The composition of apoplast fluid recovered from intact developing tomato fruit

A pressure dehydration technique for recovering sap from the apoplast of the pericarp tissue of developing tomato fruit has recently been developed. Samples of this sap from two cultivars have now been analysed for sugars, amino acids, organic acids, ammonia and inorganic ions. The measured solutes accounted for 92 and 97% of the osmolality of the apoplast sap from the two cultivars. The osmotic potential of the apoplast samples was similar in the two cultivars, and the apoplast samples were distinctly different in osmolality and in composition from samples of the bulk sap obtained after thawing frozen tissue. Hexoses and inorganic compounds, principally potassium and chloride, accounted for 75% of the osmotic potential of the apoplast samples. There is little prior information on the composition of the apoplast in fruit. The impact of this new knowledge is discussed in relation to the uptake of solutes into fruit cells, the partitioning of solutes between apoplast and symplast, and the ionic environment of the cell wall and wall-bound enzymes.