Novel Formation of Ectopic (Nonplacental) Capsaicinoid Secreting Vesicles on Fruit Walls Explains the Morphological Mechanism for Super-hot Chile Peppers

Abstract

<jats:p>Chile peppers (<jats:italic>Capsicum</jats:italic> sp.) are one of the most important spices in the world and a significant vegetable, providing substantial amounts of vitamins A and C. Chile peppers are also used as a medicinal and lachrymator plant because of the characteristic burning sensation they cause when consumed by mammals. This sensation is caused by capsaicinoids that are alkaloids produced in vesicles inside the fruit. A novel class of chile peppers known as “super-hots” having greater than 1 million Scoville heat units have generated much interest. We compared the morphological structure of fruit pericarp and placental tissue of “super-hot” chile peppers to those of jalapeno and bell pepper. Most chile peppers including jalapenos, only produce the capsaicinoids in secreting vesicles found on the placenta. We report on the novel discovery that these “super-hot” chile peppers have developed accessorial vesicles on the pericarp tissue in addition to the vesicles on the placental tissue, thus leading to exceedingly high Scoville heat units for these plants.</jats:p>

Capsaicinoids Production and Accumulation in Epidermal Cells on the Internal Side of the Fruit Pericarp in ‘Bhut Jolokia’ (<i>Capsicum chinense</i>)

“…The proportion of total capsaicinoids in each tissue, based on DW, was 27.9% in the pericarp, 5.3% in the seeds, and 66.7% in the combined placenta and interlocular septum (Table 1). A previous study on Bhut Jolokia reported that the Scoville heat units of the pericarp and placenta were 311207 and 1332789, respectively (Bosland et al 2015), consistent with the capsaicinoids concentrations detected in our study. In the chili pepper Trinidad Maruga Scorpion Yellow, the capsaicinoids concentration in the pericarp was 23.2 mg g 1 DW, and this tissue contained 84.3% of the total capsaicinoids in the fruit (Tanaka et al 2017).…”

“…Gene expression analyses have shown that several capsaicinoid biosynthesis genes are not expressed in the seeds of Habanero (C. chinense) (Sugiyama et al 2006b). Capsaicinoids were detected in the pericarp of extremely pungent chili pepper fruits (Bosland et al 2015, Tanaka et al 2017. Tanaka et al (2017) also detected capsaicinoids and up-regulation of capsaicinoids biosynthetic genes in the pericarp of Trinidad Moruga Scorpion Yellow.…”

“…There are extremely high concentrations of capsaicinoids in some chili pepper cultivars; for example, Bhut Jolokia and Trinidad Moruga Scorpion. Recently, capsaicinoid production was analyzed in the pericarp tissues of the extremely pungent pepper varieties Trinidad Moruga Scorpion, Trinidad Scorpion, Bhut Jolokia, and Trinidad Moruga Scorpion Yellow (Bosland et al 2015, Tanaka et al 2017. Bosland et al (2015) reported that vesicles containing capsaicinoids were produced on the inner surface of the pericarp of three extremely pungent peppers; Trinidad Moruga Scorpion, Trinidad Scorpion, and Bhut Jolokia.…”

“…Recently, capsaicinoid production was analyzed in the pericarp tissues of the extremely pungent pepper varieties Trinidad Moruga Scorpion, Trinidad Scorpion, Bhut Jolokia, and Trinidad Moruga Scorpion Yellow (Bosland et al 2015, Tanaka et al 2017. Bosland et al (2015) reported that vesicles containing capsaicinoids were produced on the inner surface of the pericarp of three extremely pungent peppers; Trinidad Moruga Scorpion, Trinidad Scorpion, and Bhut Jolokia. Up-regulated expression of multiple capsaicinoid biosynthetic genes was also detected in pericarp tissue of Trinidad Maruga Scorpion Yellow (Tanaka et al 2017).…”

Capsicum—An Abbreviated Compendium

“…Aside from their value as a spice (Bosland and Votava, 1999), capsaicinoids have well-established medicinal and antimicrobial properties (Emanuela et al, 2015;Khan et al, 2014;Surh and Lee, 1995) and affect seed dispersal and survival (Nabhan and Tewksbury 2001;Tewksbury et al, 2008). Capsacinoids are normally synthesized and accumulated in the epidermal cells of the placental tissue of the fruit (Arce-Rodríguez and Ochoa-Alejo, 2015, 2017) but also have been detected in other tissues or organs in some cultivars (Bosland et al, 2015;Noichinda et al, 2016;Tanaka et al, 2017). Advances in the understanding of the molecular biology of the capsaicinoid biosynthetic pathway often have focused on the identification of new candidate genes, the characterization of some key previously identified genes, and the exploration of possible mechanisms of regulation.…”