Wall biosynthesis and wall polysaccharide composition in pollen tubes of Malus domestica growing at low rate after monensin treatment

Tube growth rate, wall biosynthesis and wall polysaccharide composition were studied in pollen of Malus domestica Borkh. germinating in the presence of monensin, a monovalent ionophore which is known to cause swelling of Golgi apparatus cisternae in plant and animal cells. 125 nM monensin decreased tube growth rate, inhibiting tube elongation by 50% within 2 h germination. Wall biosynthesis was reduced in the treated tubes: label incorporation decreased to 61% (acid-soluble fraction) and 54% (alkali-soluble fraction) with respect to controls. Protein content of the wall ionic fraction was also decreased in the presence of the ionophore. Moreover, the sugar composition of acid or alkali-soluble wall fractions was shown to be partially affected by monensin; this could result from a decrease in number and reactivity of the large vesicles derived from dictyosomes, which was previously observed in treated apple pollen tubes.