INVESTIGATIONS OF PIGMENT GRANULE TRANSPORT-SYSTEMS IN GONODACTYLUS-OERSTEDII (CRUSTACEA, HOPLOCARIDA, STOMATOPODA) .2. EFFECTS OF LOW-TEMPERATURE ON PIGMENT GRANULE POSITION AND MICROTUBULE POPULATIONS IN RETINULAR CELLS

Pigment granules within retinular cells of the stomatopod crustacean, Gonodactylus oerstedii, undergo rapid, radial migrations in response t o changes in ambient lighting. Light stimulates centripetal migration of pigment granules towards the microvillar rhabdomeres where they abs orb and scatter incoming light, analogous in function to the closure o f a pupil. In the dark, pigment granules disperse centrifugally away f rom rhabdoms, thereby opening the pupil. Two populations of microtubul es in retinular cells of G. oerstedii are appropriately oriented for p articipation in pigment granule migration. We investigated the possibi lity that microtubules are involved in pigment granule migration by su bjecting animals to low temperature (which can depolymerize some micro tubules) and determining the effects of low temperature on pigment gra nule position and microtubule density within retinular cells. When tem perature was decreased, pigment granules in previously dark-adapted ey es aggregated around rhabdoms, in the light-adapted configuration. Low ering the temperature also decreased the density of palisade microtubu les, which extend longitudinally in retinular cells along the subrhabd omeric palisade vacuole. These changes reversed when temperature incre ased. We present a model for pigment granule migration based on the id ea that the position of pigment granules in retinular cells is depende nt upon the presence of intact palisade microtubules.