Xyloglucans were isolated by sequential extraction of the cell walls of pea (Pisum sativum L. cv. Alaska) with a xyloglucan-specific endoglucanase and KOH. The xyloglucan content and xyloglucan-oligosaccharide composition were determined for fractions obtained from the elongating and non-elongating segments of pea stems grown in the light and in darkness. The results were consistent with the hypothesis that regulated growth of the cell wall depends on xyloglucan metabolism. Furthermore, the characterization of xyloglucan extracted from leaves of light-grown pea plants indicates that xyloglucan metabolism is tissue specific. Changes in xyloglucan subunit structure observed in elongating stems are consistent with the in muro realization of a metabolic pathway that was previously proposed solely on the basis of the in vitro activities of plant glycosyl hydrolases.
α-1,4-Oligogalacturonides with degrees of polymerization (DPs) ranging from 6 to 18 or 2 to 8 were added to tobacco leaf explants and root formation was evaluated after 15 days of incubation. Auxin-induced formation of roots was inhibited by oligogalacturonides with DPs 6–18 but not by the oligogalacturonides with DPs 2–8. The inhibition of root formation by the larger oligogalacturonides was prevented by increasing the amount of auxin present in the medium. Oligogalacturonides (DPs 6–18) also inhibited root formation when added to tobacco thin cell-layer (TCL) explants in a medium that is known to induce the formation of roots. The addition of size-homogeneous oligogalacturonides, to either tobacco leaf explants or TCLs, established that oligogalacturonides with DPs between 10 and 14 were most active in inhibiting the formation of roots. These data suggest that oligogalacturonides of the same size as those known to elicit plant defense responses, and to affect floral development and membrane functions, also inhibit the induction of root morphogenesis in tobacco
A gene (EGLI) encoding an endo-p-l,4-~-glucanase (EGase, EC 3.2.1.4) of pea (Pisum sativum) has been cloned and characterized. EGL 1 encodes a 486-amino acid polypeptide, including a 24-mer putative signal peptide. The mature protein has a calculated molecular m a s of 51.3 kD and an isoelectric point of 9.1. This pea ECase shares significant similarity with ECases from other plant species, but it appears to be distinct from the EGases associated with abscission and fruit ripening. Although EGL7 transcripts are detected in all parts of pea plants, they are relatively abundant in flowers and young pods undergoing rapid growth and most abundant in elongating epicotyls of etiolated seedlings. When epicotyl segments (6 mm long, 4 mm from the apical hook) are incubated in a 5 p~ solution of the synthetic auxin analog 2,4-dichlorophenoxyacetic acid, the concentration of EGL7 mRNA increases about 1 O-fold when the segments elongate most rapidly.
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