MORPHOLOGY OF THE PERENNIAL RYEGRASS (LOLIUM-PERENNE POACEAE) COLEORHIZA AND EMERGING RADICLE WITH CONTINUOUS OR DISCONTINUOUS HYDRATION

This study was conducted using scanning electron microscopy to charact erize morphological changes in the maturing perennial ryegrass (Lolium perenne L.) coleorhiza and emerging radicle during continuous hydrati on or hydration interrupted by dehydration. With continuous hydration, coleorhizae emerged and cell expansion led to a progressive increase in tissue size. Coleorhiza cells developed extensions like epidermal r oot hairs. Although coleorhiza cells appeared undamaged by radicle eme rgence,they began deteriorating when the radicle had reached a length of approximately 2 mm. In response to dehydration, coleorhiza cells sh rank but did not rupture. If dehydration was initiated during an early stage of coleorhiza development, greater tissue shrinkage occurred at -150 MPa than at -4 MPa; otherwise, coleorhizae showed no differentia l response due to dehydration water potential. Upon rehydration, coleo rhizae dehydrated at -4 MPa regained cell turgor within 24 hr, while c oleorhizae dehydrated at -150 MPa did not. Loss of the coleorhiza (due to desiccation) did not preclude radicle emergence, which occurred up on rehydration. Radicles up to 2 mm in length were more tolerant of de hydration than were coleorhizae. These results suggest that the coleor hiza may be an expendable tissue during germination, as its likely pro tective and absorptive roles are lost following a single harsh dehydra tion event.