Photosynthesis,Carbohydrate Storage and Remobilization During Grain Filling as Affected by Sulphur Application in Winter Wheat

Photosynthesis and carbohydrate storage and remobilization was investigated during grain filling of winter wheat (Triticumaestivum L., cv. Lumai 22) in sulphur application experiments where the available sulphur (S) content in the soil of 0-20 cmsoil layer was 5.84 mg kg-1. Two levels of S were applied as S0 (0 kg S ha-1) and S1 (67.5 kg S ha-1). The results showed thatnet photosynthetic rate of flag leaf of S1 treatment was significantly higher than S0 treatment, and it increased graduallyfrom anthesis to 35 DAA. Sucrose-phosphate synthase (SPS) activity and sucrose content of S1 treatment were significantlyhigher than those of S0 treatment. The contents of total soluble sugar, sucrose, fructose, glucose, DP3 and DP ≥ 4fructan in stem and sheath of S1 treatment were significantly higher than those of S0 treatment also. The amount of totalsoluble sugar and fructans remobilization from stem and sheath and the starch accumulating rate in grain of S1 treatmentwas significantly higher than those of S0 treatment. It is suggested that sulphur application increase photosynthateremobilization from stem and sheath to grain at later filling stage.

The role of soluble sugars during drought in tropical tree seedlings with contrasting tolerances

Aims Non-structural carbohydrates(NSCs)are plant storage compounds used for metabolism,transport,osmoregulation and regrowth following the loss of plant tissue.Even in conditions suitable for optimal growth,plants continue to store NSCs.This storage may be due to passive accumulation from sink-inhibited growth or active reserves that come at the expense of growth.The former pathway implies that NSCs may be a by-product of sink limitation,while the latter suggests a functional role of NSCs for use during poor conditions.Methods Using 13C pulse labelling,we traced the source of soluble sugars in stem and root organs during drought and everwet conditions for seedlings of two tropical tree species that differ in drought tolerance to estimate the relative allocation of NSCs stored prior to drought versus NSCs assimilated during drought.We monitored growth,stomatal conductance,stem water potential and NSC storage to assess a broad carbon response to drought.Important Findings We found that the drought-sensitive species had reduced growth,conserved NSC concentrations in leaf,stem and root organs and had a larger proportion of soluble sugars in stem and root organs that originated from pre-drought storage relative to seedlings in control conditions.In contrast,the drought-tolerant species maintained growth and stem and root NSC concentrations but had reduced leaf NSCs concentrations with a larger proportion of stem and root soluble sugars originated from freshly assimilated photosynthates relative to control seedlings.These results suggest the drought-sensitive species passively accumulated NSCs during water deficit due to growth inhibition,while the drought-tolerant species actively responded to water deficit by allocating NSCs to stem and root organs.These strategies seem correlated with baseline maximum growth rates,which supports previous research suggesting a trade-off between growth and drought tolerance while providing new evidence for the importance of plasticity in NSC allocation during drought.