Drought stress is a major environmental constraint for plant growth. Climate-change-driven increases in ambient temperatures resulted in reduced or unevenly distributed rainfalls, leading to increased soil drought. Carex duriuscula C. A. Mey is a typical drought-tolerant sedge, but few reports have examined the mechanisms conferring its tolerant traits. In the present study, the drought responses of C. duriuscula were assessed by quantifying activity of antioxidant enzymes in its leaf and root tissues and evaluating the relative contribution of organic and inorganic osmolyte in plant osmotic adjustment, linking it with the patterns of the ion acquisition by roots. Two levels of stress—mild (MD) and severe (SD) drought treatments—were used, followed by re-watering. Drought stress caused reduction in a relative water content and chlorophyll content of leaves; this was accompanied by an increase in the hydrogen peroxide (H₂O₂) and superoxide (O_2⁻) contents in leaves and roots. Under MD stress, the activities of catalase (CAT), peroxidase (POD), and glutathione peroxidase (GPX) increased in leaves, whereas, in roots, only CAT and POD activities increased. SD stress led to an increase in the activities of CAT, POD, superoxide dismutase (SOD), and GPX in both tissues. The levels of proline, soluble sugars, and soluble proteins in the leaves also increased. Under both MD and SD stress conditions, C. duriuscula increased K⁺, Na⁺, and Cl⁻ uptake by plant roots, which resulted in an increased K⁺, Na⁺, and Cl⁻ concentrations in leaves and roots. This reliance on inorganic osmolytes enables a cost-efficient osmotic adjustment in C. duriuscula. Overall, this study revealed that C. duriuscula was able to survive arid environments due to an efficient operation of its ROS-scavenging systems and osmotic adjustment mechanisms.

Indole-3-acetic acid (IAA) and salicylic acid (SA) are two important phytohormones. In this work, for the first time, a ratiometric electrochemical sensor was developed for quantifying IAA and SA simultaneously. A composite of multi wall carbon nanotubes (MWNT) and carbon black (CB) was used to enhance the sensitivity of electrochemical detection. Ferrocene (Fc) was used as the reference molecule to offer a built-in correction to improve the accuracy. A good linearity was constructed between the I_IAA/I_Fc and the concentration of IAA from 25 μM to 1000 μM. The linear equation was y = 0.00159x + 0.124 (R² = 0.9887). The LOD for IAA was 1.99 μM. Meanwhile, the I_SA/I_Fc gradually increased with increasing concentration of SA. The linear regression equation for SA was y = 0.00107x + 0.34465 (R² = 0.9488) with the LOD of 3.30 μM. Thus, the as-prepared multifunctional ratiometric electrochemical sensor was successfully applied to detect IAA and SA at the same time. This sensor was also successfully used to detect IAA and SA in the homogenates of soybean seedlings under salt stress, confirming the practical applicability of the sensor. And the obtained results agreed well with those obtained by the ultra performance liquid chromatography-mass spectrometry (UPLC-MS) method.

Detection of signal molecules in living plants is of great relevance for precision farming. In this work, to establish a more effective method for monitoring salicylic acid (SA) in the leaves of living plants, a ratiometric electrochemical sensor was fabricated based on a Cu metal–organic framework (Cu-MOF) and carbon black (CB) composite. The Cu-MOF and CB composite was used to catalyze SA oxidation. Ratiometric oxidation current peak intensities I_SA/I_Cu-MOFs were used as the response signal for SA. I_SA/I_Cu-MOFs linearly enhanced with the increase of SA concentration, together with low limits of detection (12.50 μM). Moreover, our sensor is fabricated on a screen-printed electrode (SPE), which is especially suitable for applying to the flat leaves of plants. Using this sensor, the SA level in the leaves of cucumber seedlings was monitored in vivo under salt stress. The proposed sensor is accurate, reliable and practical. This is the first report for developing a ratiometric electrochemical sensor for detecting SA in living plants. Our work can also provide a strategy for in vivo studies on the leaves of plants.

Proline is an important amino acid, which is crucial to plant growth and development. Accurate analysis of proline content is of great significance for understanding its physiological mechanism in plants. In this paper, according to the requirements for in‐situ detection in plants in precision agriculture, an electrochemical molecular imprinted polymers (MIP) sensor for determining proline in living plants was developed. Polypyrrole (PPy) was used as the functional monomer. To improve the performance of the MIP sensor, Au nanoparticles (NPs) were electrodeposited on the screen‐printed electrodes (SPEs) electrode. Thionine (Thi) was then electropolymerized on the SPEs to be used as an internal reference signal molecule. The MIP‐based proline sensor has the widest detection range of 1×10⁻¹⁶ −0.01 M. And its detection limit is the lowest (9.18 aM) so far. It was also used for measuring free proline in the leaves of living cucumber seedlings under salt stress. The MIP‐based proline sensor has an important prospect for detecting the physiological status of plants in situ and will play an important role in smart agriculture.