Scientists have created a tiny, non-invasive biosensor that tracks real-time sugar levels inside plants. Their study offers insights into how plants absorb and transport sucrose.
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Sucrose plays a vital role in plant physiology. A key source of energy, it is also a key signaling molecule that influences growth, development, and stress responses. It's central to long-distance transport between plant organs, helping allocate resources from source tissues, like leaves, to storage or growing tissues elsewhere in the plant.
Researchers have been investigating these sucrose transport mechanisms for some time; however, most existing techniques, such as biochemical assays, require destructive sampling. This not only prevents continuous monitoring but also disrupts the internal environment of the plant.
Given the complexity and speed of sucrose movement, tools with high spatial and temporal resolution that function in vivo are necessary to understand these mechanisms better.
Minimally Invasive, Real-Time BiosensorA Minimally Invasive, Real-Time Biosensor
In a recent Biosensors and Bioelectronics study, researchers demonstrated their needle-type biosensor, which can detect sucrose directly within living plant tissues. The sensor is nondestructive and provides dynamic, continuous data using a gel interface embedded with a trio of enzymes: invertase, autorotate, and glucose oxidase.
First, invertase hydrolyses sucrose into glucose and fructose. Mutarotase then converts the glucose into a form that glucose oxidase can efficiently process. The glucose oxidase catalyses an electrochemical reaction, generating a measurable signal at the sensor's electrode. The electrochemical circuit is completed by a bilirubin oxidase-based cathode integrated into the sensor, which ensures efficient signal flow.
The enzymatic components are immobilised within an agarose gel matrix affixed to a micro-electrode. This construction allows the sensor to detect sucrose concentrations as low as 100 micromolar, with a range extending up to 60 millimolar. This range allows the sensor to cover an extensive range of physiological concentrations typically found in plant tissues. The sensor has a response time of approximately 90 seconds and can be inserted into stems or leaves with negligible tissue damage.
Lab and Field Testing
The researchers conducted extensive in vitro and in vivo experiments to evaluate the biosensor's performance. They assessed the sensor's sensitivity in laboratory conditions, operational stability over 72 hours, and reproducibility across multiple readings.
To assess its real-world capabilities, they inserted the device into Psidium cattleianum (strawberry guava) stems and Cryptomeria japonica (Japanese cedar) leaves. These tests tracked sucrose transport over 24-hour cycles and under controlled light and dark conditions. The biosensor continuously recorded changes in sucrose concentration, revealing fluctuations driven by environmental cues.
Isotope Tracing Confirms Stomatal Uptake
To explore the mechanism behind sucrose entry into plant tissues, the team used water enriched with the stable isotope oxygen-18. This allowed them to track how water (and any dissolved sucrose) entered the plant through the stomata.
The water and dissolved sucrose were absorbed through stomatal openings, which was confirmed from isotope enrichment comparisons in the leaves and with the sensor data.
This provided in vivo confirmation of a previously hypothesised mechanism: that the stomata, best known for regulating gas and water exchange, may also serve as entry points for sucrose under certain conditions.
Key Findings: Sucrose Transport Responds to Light
The biosensor revealed further information: In strawberry guava, concentrations peaked during the night, supporting the understanding that sugars produced during photosynthesis in daylight are translocated to growing tissues after dark.
However, in Japanese cedar, sucrose levels rose sharply during periods of light when the stomata were open and dropped during darkness when the stomata closed. These shifts indicated that sucrose uptake was linked directly to stomatal activity, which in turn is regulated by light.
A delay of about 45 minutes was observed between light exposure and a rise in stem sucrose concentration. This agrees with previously established transport kinetics, offering further support for the idea that sucrose entry via stomata is both active and environmentally responsive.
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Rethinking Sucrose Uptake Pathways
This biosensor could be a valuable new tool for studying sucrose dynamics in plants. Its high sensitivity, broad detection range, and ability to function inside living tissues over long periods make it well-suited for detailed physiological investigations.
The key finding was the idea that the stomata may play a dual role, working not just for gas exchange and transpiration but also in mediating sucrose uptake. This challenges conventional assumptions that carbohydrate transport is strictly internal and passive. Instead, it points to a more responsive and environmentally linked process, where external cues like light can directly influence sugar intake.
Journal Reference
S. Wu et al. (2025) A plant-insertable multi-enzyme biosensor for the real-time monitoring of stomatal sucrose uptake. Biosensors and Bioelectronics, https://doi.org/10.1016/j.bios.2025.117674