Ndhlovu Nqobile Truelove, Solhaug Knut Asbjørn, Minibayeva Farida, Beckett Richard Peter
School of Life Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209, South Africa.
Faculty of Environmental, Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, 1432 Ås, Norway.
Plants (Basel). 2022 Oct 15;11(20):2726. doi: 10.3390/plants11202726.
Lichens often grow in microhabitats where they absorb more light than they can use for fixing carbon, and this excess energy can cause the formation of harmful reactive oxygen species (ROS). Lichen mycobionts can reduce ROS formation by synthesizing light-screening pigments such as melanins in the upper cortex, while the photobionts can dissipate excess energy radiationlessly using non-photochemical quenching (NPQ). An inherent problem with using fluorimetry techniques to compare NPQ in pale and melanised thalli is that NPQ is normally measured through a variously pigmented upper cortex. Here we used a dissection technique to remove the lower cortices and medullas of and and then measure NPQ from the underside of the thallus. Results confirmed that NPQ can be satisfactorily assessed with a standard fluorimeter by taking measurement from above using intact thalli. However, photobionts from the bottom of the photobiont layer tend to have slightly lower rates of PSII activity and lower NPQ than those at the top, i.e., display mild "shade" characteristics. Analysis of pale and melanised thalli of other species indicates that NPQ in melanised thalli can be higher, similar or lower than pale thalli, probably depending on the light history of the microhabitat and presence of other tolerance mechanisms.
地衣通常生长在微生境中，它们吸收的光量超过了用于固定碳的量，这种多余的能量会导致有害活性氧（ROS）的形成。地衣共生菌可以通过在上皮层合成诸如黑色素等遮光色素来减少ROS的形成，而共生藻可以利用非光化学猝灭（NPQ）无辐射地耗散多余的能量辐射。使用荧光技术比较浅色和黑化地衣体中NPQ的一个固有问题是，NPQ通常是通过色素各异的上皮层来测量的。在这里，我们使用解剖技术去除了[物种名称1]和[物种名称2]的下皮层和髓部，然后从地衣体的下侧测量NPQ。结果证实，使用完整的地衣体从上方进行测量时，标准荧光计可以令人满意地评估NPQ。然而，共生藻层底部的共生藻的PSII活性率往往略低于顶部的共生藻，NPQ也较低，即表现出轻微的“阴生”特征。对其他物种的浅色和黑化地衣体的分析表明，黑化地衣体中的NPQ可能高于、类似于或低于浅色地衣体，这可能取决于微生境的光照历史和其他耐受机制的存在。
