The export of amino acid in the phloem is altered in wheat plants lacking the short arm of chromosome 7B

Abstract

Grain protein content is one of the major determinants of the baking and nutritional quality of wheat. It has previously been reported that the ditelosomic line of wheat (Triticum aestivum L.) CSDT7BL, where the short arm of chromosome 7B is missing, shows a lower grain protein concentration than the normal line, but a similar grain yield. In the present paper the growth and nitrogen (N) metabolism of wheat plants cv. Chinese Spring (CS) and its ditelosomic line CSDT7BL were compared. When plants were grown to maturity in pots with different N supplements, the wild-type line showed a higher grain protein concentration and a lower straw N concentration than the ditelosomic line at every N level analysed, suggesting a deficiency in the N remobilization capacity. When 15-d-old plants were grown in a growth cabinet in pots with sand, and supplied with nutrient solutions of different nitrate concentrations, the ditelosomic line showed no differences in N uptake per unit of root dry weight, nitrate reductase activity, nitrate, total N concentration or free amino acid concentration. However, the ditelosomic line showed a decreased capacity to export amino acids in the phloem under high N, independently of the N source. This deficiency was also observed under dark-induced senescence. The diminished export of amino acids to the phloem was principally caused by a decrease in the export of Glu, Asp, and Gln. It is suggested that the decrease in grain protein concentration in the ditelosomic line is a consequence of defective export in the phloem of these amino acids.

Nitrogen uptake and remobilization in tetraploid 'Langdon' durum wheat and a recombinant substitution line with the high grain protein gene Gpc-B1

“…The leaf proteins, mostly Rubisco, are hydrolysed to amino acids during senescence by proteolytic enzymes, and are then exported to the phloem (Ho¨rtensteiner and Feller 2002). It has been shown that GPC is related to the soluble amino acids in the flag leaf (Barneix and Guitman 1993) and to the amount of amino acids exported to the phloem (Caputo et al 2001). The present experiments showed for the first time that at anthesis the flag leaves of the RSL no.…”

Leaf senescence and nutrient remobilisation in barley and wheat

“…The major phloem‐exported amino acid in barley and wheat is glutamate, followed by varying levels of aspartate, glutamine, threonine and serine (Winter et al. 1992; Caputo et al. 2001; Kichey et al.…”

“…Free amino acids are exported via the phloem to the developing grain, either directly or indirectly via the root or the glumes (Simpson et al 1983). The major phloem-exported amino acid in barley and wheat is glutamate, followed by varying levels of aspartate, glutamine, threonine and serine (Winter et al 1992;Caputo et al 2001;Kichey et al 2006). Thus, glutamate, originating in 2-oxoglutarate, plays a central role in the remobilisation of nitrogen (Forde & Lea 2007).…”

Physiology and biochemistry of source-regulated protein accumulation in the wheat grain

“…A gene for high GPC has been proposed in chromosome 5D (Turner et al, 2004), and a putative gene affecting GPC has been located in the short arm of chromosome 7B of wheat cv. Chinese Spring (Barneix et al, 1998;Caputo et al, 2001). Recombinant substitution lines derived from a substitution line of chromosome 6B from Triticum turgidum L. var.…”

“…The final GPC has been correlated with the free amino acid concentrations in the flag leaf during grain filling (Millet et al, 1992;Barneix and Guitman, 1993), and it has been shown that the ditelosomic line of wheat Chinese Spring CSDT7BL that is deficient in the export of several amino acids to the phloem also shows a decreased GPC compared to the normal line (Caputo et al, 2001). It has also been shown that the high GPC lines of T. turgidum L. var.…”