LATEX AGGLOMERATION AND COAGULATION IN LATICIFERS OF LIVE TARAXACUM KOK-SAGHYZ (RUBBER DANDELION) ROOTS
The commercialization of Taraxacum kok-saghyz (rubber dandelion) as an alternative rubber crop requires fundamental knowledge of latex, an aqueous suspension of rubber particles, and rubber yield and quality. Rubber particles are formed in the root laticifers from Golgi bodies via the vesicular trafficking system in the cytosol and are then translocated into the vacuoles for storage. However, when freshly harvested roots are processed to extract the latex, much of the latex has already coagulated into solid rubber, reducing the commercial viability of latex extraction from this species. The process of in vivo loss of the latex fraction was investigated histologically, by transmission electron microscopy, in roots of plants grown in soil or hydroponically. In both root types, some rubber particles agglomerated in the cytosol as a precursor to coagulation. Other rubber particles agglomerated and then coagulated after rubber particles were translocated into vacuoles, and also after the cell internal cytoplasmic structure degraded. Uniquely large rubber particles were formed in the vacuoles of hydroponically grown plants by particle coalescence, but were not found in soil-grown roots. Eventually, some root laticifers of both root types filled with solid rubber. The instability of the aqueous latex phase postontogeny through rubber particle agglomeration, coalescence, and coagulation suggests that commercial processes likely would involve root drying to convert residual latex into solid rubber followed by aqueous- or solvent-based extraction.ABSTRACT
(a) Typical multivacuolar laticifer cell from a 12-mo-old plant grown in soil. (b) Univacuolar laticifer cell from a 6-mo-old plant grown hydroponically. White arrows indicate plastidic rubber particles, and black arrows indicate cytoplasmic rubber particles. CW, cell wall; LP, laticifer plastid; V, vacuole.
Schema of the different ways rubber particles can change state. Particles may adhere to each other, forming agglomerates that can be dispersed. The membranes of adjacent particles may merge cause the particles to coalesce and from a larger particle. Particle may also lose their individual integrity and form masses of coagulated rubber.
Solid rubber formation from rubber particle agglomeration and coagulation after cytoplasm degradation in 4- and 8-mo-old soil-grown roots. (a) Dispersed rubber particles in cells with degraded cytoplasm. (b) Rubber particles coalesced with each other (wide arrow) and then formed masses of rubber in the laticifer cells (narrow arrow). (c) The cell walls of the laticifer cells perforated and anastomosed, allowing the solid rubber to merge across the neighboring laticifer cells. CW, cell wall.
Solid rubber formation beginning in normal cytosol in 4- (left) and 8-mo-old (right) soil-grown roots. (a) Rubber particles began to coalesce into irregular rubber masses in the cytosol. (b, c) Degradation of the cytosol around rubber masses. (d) Large masses of solid rubber formed in laticifer cells. (e) Adjacent laticifer cells showed solid rubber in cells with (wide arrow) and without cytosol (narrow arrow). (f) Solid rubber formed in multiple laticifer cells. CW, cell wall; RP, rubber particle; SR, solid rubber.
Solid rubber formation in the laticifer cells of hydroponically grown roots. (a–c) Formation stages of solid rubber after the cytosol had degraded. (d–f) Formation of solid rubber by particle coalescence before the cytosol degraded.
Formation of large rubber particles in laticifer cells of hydroponically grown roots. (a) Small rubber particles coalesce with one another. (b) Fully formed large rubber particle. (c) Invagination of the cytoplasm and splitting of the tonoplast. (d) First section of the rubber particle is being pinched into the vacuole. (e) Ejecting the rest of the rubber particle into the vacuole. (f) Aerial view of large rubber particles observed in hydroponically grown roots. CW, cell wall; RP, rubber particle; V, vacuole.
Schema of the process of large rubber article formation and compartmentalization in seven laticifers of hydroponically grown roots. The letters in circles correspond to the electron micrographs in Figure 5. Parallel lines represent the tonoplast (T), areas shaded with dots represent the cytoplasm (C), unshaded white areas represent the vacuole interior (V), and black represents the rubber particles (RP).
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