Maintaining crop productivity under limited irrigation water requires some new strategies. This study investigated the influence of drought stress and the application of plant growth regulators (PGRs) including jasmonic acid, brassinosteroids, and putrescine on photosynthetic performance of fennel (Foeniculum vulgare Mill). The results indicated that fennel exhibited active osmoregulation which prevented a sharp decrease in relative water content. Fennel successfully maintained high leaf chlorophyll index, Net photosynthesis rate, and transpiration under mild stress, however, severe stress reduced the photosynthetic parameters by 22%, 24%, and 50%, respectively. Drought stress increased chlorophyll a fluorescence when fennel plants exposed to the stress condition. Vₖ and Wₖ parameters related to the donor side of photoinhibition of photosystem II (PSII) increased by 44% when severe drought stress imposed at the vegetative stage and 34% when occurred during the flowering. The elevation of Vₖ and Wₖ indicated a failure in water splitting in PSII. The VJ and VI parameters of acceptor sides increased by 16% and 22%, respectively when drought stress imposed at the vegetative phase and to 19% and 30%, when drought stress occurred during reproductive phase. Using PGRs resulted in reduced VJ, VI, Vₖ, and Wₖ, suggesting that some degree of recovery of damages occurred. All three PGRs stimulated biomass production and on average, plants yielded roughly 1.6 fold higher than the control plants. The influences of PGRs were mainly independent of drought stress level.

中文翻译：

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评估茴香（Foeniculum Vulgare Mill）的光合性能受植物生长调节剂和营养和生殖阶段施加的干旱胁迫影响

在有限的灌溉用水下保持作物生产力需要一些新的策略。本研究调查了干旱胁迫和植物生长调节剂 (PGR) 的应用，包括茉莉酸、油菜素类固醇和腐胺对茴香 (Foeniculum vulgare Mill) 光合性能的影响。结果表明，茴香表现出积极的渗透调节，可防止相对水含量的急剧下降。茴香在轻度胁迫下成功保持了较高的叶绿素指数、净光合速率和蒸腾作用，而重度胁迫使光合参数分别降低了 22%、24% 和 50%。当茴香植物暴露在胁迫条件下时，干旱胁迫会增加叶绿素 a 荧光。与光系统​​II（PSII）光抑制供体侧相关的Vₖ和Wₖ参数在营养阶段施加严重干旱胁迫时增加了44％，在开花期间发生时增加了34％。Vₖ 和 Wₖ 的升高表明 PSII 中的水分解失败。在营养期施加干旱胁迫时，受体侧的 VJ 和 VI 参数分别增加了 16% 和 22%，而在生殖期发生干旱胁迫时，它们的 VJ 和 VI 参数分别增加了 19% 和 30%。使用 PGR 导致 VJ、VI、Vₖ 和 Wₖ 降低，表明发生了某种程度的损害恢复。所有三种 PGR 都刺激了生物量生产，平均而言，植物的产量比对照植物高出大约 1.6 倍。PGRs的影响主要与干旱胁迫水平无关。