Abstract

Lichens are a symbiosis between a fungus and one or more photosynthetic microorganisms that enables the symbionts to thrive in places and conditions they could not compete independently. Exchanges of water and sugars between the symbionts are the established mechanisms that support lichen symbiosis. Herein, we present a new linkage between algal photosynthesis and fungal respiration in lichen Flavoparmelia caperata that extends the physiological nature of symbiotic co-dependent metabolisms, mutually boosting energy conversion rates in both symbionts. Measurements of electron transport by oximetry show that photosynthetic O₂ is consumed internally by fungal respiration. At low light intensity, very low levels of O₂ are released, while photosynthetic electron transport from water oxidation is normal as shown by intrinsic chlorophyll variable fluorescence yield (period-4 oscillations in flash-induced Fv/Fm). The rate of algal O₂ production increases following consecutive series of illumination periods, at low and with limited saturation at high light intensities, in contrast to light saturation in free-living algae. We attribute this effect to arise from the availability of more CO₂ produced by fungal respiration of photosynthetically generated sugars. We conclude that the lichen symbionts are metabolically coupled by energy conversion through exchange of terminal electron donors and acceptors used in both photosynthesis and fungal respiration. Algal sugars and O₂ are consumed by the fungal symbiont, while fungal delivered CO₂ is consumed by the alga.

中文翻译：

---

共生扩展：地衣共生体的光合作用O 2和真菌呼吸的CO 2交换相互促进代谢

摘要

地衣是真菌与一种或多种光合微生物之间的共生体，可使共生体在无法独立竞争的地方和条件下壮成长。共生体之间水和糖的交换是支持地衣共生的既定机制。在此，我们提出之间的新的联动藻类光合作用和真菌呼吸地衣Flavoparmelia caperata延伸共生依赖性代谢，相互升压能量转换率在两者共生体的生理性质。通过血氧测定法进行的电子传输的测量表明，真菌呼吸作用在内部消耗了光合作用的O ₂。在低光强度下，O _2的水平非常低释放，而水氧化的光合作用电子传输是正常的，如固有的叶绿素可变荧光产量（在闪光诱导的Fv / Fm中的周期4振荡）所示。与自由活动藻类的光饱和相反，藻类O _2的产生速率在连续的一系列照明周期之后增加，在低强度下以及在高光强度下具有有限的饱和度。我们归因于这种影响是由于光合作用产生的糖类的真菌呼吸作用所产生的更多CO ₂的可用性而引起的。我们得出的结论是，通过交换光合作用和真菌呼吸中使用的末端电子供体和受体，能量交换将地衣共生体代谢耦合。海藻糖和O ₂被真菌共生体消耗，而真菌释放的CO ₂被藻类消耗。