Isolation of a heat-stable maize endosperm ADP-glucose pyrophosphorylase variant

Heat stress reduces maize yield and several lines of evidence suggest that the heat lability of maize endosperm ADP-glucose pyrophosphorylase (AGPase) contributes to this yield loss. AGPase catalyzes a rate-limiting step in starch synthesis. Herein, we present a novel maize endosperm AGPase small subunit variant, termed BT2-TI that harbors a single amino acid change of residue 462 from threonine to isoleucine. The mutant was isolated by random mutagenesis and heterologous expression in a bacterial system. BT2-TI exhibits enhanced heat stability compared to wildtype maize endosperm AGPase.The TI mutation was placed into another heat-stable small subunit variant, MP. MP is composed of sequences from the maize endosperm and the potato tuber small subunit. The MP-TI small subunit variant exhibited greater heat stability than did MP. Characterization of heat stability as well as kinetic and allosteric properties suggests that MP-TI may lead to increased starch yield when expressed in monocot endosperms.     

Effects of land preparation and maize cultivar on efficiency of N-fertilizer applied at different times and by different methods in maize—mungbean association using15N

Summary A field experiment was conducted using¹⁵N-labelled urea on a Reddish Brown Lateritic (Peleustult) soil. Growing two crops on flat land and on soil ridges of 15 cm height produced similar comparative effects from fertilizer on maize. However, fertilizer applied by broadcasting on maize with a 50 cm effective band followed by incorporating was more useful to mungbean than that applied by banding below the cereal seed rows when crops were grown on flat land. The reverse was observed when crops were grown on ridges. It was deduced that the maize cultivar was not likely to affect comparative efficiencies of fertilizer. For fertilizer application at sowing, broadcasting in 50 cm maize effective band followed by incorporating was slightly superior to banding below maize seed rows. Side-dressing of fertilizer to maize at 4 weeks after sowing was superior to application at sowing. Evenly-split application, at sowing and at 4 weeks after sowing, was either only slightly superior or comparable to non-split application by banding below maize seed rows at sowing, depending on placement method of the first application. Soil moisture status as a possible factor rendering discrepancy in the comparative efficiencies obtained by different authors is discussed.     

Environmental assessment of maize production alternatives: Traditional,intensive and GMO-based cropping patterns

The evolution of maize production patterns in Argentina is evaluated over the last 25 years to compare costs, benefits, environmental performance and sustainability as well as to identify the main driving sources and improvement potential. Results from Argentina cropping systems are compared to other systems worldwide in order to put the Argentina results in a broader context. The study focuses on three farming categories: (1) traditional, low-intensity systems, (2) conventional, high-intensity systems, and (3) GMO-based cropping systems. Low input intensity systems include traditional cropping patterns with seed selection by farmers and conventional hybrid seed coupled to plowing and crop-animal rotation techniques; high input intensity systems use conventional hybrid seeds and recommended chemicals, irrigation and machinery with important soil erosion consequences; and GMO-based cropping systems use herbicide resistant transgenic hybrids, pesticides, higher fertilizer rates, and no-till practices. In each of the three cases, input flows are compared to the achieved yield (in mass and income terms) to better understand relative efficiencies and options for improvement. The study of GMO systems required a preliminary investigation of GMO seed production by seed companies, where a large investment in terms of prior knowledge and high-tech laboratory research is required. The assessments used the Emergy Accounting (EMA) approach. EMA includes material, energy, labor, money, and knowledge flows into the assessment and expands its focus over larger time and spatial scales than conventional economic and cumulative energy demand methods. Emergy-based environmental indicators of grain production for high-intensity hybrid and GMO systems both show a lower performance than low-intensity, traditional patterns in terms of resource return, renewability and sustainability. The fraction of renewability in low-intensity systems is between 28% and 63%, while it is between 8% and 26% for high-intensity hybrid and GMO systems. Calculated indicators also show that GMO-based maize production patterns do not guarantee the expected improvement over conventional high-intensity cropping systems or low-intensity systems in terms of performance and sustainability. Strong reliance on nonrenewable resources and technology, as well as role of direct and indirect labor costs are important factors in determining long-term sustainability and environmental stability of maize production systems.     

长江经济带林地和其他生物质碳储量及碳汇量研究

以全国林业应对气候变化碳汇计量监测体系建设结果数据为基础，应用森林碳库专项调查建立的碳计量模型和参数，结合历次森林资源清查成果等数据，估算了2020年长江经济带林地和其他生物质碳储量和碳汇量。研究表明：（1）2020年长江经济带林地碳储量24543.58 Tg C （其中森林植被碳储量为4372.85Tg C），散生木和四旁树等其他生物质碳储量329.59 Tg C。2020年长江经济带林地碳汇量81.81 Tg C/a （300.26Tg CO₂/a）、散生木和四旁树等其他生物质碳汇量6.60 Tg C/a （24.21 Tg CO₂/a）。无论是林地和其他生物质碳储量、碳汇量、还是森林植被碳储量，乔木林地所占比例最大（69%-85%）；长江经济带11个省市中，云南省最大，上海市最小；林地碳储量中土壤有机质碳库贡献最大（81.46%），林地碳汇量中生物量碳库贡献最大（90.99%）；林地碳汇量中"一直为林地的土地"产生碳汇量贡献最大（71.74%），其中一直为乔木林的土地产生的碳汇量占69.89%；（2）阐述了长江防护林工程、天然林资源保护工程、珠江防护林工程和沿海防护林工程4大重点生态工程对长江经济带碳储量和碳汇量的贡献，长江防护林工程贡献率最大（81%-83%），其次是天然林资源保护工程（32%-38%），珠江防护林工程和沿海防护林工程影响较小。分析了人工造林、中幼林抚育、次生林和低效林改造、退化林修复等生态保护修复措施对长江经济带碳储量和碳汇量的贡献，并提出了碳中和愿景下森林固碳增汇的有效途径。     

Molecular evolution of human T-cell leukemia virus

Summary In light of previous data, which suggested thatAc-like sequences might have undergone a significant radiation in the recent past, I examined the copy number ofAc-like sequences in representatives of all theZea taxa, both maize and teosinte. The maize and teosinte samples contained approximately equal numbers ofAc-like sequences. FewAc-like sequences were in unmethylated regions of DNA. Unmethylated elements were distributed randomly among both maize and teosinte lines. The appearance in a line of a discrete band resulting from digestion with one methylation-sensitive restriction enzyme was correlated with the appearance of discrete bands with other methylation-sensitive bands. This suggests that individualAc-like elements are occasionally demethylated in many sites. No unmethylated element having restriction fragments of the lengths predicted from the publishedAc sequence was seen in the approximately 326 elements examined.     

A maize bacterial artificial chromosome (BAC) library from the European flint inbred line F2

We report here the construction and characterisation of a BAC library from the maize flint inbred line F2, widely used in European maize breeding programs. The library contains 86,858 clones with an average insert size of approximately 90 kb, giving approximately 3.2-times genome coverage. High-efficiency BAC cloning was achieved through the use of a single size selection for the high-molecular-weight genomic DNA, and co-transformation of the ligation with yeast tRNA to optimise transformation efficiency. Characterisation of the library showed that less than 0.5% of the clones contained no inserts, while 5.52% of clones consisted of chloroplast DNA. The library was gridded onto 29 nylon filters in a double-spotted 8 × 8 array, and screened by hybridisation with a number of single-copy and gene-family probes. A 3-dimensional DNA pooling scheme was used to allow rapid PCR screening of the library based on primer pairs from simple sequence repeat (SSR) and expressed sequence tag (EST) markers. Positive clones were obtained in all hybridisation and PCR screens carried out so far. Six BAC clones, which hybridised to a portion of the cloned Rp1-D rust resistance gene, were further characterised and found to form contigs covering most of this complex resistance locus. Received: 30 August 2000 / Accepted: 6 December 2000     

Nutritional Evaluation of Genetically Modified Maize Corn Performed on Rats

The aim of this study was to determine the composition and nutritional value of conventional and transgenic, so-called Roundup Ready (RR) maize with an introduced gene of glyphosate resistance. Crude protein, crude fibre, ash, fat, starch, sugar, amino acids, fatty acid and macroelement levels were determined by chemical analysis. In both maize lines a low level of Ca (0.15g.kg m 1 DM) and of the essential amino acids lysine and tryptophan (2.6 and 1.7g.kg^{m 1} DM, respectively) were observed. In the biological experiment carried out on rats the tested maize lines were the only dietary sources of nitrogen, thus, the experimental diets contained 9% CP in dietary dry matter. In the feeding experiment no significant differences in the protein efficiency ratio (PER) were observed between groups receiving conventional or transgenic maize (1.51 and 1.41, respectively). Also almost equal results were obtained in the balance experiments. Both maize lines revealed a high nitrogen digestibility (84.9 and 84.5%, respectively) and the net protein utilization amounted to 63.5 and 63.2%, respectively. From these results can be concluded that regarding nutrient composition and utilisation, genetically modified (RR) maize is equivalent to isogenic maize.