How can your houseplant survive up to a month and a half without watering?
The research highlights the additional regulatory mechanisms that allow this plant to maintain the structure and function of its photosynthetic apparatus virtually unchanged even after 45 days of water deficit. Their results show that the basic units of the photosynthetic membranes of the chloroplasts shrink by only 1 nm following water loss, but recover 18 hours after rewatering.
Drought and evolution: how long can plants adapt?
The evolutionary conquest of land posed a particular challenge for plants accustomed to aquatic environments, which had to adapt to many environmental factors, including in particular the need to survive even long periods without rainfall. Some species have developed specific strategies to survive these periods, but most of our economically important crops are sensitive to drought, which has become increasingly common in Hungary and worldwide in several regions in recent decades as a result of climate change.
Water scarcity negatively affects the metabolic processes of plants, including energy-producing photosynthesis, thereby affecting their growth and yields, and in extreme cases can lead to plant death. In the European Union and the United Kingdom alone, drought-related (field) economic losses are estimated at an average of €9 billion per year. Drought is viewed as one of the leading drivers of agricutural production risks. This makes it particularly important to study and understand the metabolism of plant species that are able to maintain photosynthetic activity and survive during extended periods of drought.
"The never never plant (Ctenanthe setosa) is a plant native to South America which is found as a houseplant or as an ornamental crop inside green walls or tropical-inspired buildings. We got them from the collection of the ELTE Botanical Garden. Because they can survive up to 45 or 60 days without watering, they are ideal for people who tend to forget to water their houseplants" notes Richard Hembrom, a PhD candidate from India and first author of the paper published on the subject. Thanks to a Stipendium Hungaricum scholarship, Richard, who is pursuing his doctoral studies at ELTE, has been studying how drought stress affects the structure and function of plant chloroplasts, particularly their photosynthetic activity.
Richard Hembrom (PhD candidate) measures the chlorophyll content of the never never plant at the Department of Plant Anatomy, ELTE
The anatomy of drought tolerance
The research showed that although the water content of the plant's leaves gradually decreased with drought and the leaves became completely curled to reduce water loss by evaporation, the function and structure of the chloroplasts hardly changed during the long dry period. Below the upper (adaxial) and lower (abaxial) epidermis of the leaves, a special cell layer is located, which presumably plays a role in water storage, as this layer of cells on the upper side has thinned most significantly during the drought. The purplish colour of the lower (abaxial) leaf side is due to the presence of a pigment called anthocyanin, which may play a role in protecting the leaves from strong light when they are stressed and curled.
Never never plant with partially curled, drought-stressed leaves, with the the purple leaf coloration of the lower (abaxial) leaf side being exposed to the light
The structural analysis of plastids is particularly challenging under drought stress, as for electron microscopic analyses, most samples have to be prepared according to a complex protocol involving aqueous or other solvent phase solutions. Thus, it cannot be guaranteed that the typical state of the leaf under drought stress can be preserved during this time, and water added during sample preparation will not affect the results obtained or lead to artefacts. This issue is of particular interest, as in several articles other researchers have described, based on their electron microscopy studies, that the inner lumen of the sac-like, so-called thylakoid membranes in the chloroplasts swells under drought stress. However, swelling presumably requires water, of which there is very little in plant cells under such conditions, which sounds contradictional.
Cross-section of a never never plant’s leaf in a light microscope (left image) and a chloroplast in a transmission electron microscope (scale bar: 1 micrometre, stars: grana, arrows: plastid envelope membrane)
Resolving the contradiction - or the relationship between physicists, biologists and neutron scattering
The collaboration between ELTE plant biologists studying plants and physicists with expertise in small-angle neutron scattering measurements, also used in materials research, provided an excellent opportunity to resolve this controversy.
"When the plant leaf is placed in the neutron beam, the neutrons are scattered by its photosynthetic thylakoid membranes, the so-called grana, which consist of several layers of thylakoids piled on the top of each other in a regular arrangement. From the scattering pattern, it was possible to determine precisely the repeat distance value, that characterises the structure of the membranes and corresponds to the size of the repetitive basic units of grana. This value decreased from approx. 20 nm in the control plants to 19 nm in the dehydrated plants" explains Renáta Ünnep of the HUN-REN Energy Research Institute the main results of the measurement.
Leaves of drought-stressed (left) and control (right) never never plants placed in the neutron beam at the Budapest Neutron Centre
A similar decrease of the repeat distance values could be detected in electron microscopic images obtained and examined after conventional sample preparation. Both methods showed that there is a high biological variability between this nanoscale structure (repeat distance) of the grana present in different plants, in different leaves of the same plant and even in different regions of each leaf, and is therefore difficult to compare.
"The huge advantage of small-angle neutron scattering measurements in this case is that by placing a drought-stressed plant in the neutron beam of the world's most powerful accelerator-based neutron source in Tennessee, you can follow the changes in granum structure following rewetting at resolutions of minutes to hours. This allows us to observe how the repeat distance value of the granum gradually returns to around 20 nm 18 hours after rewatering" says Gergely Nagy of Oak Ridge National Laboratory in the US, who made these measurements. "Here, we are looking at the same grana in the same leaf region after a drought period and after rewatering. Whereas electron microscopy sampling is invasive, you have to cut a piece of leaf off, so in that case we can't follow the structural alterations of the same chloroplasts and grana in time and without any interference and sample preparation - only neutrons can do that," he adds.
Renáta Ünnep and Gergely Nagy have already investigated the plastids of many plants and algae using this method, and they have also had several previous collaborations with the Plastid Biology Laboratory led by Katalin Solymosi at the Department of Plant Anatomy at ELTE. However, this is the first time that the structure of the plastids of completely intact rooted and potted plants has been investigated using small-angle neutron scattering. In previous cases, cut leaves or leaf fragments were examined, and in many cases the samples were treated with heavy water (deuterium oxide) to obtain higher contrast and better signal. Fortunately, this was not necessary in the case of the never never plant, so that the leaves of the drought-stressed and then rewetted plant could be observed in their truly natural state.
Structure of a granum (star) in an electron microscope (left, green arrow: envelope membrane, white arrow: stromal thylakoid) and a model demonstrating the repeat distance (basic unit of the granum)
"It is important to emphasize, however, that by examining a sufficient number of electron microscopic samples, we can reach similar conclusions as with neutrons. In addition to information about granum repeat distance values, electron microscopy also provides many further important details about the structure of the chloroplasts and the cells" notes Katalin Solymosi. "The two methods therefore tend to complement and reinforce each other, and clearly confirm that in this case, drying is indeed associated with shrinkage of the thylakoid membranes (grana) and rewetting with their expansion" concludes Katalin Solymosi.
A drought tolerant guide for future thinkers
In addition to the pioneering use of small angle neutron scattering for structural analysis in this work, the molecular organisation and function of the photosynthetic apparatus of the plant has been studied in detail. Further research is underway to better understand the additional regulatory mechanisms that allow this plant to maintain the structure and function of its photosynthetic apparatus virtually unchanged even after 45 days of water deficit.
Understanding these basic structural and functional processes could, in the long term, contribute to the breeding of more drought-adapted crops.
Data of the published paper: Richard Hembrom, Renáta Ünnep, Éva Sárvári, Gergely Nagy, Katalin Solymosi (2025) Dynamic in vivo monitoring of granum structural changes of Ctenanthe setosa (Roscoe) Eichler during drought stress and subsequent recovery. Physiologia Plantarum 177 (1) e14621. https://doi.org/10.1111/ppl.14621.