Remobilization of Nitrogen and Carbohydrate from Stems of Bread Wheat in Response to Heat Stress during Grain Filling

Abstract

When wheat (Triticum aestivum L.) is grown under heatstress conditions during grain filling, preanthesis stored total non-structural carbohydrates (TNC) and nitrogen (N) could serve as alternative source of assimilates. This study was performed to evaluate wheat genotypes for their ability to accumulate and remobilize TNC and N stored in their stem to support grain filling under heat stress. Eighteen genotypes were used for N remobilization study while nine of them were used for TNC remobilization study. They were grown in pots and placed in a vinyl house with the maximum temperature kept below 30°C. Five days after anthesis (5DAA), half of the pots were taken to phytotrons where temperature was gradually increased and the maximum was set at 38°C. Grain yield and grain weight decreased by about 35 % under heat stress. Significant differences were found among genotypes in percentage reduction in grain yield, grain weight, grain filling duration and harvest index because of heat stress. The N and TNC concentrations of the stem at 5DAA were significantly different among genotypes. Heat stress significantly reduced the N remobilization efficiency of most of genotypes. However, heat stress significantly increased TNC remobilization efficiency and significant variation were observed among genotypes. N remobilization efficiency across treatments significantly correlated with grain yield, grain weight, harvest index and grain filling duration. TNC at 5DAA negatively correlated with N at 5DAA and harvest index, but the TNC remobilization efficiency under heat stress positively correlated with mainstem grain yield, grain weight and harvest index. The rate of chlorophyll loss from flag leaf positively correlated with N and TNC remobilization efficiencies under heat stress suggesting a link between leaf senescence and remobilization efficiency.The results indicate that heat stress negatively affected grain yield, its components and N remobilization while it increased TNC remobilization because of the increasing demand for resources.

Plant N Fluxes and Modulation by Nitrogen, Heat and Water Stresses: A Review Based on Comparison of Legumes and Non Legume Plants

“…However, for a moderate temperature range, this hypothesis was not verified in pea or soybean as the rate of apparent N remobilization was similar among temperatures (Grangirard et al, 2001;Larmure et al, 2005). Moreover, more recent results in wheat suggest on the contrary that heat stress reduced N remobilization (Ercoli et al, 2010;Tahir & Nakata 2005); in agreement with the results of 15 N assimilate labeling experiments in rice, suggesting that high temperatures induce a decrease in N transport from shoots to the ears via the phloem (Ito et al, 2009). Further investigations may improve the understanding of the effect of high temperature on N assimilate partitioning and their physiological basis.…”

“…Increased remobilisation efficiency of reserves from leaves, stems or other plant parts has been suggested as potential strategy to improve grain filling and yield in wheat under heat stress (Wahid et al, 2007). This suggestion is mostly based on C assimilate movements : heat stress in wheat significantly increased total non-structural carbohydrates (TNC) remobilization efficiency with significant differences observed among genotypes (Blum et al, 1994 ;Tahir & Nakata, 2005). Some results have suggested that the acceleration of senescence by temperature was due to an increase in N assimilate remobilization to seeds (Spiertz, 1977 in wheat).…”

Quality of winter wheat in relation to heat and drought shock after anthesis

“…By contrast, in the present experiments heat stress led to a 31% yield loss when applied 12 days after heading. High temperature during the grain-filling period had a negative effect on the grain yield, which could be attributed to the drastic reduction in the kernel weight (Gibson & Paulsen 1999;Tahir & Nakata 2005). The yield reduction observed when developing cereal grains were exposed to high temperature could also be attributed to the lower final starch content.…”

Stable carbon isotope analysis as a direct means of inferring crop water status and water management practices

“…in spring rainfall) may remain available to plants when grain filling commences. Second, reserve carbohydrates, that can make up as much as 40 ‰ of grain mass (Gebbing and Schnyder 1999;Tahir and Nakata 2005; Takahashi, Tsuchihashi and Nakaseko 1993), form over several weeks prior to grain filling and so reflect water availability earlier in the growth period. Archaeological interpretations of Δ¹³C values, therefore, should not assume that they represent the grain filling period only.…”