The influence of drought stress on the development of maize seedlings and the dynamics of activity of enzymes in their tissues

Investigated the dynamics of the activity of glucose-6-phosphate dehydrogenase (G6PDG, EC 1.1.1.49) and malate dehydrogenase decarboxylating (MDHD, malic- enzyme, EC 1.1.1.40) enzymes that play an important role in the formation of NADPH pool of cells, under drought stress. It has been established that the development of maize seedlings is accompanied by a weakening of the activity of the G6PDH and a noticeable increase in the activity of MDHD. A drought stress causes activation of both of enzymes, in particular G6PGH, both in the root and in the stem tissues of the seedlings. An increase in the concentration is accompanied by the induction of MDHD activity to a greater extent, than that of G6PDH. Key words: maize seedling, drought stress, glucose-6-phosphate dehidrogenase, malate dehydrogenase decarboxylating

Application of micronutrients and insurance herbicides in corn growing technologies

Studies have found that growing maize for grain on light low-humus soils of the left-Bank Polesie of Ukraine wih the use of microelements on the increased background of mineral nutrition provided the best indicators of economic efficiency. It is recommended to sow early- maturing (80 %) and mid-maturing- (20 %) hybrids with FAO 150-250 on the background of mineral fertilizers N120P60K60, applying herbicide MaizeTer power in the 3-5-leaf phase of a crop and fulfil out-off-root spraying crops with complex preparations “Rosaliq Aquatic” or ” Germ corn “. Key words: maize, insured herbicides, micro-fertilizers, early-maturing, mid-maturing, hybrids.

A new meiotic abnormality in Zea mays: multiple spindles associated with abnormal cytokinesis in both divisions

We report here a new meiotic abnormality recorded in one plant of an inbred line of Zea mays. After an apparently normal prophase I, chromosomes did not congregate in a single metaphase plate. Bivalents remained scattered in the cytoplasm, giving rise to several spindles. Despite the occurrence of multiple spindles, meiosis I proceeded normally, forming a varied number of nuclei at telophase I. The presence of one or a few chromosomes in the nucleus was enough to induce local cytokinesis, which was evident from metaphase I. Each cell resulting from meiosis I expressed its own program and progressed through the cell cycle. Therefore, failure of chromosome congregation on a single plate also occurred at meiosis II, where further irregular cytokinesis was observed. As a consequence of the two abnormalities, polyads occurred, resulting in pollen grains of different sizes and in sterility at a frequency of up to 93.5%.Key words: maize, meiosis, cytokinesis, multiple spindles, polyads.

Maize kernel moisture, carbon and nitrogen concentrations from silking to physiological maturity

Grain characteristics prior to physiological maturity are important for silage harvest and for grain harvest when grain fill has been prematurely terminated by factors such as hail or early frost. The objective of this study was to investigate changes in grain moisture, C and N concentrations associated with the progression of milk line from silking to physiological maturity for hybrids with maturity ratings between 76 and 95 Minnesota relative maturity days. A field experiment with a total of 15 hybrids was carried out on a well-drained sandy loam soil at Ottawa, Canada, from 1995 to 1997, inclusive. A large number of uniform plants with the same phenology were marked in each plot near tasseling, and ears were sampled from these plants at weekly intervals from R1 to final harvest. It was noted that 50% milk line was associated with a range of kernel moisture concentrations: in 1995, a relatively warm year, kernel moisture was 389 g kg–1 when 50% milk line occurred; in 1996, a relatively cool year, kernel moisture was over 420 g kg–1 at 50% milk line. During the course of grain fill, C concentrations remained relatively constant whereas N concentrations were dramatically reduced from as high as 50 g kg–1 to approximately 15 g kg–1. Maximum dry matter accumulation was reached at 325 g kg–1 moisture. In general, later-maturing hybrids appeared to have longer duration from silking to 50% milk line; however, they took less time to reach physiological maturity (faster grain fill and dry down). Although benchmarks of 50% milk line and 0% milk line are commonly used for silage and grain production, there is a range of grain moisture-milk line relationships among genotypes and under different environmental conditions during grain fill. Key words: Maize, milk line progression, kernel moisture, carbon and nitrogen

Distribution of carbohydrate during grainfill in Leafy and normal maize hybrids

The Leafy (Lfy) genotype in corn has extra leaves above the ear in comparison to normal non-leafy genotypes and has been shown to increase yields in some geographical areas. In this study, carbohydrate distribution in three Lfy hybrids (two of which were "staygreen") and a normal check (Pioneer 3790) were analyzed in a short-season area (2800 Crop Heat Units, suitable for 85 day Relative Maturity hybrids). Total sugar and starch were determined at all aboveground levels of leaf and stem on 1 August 1990 and this distribution was used to calculate total canopy carbohydrates in two subsequent years from samplings of leaf and stem at only three or four canopy levels bracketing the ear level. Husk, cob and kernel components were also analyzed at three sampling times during grainfill. Major differences in the 2 yr were observed, but in general there was approximately twice the carbohydrate in the canopy at and above the ear in the Lfy genotypes compared to the check. There was also more carbohydrate in the husk and cob in the Lfy lines, but substantially less carbohydrate below the ear in these lines. Rates of grainfill were generally higher in the Lfy hybrids, but the rate of Lfy hybrid A, the early senescent hybrid, was slower in the cooler growing season. Despite the greater amount of carbohydrate in the Lfy hybrids in comparison to the traditional check, their grain yields were not greatly increased, indicating that the kernel component provided a weak sink. This characteristic is probably associated with the long season and tropical origin of the Lfy germplasm. Key words: Maize, grainfill, leafy, carbohydrate distribution, phenology, sink size

Uptake of fertilizer sulfur by maize from soils of low sulfur status as affected by vesicular-arbuscular mycorrhizae

Vesicular-arbuscular mycorrhizae (VAM) generally enhances uptake and translocation of P and encourages plant growth and development in nutrient-deficient soils. Contradictory reports about the role of VAM in S uptake and translocation may result from insufficient consideration of soil S status. In this study, using soils of low S status, VAM inoculation increased the content of radioactively labelled S (35S) in shoots of maize plants. Key words: Maize plant, S-uptake, Vesicular-arbuscular mycorrhizae fungi

Maize simple repetitive DNA sequences: abundance and allele variation

Microsatellites or simple sequence repeats, first demonstrated in human and other mammalian genomes, are being identified in many plant species. A database survey of 576 maize sequences from the GenBank and EMBL databases was made to determine the abundance of maize microsatellites. Two hundred potential microsatellites were identified. The relative abundance of the different repetitive motifs varied considerably and all possible dinucleotide and trinucleotide motif types were found. The three most abundant classes of microsatellites identified in this search were (AG/CT)n, (CCT/GGA)n, and (CCG/GGC)n repeats. Allelic variation was surveyed with 9 maize inbred lines representing diverse pedigrees. Amplification of DNA from these lines and analysis using high resolution agarose gels showed that 69 of the 200 potential microsatellites were polymorphic and yielded 2–4 alleles. A more complete screen of these loci against a wider array of maize germplasm using denaturing sequencing gels is now being conducted to more thoroughly evaluate these loci. Key words : maize, microsatellites, simple sequence repeat, molecular marker.

Cloning maize telomeres by complementation in Saccharomyces cerevisiae

Maize telomeric restriction fragments were cloned by virtue of their ability to function as telomeres on a linear plasmid in Saccharomyces cerevisiae. Nine maize telomeric YAC transformants (MTYs) were selected by hybridization to the Arabidopsis telomere repeat (CCCTAAA) from a pool of 1537 primary transformants. Bal31 digestion of MTY3 and MTY9 DNA indicated that the telomere hybridizing tracts are located at the terminus of the linear chromosome and therefore function as telomeres in yeast. Subclones generated for pMTY7 (pMTY7SC1) and pMTY9 (pMTY9ER) hybridized to Bal31 sensitive restriction fragments in maize DNA, indicating that maize telomeric restriction fragments had been cloned. Both pMTY7SC and pMTY9ER detected telomeric RFLPs, allowing the endpoints of seven chromosome arms to be determined. Additionally, pMTY7ER mapped to the centromeric regions of chromosomes 2 and 3, suggesting a relationship between centromeric and telomeric sequences. DNA sequencing of pMTY7SC and pMTY9ER revealed that both subclones contained CA-rich regions with sporadic occurrences of the telomere repeat and its degenerate repeats. Key words : maize, telomere, RFLP, telomeric.

Characterization of four dispersed repetitive DNA sequences from Zea mays and their use in constructing contiguous DNA fragments using YAC clones

We have isolated four repetitive DNA fragments from maize DNA. Only one of these sequences showed homology to sequences within the EMBL database, despite each having an estimated copy number of between 3 × 104 and 5 × 104 per haploid genome. Hybridization of the four repeats to maize mitotic chromosomes showed that the sequences are evenly dispersed throughout most, but not all, of the maize genome, whereas hybridization to yeast colonies containing random maize DNA fragments inserted into yeast artificial chromosomes (YACs) indicated that there was considerable clustering of the repeats at a local level. We have exploited the distribution of the repeats to produce repetitive sequence fingerprints of individual YAC clones. These fingerprints not only provide information about the occurrence and organization of the repetitive sequences within the maize genome, but they can also be used to determine the organization of overlapping maize YAC clones within a contiguous fragment (contigs). Key words : maize, repetitive DNA, YACs.

Plant population and hybrid considerations for dryland corn production on drought-susceptible soils

Selection of a target population for dryland corn (Zea mays) production on drought-susceptible soils is a difficult decision, as a stand appropriate for drought conditions may not fully utilize the environment during a non-stress year. One possible management strategy is to use a low seeding rate and hybrids with ear characteristics that promote yield stability over a range of environments and plant populations. To evaluate this strategy, a 2-yr field study was conducted on a Rumford loamy sand. The performance of four hybrids — 1) full season, flexible ear; 2) short season, flexible ear; 3) full season, prolific; and 4) short season, prolific — was evaluated at four populations — 29 600, 39 500, 49 400, and 59 300 plants ha−1 — in two different growing seasons. Seasonal precipitation in 1988 was 14 cm below the average of 50 cm; 1989 seasonal precipitation was 37 cm above average. Average grain yields were 40% lower in 1988 than in 1989, and the yield loss was due primarily to a decrease in ear size. All hybrids demonstrated the ability to compensate for changes in population in 1988. Averaged across years, highest yields were produced with the two highest populations. The full-season, prolific hybrid was the most productive at every population. Key words: Maize, Zea mays, genotype × environment interactions, plant population, prolificacy, ear size