Abstract
Summary Polyethylene glycol (PEG) is often used as an osmoticum to induce water stress in plant tissues. Callus cultures of Pinus taeda L. and Sorghum bicolor (L.) Moench were supported on Murashige and Skoog (MS) liquid medium amended with PEG for a 7- to 8-week period. During this culture period, callus PEG content was quantified by a spectrophotometric procedure using trichloroacetic acid. After 1 week, PEG absorption reached 35 % of the callus dry mass; callus PEG content remained in the 35 to 50 % range for the duration of the culture period. Compartmentation of PEG within calli was determined by measuring PEG efflux into MS medium over time, disrupting the plasmalemma using either elevated temperature (54°C) or freezing treatment, and measuring the residual PEG content of callus homogenates. Both elevated and freezing treatments accelerated PEG efflux from calli. The additional PEG released by freezing and elevated temperatures accounted for 2 to 11 % of the total callus PEG content; this was assumed to have been released from the symplast or the plasmalemma. The other 89 to 98 % of the total callus PEG was considered apoplastic.
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