Wounding induces changes in tuber polyamine content, polyamine metabolic gene expression, and enzyme activity during closing layer formation and initiation of wound periderm formation

Authors: Lulai, Edward; Neubauer, Jonathan; Young, Linda; Suttle, Jeffrey

Submitted to: Journal of Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/10/2014
Publication Date: 1/5/2015
Citation: Lulai, E.C., Neubauer, J., Olson, L.L., Suttle, J.C. 2015. Wounding induces changes in tuber polyamine content, polyamine metabolic gene expression, and enzyme activity during closing layer formation and initiation of wound periderm formation. Journal of Plant Physiology. 176:89-95.

Interpretive Summary: Potato tuber wounds incurred during harvest, handling into and out of storage and upon seed cutting require rapid suberization as a major part of the wound-healing processes to prevent infection, desiccation, defect development and loss of nutritional value. The induction and regulation of rapid suberization of wounds is of great economic importance. Wound related losses cost growers, processors and storage operators well over $300 million/year; this does not include subsequent losses incurred by the grocer and consumer. Despite the large economic and nutritional importance of tuber wound-healing, little is known about the potential modulators of the molecular mechanisms and related genes controlling these processes and how they are expressed during the two major stages of wound-induced suberization, i.e. closing layer formation followed by wound periderm formation. This knowledge gap and poor understanding of wound-healing is due to the complexity of the wound-healing processes and, in particular, with associated regulation and modulation of these processes. A group of metabolic compounds referred to as polyamines (PA) have been shown to be involved in modulating a variety of responses to biotic and abiotic plant stresses and have been suggested to play critical roles in tuber wound responses. However, the time course for fundamental wound-induced changes in tuber PA content and changes in the activity of key enzymes and expression of genes involved in PA biosynthesis and degradation have not been determined and coordinated with major wound-healing processes. The objective of this study was to determine these wound-induced changes in: 1) free PA content, 2) changes in the activity of arginine and ornithine decarboxylase (ADC and ODC) as the determinants of the first committed step in PA biosynthesis, 3) the expression of genes involved in PA biosynthesis and catabolism, and 4) to indicate how these changes coordinate with previously established time courses for the first stage of wound-healing (closing layer formation), the initiation of the second stage of wound-healing (wound-periderm formation) and important associated changes in cell biology (i.e. wound-induced DNA biosynthesis and timing of cell divisional processes). Wounding induced increases in the PAs putrescine (Put) and spermidine (Spd), but had only minor effects on spermine (Spm) content during the 168 h time course which covered initiation and completion of the closing layer (this included the period of entry and exit of cells from the DNA synthesis phase) and initiation of cell division and wound periderm formation. As determinants of the first committed step in PA biosynthesis, ADC and ODC activities were below levels of detectability in resting tubers; this may, in part, account for static levels of PA in resting tissues. However, activity of both enzymes rapidly increased in response to wounding and remained elevated over the 168 h time course; this is consistent with their roles as “gate keepers” to PA biosynthesis and possible roles in the second stage of wound healing. Expression of another decarboxylase gene encoding S-adenosylmethionine decarboxylase, required for Spd and Spm biosynthesis, increase by 6 h after wounding and remained elevated throughout the time course to support synthesis. A catabolic gene, encoding polyamine oxidase, was down-regulated after wounding suggesting control over H2O2 production. Results indicated a rapid wound-induced response for PA biosynthesis during closing layer formation and the time of nuclei entry and exit from the DNA synthesis phase. PA content remained elevated as wound-induced cells became meristematic and initiated formation of the wound periderm suggesting sustained involvement in wound-healing. Collectively, the results support the hypothetical involvement of PAs in a range of wound-healing proce

Technical Abstract: Tuber wound-healing processes are complex, and the associated regulation and modulation of these processes are poorly understood. Polyamines (PA) have been shown to be involved in modulating a variety of responses to biotic and abiotic plant stresses and have been suggested to be involved in tuber wound responses. However, the time course of wound-induced changes in tuber PA content, activity of key biosynthetic enzymes and associated gene expression has not been determined and coordinated with major wound-healing processes. The objective of this study was to determine these wound-induced changes and their coordination with wound-healing processes. Wounding induced increases in putrescine (Put) and spermidine (Spd), but had only minor effects on spermine (Spm) content during the 168 h time course which encompassed the initiation and completion of the closing layer formation, initiation of cell division, and wound periderm formation. As determinants of the first committed step in PA biosynthesis, arginine and ornithine decarboxylase (ADC and ODC, respectively) activities were below levels of detectability in resting tubers and expression of genes encoding these two enzymes was low. Within six hours of wounding, increases in the in vitro activities of ADC and ODC and expression of their cognate genes were observed. Expression of a gene encoding S-adenosylmethionine decarboxylase, required for Spd and Spm biosynthesis, was also increased 6 h after wounding and remained elevated throughout the time course. Expression of a polyamine catabolic gene, encoding polyamine oxidase, was down-regulated after wounding. Results indicated a rapid wound-induced increase in PA biosynthesis during closing layer formation and the time of nuclei entry and exit from S-phase. PA content remained elevated as wound-induced cells became meristematic and initiated formation of the wound periderm suggesting sustained involvement in wound-healing.