DISSERTATION RESEARCH: Evolution and Function of Farina in the Desiccation-Tolerant Notholaenid Ferns (Pteridaceae)

蕨类植物通常被认为只限于阴凉和潮湿的栖息地，但notholaenid蕨类植物适应，并在美国西南部和北方墨西哥的沙漠中多样化。假蕨类植物在旱季进入休眠状态，但当水分恢复时，它们会迅速补充水分并恢复光合作用活性。据推测，这种干旱适应与一种称为“farina”的蜡质物质有关，这种物质主要由植物色素组成，在叶子下表面形成一层白色到黄色的层。当叶子卷曲起来以应对水分胁迫时，这片叶子的表面直接暴露在阳光下。已经提出了蜡质层的两个主要功能假设：1）它作为一个“屏障”，以帮助减少水分蒸发损失; 2）它作为一个“防晒霜”，以保护水分胁迫的叶片免受过热和紫外线辐射造成的损害。本研究旨在通过解剖学、生物化学、地理学、生理生态学和分子系统学方法相结合的方法，探讨粉质在假蕨科蕨类植物中的进化和功能，并解决理解植物如何科普干旱胁迫和高日照的关键空白。这些数据将提供新的见解的功能作用，粉蕨类植物叶片和抗旱性更普遍的，可能适用于其他植物群体。一名研究生将接受多种方法的培训，并将开发一个新的本科生培训模块，使用生态位建模来调查植物进化的模式。 本研究有三个主要目标：第一个是关键，以了解在这一组的花粉的进化，并涉及重建notholaenid蕨类植物之间的种间系统发育关系，使用DNA序列从核和质体标记。目的二将集中在Notholaena standleyi，一个广泛分布的物种，具有三个公认的黄酮类化合物化学型。这些化学型的系统发育关系，类黄酮成分，倍性水平和地理分布将进行探讨，以确定是否多倍体和非生物生态位分歧有助于塑造他们目前的parapatric分布。目的三：通过测定干旱处理后、去淀粉前后的气体交换率、水分利用效率和光合恢复率，探讨淀粉的生理生态功能。还将研究花粉的详细解剖学和光学性质。

Ferns are commonly thought to be restricted to shady and moist habitats, but notholaenid ferns are adapted to, and have diversified within, the deserts of the southwestern United States and Northern Mexico. Notholaenids ferns become dormant during the dry season but quickly rehydrate and restore photosynthetic activity when moisture returns. This drought adaptation is hypothesized to be related to a waxy substance called 'farina', primarily composed of plant pigments, that form a whitish-to-yellowish layer on the leaf undersurface. When leaves curl up in response to water stress, this leaf surface is directly exposed to sunlight. Two primary functional hypotheses for the waxy layer have been proposed: 1) it acts as a 'barrier' to help reduce water loss from evaporation; 2) it acts as a 'sunscreen' to protect water-stressed leaves from damage caused by overheating and UV-radiation. This study aims to investigate the evolution and function of farina in notholaenid ferns and address a critical gap in understanding how plants cope with drought stress and high solar irradiance by using a combination of anatomical, biochemical, biogeographical, ecophysiological, and molecular phylogenetic approaches. These data will provide new insights into the functional role of farina on fern leaves and drought resistance more generally that may be applied to other plant groups. One graduate student will be trained in a diversity of approaches, and a new undergraduate training module will be developed using ecological niche modeling to investigate the patterns of plant evolution. This study has three primary objectives: The first is key to understanding the evolution of farina in this group, and involves reconstructing the interspecific phylogenetic relationships among notholaenid ferns using DNA sequences from both nuclear and plastid markers. Objective two will focus on Notholaena standleyi, a widespread species with three well-recognized flavonoid chemotypes. The phylogenetic relationships, flavonoid constituents, ploidy levels, and geographic distribution of these chemotypes will be explored to determine whether polyploidy and abiotic niche divergence have helped to shape their current parapatric distributions. Objective three will investigate the proposed ecophysiological functions of farina by measuring gas exchange rates, water-use efficiency, and photosynthetic-recovery rates after drought treatment, before and after removing the farina. Detailed anatomical and optical properties of farina will also be examined.