Solute Accumulation in Leaves of a Fragaria chiloensis and a F. virginiana Selection Responds to Water Deficit Stress

The effect of water deficit stress on the foliar solute concentration of Fragaria chiloensis Duch. cv. `BSP14' (FC) and F. virginiana Duch. cv. `NCC85-13V (FV) was studied to assess solute contribution to osmotic adjustment. Plants were stressed for three wilting cycles by withholding water until incipient wilting, followed by a recovery period. The length of each cycle for the FC selection was J-fold that for the FV selection. Wilting of FC plants occurred at a leaf water potential (ψ) 1.1 MPa lower, a leaf osmotic potential (ψ π ) 0.45 MPa lower, and a relative water content (RWC) 14% lower than for FV plants. Leaf ψ π at full turgor (ψ π 100 ) was reduced in the FC selection from 0.11 to 0.27 MPa but not in the FV selection. Water deficit stress increased the total foliar soluble carbohydrate (TSC) concentration from 1.4- to 2.4-fold for FC during each cycle. Glucose and fructose were the primary carbohydrates, comprising >50% of the TSC. Leaf starch concentration decreased appreciably to 4% to 6% of nonstressed (control) levels for FC during each cycle. In the FC selection, the TSC: starch ratio was considerably higher, 30- to 50-fold, in stressed than in control plants. No consistent changes in solute or starch concentration were observed in the FV selection. Total free amino acid concentration increased from 1.8- to 2.7-fold in FC plants in response to stress. Proline accumulation was not detected. The solutes, TSC and amino acids, accounted for <40% of the measured ψ π 100 in control plants, although the average contribution of these solutes to the measured leaf ψ π 100 increased to 40% or more in stressed FC plants. However, the stress-induced increase in solute concentration fully accounted for the reduction of leaf ψ π 100 in the FC selection plants.