Carbohydrate deposition and partitioning in elongating leaves of wheat under saline soil conditions

The objective of this study was to quantitatively evaluate the effect of sa linity on the spatial distribution of glucose, fructose, sucrose, fructan a nd total C contents, as well as on their net deposition rates in the elonga tion and maturation zones of leaf 4 of the main stem of spring wheat (Triti cum aestivum L.) during its linear growth phase. Plants were grown in growt h chambers in 1.5-L pots containing an illitic-chloritic silty loam treated with or without 120 mM NaCl. 3 d after emergence of leaf 4, sampling start ed at 3 and 13 h into the 16 h photoperiod. The distribution of carbohydrat es along the leaf axis showed distinct patterns that were altered by salini ty and time in the photoperiod. Glucose and fructose concentrations were lo w at the base of the elongation zone and increased sharply up to the end of the leaf elongation zone in the two treatments. In contrast, sucrose conce ntration in the elongation zone was high at the leaf base and decreased sha rply with distance from the base up to the end of the leaf elongation zone in both treatments. The main effect of salinity on the water-soluble carboh ydrates (WSC) was that it significantly increased sucrose concentration in the elongation zone throughout the day and accumulation in the photosynthet ically active zone during the photoperiod. Net deposition rates of sucrose and fructan in the elongation zone were enhanced by 120 mM NaCl. Salinity d id not affect the sucrose import rate (g C kg(-1) H2O h(-1)) in the sink (t he elongation and secondary cell wall deposition zone). However, the partit ioning of imported sucrose to WSC and structural C varied with salinity. In the basal part of the leaf (0-15 mm above the leaf base), net deposition o f sucrose in the control treatment accounted for 7% of imported sucrose, co mpared with 17% at 120 mM NaCl. Eighty-seven percent of imported sucrose in the control treatment and 75% in the salinized treatment was used for synt hesis of structural biomass (estimated as total C minus WSC-C). Conversely, in the 15-30 mm zone (i.e. in the distal part of the elongation zone and t he secondary cell wall deposition zone), a greater fraction of imported suc rose was partitioned to synthesis of structural C under saline conditions. There was no significant effect of salinity on sucrose use in the region 30 -60 mm.