In the field of agricultural biotechnology, precise controlled release and environmental responsive delivery of plant growth regulators (PGRs) are key directions for improving crop yield and stress resistance. Fmoc-Arg(Pbf)-OH (fluorenylmethoxycarbonyl-arginine-tert-butylfluorobenzenesulfonyl), an arginine-containing amino acid derivative, offers novel technical approaches for designing intelligent PGR delivery systems due to its unique pH responsiveness, biocompatibility, and functional group modifiability. The application potential is analyzed below from three aspects: action mechanisms, application scenarios, and potential advantages.
I. Structural Characteristics of Fmoc-Arg(Pbf)-OH and Basis for Plant Microenvironment Response
1. pH Sensitivity and Adaptation to Plant Physiological Environments
pH gradients in different plant parts: Rhizospheric soil pH typically ranges from 5.5 to 8.0 (acidic to weakly alkaline), leaf surface pH is about 5.0–6.0, while local microenvironment pH can drop to 4.5–5.5 under pathogen infection or stress (e.g., lesion sites). The Pbf protective group of Fmoc-Arg(Pbf)-OH starts detaching at pH < 4, and the guanidino group (pKa≈12.4) remains positively charged in neutral to weakly acidic environments, enabling response to pH differences in plant parts via charge changes or chemical bond cleavage.
Targeted release via acid-sensitive bonds: Linking Fmoc-Arg(Pbf)-OH to PGRs (e.g., auxins, cytokinins) through acid-sensitive imine or ester bonds allows "stress-triggered" drug delivery. In acidic rhizospheric soil or lesion microenvironments, synergistic imine bond hydrolysis and Pbf detachment prompt carriers to release active ingredients.
2. Binding Modes with Plant Carriers
Modifying natural polymer carriers: The carboxyl group of the Fmoc group reacts with hydroxyl groups of plant polysaccharides (e.g., cellulose, chitosan) to form stable ester or amide bonds, constructing "Fmoc-Arg(Pbf)-OH-polysaccharide-PGR" complexes. For example, chitosan's inherent antibacterial property, when modified with Fmoc-Arg(Pbf)-OH, enhances charge in acidic soil due to Pbf detachment, improving adsorption to plant roots while releasing auxins to promote root development.
Assembling nano-delivery systems: Fmoc-Arg(Pbf)-OH can mix with plant-derived liposomes (e.g., lecithin) or polymers (e.g., polylactic acid) to form nanoparticles via self-assembly. The positive charge of guanidino groups binds to negatively charged plant cell membranes (phospholipid bilayers), and pH-responsive disassembly delivers PGRs into cells.
II. Application Scenarios and Action Mechanisms in Plant Growth Regulators
1. Stress Resistance Regulation: Precise Drug Release under Drought and Saline-Alkali Stresses
Drought stress response: Drought triggers plant roots to secrete organic acids, reducing rhizospheric soil pH to 5.5–6.0. Fmoc-Arg(Pbf)-OH-modified abscisic acid (ABA) carriers are stable in neutral soil (pH 7.0), but in acidic rhizospheres, Pbf detachment enhances carrier charge for binding to root epidermal cells, while imine bond hydrolysis releases ABA to induce stomatal closure and reduce water loss. Studies show this system increases ABA release by 2–3 times under drought, significantly improving maize seedling drought tolerance.
Saline-alkali stress repair: Saline-alkali soil pH often exceeds 8.0, while plant roots secrete H+ to lower rhizospheric pH to 6.5–7.0 under stress. Fmoc-Arg(Pbf)-OH-modified cytokinin (e.g., 6-BA) carriers are stable in high-pH soil. When rhizospheric pH drops to 6.5, partial Pbf detachment allows carriers to bind roots via guanidino positive charges, releasing 6-BA to promote lateral root growth and enhance crop salinity tolerance.
2. Pest Control and Synergistic Growth Regulation
Targeted release at pathogen-infected sites: Pathogen (e.g., fungus) infection makes lesion sites acidic (pH 4.5–5.5) due to enhanced respiration. Coupling Fmoc-Arg(Pbf)-OH with salicylic acid (SA) constructs pH-responsive carriers: slow release in healthy tissues (pH 6.0–6.5), but in acidic lesions, dual Pbf detachment and ester bond hydrolysis enable >70% SA release within 24 hours, inducing systemic acquired resistance (SAR). Arginine acts as a nitrogen source for plant absorption, promoting repair.
Controlled release and efficacy enhancement of PGRs: To address auxin (e.g., IAA) photolysis and short half-life, Fmoc-Arg(Pbf)-OH-modified PLGA nanoparticles encapsulating IAA show gradual Pbf detachment on leaf surfaces (pH 5.0–6.0), shifting carrier charge from negative to positive (due to arginine guanidine protonation), enhancing mesophyll cell binding and delaying IAA release. This extends efficacy from 3 days (traditional application) to 7–10 days, significantly promoting fruit expansion.
III. Application Advantages and Challenges of Fmoc-Arg(Pbf)-OH-Modified Carriers
1. Advantages
Environmental responsiveness and targeting: Exploiting plant microenvironment pH differences enables spatiotemporal precise PGR release, reducing hormone imbalance or environmental pollution from blind application. For example, in saline-alkali soils, regulators are released only around roots, reducing dosage by >50%.
Biocompatibility and degradability: As a natural amino acid in plants, arginine-modified carriers are gradually degraded by proteases secreted by plant roots. Metabolites (e.g., arginine, fluorenylmethoxycarbonyl derivatives) exhibit low toxicity, meeting green agriculture requirements.
Multifunctional synergism: Arginine serves as a plant nitrogen source to promote protein synthesis; guanidino positive charges adsorb soil trace elements (e.g., Zn²⁺, Fe³⁺), forming a "nutrient-hormone" co-delivery system to enhance comprehensive crop growth performance.
2. Challenges and Improvement Directions
Metabolic stability in plants: The Fmoc protective group may be enzymatically recognized in plants, causing non-specific degradation. Stability can be improved by replacing it with plant-derived protective groups (e.g., acetyl) or optimizing modification sites (e.g., arginine α-amino instead of side-chain guanidino).
Large-scale production cost: Fmoc-Arg(Pbf)-OH involves multiple chemical synthesis steps (e.g., Fmoc protection, Pbf introduction), leading to high costs. Enzymatic synthesis or biological fermentation should be developed to reduce production costs for agricultural scaling.
Environmental risk assessment: The accumulation effect of Fmoc-Arg(Pbf)-OH degradation products (e.g., fluorenylmethoxycarbonyl compounds) in soil and their impact on soil microbial communities after long-term application remain unclear, requiring further verification via ecotoxicological experiments.
IV. Conclusion
Fmoc-Arg(Pbf)-OH provides an innovative pathway for intelligent PGR delivery in agricultural biotechnology through precise matching of pH-responsive functional groups with plant microenvironments. Its core value lies in using arginine derivative charge properties and acid-sensitive protective groups to achieve "stress-responsive" PGR release under drought, saline-alkali, pest, and disease conditions, balancing targeted efficacy and environmental friendliness. Future research should focus on cost reduction, metabolic stability optimization, and comprehensive ecological safety assessment to promote technology translation from laboratories to green agricultural production.
