No abstract

No abstract

SummaryThe metabolism by suspension-cultured tobacco cells of oligogalacturonides was investigated. Dodecagalacturonic acid-

The biological activity of reducing-end-modified oligogalacturonides was quantified in four tobacco (Nicotiana tabacum) tissue culture bioassays. The derivatives used were oligogalacturonides with the C-1 of their reducing end (a) covalently linked to a biotin hydrazide, (b) covalently linked to tyramine, (c) chemically reduced to a primary alcohol, or (d) enzymatically oxidized to a carboxylic acid. These derivatives were tested for their ability to (a) alter morphogenesis of N. tabacum cv Samsun thin cell-layer explants, (b) elicit extracellular alkalinization by suspension-cultured cv Samsun cells, (c) elicit extracellular alkalinization by suspensioncultured N. tabacum cv Xanthi cells, and (d) elicit H 2 O 2 accumulation in the cv Xanthi cells. In all four bioassays, each of the derivatives had reduced biological activity compared with the corresponding underivatized oligogalacturonides, demonstrating that the reducing end is a key element for the recognition of oligogalacturonides in these systems. However, the degree of reduction in biological activity depends on the tissue culture system used and on the nature of the specific reducing-end modification. These results suggest that oligogalacturonides are perceived differently in each tissue culture system.Carbohydrates that act as signal molecules in plants (oligosaccharins) have been isolated from plant and fungal cell wall polysaccharides, from the cell walls of bacterial symbionts of plants, and from fungal glycopeptides (for review, see Ryan and Farmer, 1991;Darvill et al., 1992;Cô té and Hahn, 1994). We are interested in determining the mechanism by which one type of the plant cell wallderived oligosaccharins, the oligogalacturonides, elicit biological responses in plants.The biological effects elicited in plants by oligosaccharins are diverse (for review, see Ryan and Farmer, 1991;Darvill et al., 1992;Cô té and Hahn, 1994) but can generally be placed in two groups: delayed responses and rapid responses. Delayed responses are usually observed hours or days after oligosaccharin treatment and are often directly involved in adaptation to environmental conditions, whereas rapid responses generally occur at the plant cell surface and are observed within minutes after addition of oligosaccharins. The delayed responses elicited by oligogalacturonides can be broadly divided into those in which defense responses are induced and those in which growth and development are modified. The defense-related responses, depending on the plant species, include phytoalexin accumulation (Hahn et al., 1981), lignification of cell walls (Robertsen, 1986), and proteinase inhibitor accumulation (Bishop et al., 1984). The responses involving growth and development include induction of ethylene in tomato fruit (Brecht and Huber, 1988), inhibition of auxin-induced pea stem elongation (Branca et al., 1988), and regulation of tobacco (Nicotiana tabacum) TCL explant morphogenesis (Eberhard et al., 1989). The rapid responses induced by oligogalacturonides include enhanced protein phosp...

No abstract

No abstract

Oligogalacturonic acid (OGA) affects plant growth and development in an antagonistic manner to that of the auxin indole-3-acetic acid (IAA), the mechanism by which remains to be determined. This study describes the relationship between IAA and OGA activity in intact cucumber (Cucumis sativus) seedlings. Both OGA and IAA induced rapid and transient extracellular alkalinization; however, the characteristics of the OGA and IAA responses differed in their kinetics, magnitude, calcium dependence, and region of the root in which they induced their maximal response. IAA (1 m) induced a saturating alkalinization response of approximately 0.2 pH unit and a rapid reduction (approximately 80%) in root growth that only partially recovered over 20 h. OGAs, specifically those with a degree of polymerization of 10 to 13, induced a maximal alkalinization response of 0.48 pH unit, but OGA treatment did not alter root growth. Saturating concentrations of OGA did not block IAA-induced alkalinization or the initial IAA-induced inhibition of root growth but allowed IAA-treated roots to recover their initial growth rate within 270 min. IAA-induced alkalinization occurs primarily in the growing apical region of the root, whereas OGA induced its maximal response in the basal region of the root. This study demonstrates that OGA and IAA act by distinct mechanisms and that OGA does not simply act by inhibition of IAA action. These results also suggest that IAA-induced extracellular alkalinization is not sufficient to account for the mechanism by which IAA inhibits root growth.Oligogalacturonic acid (134-linked ␣-d-oligo-Gal-UA; OGA) is a biologically active oligosaccharide produced by hydrolysis of de-esterified pectin (polyGalUA). OGA has been studied extensively in plant tissue cultures and dissected plants and has been shown to alter growth and development, including inhibition of auxin-induced elongation and ethylene accumulation in pea (Pisum sativum) stems (Branca et al., 1988) and regulation of organogenesis in tobacco (Nicotiana tabacum) explants (Eberhard et al., 1989;Bellincampi et al., 1993), to elicit a number of defense responses, including accumulation of phytoalexins (Hahn et al., 1981) and proteinase inhibitors (Bishop et al., 1984), and to induce rapid responses at the plasma membrane, such as trans-membrane ion flux (Mathieu et al., 1991) and phosphorylation of plasma membrane proteins (Farmer et al., 1991). Most of these responses are elicited maximally by OGAs with a degree of polymerization (DP) of 10 to 14 in the concentration range of 10 Ϫ6 to 10 Ϫ9 m; OGAs outside this size range are typically at least 10-fold less active. This indicates that OGA acts by a specific highaffinity mechanism in a manner similar to the classic plant hormones. However, it has not been demonstrated that biologically active OGA of the appropriates size and concentration are present in plant tissues.It has recently been shown that wounding and the wound-induced signal, systemin, induce the systemic accumulation of polygalacturonase, which m...

The cytokinins benzylaminopurine, kinetin and isopentenyladenine induce photomorphogenesis in dark-grown gametophytes of the fern Ceratopteris richardii. At sub-nanomolar concentrations each altered the rate and pattern of cell division, elongation and differentiation, mimicking aspects of the light-mediated transition from filamentous to prothallial growth. Untreated dark-grown gametophytes grow as narrow, elongate, asexual filaments with an apical meristem. Cytokinin treatments as low as 10(-12) M reduced the length-to-width ratio through decreased cell elongation, increased periclinal cell division and induced the formation of rhizoid initials in the cells immediately below the apical meristem. Higher concentrations (10(-9)-10(-8) M) induced conversion of the meristem from apical to notch morphology. Cytokinins induced both red- and blue-light-mediated photomorphogenic events, suggesting stimulation of both phytochrome and cryptochrome signaling; however, cytokinin treatment only partially substituted for light in that it did not induce hermaphroditic sexual development or spore germination in the dark. Additionally, cytokinins did not increase chlorophyll synthesis in dark-grown gametophytes, which unlike angiosperms are able to produce mature chloroplasts in the dark. Cytokinin treatment had only slight effects on light-grown gametophytes. These results suggest evolutionary conservation between angiosperms and pteridophytes in the role of cytokinins in regulating photomorphogenesis.