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Nancy Ruiz-Lau, Fátima Medina-Lara, Yereni Minero-García, Luis W. Torres-Tapia, Sergio R. Peraza-Sánchez and Manuel Martínez-Estévez

Capsaicinoids, the chemical compounds that confer the pungency trait to peppers, are accumulated at different levels in all species of the genus Capsicum. There is much evidence suggesting that the synthesis of capsaicinoids occurs in the placenta interlocular septum of pepper fruits; however, the exact localization of the capsaicinoids biosynthesis accumulation pathways is still under debate. Thus, the aim of the present work was to evaluate whether pepper plants synthesize or accumulate capsaicinoids in vegetative organs as an indirect way to elucidate the systemic regulation of the capsaicinoid biosynthesis. For that purpose, we studied habanero pepper grown in the Yucatan Peninsula, which is among the hottest pepper worldwide. Our results, obtained by chromatographic and enzymatic measurements, provide solid evidence that habanero pepper plants do not accumulate capsaicinoids in the vegetative organs analyzed, even under water stress conditions. Thus, it is probable that the accumulation of capsaicinoids is restricted to reproductive organs.

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Fátima Medina-Lara, Ileana Echevarría-Machado, Ramón Pacheco-Arjona, Nancy Ruiz-Lau, Adolfo Guzmán-Antonio and Manuel Martinez-Estevez

Habanero pepper (Capsicum chinense Jacq.) is a very important crop in Mexico and demand for it is increasing in national and international markets. The habanero pepper produced on the Yucatan Peninsula is considered of superior quality to that grown in the rest of the world as a result of its shelf life and pungency. Despite its importance, little research has been done on cultivation conditions that may affect its productivity and fruit quality. The effect of N or K fertilization on habanero pepper development and fruit pungency was evaluated. Plants under fertilization stress (control) had high capsaicin content. Nitrogen fertilization significantly increased plant growth and fruit while maintaining high capsaicin levels. Optimum response was produced with 15 mm urea as the N source. Potassium fertilization had no positive effects on growth or productivity. The N treatments modified endogenous K levels in the pepper plants and vice versa. The K : N ratio (specifically in leaves and roots) varied between treatments with values greater than 1 in the K treatments, near 0.5 in the control, and less than 0.5 in the N treatments. This parameter may be an important indicator of habanero pepper productivity and requires study under different fertilization regimes.

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Camilo Escalante-Magaña, Luis F. Aguilar-Caamal, Ileana Echevarría-Machado, Fátima Medina-Lara, Lucila Sánchez Cach and Manuel Martínez-Estévez

Water stress is the main factor responsible for decreased productivity, which affects the growth and development of crops. Plants respond to stress by accumulating compatible solutes, which have a key role in osmotic adjustment, thereby resulting in osmoprotection of the plants. The loss of water can increase the concentration of compatible osmolytes and molecules that regulate the plant metabolism. These solutes can be metabolized as sugars (sucrose, fructose, trehalosa), amino acids (proline), an amphoteric quaternary amine (glycine betaine), and other low-molecular-weight metabolites. However, among all these compatible solutes, proline and glycine betaine occur the most. Proline is an amino acid that can accumulate in low concentrations under optimal conditions; however, stress conditions contribute to its increased content. Few data are available regarding the levels of endogenous glycine betaine on Solanaceae, which is considered a nonaccumulator under water deficit conditions. The objective of this research was to evaluate the role of compatible osmolytes, glycine betaine and proline, in Capsicum sp. plants under different water deficit conditions. In this study, the presence of endogenous levels of proline and glycine betaine in two species of pepper (Capsicum chinense var. Genesis and Rex and Capsicum annuum var. Padron) were found. The concentration levels of proline were 362, 292, and 246 μmol·g−1 DW for Genesis, Rex and Padron respectively, and irrigation conditions (rehydration) of proline levels increased to 381, 395, and 383 μmol·g−1 DW at 21 days. However, glycine betaine levels were 30–70 μmol·g−1 DW. The relative water content, electrolyte leakage, and soil water potential were also analyzed; therefore, the information suggests that proline contributes better to tolerance to water deficit in the genus Capsicum after 14 days of water deficit treatment. It seems that the contribution of glycine betaine is less effective than that of proline; therefore, it does not have an important role in osmotic adjustment.

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Nancy Ruiz-Lau, Fátima Medina-Lara, Yereni Minero-García, Enid Zamudio-Moreno, Adolfo Guzmán-Antonio, Ileana Echevarría-Machado and Manuel Martínez-Estévez

The pungency of chili peppers is conferred by compounds called capsaicinoids that are produced only in the fruits of the Capsicum genus. Accumulation of capsaicinoids in these fruits may be affected by environmental conditions such as water and nutrient stresses, although these effects may vary even among genotypes within a species. The Habanero pepper (Capsicum chinense Jacq.), grown in the Yucatán, is in especially high demand as a result of its unique flavor, aroma, and pungency and is the second most important commercial crop in the state after the tomato. Although the Habanero pepper is a significant economic resource for the region, few studies have investigated the effects of abiotic stresses on capsaicinoid production. In this study, the effects of water stress on plant growth, capsaicinoid accumulation, and capsaicin synthase activity were evaluated. Habanero pepper plants under water stress had a lower height, root dry weight, and root/shoot relation than control plants, which were irrigated daily. However, fruit growth and production were unaffected by water stress. Capsaicin and dihydrocapsaicin concentrations increased in fruits of stressed plants compared with control plants, and this effect was correlated with fruit age. However, capsaicin synthase activity was reduced in response to water stress, and this effect depended on both stress severity and fruit age. These results provide new information on the regulation of capsaicinoid metabolism in response to abiotic stress from the fruit of a highly pungent chili pepper.