ABSCISIC-ACID AND PHOTOSYNTHESIS IN ISOLATED LEAF MESOPHYLL CELL

Abscisic acid (AbA) treatments of concentrations of up to 135 .mu.M did not inhibit photosynthesis in enzymatically isolated leaf mesophyll cells of Phaseolus vulgaris, Nicotiana tabacum and Lycopersicum esculentum over periods of up to 5 h. Thin slices of leaves preincubated in hypertonic solutions identical to those used to isolate cells synthesized AbA rapidly; accumulation of AbA in the cells was low due to extensive release of the newly synthesized AbA into the medium. The levels of endogenously made AbA in leaf cells of P. vulgaris rose from a low of 0.27 .mu.M to a high of 6.74 .mu.M during 2 h preincubation. Exogenously applied AbA can be taken up by the cells as demonstrated using [14C]AbA. AbA applied at concentrations 19 times higher than endogenous levels does not change the rate of photosynthesis.