THE ROLE OF THE CYTOSKELETON AND DICTYOSOME ACTIVITY IN THE PULSATORYGROWTH OF NICOTIANA-TABACUM AND PETUNIA-HYBRIDA POLLEN TUBES

Pollen tubes of Nicotiana tabacum and Petunia hybrida show pulsatory g rowth. Phases of slow growth lasting minutes are interrupted by pulse- like elongations lasting 10-20 seconds involving an increase of growth rate by up to 24-fold. Inhibition of dictyosome activity with brefeld in A or monensin did not result in an inhibition of pulsatory growth b ut eventually stopped pollen tube elongation. In contrast to this the inhibition of the cytoskeletal elements with cytochalasin D and colchi cine caused the pollen tubes to abandon the pulse-like elongations. It was concluded that the activity of the dictyosomes does not have a co ntrolling function in the mechanism of pulsatory growth, even though i t is necessary for pollen tube elongation, since cell wall material is provided by secretory vesicles deriving from the Golgi apparatus. In contrast the cytoskeletal elements, actin and microtubules, seem to pl ay an important regulatory role in the pulse-like elongations. In addi tion, it was observed that during the experiments several pollen tubes burst upon the completion of a pulse-like expansion, indicating on th e one hand that the internal turgor is the driving force of the pulse- like expansions. On the other hand, the bursting shows that the pollen tube cell wall is rather weak at the end of a pulse, indicating that at this point of time it is either thinner or less stable than during the slow growth phase or at the beginning of a pulse.