Calcium carbonate macroparticles as delivery system for gradient slow release hormone for in vitro plant growth regulation of Arabidopsis thaliana

The introduction of a controlled and gradual release of plant growth regulators holds great promise for directing the development of in vitro plants, as these regulators facilitate the precise regulation of physiological phenomena such as root formation, shoot induction, flowering and response to environmental stimuli. To address this challenge, our study introduces for the first time calcium carbonate-based macroparticles specifically designed for the encapsulation and gradual release of the auxin 1-naphthalene acetic acid in vicinity of an Arabidopsis thaliana plant. These macroparticles have demonstrated improved loading efficiency and a controlled gradual release profile due to their unique gradient release mechanism and simple preparation process. In in vitro Arabidopsis thaliana seedlings, their application resulted in a significant 58 % increase in lateral root formation in the primary root and a 68 % increase in adventitious root formation in the hypocotyl compared with the control treatment. Our findings represent a pioneering approach to achieve precise spatial/temporal hormone gradients in plant tissues, effectively improving the impact of plant growth regulator applications, bridging the gap between classical in vitro studies and innovative methods.