ADAPTATION TO POLYETHYLENE STRESS MAINTAINS TOTIPOTENCY OF CELL LINES OF ORYZA SATIVA L. CV. SWAT-1 FOR A LONGER PERIOD

Abstract

Cell suspension cultures of rice cv Swat-1 were adapted to osmotic (polyethylene glycol, PEG) and ionic (lithium chloride) stresses to find components of stress having greater inhibitory effects on regeneration frequency of cells. In early stage suspension were in cell aggregates or in micro calli form and regeneration frequency of one month old suspensions was about 74%. One month old cultures were incrementally adapted to 20% PEG and 20 mM LiCl. After 50 repeated batch cultures the size of cell aggregates of control and LiCl adapted cell lines turned into fine suspensions, while the suspension of PEG adapted lines remained in small clusters with whitish pale coloration. The relative growth rates of adapted and unadapted cell lines were similar at respective media but the regeneration potential of unadapted and LiCl adapted lines dropped to 30% and 10 %, respectively. In contrast regeneration frequency of PEG adapted line increased to 80% with early recovery of plantlets. These data reveal that regeneration capacity of cell cultures decreases with age of cultures and with ionic stress, while osmotic stress not only maintain but enhance regeneration frequency of cell cultures over a longer time.