Sustained Release of Hydrogen Sulfide from Di(t-butanol)dithiophosphate Phenethylamine Salt Encapsulated into Poly(lactic acid) Microparticles to Enhance the Growth of Radish Plants

The slow release of hydrogen sulfide has been shown to be beneficial to plants by protecting them from environmental stressors, increasing germination, and extending the lifetime of harvested fruits. A major challenge in this field is controlling the amount and location of release of hydrogen sulfide so that it is available for use by plants at optimal amounts. This article reports a dual method to release hydrogen sulfide near the roots of plants by controlling its release using the hydrolysis of a dithiophosphate and the degradation of poly(lactic acid) [PLA]. Di(-butanol)dithiophosphate phenylethylamine (BDPA) was dissolved in a solution of PLA, and the solvent was allowed to evaporate. The resulting solid was crushed in a blender and separated into microparticles with two different size distributions of 250-500 or 500-2000 μm. The microparticles were characterized by powder X-ray diffraction to measure the presence of microcrystals of BDPA within PLA, and images obtained using scanning electron microscopy with energy dispersive X-ray analysis confirmed the presence of these crystals. Microparticles of BDPA loaded within PLA were characterized for their release of phosphorus and hydrogen sulfide, which both showed a burst release within 3 days, followed by a steady release. Radish plants grown with microparticles of PLA loaded with BDPA had up to a 141% increase in harvest yield compared to plants grown in the presence of free BDPA not loaded into PLA, PLA microparticles without BDPA, and control plants grown without PLA or BDPA. These experiments showed that loading hydrogen sulfide-releasing chemicals into PLA is a promising method to improve the effect of hydrogen sulfide on plants.