# Identification and Characterization of Organic Calcium Crystals in the Plumeria pudica and Plumeria rubra Latexes

## TL;DR

This study identifies and characterizes organic calcium crystals in the latex of Plumeria pudica and Plumeria rubra, revealing new crystal structures and their potential roles in the plant.

## Contribution

The first documentation of hydrated calcium malonate and calcium-containing cerberic acid B in plant latex.

## Key findings

- Hydrated calcium malonate crystals were identified in Plumeria pudica latex for the first time in plants.
- Calcium-containing cerberic acid B was found in Plumeria rubra latex, also a first-time report.
- Crystal structures varied in form and stability, with differences observed between crude and diluted latex samples.

## Abstract

Latex is usually
a milky fluid but can also be clear,
brown, or
orange. It consists of organic compounds (rubber particles and primary
and secondary metabolites) and proteins dispersed in an aqueous phase.
Four latex fluids were examined through optical microscopy, and organic
crystals were found. Crystal structures were observed in Plumeria
rubra and P. pudica, while no crystal was
found in the latex of Calotropis procera and Himatanthus drasticus. Various sizes and shapes of crystals,
including raphides, styloids, crystalline sands, and prismatic forms,
were documented. The structures were stable for a 96 h period at 25
°C. The relative abundance of crystal forms varied based on whether
the latex was crude or water-diluted. All crystal forms related to P. pudica were identified as hydrated calcium malonate [Ca­(C3H2O4)­(H2O)2]·2H2O, representing the first documentation of these structures
in plants. Calcium malonate crystals also were identified in the latex
of P. rubra, which were mainly in the forms of raphides
and styloids. Nonetheless, the crystalline sands and prismatic forms
found in P. rubra latex exhibited an additional carbon
ring in their structure ([C20H34Ca2O19]) identified as cerberic acid B. This result also
represents the first report of calcium-containing cerberic acid B.
The results were discussed based on the possible functions of these
molecules within laticifers.