Mai, M. H. | Search bioRxiv

bioRxiv2025

Secreting salt glands constrain cuticle fracture to enhance desalination efficiency

Plants responding to excessive soil salinity by discharging brine onto their leaf surface risk dehydration through the osmotic continuity between the living tissue and the surface brine, which further enriches with evaporation. Cuticle cracks have long been identified as essential for salt to reach the leaf surface but provide the potentially desiccating continuity between the brine and the gland interior. Using the secreting salt gland of Nolana mollis as a model system, we integrate mathematical modeling, imaging, and physiological measurements to examine the mechanical and biochemical processes required for efficient desalination. We find that the subcuticular space between the concentrated surface brine and the more dilute secreting cell eases the energetic limits of active desalination by reducing the concentration gradient of salt across the cell membrane. We show that crack size plays a critical role in balancing the osmotic and pressure gradients required for salt removal without runaway foliar desiccation.

plant biology↗

bioRxiv2025

Gibberellin enhances germination of Nolana mollis and Heliotropium pycnophyllum seeds

Desert plants often exhibit seed dormancy, which enables seeds to wait out unfavorable conditions and germinate when there is enough water for the seedling to establish securely. Here, we tested several dormancy-breaking mechanisms for Nolana mollis and Heliotropium pycnophyllum, including storage temperature, scarification, hormones, germination temperature, and light cycles during germination. For both species, gibberellin enhanced germination significantly. All other treatments, or combinations of treatments, had no significant effect. Our results can be applied to restoration efforts in arid areas, or in urban areas in arid climates, where the use of native species reduces watering necessities.

plant biology↗

bioRxiv2024

Relieving the transfusion tissue traffic jam: a network model of radial transport in conifer needles

The linear geometry of conifer leaves (e.g., pine needles) imposes architectural constraints on solute transport. The needles structural solution to prevent axial stagnation, however, introduces an additional challenge to radial transport by restricting loading and unloading of sugar and water, respectively, to a narrow zone at the periphery of the vascular bundle. Moreover, a Casparian strip blocks apoplastic flow through the endodermis between the vasculature and photosynthetic tissue, forcing countercurrents of water and sugar to travel simultaneously through the cell lumen at this interface. In between these two potential bottlenecks is the transfusion tissue, a distinctive anatomical feature of conifer needles. Here we develop a network-based mathematical model to explore how the structure of the intervening transfusion tissue facilitates radial transport of sugar and water. To describe extravascular transport with cellular resolution, we construct networks from images of Pinus pinea needles obtained through X-ray CT, as well as fluorescence and electron microscopy. Our results show that the physical separation of sugar and water pathways within the transfusion tissue mitigates the consequences of constricting flow at both the vascular access points and the endodermis. SIGNIFICANCEThe efficiency with which plants transport water and sugar across many scales affects their survival and success. At the leaf scale, accommodating the opposing flows of water and sugar is a nontrivial challenge, especially when foliar geometry imposes architectural limitations (e.g., in linear leaves (needles) of conifers). The transfusion tissue is a characteristic component of the conifer needle which mediates the radial transport of sugar and water. Our network model shows that the transfusion tissue alleviates the sugar-water traffic jams that would otherwise develop between the vascular system and photosynthetic cells. Our mathematical model provides finer resolution than what is currently possible with experimental approaches.

plant biology↗