Thermogenesis, Flowering and the Association with Variation in Floral Odour Attractants in Magnolia sprengeri (Magnoliaceae)

Abstract

Magnolia sprengeri Pamp. is an ornamentally and ecologically important tree that blooms at cold temperatures in early spring. In this study, thermogenesis and variation in the chemical compounds of floral odours and insect visitation in relation to flowering cycles were studied to increase our understanding of the role of floral thermogenesis in the pollination biology of M. sprengeri. There were five distinct floral stages across the floral cycle of this species: pre-pistillate, pistillate, pre-staminate, staminate and post-staminate. Floral thermogenesis during anthesis and consisted of two distinct peaks: one at the pistillate stage and the other at the staminate stage. Insects of five families visited M. sprengeri during the floral cycle, and sap beetles (Epuraea sp., Nitidulidae) were determined to be the most effective pollinators, whereas bees (Apis cerana, Apidae) were considered to be occasional pollinators. A strong fragrance was released during thermogenesis, consisting of 18 chemical compounds. Although the relative proportions of these compounds varied at different floral stages across anthesis, linalool, 1-iodo-2-methylundecane and 2,2,6-trimethyl-6-vinyltetrahydro-2H-pyran-3-ol were dominant. Importantly, we found that the floral blends released during the pistillate and staminate stages were very similar, and coincided with flower visitation by sap beetles and the two thermogenic episodes. Based on these results, we propose that odour acts as a signal for a reward (pollen) and that an odour mimicry of staminate-stage flowers occurs during the pistillate stage.

Temporal Petal Closure Benefits Reproductive Development of Magnolia denudata (Magnoliaceae) in Early Spring

“…It is intriguing to note that there is vast variation of flower opening types within the Magnolia genus. Magnolia sprengeri , like M. denudata in the current study, flowers in daytime (Wang et al, 2014), while M. ovata and M. virginiana in night (Gottsberger et al, 2012; Losada et al, 2014). Some Magnolia species, such as M. praecocissima, M. schiedeana , and M. tamaulipana have a single flower opening (Dieringer and Espinosa, 1994; Ishida, 1996; Dieringer et al, 1999), while others show repetitive opening, such as M. denudata, M. sprengeri, M. ovata , and M. virginiana (Wang et al, 2010, 2014; Gottsberger et al, 2012; Losada et al, 2014).…”

“…Some Magnolia species, such as M. praecocissima, M. schiedeana , and M. tamaulipana have a single flower opening (Dieringer and Espinosa, 1994; Ishida, 1996; Dieringer et al, 1999), while others show repetitive opening, such as M. denudata, M. sprengeri, M. ovata , and M. virginiana (Wang et al, 2010, 2014; Gottsberger et al, 2012; Losada et al, 2014). Considering that these Magnolia species are living in different habitats and pollination was mediated by different insects (Dieringer et al, 1999; Gottsberger et al, 2012; Wang et al, 2014), the vast variance in flowering types might be an adaptation to their pollinators with distinct activity rhythms.…”

Perspectives on functions of AOX and UCP in floral thermogenesis

“…开花生热不仅可以防止花器官遭受低温 损伤 [20] , 还可以通过热能回报(heat reward)的方式招 徕昆虫访花 [21] . 本研究组 [2] 发现, 开花生热还可以通过 促进花香的释放进而吸引昆虫访花. 尤为重要的是, 最 近本研究组 [3] 还发现, 生热中的花提供的温暖环境可 .…”

“…尽管当时的成像分辨 率很低, 但是这一技术足以检测出温度在生热的花中 并非均匀分布 [23] . nora esculenta在雌蕊期发生显著的开花生热现象 [18] , 天南星科Helicodiceros muscivorus和Arum concinna-tum则在雄蕊期大量释放热量 [24] , 而木兰科玉兰和武 当木兰在雌蕊期和雄蕊期均有生热高峰 [2,9] .…”

“…植物开花生热最早由 法国博物学家Lamarck在天南星科海芋属(Arum)中发 现. 随后, 研究者相继在木兰科(Magnoliaceae) [2,9,10] 、 泽泻科(Alismataceae) [ 4 ] 、五味子科(Schisandraceae) [11] 、苏铁科(Gycadaceae) [5] 、马兜铃科(Aristolochiaceae) [12] 、棕榈科(Aracaceae) [11] 、环花草科(Cyclanthaceae) [13] 、番荔枝科(Annonaceae) [14,15] 、莲科 (Nelumbonaceae) [16,17] 、菌花科(Hydnoraceae) [18] 以及大 花草科(Rafflesiaceae) [19] 等14科34属中发现开花生热 现象. 这些生热植物科属的发现表明, 开花生热现象在 植物中广泛存在, 也暗示着开花生热可能具有重要的 生物学功能.…”