The water-soluble carbohydrate (WSC) that accumulates in the stems of wheat during growth can be an important contributor to grain filling, particularly under conditions when assimilation is limited, such as during end-of-season drought. WSC concentration was measured at anthesis across a diverse set of wheat genotypes over multiple environments. Environmental differences in WSC concentration were large (means for the set ranging between 108 and 203 mg g–1 dry weight), and there were significant and repeatable differences in WSC accumulation among genotypes (means ranging from 112 to 213 mg g–1 dry weight averaged across environments), associated with large broad-sense heritability (H = 0.90 ± 0.12). These results suggest that breeding for high WSC should be possible in wheat. The composition of the WSC, examined in selected genotypes, indicated that the variation in total WSC was attributed mainly to variation in the fructan component, with the other major soluble carbohydrates, sucrose and hexose, varying less. The degree of polymerisation (DP) of fructo-oligosaccharides was up to ~13 in samples where higher levels of WSC were accumulated, owing either to genotype or environment, but the higher DP components (DP > 6) were decreased in samples of lower total WSC. The results are consistent with fructan biosynthesis occurring via a sequential mechanism that is dependent on the availability of sucrose, and differences in WSC contents of genotypes are unlikely to be due to major mechanistic differences.

With the aim of improving the nutritive value of an important grain legume crop, a chimeric gene specifying seed-specific expression of a sulfur-rich, sunf lower seed albumin was stably transformed into narrow-leafed lupin (Lupinus angustifolius L.). Sunf lower seed albumin accounted for 5% of extractable seed protein in a line containing a single tandem insertion of the transferred DNA. The transgenic seeds contained less sulfate and more total amino acid sulfur than the nontransgenic parent line. This was associated with a 94% increase in methionine content and a 12% reduction in cysteine content. There was no statistically significant change in other amino acids or in total nitrogen or total sulfur contents of the seeds. In feeding trials with rats, the transgenic seeds gave statistically significant increases in live weight gain, true protein digestibility, biological value, and net protein utilization, compared with wild-type seeds. These findings demonstrate the feasibility of using genetic engineering to improve the nutritive value of grain crops.

No abstract

Several environmental factors including drought and disease can reduce leaf area and photosynthesis during grain-filling to decrease grain yield and kernel weight of cereal crops. Water-soluble carbohydrates (WSC) accumulated around anthesis can be mobilised to assist in filling of developing grains when post-anthesis assimilation is low. Cultivar differences support opportunities to select for high WSC but little is known of the extent or nature of genetic control for this trait in wheat. Three wheat mapping populations (Cranbrook/Halberd, Sunco/Tasman, and CD87/Katepwa) were phenotyped for WSC and other agronomic traits across multiple environments. The range for WSC concentration (WSC-C) was large among progeny contributing to moderate-to-high narrow-sense heritabilities within environments (h2 = 0.51–0.77). Modest genotype × environment interaction reduced the correlation of genotype means across environments (rp = 0.37–0.78, P < 0.01) to reduce heritability on a line-mean (h2 = 0.55–0.87) basis. Transgressive segregation was large and genetic control complex, with 7–16 QTLs being identified for WSC-C in each population. Heritability was smaller (h2 = 0.32–0.54) for WSC mass per unit area (WSC-A), reflecting large genotype × environment interaction and residual variance with estimating anthesis biomass. Fewer significant QTLs (4–8) were identified for this trait in each population, while sizes of individual genetic effects varied between populations but were repeatable across environments. Several genomic regions were common across populations including those associated with plant height (e.g. Rht-B1) and/or anthesis date (e.g. Ppd1). Genotypes with high WSC-C were commonly shorter, flowered earlier, and produced significantly (P < 0.01) fewer tillers than those of low WSC-C. This resulted in similar yields, lower final biomass, and fewer grains per m2, but greater dry weight partitioning to grain, kernel weight, and less grain screenings in high compared with low WSC-C genotypes. By contrast, lines high for WSC-A produced more fertile tillers associated with similar or greater anthesis and maturity biomass, grain number, and yield, yet similar kernel weight or size compared with genotypes with low WSC-A. The data support an important role for WSC-A in assuring stable yield and grain size. However, the small effects of many independent WSC QTLs may limit their direct use for marker-aided selection in breeding programs. We suggest using molecular markers to enrich populations for favourable height and anthesis date alleles before the more costly phenotypic selection among partially inbred families for greater WSC-A.

Bruchid larvae cause major losses of grain legume crops throughout the world. Some bruchid species, such as the cowpea weevil and the azuki bean weevil, are pests that damage stored seeds. Others, such as the pea weevil (Bruchus pisorum), attack the crop growing i n the field. We transferred the cDNA encoding the a-amylase inhibitor (a-AI) found in the seeds of the common bean (Phaseolus vulgaris) into pea (Pisum sativum) using Agrobacferium-mediated transformation. Expression was driven by the promoter of phytohemagglutinin, another bean seed protein. The a-amylase inhibitor gene was stably expressed in the transgenic pea seeds at least to the T, seed generation, and a-AI accumulated i n the seeds up to 3% of soluble protein. This level is somewhat higher than that normally found in beans, which contain 1 to 2 % a-AI. In the 1 , seed generation the development of pea weevil larvae was blocked at an early stage. Seed damage was minimal and seed yield was not significantly reduced in the transgenic plants. These results confirm the feasibility of protecting other grain legumes such as lentils, mungbean, groundnuts, and chickpeas against a variety of bruchids using the same approach. Although a-AI also inhibits human a-amylase, cooked peas should not have a negative impact on human energy metabolism.The common bean (Phaseolus vulgaris L.) contains a family of structurally related seed proteins: PHA-E and -L, arcelin, and a-AI. PHA-E and PHA-L are strong agglutinins, i.e. classical lectins that bind carbohydrate, and arcelin, which is found only in certain wild accessions of the common bean, may be a weak agglutinin (Hartweck et al., 1991). The bean a-AI has 65 to 70% amino acid sequence identity with the other three but lacks at least one of the conserved residues needed for lectin activity. Its biochemical mode of action is to form a one-to-one complex with certain amylases (for reviews, see Chrispeels and Raikhel, 1991;Rouge et al., 1993).

No abstract

The postruminal supply of the sulfur-containing amino acids, methionine and cysteine, has been reported to be a major limitation to wool growth in sheep. We aim to improve the protein quality of forage for ruminants by introducing into alfalfa chimeric genes encoding a ruminally stable, sulfur amino acid-rich protein from sunflower seeds. Four gene constructs were transferred to Australian commercial cultivars of alfalfa using Agrobacterium tumefaciens-mediated transformation and selection with phosphinothricin (PPT). Modification of the sunflower seed albumin protein-coding region by addition of the coding information for an endoplasmic reticulum (ER) retention signal was found to greatly increase the level to which the sulfur amino acid-rich protein accumulated in the leaves of transgenic alfalfa plants. The Cauliflower Mosaic Virus (CaMV) 35S promoter and two light-regulated plant gene promoter regions were compared for their ability to direct high-level expression of the introduced genes in alfalfa leaves. The highest expression of sunflower seed albumin was found in transformants bearing a gene incorporating the promoter from the Arabidopsis thaliana ats1A gene, which encodes the ribulose bisphosphate carboxylase small subunit. The highest level of sunflower seed albumin found in transgenic alfalfa leaves was estimated to constitute .1% of soluble leaf protein. This level of accumulation of the foreign protein would be predicted to supply an extra 40 mg of sulfur amino acids daily to sheep fed the modified forage. Published studies in which wool growth rates were significantly increased employed supplementation of approximately 1 to 2 g of sulfur amino acids daily.

SummarySulfur amino acid composition is an important determinant of seed protein quality. A chimeric gene encoding sun¯ower seed albumin (SSA), one of the most sulfur-rich seed storage proteins identi®ed so far, was introduced into rice (Oryza sativa) in order to modify cysteine and methionine content of the seed. Analysis of a transgenic line expressing SSA at approximately 7% of total seed protein revealed that the mature grain showed little change in the total sulfur amino acid content compared to the parental genotype. This result indicated that the transgenic rice grain was unable to respond to the added demand for cysteine and methionine imposed by the production of SSA. Analysis of the protein composition of the transgenic grain showed changes in the relative levels of the major seed storage proteins, as well as some non-storage proteins, compared to non-transgenic controls. Changes observed at the protein level were concomitant with differences in mRNA accumulation but not always with the level of transcription. The limited sulfur reserves appeared to be re-allocated from endogenous proteins to the new sulfur sink in the transgenic grain. We hypothesize that this response is mediated by a signal transduction pathway that normally modulates seed storage protein composition in response to environmental¯uctuations in sulfur availability, via both transcriptional and post-transcriptional control of gene expression.