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

Abstract

The objective of this study was to quantitatively evaluate the effect of salinity on the spatial distributionof glucose, fructose, sucrose, fructan and total C contents, as well as on their net deposition rates in the elongation and maturation zones of leaf 4 of the main stem of spring wheat (Triticum aestivum L.) during its linear growth phase. Plants were grown in growth 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 started at 3 and 13 h into the 16 h photoperiod. The distribution of carbohydrates along the leaf axis showed distinct patterns that were altered by salinity and time in the photoperiod. Glucose and fructose concentrations were low 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 concentration in the elongation zone was high at the leaf base and decreased sharply 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 carbohydrates (WSC) was that it significantly increased sucrose concentration in the elongation zone throughout the day and accumulation in the photo-synthetically active zone during the photoperiod. Net deposition rates of sucrose and fructan in the elongation zone were enhanced by 120 mM NaCl. Salinity did not affect the sucrose import rate (g C kg ^-1 H₂O h ^-1 ) in the sink (the elongation and secondary cell wall deposition zone). However, the partitioning 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 of sucrose in the control treatment accounted for 7% of imported sucrose, compared 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 synthesis 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 the secondary cell wall deposition zone), a greater fraction of imported sucrose 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.