The Endogenous Sulfated Pentapeptide Phytosulfokine-α Stimulates Tracheary Element Differentiation of Isolated Mesophyll Cells of Zinnia1

Abstract

Dispersed zinnia (Zinnia elegans) mesophyll cells cannot differentiate into tracheary elements (TEs) at low cell density conditions even if auxin and cytokinin are present in the medium, indicating the involvement of intercellular interactions during the initiation and/or subsequent progresses in TE differentiation. When zinnia cells were incubated at a low density (2.5 ؋ 10 4 cells mL ؊1 ) in TE-inductive medium in the presence of various concentrations of phytosulfokine (PSK)-␣, which was originally identified as an intercellular signal peptide involved in cell proliferation, TE differentiation was strongly stimulated in a dose-dependent fashion; more than 35% of the living cells differentiated into TEs by 5 d of culture in the presence of 10 nM PSK-␣. Enzyme-linked immunosorbent assay and mass spectroscopy confirmed that cultured zinnia cells produce nanomolar levels of PSKs under inductive conditions. These results suggest that PSK-␣ is a factor responsible for TE differentiation of zinnia mesophyll cells.

Flow cytometric analysis of tracheary element differentiation in Zinnia elegans cells

“…TE formation has also been found to coincide with changes in the extracellular pH of the culturing medium (24). Effort has been focused on the intercellular communication during this process, with several xylogen compounds having been described (25,26). The implication of PCD provides another paradigm for induction and regulation of the tracheid cell death.…”

Existence of a plant tyrosylprotein sulfotransferase: novel plant enzyme catalyzing tyrosine O‐sulfation of preprophytosulfokine variants in vitro

“…Subsequent studies demonstrated the existence of PSK-K in CM derived from both monocot [7] and dicot [8,9] cell cultures. Furthermore, isolation of a rice (Oryza sativa L.) cDNA, OsPSK, encoding a putative PSK-K precursor has been achieved [10] and it was also shown that rice suspension cells contain both speci¢c high-and low-a¤n-ity saturable PSK-K binding sites on their plasma membranes [11].…”

Formation of plant tracheary elements in vitro – a review

“…Tracheary element differentiation occurs synchronously at high frequency above initial cell densities of 4.2 × 10 4 cells mL L −1 , but is significantly suppressed below this threshold. This result indicates that intercellular interactions are involved in the initiation and/or subsequent progresses in TE differentiation (Matsubayashi et al 1999). McCann et al (2000) reported that plant condition and leaf age are critical factors influencing TE differentiation in the Zinnia elegans in vitro system.…”