Root photosynthesis prevents hypoxia in the epiphytic orchid Phalaenopsis

Luca Brunello; Ester Polverini; Giulia Lauria; Marco Landi; Lucia Guidi; Elena Loreti; Pierdomenico Perata

doi:10.1071/FP23227

RESEARCH ARTICLE (Open Access)

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Root photosynthesis prevents hypoxia in the epiphytic orchid Phalaenopsis

Luca Brunello

^A , Ester Polverini ^A , Giulia Lauria ^B , Marco Landi ^B , Lucia Guidi ^B , Elena Loreti

^C and Pierdomenico Perata

^A ^*

+ Author Affiliations

- Author Affiliations

^A PlantLab, Center of Plant Sciences, Sant’Anna School of Advanced Studies, Via Guidiccioni 10, San Giuliano Terme 56010, Italy.

^B Department of Agriculture, Food and Environment, University of Pisa, Via del Borghetto 80, Pisa 56124, Italy.

^C Institute of Agricultural Biology and Biotechnology, National Research Council, Via Moruzzi 1, Pisa 56124, Italy.

^* Correspondence to: p.perata@santannapisa.it

Handling Editor: Romy Schmidt-Schippers

Functional Plant Biology 51, FP23227 https://doi.org/10.1071/FP23227

Submitted: 4 October 2023 Accepted: 14 February 2024 Published: 6 March 2024

© 2024 The Author(s) (or their employer(s)). Published by CSIRO Publishing. This is an open access article distributed under the Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License (CC BY-NC-ND)

Abstract

Orchids (Phalaenopsis spp.) growing in tropical and subtropical regions are epiphytes. As such, they grow on trees with the root system utilised to anchor themselves to tree branches. These roots are highly specialised, display a large diameter and are often green, suggesting the ability to carry out photosynthesis. However, the role of photosynthesis in orchid roots is controversial. Orchids that are leafless can photosynthesise in their roots, thus indicating that some orchid roots carry out photosynthesis in a similar manner to leaves. However, the primary site of photosynthesis in orchids are in their leaves, and the roots of epiphytic orchids may mostly conduct internal refixation of respiratory CO₂. Besides contributing to the overall carbon metabolism of orchid plants, oxygen produced through root photosynthesis may also be important by alleviating potential root hypoxia. The bulky tissue of most epiphytic orchid roots suggests that oxygen diffusion in these roots can be limited. Here, we demonstrate that the bulky roots of a widely commercially cultivated orchid belonging to the genus Phalaenopsis are hypoxic in the dark. These roots are photosynthetically active and produce oxygen when exposed to light, thus mitigating root hypoxia.

Keywords: epiphytes, hypoxic niches, orchid, oxygen, Phalaenopsis, photosynthesis, root.

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