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1 March 2012 Research Article: Effects of salt stress on capsaicin content, growth, and fluorescence in a Jalapeño cultivar of Capsicum annuum (Solanaceae)
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Although there are many different species of pepper plants (Capsicum spp.), all are from the New World tropics, and landraces such as Jalapeño (Capsicum annuum cv. Jalapeño) have been selected for optimum performance in response to local abiotic and biotic stresses. Pepper plants produce the phenolic compound capsaicin, primarily in the placenta of fruits, possibly to deter mammalian herbivores in favor of avian frugivores. Capsaicin content is influenced by genetic and environmental conditions including soil moisture and fertility, temperature, and light. In order to explore the relationship between abiotic stress and fruit capsaicin content, Jalapeño pepper plants were grown from seed, and then treated with 0.0, 0.5, 1.0, and 1.5% NaCl solution. Capsaicin extracts from Jalapeño fruits were analyzed using High Performance Liquid Chromatography (HPLC). None of the parameters tested were significantly different between the control or treatment groups, but the following trends were found in the data. Plants at the two highest salinities had higher levels of capsaicin compared to the control and lowest salinity group (0.160 vs. 0.132 mg capsaicin/g dry fruit, respectively). Fluorometry readings of photosynthetic efficiency (Fv/Fm) demonstrated that at 0.0 and 0.5% NaCl plants had a more optimal ratio (0.70) compared to plants treated with 1.0 and 1.5% NaCl (0.63). Total plant biomass did not decrease with increased salinity. However, a root:shoot analysis demonstrated that plants grown in 1.5% NaCl allocated a higher proportion of their photosynthate to root production (0.796) compared to the control plants grown at 0.0% NaCl (0.691). At the highest salinity level plants doubled their fruit production and allocated more of their photosynthate towards sexual reproduction as opposed to vegetative growth. Because of the consistent (although non-significant) trends in the parameters measured, a biological response to increased salinity suggests a true biological response. Therefore, further investigations with higher levels of salt stress or longer growing periods may lead to statistically significant changes in morphometric data and capsaicin production.

Sarah Arrowsmith, Todd P. Egan, J. Forrest Meekins, Dale Powers, and Marcia Metcalfe "Research Article: Effects of salt stress on capsaicin content, growth, and fluorescence in a Jalapeño cultivar of Capsicum annuum (Solanaceae)," BIOS 83(1), 1-7, (1 March 2012).
Received: 7 June 2011; Accepted: 1 September 2011; Published: 1 March 2012

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