Cell division promoting activity of naturally occurring dehydrodiconiferyl glucosides: do cell wall components control cell division?

Abstract

Naturally occurring isomers of the dehydrodiconiferyl glucosides have been isolated from Vinca rosea crown gall tumors and have been tested for cell division promoting activities in the tobacco pith and leaf assay systems. The enantiomeric isomers A and B are active, although they are required at concentrations up to 2 orders of magnitude higher than zeatin riboside to promote comparable growth. We estimate that the active dehydrodiconiferyl glucosides are present in rapidly growing tissues (tumor tissue, habituated tissue, cultured nontransformed tissue) in micromolar concentrations. In quiescent tobacco pith tissue, the levels of these compounds are reduced by a factor of 100. These results suggest that cytokinin may exert control ofcell division through the accumulation of molecules (the dehydrodiconiferyl glucosides) that are apparent cell wall components.Cytokinins are naturally occurring plant growth regulators that play a central role in the control of plant cell division (1, 2). In addition, these N6-substituted adenine derivatives are involved in the control of a variety of other phenotypese.g., initiation of shoot organogenesis and inhibition of leaf senescence (3,4). The molecular and biochemical bases of the cytokinin-mediated control of these processes remain unknown. Wood and colleagues (5-7) provided evidence for cell division factors isolated from Vinca rosea crown gall tumors that could substitute for cytokinins in the tobacco pith assay. We have now shown (8) that the original fraction contained, at least in part, two dehydrodiconiferyl glucosides (DCGs). Here we further characterize the DCGs D, E, F, and G and demonstrate cell division promoting activity for isomers A, B, and E as ascertained by both tobacco pith and leaf bioassay. (9) supplemented with 1.0 uM naphthalene acetic acid (NAA) and zeatin riboside (ZR) or the DCG isomers as indicated. In some experiments, the pith tissues were placed in plastic plates (60 x 15 mm) containing 4.0 ml of medium. The ZR and DCGs were filter-sterilized and added aseptically to cooling autoclaved medium. The tissues were grown at 25TC under cool white fluorescent lights with a light/dark cycle of 16:8 hr. They were observed regularly under a binocular dissecting microscope and harvested after 3 weeks. For leaf assays, 9-mm2 fiagments (1-2 mg) were excised from 12-to 15-cm-long leaves, taking care to remove major veins. The explants were then placed in plastic Petri plates (35 x 10 mm) containing 2.0 ml of test medium. Tissues were photographed and harvested after 3 weeks. For organogenesis assays, leaf explants (9 mm2) were placed into plastic Petri dishes (60 x 15 mm) containing 5 ml of LS medium lacking NAA but supplemented with ZR or DCG. These were incubated at 25°C with a light/dark cycle of 16:8 hr and monitored regularly. Final scoring was tabulated after 6 weeks.For histological examination, tissues were fixed in 3.5% glutaraldehyde in 0.05 M phosphate buffer (pH 6.8) and embedded in glycol methacrylate (JB-4, Polyscience, Warrington, P...

Morphogenetic Rescue of Rhizobium meliloti Nodulation Mutants by trans-Zeatin Secretion

“…In this sense, the cytokinin and Nod factor signal transduction pathways may "intersect" (i.e., share a common step), and the influence of nitrogen and developmental position must be exerted downstream of this common step. Potential target mechanisms include protein kinases, phosphatases, and cyclins homologous to yeast and mammalian cell cycle-related genes (see Jacobs, 1992), endogenous calcium flux regulators (Saunders andHepler, 1982, 1983), dehydroconiferyl glucosides (Binns et al, 1987), and novel cell cycle regulatory compounds such as trigonelline (Evans et al, 1987). Yet a third model is that NodRmlV (Ac,S) induces nodule morphogenesis by a mechanism involving a novel unknown pathway and that cytokinins indirectly affect one of the steps of this novel pathway.…”

Variation in Lignin Content and Composition (Mechanisms of Control and Implications for the Genetic Improvement of Plants)

“…It is also necessary to define the extent to which lignin can be modified in content and quality without compromising important aspects of development, physiology, and stress compensation. Other phenolic compounds that are derived from the same biosynthetic route a s lignins play important roles in plant development (Binns et al, 1987;Lynn et al, 1987). Therefore alterations in this pathway may have pleiotropic effects like those observed with PAL sense suppression in transgenic tobacco.…”

A coumaroyl-ester-3-hydroxylase Insertion Mutant Reveals the Existence of Nonredundant meta-Hydroxylation Pathways and Essential Roles for Phenolic Precursors in Cell Expansion and Plant Growth

“…Phenolic compounds have been reported to play a role in cell division and expansion, either directly or as components of a cytokinin-dependent signaling cascade . A major role in this respect was attributed to dehydrodiconiferyl alcohol glucoside (DCG), which was shown to directly activate cell growth and division in tobacco (Nicotiana tabacum) pith, leaves, or cell cultures (Binns et al, 1987;Tamagnone et al, 1998). DCG, as lignin G monomers, is expected to directly derive from CYP98A3 products (Fig.…”

“…The pathways inactivated are shown in gray. The monolignol DCG has been described as a growth regulator (Binns et al, 1987;Tamagnone et al, 1998). Aromatic amino acids, including Phe, are synthesized in the plastids via the so-called shikimate pathway (Herrmann and Weaver, 1999).…”