Carbon quantum dots as a nanotechnology-based approach to modulating enzymatic activity during white mustard (Sinapis alba L.) seeds germination

The application of nanoparticles has been reported as a sustainable
approach to improving seed germination and influencing agricultural and biochemical
parameters. This study aimed to evaluate the effects of carbon-based nanoparticles on
hydrolytic enzyme activities during white mustard (Sinapis alba L.) germination. Carbon
quantum dots (CQDs) were synthesized using a hydrothermal method (200 °C for 2 h)
and characterized by UV–vis absorption, excitation and emission spectroscopy, and X-ray
photoelectron spectroscopy (XPS). Mustard seeds were treated with CQDs at 1
μg/mL during imbibition (12 hours) and by spraying during germination. Germination
was conducted at 25 °C in the dark, with a 96 hours kinetic study and sample collection
every 24 hours. Germinated seeds receiving no treatment were used as the
experimental controls, while non-germinated seeds subjected only to imbibition served
as a reference for comparison. α-Amylase and protease activities (U/g) were
determined spectrophotometrically using starch and azocasein as substrates,
respectively. Lipase activity (U/g) was measured using a titrimetric method. Soluble
protein content was determined by the Lowry method. XPS characterization of the
CQDs revealed an elemental composition of 74.72% C1s, 22.22% O1s, 0.99% N1s,
and 0.07% S2p. The obtained spectra showed two main peaks corresponding to π-π*
(240 nm) and n-π* (350 nm) electronic transitions. Germination progressively increased
enzymatic activity over time, reflecting the mobilization of starch, protein, and lipid
reserves to provide energy (ATP) for seedling development. By the end of the process,
increases of 766%, 4754%, and 203% were observed for α-amylase, protease, and
lipase, respectively, compared to non-germinated seeds. α-Amylase activity increased
by 67% following CQDs application at 72 hours (572.64 U/g) compared to the control
(343.90 U/g), suggesting a potential acceleration of starch metabolism. Regarding
CQDs application, proteolytic activity values of 124.34 U/g and 113.95 U/g were
observed at 72 and 96 hours of germination, respectively, compared to untreated seeds
germinated for the same periods (62.89 and 47.10 U/g), representing percentage
increases of 98% and 142%. These findings suggest that the effect of CQDs on protein
reserve mobilization tends to occur during later stages of white mustard sprout
development. CQDs application did not result in a significant additive effect (p > 0.05)
on lipase activity, the increases observed over time were attributed to the germination
process itself. It is concluded that the application of CQDs enhanced α-amylase and
protease activity during specific periods of white mustard germination, particularly at 72
hours, highlighting the potential of nanotechnology as a sustainable and accessible tool
to positively modulate enzymatic metabolism and possibly facilitate the mobilization of
reserves, thereby accelerating the germination process.
Funding Source: Coordenação de Aperfeiçoamento de Pessoal de Nível Superior –
CAPES (Finance code 001).