Pectic Polysaccharides in the Growth of Plant Cells: Molecular Structural Factors and Their Role in the Germination of White Mustard

Cytochemical localization of beta-(1----4)-D-glucans in plant and fungal cells using an exoglucanase-gold complex

An exoglucanase (exo-1,4-beta-glucanase), purified from a cellulase produced by the fungus Trichoderma harzianum, was tagged with colloidal gold particles and applied on plant and fungal tissue sections for localizing beta-(1----4)-linked glucans. The present review reports the conditions required for the preparation of this enzyme-gold complex and for its application in transmission electron microscopy. The exoglucanase-gold complex was found to be a powerful probe for labelling accurately cellulosic glucans in tissues processed under conventional procedures. This approach represents a promising alternative to previous methods such as autoradiography or subtractive cytochemistry in the study of wall topochemistry. It will undoubtedly acquire increasing applicability and relevance in various fields of plant science including physiology and pathology.

Characterization of long-term extension of isolated cell walls from growing cucumber hypocotyls

Walls from frozen-thawed cucumber (Cucumis sativus L.) hypocotyls extend for many hours when placed in tension under acidic conditions. This study examined whether such "creep" is a purely physical process dependent on wall viscoelasticity alone or whether enzymatic activities are needed to maintain wall extension. Chemical denaturants inhibited wall creep, some acting reversibly and others irreversibly. Brief (15 s) boiling in water irreversibly inhibited creep, as did pre-incubation with proteases. Creep exhibited a high Q10 (3.8) between 20° and 30°C, with slow inactivation at higher temperatures, whereas the viscous flow of pectin solutions exhibited a much lower Q10 (1.35). On the basis of its temperature sensitivity, involvement of pectic gel-sol transitions was judged to be of little importance in creep. Pre-incubation of walls in neutral pH irreversibly inactivated their ability to creep, with a half-time of about 40 min. At 1 mM, Cu(2+), Hg(2+) and Al(3+) were strongly inhibitory whereas most other cations, including Ca(2+), had little effect. Sulfhydryl-reducing agents strongly stimulated creep, apparently by stabilizing wall enzyme(s). The physical effects of these treatments on polymer interactions were examined by Instron and stress-relaxation analyses. Some treatments, such as pH and Cu(2+), had significant effects on wall viscoelasticity, but others had little or no apparent effect, thus implicating an enzymatic creep mechanism. The results indicate that creep depends on relatively rugged enzymes that are firmly attached to or entangled in the wall. The sensitivity of creep to SH-reducing agents indicates that thiol reduction of wall enzymes might provide a control mechanism for endogenous cell growth.