Biochemical Potential of Potato Tubers To Synthesize Blackspot Pigments in Relation to Their Actual Blackspot Susceptibility

Abstract

In a study of six potato varieties (Solanum tuberosum L.), which were grown under two different fertilization regimes, the biochemical potential of tuber tissue to synthesize blackspot pigments was distinguished from the actual blackspot susceptibility exhibited after impact application. Blackspot susceptibility and biochemical potential for pigment synthesis were not correlated, which supports the hypothesis that the extent to which the blackspot potential is actually being used is mediated by the sensitivity to cell decompartmentation. Quantification of polyphenol oxidase (PPO), soluble protein, and endogenous PPO substrates demonstrated that the content of free tyrosine is the predominant determinant for the biochemical potential for blackspot synthesis. PPO was not a limiting factor for pigment synthesis, even if PPO content was relatively low. It was therefore concluded that manipulation of PPO activity may offer a solution to the problem of blackspot formation only if it leads to a virtually complete elimination of PPO activity. Keywords: Solanum tuberosum L.; Solanaceae; potato; blackspot; bruise; melanin; tyrosine; chlorogenic acid; caffeic acid; polyphenol oxidase; enzymic browning

Diploid Potato Hybrids as Sources of Resistance to Blackspot Bruising

“…The observed lack of correlation between low tyrosine content and resistance to bruising indicated that substrate level does not seem to be preliminary factor playing a main role in mechanism of bruising formation. This conclusion is in agreement with results of other studies (Mondy and Munshi 1993;Stevens and Davelaar 1997;Strehmel et al 2010).…”

“…Mondy and Munshi (1993) studied two potato cultivars, one resistant and one susceptible to bruising, have found that tyrosine level was not a limiting factor for bruising determination, since in the susceptible cultivar they observed a lower level of tyrosine. Stevens and Davelaar (1997) have demonstrated positive correlation between potential to discoloration formation and tyrosine content, but at the same time they have not found correlation between blackspot bruise susceptibility and level of tyrosine. Strehmel and coworkers (2010) have proved that the level of tyrosine did not change significantly after mechanical impact in two tested cultivars.…”

“…The results of some earlier studies have indicated that tyrosine level is well correlated with enzymatic discoloration potential after tissue homogenization and after abrasive peeling (Dean et al 1993). On the other hand, no correlation between bruising and tyrosine level has been found in studies using impact method (Mondy and Munshi 1993;Stevens and Davelaar 1997;Strehmel et al 2010). Mondy and Munshi (1993) studied two potato cultivars, one resistant and one susceptible to bruising, have found that tyrosine level was not a limiting factor for bruising determination, since in the susceptible cultivar they observed a lower level of tyrosine.…”

Biotech Potatoes in the 21st Century: 20 Years Since the First Biotech Potato

“…Black Spot Bruise Resistance Tuber blackspot caused by impact and pressure during harvest and storage, as well as tuber tissue browning after cutting, is caused by the oxidation of phenolic compounds by the enzyme polyphenol oxidase (PPO) to quinones, which polymerize to cause dark pigmentation (Stevens and Davelaar 1997). Silencing of PPO genes in potato leads to a reduction in enzymatic browning of tuber tissue due to wounding and bruising from impact (Bachem et al 1994;Coetzer et al 2001;Chi et al 2014).…”

Crop Improvement through Modification of the Plant's Own Genome

“…Our results also indicate that backbone integration frequencies for P-DNA vectors are similar to those for conventional T-DNA vectors (data not shown). Polyphenol oxidases (PPOs) play a role in the activation of defenses against pests and pathogens (Thipyapong and Steffens, 1997) but also trigger enzymatic browning, which negatively impacts potato storage and processing quality (Stevens and Davelaar, 1997). To control enzymatic browning without impairing inducible defense mechanisms, we isolated clones from a variety of potato cDNA libraries and selected the gene that is predominantly expressed in mature tubers, weakly expressed in microtubers, not expressed in leaves, and not induced upon infection (data not shown).…”