FIGURE 2.

Cartoon summarizing Ca ²⁺–pectate-dependent growth control in the alga Chara corallina. (A) In this species, cellulose microfibrils are parallel and oriented transversely to the elongation axis. Ca²⁺ (red ovals)-pectate complexes are load-bearing. One stretched and two relaxed Ca²⁺–pectate complexes are shown. Newly deposited pectate will chelate Ca²⁺ preferentially out of the stretched complexes, thus leading to wall relaxation and turgor-driven mechanical deformation until other complexes become load-bearing. (B) Cartoon of an “eggbox” consisting of two antiparallel poly-galacturonic acid chains complexed by Ca²⁺.