GROWTH OF POLLEN TUBES OF PAPAVER RHOEAS IS REGULATED BY A SLOW-MOVING CALCIUM WAVE PROPAGATED BY INOSITOL 1,4,5-TRISPHOSPHATE

A signaling role for cytosolic free Ca2+ ([Ca2+](i)) in regulating Pap aver rhoeas pollen tube growth during the self-incompatibility respons e has been demonstrated previously, In this article, we investigate th e involvement of the phosphoinositide signal transduction pathway in C a2+-mediated pollen tube inhibition, We demonstrate that P. rhoeas pol len tubes have a Ca2+-dependent polyphosphoinositide-specific phosphol ipase C activity that is inhibited by neomycin, [Ca2+](i) imaging af t er photolysis of caged inositol (1,4,5)-trisphosphate (Ins[1,4,5]P-3) in pollen tubes demonstrated that Ins(1,4,5)P-3 could induce Ca2+ rele ase, which was inhibited by heparin and neomycin, Mastoparan, which st imulated Ins(1,4,5)P-3 production, also induced a rapid increase in Ca 2+, which was inhibited by neomycin, These data provide direct evidenc e for the involvement of a functional phosphoinositide signal-transduc ing system in the regulation of pollen tube growth. We suggest that th e observed Ca2+ increases are mediated, at least in part, by Ins(1,4,5 )P-3-induced Ca2+ release. Furthermore, we provide data suggesting tha t Ca2+ waves, which have not previously been reported in plant cells, can be induced in pollen tubes.