光質對台灣香檬葉片揮發性化合物組成之影響

台灣香檬因有豐富的機能性成分和獨特的香氣特色而深具開發潛力，同時葉片揮發性化合物組成表現為辨別柑橘種源的重要依據，但揮發性化合物組成的表現受諸多環境因子影響，環境因子影響柑橘植物葉片揮發性化合物的相關研究較少，因此本研究針對光質的影響進行一系列的試驗。以一年生台灣香檬盆苗為材料，先以近紅外光(730±10 nm)、紅光(660±10 nm)、綠光(520±10 nm)和藍光(450±10 nm)等四種光質之發光二極體(light-emitting diode, LED)為光源，以150 µmol·m-2·s-1 光強度，每日照射 12 h，持續照射 7 日，於照光處理期間持續取樣並分析柑橘葉片VOCs的表現變化。結果顯示，近紅外光處理 5日可提高葉片中的3-hexenal、(E)-2-hexenal的組成比例；而紅光、藍光與綠光處理則無明顯效應。進一步以200 µmol·m-2·s-1混合白光為基礎光源，另分別補充150 µmol·m-2·s-1的近紅外光、紅光、藍光，在相同光週期條件連續照光 9 日。補充紅光處理 3 日使葉片中芳樟醇(linalool)、α-松油醇(α-terpineol)、萜品-4-醇(terpene-4-ol)與反式-檜烯水合物(trans-sabinene hydrate)等單萜類含氧化合物(oxygenated monoterpenes)的相對含量與組成比例增加，但該類成分表現於補充紅光至第9日時則逐漸減少。補充藍光處理 3 日後，單萜類含氧化合物的組成比例略微降低，但增加葉片中的辛醛(octanal)、癸醛(decanal)等飽和醛類(saturated aldehyde)的相對含量。補充近紅外光處理 3 日後，僅單萜類碳氫化合物(monoterpene carbohydrates)與倍半萜類碳氫化合物(sesquiterpene carbohydrates)的相對含量略為降低。研究結果顯示照光 3 日後，各光質處理皆改變了單萜類含氧化合物的組成比例，但光質處理並不會引發新的揮發性化合物種類。臺灣香檬葉片主要揮發性化合物如γ-松油烯(γ-terpinene)和石竹烯(caryophyllene)仍為主要的VOCs組成。提高藍光補光強度至 300 µmol·m-2·s-1時，單萜類含氧化合物的組成比例顯著降低；提高紅光補光強度至 300 µmol·m-2·s-1並未提高單萜類含氧化合物的組成比例，且提高的紅光補光強度會降低光系統II的最大量子產量(maximum quantum yield of PSII, Fv/Fm)與造成電子傳遞速率(electron transport rate, ETR)的衰弱。本研究亦發現葉片單萜類含氧化合物的相對含量與葉綠素螢光參數中的光系統II的最大量子產量(maximum quantum yield of PSII, Fv/Fm)或光適應後最大螢光值(maximal fluorescence yield, F’m)之間存在高度正相關，揭露葉片表達萜類化合物與葉片光合生理表現的關聯。研究一系列的結果逐步說明短期的光質效應在台灣香檬葉片揮發性化合物中的影響模式。這些研究成果有助於釐清光質與柑橘葉片揮發性化合物表現的關聯，提供短期光質處理調控柑橘葉片揮發性化合物之學理基礎。

關鍵字

???????(日) ；環境因子；短期光質處理；頂空-固相微萃取；芳樟醇；葉綠素螢光

並列摘要

Citrus depressa Hayata, with its rich functional components and unique aromatic characteristics, holds significant development potential. The composition of volatile organic compounds (VOCs) in citrus leaves serves as a crucial basis for identifying inter- and intraspecies of Citrus plant. However, limited research exists on the influence of environmental factors on the composition of leaf VOCs in Citrus plants. This study investigated the effects of light quality on Citrus depressa. One-year-old potted seedlings of Citrus depressa were exposed to four light qualities: near-infrared light (730±10 nm), red light (660±10 nm), green light (520±10 nm), and blue light (450±10 nm) emitted by light-emitting diodes (LEDs) at an intensity of 150 µmol·m-2·s-1, with a daily 12-hour photoperiod for seven consecutive days. Leaf samples were collected in the end of light period to analyze the changes in VOC expression. Results showed an increase in the composition ratios of 3-hexenal and (E)-2-hexenal after fifth day of near-infrared light treatment, while no significant effects were observed with other light treatments. Subsequent experiments were conducted using a mixed white light source at a base intensity of 200 µmol·m-2·s-1, supplemented with near-infrared light, red light, or blue light at an additional intensity of 150 µmol·m-2·s-1. The plants were subjected to the same photoperiod for nine consecutive days. After three days of red light supplementation, the relative content and composition ratios of oxygenated monoterpenes, including linalool, α-terpineol, terpene-4-ol, and trans-sabinene hydrate, increased in the leaves, but an inhibitory effect was observed after supplemental red light exposure until the ninth day. The composition ratios of oxygenated monoterpenes slightly decreased with blue light supplementation on the third day, while the relative content of saturated aldehydes such as octanal and decanal increased in the leaves. After three days of near-infrared light supplementation, only the relative content of monoterpene and sesquiterpene carbohydrates slightly decreased. The results revealed that all light qualities altered the composition ratios of oxygenated monoterpenes after three days of light treatment. However, the effect of light quality treatments did not induce the production of new volatile compound. The main VOCs in Citrus depressa leaves, including γ-terpinene and caryophyllene, remained the dominant components. Increasing the supplementary blue light intensity to 300 µmol·m-2·s-1 significantly decreased the composition ratios of oxygenated monoterpenes, while increasing the supplementary red light intensity to 300 µmol·m-2·s-1 did not enhance the composition ratios of oxygenated monoterpenes and led to a decline in the maximum quantum yield of PSII (Fv/Fm) and electron transport rate (ETR) of the photosystem II. Furthermore, a significant positive correlation was observed between the relative content of oxygenated monoterpenes and chlorophyll fluorescence parameters, such as Fv/Fm or maximal fluorescence yield (F'm), highlighting the relationship between the expression of terpenoid compounds and leaf photosynthetic performance. The findings of this study provide insights into the short-term effects of light quality on the expression of volatile compounds in Citrus depressa leaves. They contribute to a better understanding of the relationship between light quality and the expression of leaf VOCs in citrus plants, offering a theoretical foundation for the short-term light quality regulation of leaf volatile compounds in Citrus plants.