Localization of the genes controlling B chromosome transmission rate in maize (Zea mays ssp. mays, Poaceae)

In previous papers we found that the frequency of B chromosomes in native races of maize varies considerably in different populations. Moreover, we found genotypes that control high and low transmission rates (TR) of B chromosomes in the Pisingallo race. In the present work crosses were made to determine whether the genes controlling B-TR are located on the normal chromosome set (As) or on the B chromosomes (Bs). We made female f.0B × male m.2B crosses between and within high (H) and low (L) B-TR groups. The Bs were transmitted on the male side in all cases. The mean B-TR from the progeny of f.0B (H) × m.2B (H) and f.0B (H) × m.2B (L) crosses was significantly higher than that from f.0B (L) × m.2B (L) and f.0B (L) × m.2B (H) crosses. The results show that the B-TR of the crosses corresponds to the H or L B-TR of the 0B female parents irrespective of the Bs of the male parent. This indicates that B-TR is genetically controlled by the 0B female parent and that these genes are located on the A chromosomes.     

Genome size and numerical polymorphism for the B chromosome in races of maize (Zea mays ssp. mays, Poaceae)

Twenty-one native populations (1120 individuals) of maize from Northern Argentina were studied. These populations, which belong to 13 native races, were cultivated at different altitudes (80-3620 m). Nineteen of the populations analyzed showed B chromosome (Bs) numerical polymorphism. The frequency of individuals with Bs varied from 0 to 94%. The number of Bs per plant varied from 0 to 8 Bs, with the predominant doses being 0, 1, 2, and 3. Those populations with varying number of Bs showed a positive and statistically significant correlation of mean number of Bs with altitude. The DNA content, in plants without Bs (A-DNA)(2n = 20), of 17 populations of the 21 studied was determined. A 36% variation (5.0-6.8 pg) in A-DNA content was found. A significant negative correlation between A-DNA content and altitude of cultivation and between A-DNA content and mean number of Bs was found. This indicates that there is a close interrelationship between the DNA content of A chromosomes and doses of Bs. These results suggest that there is a maximum limit to the mass of nuclear DNA so that Bs are tolerated as long as this maximum limit is not exceeded.     

Genetics of resistance to the pink stem borer (Sesamia nonagrioides) in maize (Zea mays)

Our knowledge of the genetics of resistance to the pink stem borer ( Sesamia nonagrioides ) in maize ( Zea mays ) is restricted to a few crosses among maize inbreds. The objectives of this study were to enlarge our understanding of the genetics of traits related to damage by pink stem borer and yield under infestation and to use generation means analyses to compare per se and testcross performance for detecting epistatic effects. All generations, either per se or crossed to testers, were evaluated in a 10 × 10 triple lattice design under artificial infestation with S. nonagrioides in 2005 and 2006. Most traits fit an additive–dominance model; but evidence for epistasis for resistance and yield under infestation was shown. Epistasis, in general, did not appear to play an important role in the inheritance of yield under pink stem borer infestation. However, the epistasis contribution to maize yield performance could be important in some outstanding crosses such as EP42 × A637. Testcross generation means revealed epistatic effects undetected by the generation means analysis, but neither method was able to eliminate dominance effects that could prevail over epistatic effects.     

Fine scale genetic structure in the wild ancestor of maize (Zea mays ssp. parviglumis)

Analysis of fine scale genetic structure in continuous populations of outcrossing plant species has traditionally been limited by the availability of sufficient markers. We used a set of 468 SNPs to characterize fine‐scale genetic structure within and between two dense stands of the wild ancestor of maize, teosinte (Zea mays ssp. parviglumis). Our analyses confirmed that teosinte is highly outcrossing and showed little population structure over short distances. We found that the two populations were clearly genetically differentiated, although the actual level of differentiation was low. Spatial autocorrelation of relatedness was observed within both sites but was somewhat stronger in one of the populations. Using principal component analysis, we found evidence for significant local differentiation in the population with stronger spatial autocorrelation. This differentiation was associated with pronounced shifts in the first two principal components along the field. These shifts corresponded to changes in allele frequencies, potentially due to local topographical features. There was little evidence for selection at individual loci as a contributing factor to differentiation. Our results demonstrate that significant local differentiation may, but need not, co‐occur with spatial autocorrelation of relatedness. The present study represents one of the most detailed analyses of local genetic structure to date and provides a benchmark for future studies dealing with fine scale patterns of genetic diversity in natural plant populations.     

Sporophytic nondisjunction of the maize B chromosome at high copy numbers

It has been known for decades that the maize B chromosome undergoes nondisjunction at the second pollen mitosis.Fluorescence in-situ hybridization(FISH)was used to undertake a quantitative study of maize plants with differing numbers of B chromosomes to observe if instability increases by increasing B dosage in root tip tissue.B chromosome nondisjunction was basically absent at low copy number,but increased at higher B numbers.Thus,B nondisjunction rates are dependent on the dosage of B's in the sporophyte.Differences in nondisjunction were also documented between odd and even doses of the B.In plants that have inherited odd humbered doses of the B chromosome,B loss is nearly twice as likely as B gain in a somatic division.When comparing plants with even doses of B's to plants with odd doses of B's,plants with even numbers had a significantly higher chance to increase in number.Therefore,the B's nondisjunctive capacity,previously thought to be primarily restricted to the gametophyte,is present in sporophytic cells.     

Sporophytic nondisjunction of the maize B chromosome at high copy numbers

It has been known for decades that the maize B chromosome undergoes nondisjunction at the second pollen mitosis.Fluorescence in-situ hybridization (FISH) was used to undertake a quantitative study of maize plants with differing numbers of B chromosomes to observe if instability increases by increasing B dosage in root tip tissue.B chromosome nondisjunction was basically absent at low copy number,but increased at higher B numbers.Thus,B nondisjunction rates are dependent on the dosage of B's in the sporophyt...     

Early inflorescence and floral development in Zea mays land race Chapalote (Poaceae)

Tassel and ear primordia were collected from greenhouse-grown specimens of the Mexican maize landrace Chapalote and prepared for scanning electron microscopic (SEM) examination. Measurements of inflorescence apices and spikelet pair primordia (spp) were made from SEM micrographs. Correlation of inflorescence apex diameter with number of spikelet ranks showed no significant difference between tassels and ears, except at the two-rank level where the ear apical meristem had a significantly smaller diameter than corresponding two-ranked tassels. Within individual inflorescences, spp in different ranks enlarged at comparable rates, although the rates from one ear to the next along the stem differed. In both tassels and ears, spp divide to form paired sessile and pedicellate spikelet primordia when the spp is 150 μm wide; ear axes are significantly thicker than tassel axes at the time of bifurcation. The similarities in growth between ear and tassel primordia lend further support to the hypothesis that both the maize tassel and ear are derived from a common inflorescence pattern, a pattern shared with teosinte. Inflorescence primordial growth also suggests that a key character difference between teosinte and maize, distichous vs. polystichous arrangement of spikelets, may be related to size of the apical dome and/or rate of primordium production by the apical meristem. There appears to be more than a single morphological event in the shift from vegetative to reproductive growth. The evocation of axillary buds (ears) is independent of, and temporally separated from, the transition to flowering at the primary shoot apex (tassel).     

Genetic control of B chromosome transmission in Aegilops speltoides (Poaceae)

The transmission of B chromosomes in Aegilops speltoides was studied in 1B and 3B plants. 1B plants tend to lose the B, while the Bs are accumulated in 3B plants with respect to Mendelian expectation. The experimental conditions permitted us to deduce the number of Bs transmitted in the egg cells. The quantitative character “mean number of Bs transmitted in the egg cells” shows a large variation in both types of plants. We have carried out a mass selection experiment, selecting those plants with the highest and the lowest values for this character. A genetic component of such variation was demonstrated because significant selection gain was obtained for high transmission rate in 1B plants, and low transmission rate in 3B plants. We have also estimated some fitness variables and their relationship with B transmission by the egg cell. We found that vigor variables are not correlated with B transmission variation. However, in 3B plants there is a significant negative correlation between B transmission rate and fertility, measured as grains per plant and grains per spikelet. It seems that natural selection acts at this level, balancing the strength of the drive and preventing the excessive increase of B number.     

Role of sulfate in detoxification of arsenate-induced toxicity in Zea mays L. (SRHM 445): nutrient status and antioxidants

The study highlights the role of sulfur (S) in detoxification of arsenate-induced toxicity and the shift in essential element homeostasis in Zea mays L (SRHM 445). Overall growth of arsenate-treated plants under sulfur starvation (?S) was lower than that in the presence of excess sulfur (+S). Translocation of arsenate from roots to shoots, increased under As(?S) and decreased with As(+S). The level of micronutrients (Cu, Zn, Fe) increased in As(?S) plants. Whereas, the level of K and PO₄ was higher in As(?S) plants than in As(+S) plants. Higher malondialdehyde, protein carbonyl, and H₂O₂ levels in As(?S) plants are indicative of higher oxidative stress. Higher superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities, in As(?S) plants coincided with higher H₂O₂ levels showing the activity of these enzymes are independent of S availability. Absence of reduced glutathione/oxidized glutathione pool in (?S) plants manifested into failure of ascorbate–glutathione detoxification pathway. Hence, S has dual role of protecting the plant against arsenate-induced toxicity (1) by restricting arsenic (As) translocation to the upper parts and (2) by increasing the activity SOD and APX.     

Silicon amelioration of aluminium toxicity in teosinte (Zea mays L. ssp. mexicana)

The influence of different Al concentrations, (0, 60 and 120 M Al) on growth and internal concentrations of Al, Si and selected organic acids was analysed in plants of teosinte (Zea mays L. ssp. mexicana), a wild form of maize from acid soils from Mexico. The plants were grown in nutrient solutions (pH 4.0) with or without 4 M silicon. Analysis with the GEOCHEM speciation program did not reveal differences between free activities of Al³⁺ in solutions with and without 4 M Si, but solutions with Si yielded lower concentrations of monomeric Al species, [Al]_mono, when analysed by a modified aluminon method. Plants grown on solutions with similar [Al]_mono, but differing in silicon, showed highly significant differences in growth and tissue concentrations of Al and organic acids. Silicon prevented growth inhibition at [Al]_mono concentrations as high as 35 M, while plants grown without Si suffered severe growth reductions with 33 M [Al]_mono. In solutions with similar [Al]_mono concentrations plants with Si had lower tissue Al concentrations and higher concentrations of malic acid than plants without Si. In view of both the significant influence of Si on the response of plants to Al toxicity and the fact that some soluble Si is always present in soil solutions, the addition of low Si concentrations to nutrient solutions used for Al-tolerance screening is recommended.     

Oxygen-dependent stomatal opening in Zea mays leaves. Effect of Light and carbon dioxide

The oxygen requirement for stomatal opening in maize plants ( Zea mays L. hybrid INRA 508) was studied at different CO₂ concentrations and light intensities. In the absence of CO₂, stomatal opening always required O₂, but this requirement decreased with increasing light intensity. In darkness, the lowest O₂ partial pressure needed to obtain a weak stomatal movement was about 50 Pa. This value was lowered to ca 10 Pa in light (320 μmol m⁻² s⁻¹).
On the other hand. in the absence of O₂, CO₂enabled stomatal opening to occur in the light, presumably due to the evolved photosynthetic O₂. Thus, CO₂, which generally reduced stomatal aperture, could induce stomatal movement in anoxia and light. The effect of CO₂ on stomatal opening was closely dependent on O₂ concentration and light intensity. Stomatal aperture appeared CO₂-independent at an O₂ partial pressure which was dependent on light intensity and was about 25 Pa at 320 umol m⁻² s⁻¹.
The presence of a plasmalemma oxidase, in addition to mitochondrial oxidase, might explain the differences in the O² requirement at various light intensities. The possible involvement of such a system in relation to the effect of CO₂ is discussed.     

Tissue distribution and developmental patterns of NADH-dependent and ferredoxin-dependent glutamate synthase activities in maize (Zea mays) kernels

Both NADH-dependent glutamate synthase (NADH-GOGAT, EC 1.4.1.14) and ferredoxin-dependent glutamate synthase (Fd-GOGAT, EC 1.4.7.1) activities were present in the endosperm, embryo, pedicel and pericarp of maize ( Zea mays L. var. W64A × A619) kernels. The endosperm contained the highest proportions of each activity on a per tissue basis. In the endosperm, NADH-GOGAT and Fd-GOGAT activities increased 12- and 2.5-fold, respectively, during early zein accumulation. NADH-GOGAT and Fd-GOGAT activities were expressed in the upper, middle and lower portions of the endosperm in a manner that paralleled but preceded zein accumulation. Maize endosperm NADH-GOGAT was purified 159-fold using ammonium sulfate fractionation, anion exchange chromatography and dye-ligand chromatography. Apparent K_m values for glutamine, α-ketoglutarate and NADH were 850, 19 and 1 μM, respectively. The results are consistent with endosperm GOGAT functioning to redistribute nitrogen from glutamine, the predominant nitrogenous compound delivered to the endosperm, into other amino acids needed for storage protein synthesis.     

基于分期播种的气候变化对东北地区玉米(Zea mays)生长发育和产量的影响

利用在东北地区中部开展玉米(Zea mays)分期播种试验资料,分析气候变化对玉米出苗速度、生长发育速度、灌浆过程、植株干物质积累和产量的影响,进而分析未来气候变化对东北地区玉米生产的影响及适应性对策.结果表明,气候变化对玉米生长发育和产量的影响十分明显,在水分基本适宜的条件下,东北地区气候变暖导致玉米生长季气温升高、积温增加,使玉米生长发育和灌浆速度加快,生物量增加,从而提高单产.但气候变暖的同时,气候变干会限制热量资源的利用,将缩短玉米灌浆时间,降低灌浆速率,使千粒重下降,从而造成明显减产,而且减产幅度明显大于温度升高的增产幅度.在水分条件基本得到满足的条件下,未来夏半年气候变暖对东北地区玉米生产是有利的,偏晚熟玉米品种比例可以适当扩大,东北玉米带可以向北部和东部扩展,单产和总产都会增加;但如果水分得不到满足,气候的暖干化趋势会使东北地区的中、西部玉米主产区的农业干旱变得更加严重且频繁,造成产量下降和不稳定,给玉米生产带来严重威胁,因而更应加强农业干旱的综合防御工作.     

土壤耕作及秸秆还田对夏玉米田杂草生物多样性的影响

于2008年夏玉米(Zea mays)生长期间,在连续5a秸秆全量还田的免耕、旋耕、耙耕、深松和常规耕作试验地中,研究了杂草总密度、优势杂草种类、生物多样性指数、杂草生物量和夏玉米产量。调查共记录杂草种类13种,秸秆全量还田时,免耕显著提高杂草的总密度;无秸秆还田时,常规耕作的杂草密度高于免耕、旋耕、耙耕和深松。秸秆全量还田后,免耕和深松条件下,杂草优势种为马唐和旱稗,旋耕和耙耕条件下为马唐、旱稗和牛筋草;常规耕作条件下,优势杂草为马唐、苘麻、旱稗和香附子。无秸秆还田条件下,免耕和常规耕作增加了杂草优势种的数量。秸秆全量还田后,免耕、耙耕和深松等耕作措施导致杂草群落的物种丰富度及均匀度均较高。无论哪种耕作条件,5a连续秸秆还田能够显著提高夏玉米籽粒产量和生物学产量,其中尤以常规耕作秸秆全量还田处理产量最高,且田间杂草的生物学产量与夏玉米的生物学产量呈显著负相关关系。     

Environmental effects on the early stages of tassel morphogenesis in maize (Zea mays L.)

The effects of various environmental conditions on the initiation of tassel branches (NTB) and spikelet‐pairs (NSP) were examined in the stress‐sensitive maize inbred F53. Chilling induced the most important effect, with a dramatic decrease in both NTB and NSP, provided it was applied at the end of the vegetative phase and start of the floral transition phase. The primary cause of chilling‐induced abortion of the tassel branches could be oxidative stress in the leaves, since lowering light irradiance during chilling greatly reduced the effect of cold. The comparison of inbreds F53 and F2 revealed that both genotypes exhibited a similar period of cold sensitivity at the floral transition phase, although F2 was considered from field observations as a stress‐insensitive genotype (at least for tassel development). However, our results also showed a chilling acclimation response in inbred F2 but not in inbred F53. The similarities with the work by Lejeune & Bernier (1996 Plant, Cell and Environment 19, 217–224.) concerning the effect of chilling on ear initiation in the sensitive inbred, B22, are emphasized.     

Tribology of the root cap in maize (Zea mays) and peas (Pisum sativum)

Frictional resistance to a penetrating body can account for more than 80% of the total resistance to penetration of soil. We measured the frictional resistance between growing root caps of maize and pea and ground and smooth glass surfaces, which was linearly correlated to load, allowing calculation of the coefficient of kinetic friction and adhesion. Coefficients of kinetic friction between the root caps and the ground and smooth glass surfaces were approximately 0.04 and 0.02, respectively, the first measurements of the frictional properties of root tips at rates approaching those of root elongation, and an order of magnitude smaller than those previously reported. Results suggest that roots are well designed for penetrating soil, and encounter only small frictional resistance on the root cap. These data provide important parameters for modelling soil stresses and deformation around growing root tips.     

Antifungal and growth-promoting activity of Azospirillum brasilense in Zea mays L. ssp. mexicana

Zea mays L. ssp. mexicana (teosinte) is a naturally occurring grass related to maize. The two plants have developed foliar fungal diseases that can be controlled with beneficial bacterial antagonists. While the beneficial effects on stem and root development of the application of bacteria of the genus Azospirillum is widely known, the effects of the bacteria on the control of the phytopathogenic fungi associated with teosinte leaves and seeds are unknown. Bacterium of the species A. brasilense that present acetylene reducing activity, siderophore production and the ability to antagonise pathogenic fungi in vitro and in vivo in teosinte plants were selected for this study, in which the incidence of fungal diseases caused by Alternaria, Bipolaris and Fusarium were reduced in plants. Furthermore, biomass (root and stem) production increased, improving teosinte plant health in greenhouse and field conditions.     

Starch Mobilization in Ultradried Seed of Maize (Zea mays L.) During Germination

The effects of ultradry storage on the starch mobilization in maize (Zea mays L.) seed after aging were investigated. The results indicated that there were no significant differences in the content of ATP,starch, and soluble sugar, as well as the activity of amylase, between ultradried seeds and seeds stored at -20 ℃ during germination. These results were consistent with the higher level of vigor of the ultradried seed. Sieve tube introduction of a fluorescence dye (carboxyl fluoresceindiacetate) and laser confocal microscopy were used to study the development of plasmodesmata in the ultradried seeds. The results indicated that plasmodesmata developed well in ultradried seeds. Fluorescence analysis also showed that the fluorescence intensity in the radicle of ultradried seeds was stronger than that in seeds with a higher moisture content. This suggests that ultradry treatment has no adverse effects on the seeds. After seed imbibition, cell orgaelles could be resumed. It is concluded that ultradry seed storage is beneficial for maintaining seed vigor and that starchy mobilization proceeds regularly during germination.