role of PPO in the browning of walnut explants. Results The results showed that the V media greatly reduced the death rate of explants, and 89.9 and 38.7% of the explants cultured in V media and A media survived, respectively. Compared with that of explants at 0 h, the PPO of explants cultured in A was highly active throughout the culture, but activity in those cultured in V remained low. The phenolic level of explants cultured in A increased significantly at 72 h but subsequently declined, and the content in the explants cultured in V increased to a high level only at 144 h. The POD in explants cultured in V showed high activity that did not cause browning. Gene expression assays showed that the expression of JrPPO1 was downregulated in explants cultured in both A and V. However, the expression of JrPPO2 was upregulated in explants cultured in A throughout the culture and upregulated in V at 144 h. JrPPO expression analyses in different tissues showed that JrPPO1 was highly expressed in stems, young leaves, mature leaves, catkins, pistils, and hulls, and JrPPO2 was highly expressed in mature leaves and pistils. Moreover, browning assays showed that both explants in A and leaf tissue exhibited high JrPPO2 activity. Conclusion The rapid increase in phenolic content caused the browning and death of explants. V media delayed the rapid accumulation of phenolic compounds in walnut explants in the short term, which significantly decreased explants mortality. The results suggest that JrPPO2 plays a key role in the oxidation of phenols in explants after branch injury.

Protocatechuic acid, ferulic acid and relevant defense enzymes correlate closely with walnut resistance to Xanthomonas arboricola pv. juglandis

“…The highest expression levels of PPO are usually recorded in young tissues such as new leaves and fruits, which are particularly vulnerable to disease. According to a relevant study, walnut blight disease induced the expression of JrPPO1 and PPO activity [ 21 ]. As shown in Fig.…”

“…It is a copper-containing enzyme that inhibits pathogens by converting monophenols into o-catechol compounds with oxygen as a substrate. Khodadad et al implied that the walnut-bacterial blight interaction induced JrPPO-1 and the activity of PPO after inoculating Xaj [ 21 , 22 ].…”

Managing Lethal Browning and Microbial Contamination in Musa spp. Tissue Culture: Synthesis and Perspectives

“…Tissue browning can be characterized as enzymatic or non-enzymatic, depending on whether enzymes are involved or not in the browning processes [28]. Enzymatic browning is the principal cause of explant browning in plant tissue culture [29]. When explants are sliced, phenols are released and oxidized to quinones by enzymes, resulting in enzymatic browning.…”

Penggunaan Putresin Alami dan Sintetik untuk Induksi Kalus dan Regenerasi Kultur Anter Empat Genotipe Padi

“…Flavonoid ini merupakan salah satu golongan fenol alam terbesar sehingga memicu aktivitas fenolik (PPO) pada jaringan tanaman yang berkontribusi terhadap pencoklatan enzimatik (Dong et al, 2016). Eksplan antera yang mengalami browning pada dasarnya dapat diklasifikasikan menjadi dua jenis yaitu browning secara langsung terjadi pada eksplan yang mengalami luka atau perubahan fisiologis dan browning bertahap dianggap sebagai ekspresi dari proses penuaan dari antera itu sendiri (Zhao et al, 2021). Upaya mengatasi permasalahan ini dapat dilakukan dengan menambahkan inhibitor enzim, antioksidan seperti asam askorbat dan tiosulfat, adsorben atau mempersingkat waktu subkultur untuk mengurangi terjadinya reaksi pencoklatan (Jones & Saxena, 2013).…”