Calcium Phosphate and Senescence of Orange Jubilees in the Summertime

Biological kingdoms conceal innumerous undiscovered in vivo models for assessing the biomedical potential of nanoparticles. Here, we report on a floral in vivo model that tests for biocompatibility, bioactivity, antimicrobial potency, and biological barrier penetrability of nanoparticles. The model makes use of the plucked flowers of Tecoma alata, a.k.a. Orange Jubilee, from the Bignoniaceae trumpet vine family. Two types of calcium phosphate (CP) nanoparticles, hydroxyapatite (HAp) and amorphous CP (ACP), were dispersed in deionized vase water, and their effects on the flower senescence were measured. The corolla margin diameter, the corolla tilting degree, and live vs. dead ratio were the parameters that defined the senescence metrics. Both HAp and ACP delayed the senescence of T. alata flowers in a concentration-dependent manner and in inverse proportionality with the pH. The effect was primarily attributed to the bacteriostatic activity of the nanoparticles against Gram-negative microorganisms whose growth blocks the xylem and prevents the water uptake, but also to the adsorption of flower degradation products that serve as bacterial food and signal the programmed cell death. The possibility that CP nanoparticles get deposited along the xylem lumen and take on the calcium-regulating role analogous to that of intracellular calcium oxalate crystals was discussed, too. Both HAp and ACP nanoparticles were uptaken by the flowers and primarily deposited in the calyxes, with the transport of HAp, but not ACP, to the petals being considerable, coinciding with the greater effect of HAp on the longevity at lower concentrations and reiterating that the effect is particulate and not ionic in nature. The observed effects were confirmed on another Tecoma species, Tecoma stans, a.k.a. Yellow Trumpetbush. Simple, economic, and high-throughput models enabling high statistical confidence levels, such as the floral in vivo model proposed here, can be valuable alternatives to their complex, expensive, and statistically challenging animal model analogues.