The amounts of taste components, including those for pungency, in chili pepper fruit change depending on environmental factors. Our previous study revealed that the amount of capsaicinoid was significantly increased in chili pepper fruits that were cultivated under a drought stress condition. Therefore, the present experiment was conducted to determine the effect of drought stress on pungency and the expression levels of capsaicinoid biosynthesis genes in chili peppers. Japanese chili pepper cultivars ‘Shishito’ and ‘Sapporo’ were selected and cultivated in a greenhouse under a drought stress condition or an excess water supply condition. The fruits were used for morphological analysis, and the quantification of the capsaicinoid content in the placental septum was done using high performance liquid chromatography. Gene expression analysis was carried out using a quantitative reverse transcription polymerase chain reaction for 18 capsaicinoid biosynthesis genes. Based on the obtained gene expression patterns, we divided the 18 genes into three groups. The genes in group 1 (ACL, pAMT, Pun1, WRKY9, CaKR1, CaMYB31, FAT, and KAS I) showed higher gene expression levels in the drought stress condition than in the excess water supply condition in both cultivars at 20 DAF. The genes in group 2 (KAS III, BCKDH, ACS, BCAT, and 4CL) showed higher gene expression levels in the drought stress condition than in the excess water supply condition in only one of the cultivars at 20 DAF. The genes in group 3 (PAL, C3H, HCT, C4H, and COMT) did not show any significant differences in gene expression between the two treatments in either cultivar at all DAF. The genes in our experiment showed similar expression patterns in pungent parthenocarpic fruit and control fruit of ‘Shishito’ as in a previous study. Moreover, we found that the number of seeds tended to be lower in fruits cultivated under a drought stress condition, while capsaicinoid content was higher. It is possible that drought stress firstly affected the number of seeds in the fruits, and the decrease in the number of seeds subsequently caused changes in capsaicinoid biosynthesis.

辣椒果实中味道成分的数量，包括刺激性成分，会根据环境因素而变化。我们之前的研究表明，在干旱胁迫条件下种植的辣椒果实中辣椒素的含量显着增加。因此，本实验旨在确定干旱胁迫对辣椒辣味和辣椒素生物合成基因表达水平的影响。选择日本辣椒品种“Shishito”和“Sapporo”，在干旱胁迫条件或过量供水条件下在温室中栽培。果实用于形态学分析，胎盘隔膜中辣椒素含量的定量使用高效液相色谱法进行。使用 18 个辣椒素生物合成基因的定量逆转录聚合酶链反应进行基因表达分析。根据获得的基因表达模式，我们将 18 个基因分为三组。第 1 组中的基因 (ACL、pAMT、Pun1、WRKY9、CaKR1、CaMYB31、FAT和KAS I ) 在干旱胁迫条件下比在 20 DAF 的过量供水条件下显示出更高的基因表达水平。第 2 组中的基因（KAS III、BCKDH、ACS、BCAT和4CL）在干旱胁迫条件下的基因表达水平高于仅在 20 DAF 的一个品种的过量供水条件下的基因表达水平。第 3 组中的基因（PAL、C3H、HCT、C4H和COMT ) 在所有 DAF 的任一栽培品种中两种处理之间的基因表达没有显示任何显着差异。我们实验中的基因在辛辣的单性果实和 'Shishito' 的对照果实中显示出与先前研究相似的表达模式。此外，我们发现在干旱胁迫条件下栽培的果实中种子数量往往较低，而辣椒素含量较高。干旱胁迫可能首先影响果实中的种子数，随后种子数的减少引起辣椒素生物合成的变化。