Histochemical studies on the distribution and accumulation of trans-polyisoprene in the rubber-producing plant Eucommia ulmoides.

Eucommia ulmoides rubber (EUR) is a high-quality natural rubber resource, which can be extracted from different organs of the Eucommia ulmoides tree. In this study, EUR was isolated from the leaves, barks, and pericarps, and the structural characteristics and physicochemical properties of EUR were systematically determined. The accumulation and distribution of EUR in different tissues were assessed through in situ observations combined with cellular and subcellular scales. The preliminary analyses indicated that the variations in the physicochemical properties of EUR across different tissues were associated with its accumulation microstructure. Further analyses by SEM and TEM showed that the initial cell differentiation and fusion resulted in the formation of tubular structures without any nucleus. A limited number of rubber particles were generated within the cytoplasm, concurrent with aggregation and fusion. Eventually, rubber particles filled the entire cytoplasm, and organelles disappeared to form highly aggregated filamentous structures. In addition, the number and area of EUR-containing cells were closely related to the organization sizes of barks and leaves. This study provided valuable insights into Eucommia ulmoides histology and the rubber industry.