Microtubule motor proteins and the organization of the pollen tube cytoplasm

Molecular motors are molecules that drive a wide range of activities (for e xample, organelle movement, chromosome segregation, and flagellar movement) in cells. Thus, they play essential roles in diverse cellular functions. U nderstanding their structures, mechanisms of action and different roles is therefore of great practical importance. The role of microtubules during po llen tube growth is presently not identified, nor are basic properties. We do not know, for example, where microtubules are organized, the extent of m icrotubule dynamics, and the polarity of microtubules in the pollen tube. R oles of microtubules and related motors in organelle trafficking are not cl ear. Regardless of scarce information, microtubule-based motors of both the kinesin and dynein families have been identified in the pollen tube. Most of these microtubule motors have also been found in association with membra ne-bounded organelles, which suggest that these proteins could translocate organelles or vesicles along microtubules, The biochemical features of thes e proteins are typical of the motor protein class. Immunofluorescence micro scopy of pollen tubes probed with antibodies that cross-react with microtub ule motors indicate that these proteins are localized in different regions of the pollen tuber therefore, they could have different roles. Although a number of microtubule motors have been identified in the pollen tube, the r ole of these proteins during pollen tube germination and growth or organell e movement is not yet recognized, as tube elongation and organelle movement in the pollen tube depend mostly on actin filaments. In the effort to unde rstand the specific role that microtubules and related motors have in the p ollen tube, it is therefore necessary to identify the molecular machinery t hat interacts with microtubules. Furthermore, it is crucial to clearly esta blish the types of interaction between organelles and microtubules. This re view summarizes the current state of the art on microtubule motors in the p ollen tube, mainly surrounding the putative roles of microtubule motors in organelle movement and cytoplasmic organization. Some hypotheses and specul ations are also presented.