Abstract
We previously reported that cucumber (Cucumis sativus) classIII chitinases can regulate the yield threshold tension (y) of cowpea (Vigna unguiculata) hypocotyl cell walls. In this study, we determined the pH dependency of the mechanical properties of cucumber cell walls. Both glycerol treated and freeze-thawed hypocotyl segments exhibited the decrease of y and the increase of wall extensibility (φ) by acidification of the wall. Constant load experiments revealed that only the load over the y could promote the elongation. Heat treatment (boiled, 15sec) impaired the pH-dependent adjustment of the y but did not influence on the φ. The lost y-adjusting function was almost completely recovered by the reconstitution with cell wall proteins.
These results indicate that the wall extension is probably regulated by the both y and φ. However, the growth-limiting parameter that seemed to be controlled by the wall associated proteins should not be the φ but y.
