Stem Reserve Mobilisation Supports Wheat-Grain Filling Under Heat Stress

Abstract

The grain filling of wheat (Triticum aestivum L.) is seriously impaired by heat stress due to reductions in current leaf and ear photosynthesis at high temperatures. An alternative source of carbon for grain filling is stored stem reserves. Two spring wheat cultivars (V5 and V2183) of very similar phenology and plant stature, which had previously been found to differ in grain shrivelling under drought and heat stress conditions in the field, were used to evaluate the hypothesis that the mobilisation of stored stem reserves into the growing grain is an important source of carbon for supporting grain filling under heat stress. In two experiments in Israel (1990 and 1991), the rates of stem dry matter (DM) and stem total non-structural carbohydrates (TNC) loss, grain growth and leaf senescence were monitored under optimal (control) and high (stressed) temperatures in the glasshouse (1990) and the growth chamber (1991). Cultivar V5 always sustained a smaller reduction in grain dry weight under heat stress, than V2183. Irrespective of temperature, V5 had a higher stem DM and TNC content at the onset of grain filling, greater depletion of stem dry matter (or TNC) during grain filling, and longer duration of grain filling, than V2183. During grain filling V5 generally exported about two to three times more DM from the stems than V2183, under both non-stressed and stressed conditions. On the other hand, V5 was more heat-susceptible than V2183 in terms of leaf longevity, in vivo chlorophyll stability and grain abortion under heat stress. In a third experiment (1992) five cultivars (including V5 and V2183) were subjected to chemical desiccation (0.3% potassium iodide) of the canopy in the field in order to destroy the photosynthetic source ofthe plant after anthesis. The same cultivars were subjected to heat stress (35/25�C) or non-stressed (25/15�C) conditions after anthesis in the growth chamber. It was found that grain dry weight reduction by chemical desiccation was highly correlated with grain dry weight reduction by heat stress (r2 = 0.89). Therefore, the superior capacity of V5 for grain filling from mobilised stem reserves is a consti- tutive trait which supports grain filling under heat stress which can be tested for by chemical desiccation of plants under non-stressed conditions.

Responses of Three Wheat Genotypes to High Soil Temperature during Grain Filling

“…Shoot senescence is induced by the loss of chlorophyll, which in turn, reduces the grain-fi lling duration. The rate of reduction in both chlorophyll and grain-fi lling duration was higher in Imam and Fang than the heatsensitive Siete Cerros supporting reports of Blum et al (1994) and Fokar et al (1998).…”

“…High soil and high air/soil temperatures result in imbalance between photosynthesis and respiration and decrease carbohydrate availability, which could contribute to the decrease in shoot and root growth (Xu and Huang, 2000b). On the other hand, the failure in utilizing more soluble carbohydrates by Siete Cerros at 38/38 °C might be one of the reasons for the sensitivity to whole-plant high-temperature treatment (Blum et al, 1994).…”

“…The rapid loss of chlorophyll content and the great decrease in grain-fi lling duration promoted the remobilization effi ciency of WSC from the stem in both Imam and Fang (Blum et al, 1994;Fokar et al, 1998). On the other hand, only the high soil (26/38°C) temperature treatment slightly increased the WSC remobilization effi ciency in Siete Cerros.…”

Truncation of grain filling in wheat (Triticum aestivum) triggered by brief heat stress during early grain filling: association with senescence responses and reductions in stem reserves

“…Stem reserves (WSCs) also contribute to grain filling in wheat (Blum et al 1994), and their relative contribution to final grain mass can increase under stress conditions such as drought that reduce photosynthetic capacity (e.g. rising from 13% under irrigation to 27% under drought) (Bidinger et al 1977).…”

Effects of Drought and Shading on Non-structural Carbohydrate Stored in the Stem of Potato (Solanum tuberosumL.)

“…Under normal conditions, the amount of stem NSC is more than 40% of the stem DW, and the contribution of these stored reserves is 5−20% of the grain yield (Shakiba et al, 1996). Under drought or heat stress after anthesis, however, photosynthetic activity is depressed and grain fi lling is more dependent on mobilized stem reserves and it contributed to 22−60% of the grain yield (Davidson and Chevalier, 1992;Blum et al, 1994). In this study, loss of NSC in the stem in drought and shading treatments contributed to about 37% and 54% of increased tuber DW, respectively, which was 2.5 and 3.7 times, respectively, higher than in the control (Table 3).…”