Polyamine Induction in Postharvest Banana Fruits in Response to NO Donor SNP Occurs via l-Arginine Mediated Pathway and Not via Competitive Diversion of S-Adenosyl-l-Methionine.

Veeresh Lokesh,Bhagyalakshmi Neelwarne,Kapuganti Jagadis Gupta,Namratha S Hegde,Bijesh Puthusseri,Girigowda Manjunatha,Mallesham Bulle

doi:10.3390/antiox8090358

Abstract

Nitric oxide (NO) is known to antagonize ethylene by various mechanisms; one of such mechanisms is reducing ethylene levels by competitive action on S-adenosyl-L-methionine (SAM)—a common precursor for both ethylene and polyamines (PAs) biosynthesis. In order to investigate whether this mechanism of SAM pool diversion by NO occur towards PAs biosynthesis in banana, we studied the effect of NO on alterations in the levels of PAs, which in turn modulate ethylene levels during ripening. In response to NO donor sodium nitroprusside (SNP) treatment, all three major PAs viz. putrescine, spermidine and spermine were induced in control as well as ethylene pre-treated banana fruits. However, the gene expression studies in two popular banana varieties of diverse genomes, Nanjanagudu rasabale (NR; AAB genome) and Cavendish (CAV; AAA genome) revealed the downregulation of SAM decarboxylase, an intermediate gene involved in ethylene and PA pathway after the fifth day of NO donor SNP treatment, suggesting that ethylene and PA pathways do not compete for SAM. Interestingly, arginine decarboxylase belonging to arginine-mediated route of PA biosynthesis was upregulated several folds in response to the SNP treatment. These observations revealed that NO induces PAs via l-arginine-mediated route and not via diversion of SAM pool.

Highlights

The prime task of shelf life extension for tropical climacteric fruits such as banana, peach, and mango relies on the suppression of ethylene through controlled elicitation of specific metabolic regulators, which in turn counter ethylene formation
sodium nitroprusside (SNP) treated banana fruits retained the lightness till the 10th day
The delaying effects of nitric oxide (NO) on fruit ripening by its inhibitory effect on the major ripening hormone ethylene are well studied in various fruits as well as in banana [5,6]

Summary

Introduction

The prime task of shelf life extension for tropical climacteric fruits such as banana, peach, and mango relies on the suppression of ethylene through controlled elicitation of specific metabolic regulators, which in turn counter ethylene formation. While the major biochemical transformation process in ripening climacteric fruits is well-known, research on the involvement of signal molecules is still scanty. Much focus has been placed on the involvement of a signaling molecule, nitric oxide (NO) in fruit ripening. NO is a highly reactive gaseous free radical signal molecule involved in a large array of biochemical reactions, cellular processes, and development in various organisms including plants. NO plays a key role in coordinating various biochemical pathways, among which the signaling roles in modulating the hormonal metabolism and in turn improving quality attributes and nutritional compositions of fruits are very important.

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Discussion

Conclusion