Ferns with superpowers

Appearing grey-brown and lifeless, resurrection ferns, such as Pentagramma triangularis, can withstand long periods of drought in a curled up, desiccated state only to return to a lush green again once hydrated. This ability to withstand near-complete water loss and then recover allows the resurrection ferns to thrive in habitats where other plants would not survive. However, there are certain challenges faced by vascular plants when surviving desiccation. For the fern to successfully dehydrate and rehydrate without the vasculature tissues becoming damaged, the distinct tissue types within the vasculature need to dehydrate and rehydrate in a specific and orderly manner. Water flow through the xylem vessels then needs to be re-established to supply water to tissues that are still dessicated.

The tissues within the stipe of a desiccation tolerant fern, Pentagramma triangularis, were examined using three‐channel fluorescence microscopy. The vascular cylinder contained xylem (pink), phloem (light blue) and chlorenchyma (dark with faint red chloroplasts), surrounded by endodermis (bright red with bright yellow Casparianlike strips). Photo courtesy of A. L. Jacobsen. (Holmlund et al., pp. 97–105). 

Investigating the desiccation and recovery of desiccation tolerant vascular plants has been advanced by the use of micro-computed tomography (MicroCT) to visualise the internal tissues of the plant without the need to cut it open. MicroCT uses tissue-penetrating X-rays to image the plant’s internal structures. Holmlund and colleagues used MicroCT combined with light microscopy and fluorescence microscopy to investigate the dynamics of desiccation and rehydration in the vascular tissue of P. triangularis. Using MicroCT, they were able to build up a picture of the ordered, reversible sequence of events that take place during desiccation and rehydration of the vasculature. These findings are complemented by light and fluorescence microscopy images revealing the key anatomical traits that enable this to take place. The image above shows the different structures within the P. triangularis vasculature imaged using three-channel fluorescence microscopy.

Read the article: Holmlund, H.I., Pratt, R.B., Jacobsen, A.L., Davis, S.D. and Pittermann, J. (2019) High‐resolution computed tomography reveals dynamics of desiccation and rehydration in fern petioles of a desiccation‐tolerant fern. New Phytologist, 224: 97-105. doi: 10.1111/nph.16067