Effects of CCC on Drought Resistance of Triticum aestivum, L and Zea mays, L.

Application of CCC to wheat and maize reduced transpirationin both soil and solution cultures. This reduction in transpirationwas a result of CCC reducing leaf area and increasing the root/shootratio. CCC-treated plants did not show an increased toleranceto internal water deficits induced by osmotic shocks or desiccation.CCC did increase the drought resistance of young wheat and maizeplants, but only by delaying the onset of severe internal waterdeficits, i.e. by drought avoidance.     

Heat Shock Protein Synthesis Induced by Methomyl in Maize (Zea mays L.) Seedlings

Exposure of plumules of intact maize seedlings (Zea mays L.) to S-methyl-N-[(methylcarbamoyl)-oxy]thioacetimidate (methomyl) represses synthesis of several polypeptides normally made under control conditions and induces synthesis of polypeptides similar to maize heat shock polypeptides (HSPs). Three of the methomyl-induced polypeptides (18 kilodaltons) are recognized by antibodies raised against 18 kilodalton maize heat shock polypeptides.     

Cyanide-resistant Respiration and Cold Resistance in Seedlings of Maize (Zea mays L.

Respiratory activity of mitochondria isolated from seedlingsof two cold-resistant and two cold-susceptible maize cultivarswas examined. The greater potential for cyanide-resistant respirationfound in the cold-resistant seedlings raises the possibilityof a role for the alternative respiratory pathway in cold-resistance. alternative respiration, cold-resistance, cyanide-resistant respiration, maize, mitochondria, Zea mays     

Somatic embryogenesis in Zea mays L.

Summary Combining ability studies with respect to such green fodder quality characteristics as oxalic acid, calcium, sodium, potassium and green fodder yield were carried out in a 12 × 12 diallel cross set in pearl millet (Pennisetum typhoides (Burm) S. & H.). With regard to differential expression of gene effects, studies for quality traits were carried out in different seasons and on different plant parts. The relative proportions of general and specific combining variances indicated the preponderance of non-additive genetic variance. Parents possessing desirable fodder quality characteristics were identified on the basis of combining ability and per se performance, and selection criterion for crosses was discussed. It was recommended that leaf portion should be biochemically analysed and manipulated in an environment when the genes are expressed.Part of the Ph. D. dissertation submitted to the Punjab Agricultural University by the senior author in partial fulfilment of the requirements for the degree     

Leaf vasculature in Zea mays L.

The vascular system of the Zea mays L. leaf consists of longitudinal strands interconnected by transverse bundles. In any given transverse section the longitudinal strands may be divided into three types of bundle according to size and structure: small, intermediate, large. Virtually all of the longitudinal strands intergrade structurally however, from one bundle type to another as they descend the leaf. For example, all of the strands having large-bundle anatomy appear distally as small bundles, which intergrade into intermediates and then large bundles as they descend the leaf. Only the large bundles and the intermediates that arise midway between them extend basipetally into the sheath and stem. Most of the remaining longitudinal strands of the blade do not enter the sheath but fuse with other strands above and in the region of the blade joint. Despite the marked decrease in number of longitudinal bundles at the base of the blade, both the total and mean cross-sectional areas of sieve tubes and tracheary elements increase as the bundles continuing into the sheath increase in size. Linear relationships exist between leaf width and total bundle number, and between cross-sectional area of vascular bundles and both total and mean cross-sectional areas of sieve tubes and tracheary elements.     

Internode length in Zea mays L.

[¹³C, ³H]Gibberellin A₂₀ (GA₂₀) has been fed to seedlings of normal (tall) and dwarf-5 and dwarf-1 mutants of maize (Zea mays L.). The metabolites from these feeds were identified by combined gas chromatography-mass spectrometry. [¹³C, ³H]Gibberellin A₂₀ was metabolized to [¹³C, ³H]GA₂₉-catabolite and [¹³C, ³H]GA₁ by the normal, and to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₁ by the dwarf-5 mutant. In the dwarf-1 mutant, [¹³C, ³H]GA₂₀ was metabolized to [¹³C, ³H]GA₂₉ and [¹³C, ³H]GA₂₉-catabolite; no evidence was found for the metabolism of [¹³C, ³H]GA₂₀ to [¹³C, ³H]GA₁. [¹³C, ³H]Gibberellin A₈ was not found in any of the feeds. In all feeds no dilution of ¹³C in recovered [¹³C, ³H]GA₂₀ was observed. Also in the dwarf-5 mutant, the [¹³C]label in the metabolites was apparently undiluted by endogenous [¹³C]GAs. However, dilution of the [¹³C]label in metabolites from [¹³C, ³H]GA₂₀ was observed in normal and dwarf-1 seedlings. The results from the feeding studies provide evidence that the dwarf-1 mutation of maize blocks the conversion of GA₂₀ to GA₁.Abbreviations GA_n gibberellin A_n - GC-MS combined gas chromatography-mass spectrometry - HPLC high-performance liquid chromatography - RP reverse phase     

Characterization of Photosynthetic Performance during Senescence in Stay-Green and Quick-Leaf-Senescence Zea mays L. Inbred Lines

The net photosynthetic rate, chlorophyll content, chlorophyll fluorescence and 820 nm transmission were investigated to explore the behavior of the photosynthetic apparatus, including light absorption, energy transformation and the photoactivities of photosystem II (PSII) and photosystem I (PSI) during senescence in the stay-green inbred line of maize (Zea mays) Q319 and the quick-leaf-senescence inbred line of maize HZ4. The relationship between the photosynthetic performance and the decrease in chlorophyll content in the two inbred lines was also studied. Both the field and laboratory data indicated that the chlorophyll content, net photosynthetic rate, and the photoactivities of PSII and PSI decreased later and slower in Q319 than in HZ4, indicating that Q319 is a functional stay-green inbred line. In order to avoid the influence of different development stages and environmental factors on senescence, age-matched detached leaf segments from the two inbred lines were treated with ethephon under controlled conditions to induce senescence. The net photosynthetic rate, light absorption, energy transformation, the activities of PSII acceptor side and donor side and the PSI activities decreased much slower in Q319 than in HZ4 during the ethephon-induced senescence. These results suggest that the retention of light absorption, energy transformation and activity of electron transfer contribute to the extended duration of active photosynthesis in Q319. Although the chlorophyll content decreased faster in HZ4, with decrease of chlorophyll content induced by ethephon, photosynthetic performance of Q319 deteriorated much more severely than that of HZ4, indicating that, compared with Q319, HZ4 has an advantage at maintaining higher photosynthetic activity with decrease of chlorophyll although HZ4 is a quick-leaf-senescence inbred line. We conclude that attention should be paid to two favorable characteristics in breeding long duration of active photosynthesis hybrids: 1) maintaining more chlorophyll content during senescence and 2) maintaining higher photosynthetic activity during the loss of chlorophyll.     

干旱胁迫对玉米幼苗根系中NO信号转导的影响

以玉米(Zea mays L.)幼苗根系为材料,研究其生长发育对内外源NO的感应及在干旱条件下内外源NO对其生长发育的影响.结果表明:干旱抑制根系NO释放,NO的产生可能不依赖于NO合酶系统,而依赖于NADPH硝酸还原酶的酶促反应;用活性氧清除剂NAC、NAC与干旱复合处理均能促使内源NO的产生和释放:其根系生物量的分析表明内源NO的释放明显抑制根系的生长发育.     

Calcium-induced sperm fusion in Zea mays L.

 In this study, we examined morphological changes of isolated maize (Zea mays L.) sperm cells in the presence of Brewbaker and Kwack salts (BKS) or the individual components of BKS using light, transmission electron and scanning electron microscopy. Freshly isolated sperms are 7.5 μm in diameter. Treatment with BKS for 5 h resulted in large cells with a diameter up to 41 μm. Staining of sperm nuclei with 4′, 6-diamidino-2-phenylindole (DAPI) revealed two or more nuclei in a single cell, suggesting that BKS induces cell fusion. Treatment with each BKS component showed that cell fusion occurs only in the presence of calcium nitrate. Use of several calcium salts showed the same results, suggesting that the calcium ion, alone, is responsible for the observed cell fusion. Further studies were conducted to examine the relationship between calcium distribution and sperm location in pollen tubes using chlorotetracycline and DAPI. Growing maize pollen tubes exhibited a high membrane calcium region within 20–50 μm from the tip. The Sperms are found no closer than 90 μm to the tip of the tube, suggesting that sperms are located in a low calcium region prior to being released to the degenerating synergid. Received: 12 August 1996 / Revision accepted: 6 December 1996     

Seed development and vivipary in Zea mays L.

Seed development was investigated in kernels of developing wild-type and viviparous (vp-1) Zea mays L. Embryos and endosperm of wild-type kernels began to dehydrate at approx. 35 d after pollination (DAP); viviparous embryos did not desiccate but accumulated fresh weight via coleoptile growth in the caryopses. Concentrations of endogenous abscisic acid (ABA) in the embryo were relatively high early in development, being approx. 150 ng·g^-1 fresh weight at 20 DAP. The ABA content declined thereafter, falling to approx. 50 ng·g^-1 at 30 DAP. Endosperm ABA content was always low, being less than 20 ng·g^-1. There were no differences between wild-type and vp-1 tissues. Immature kernels did not germinate when removed from the ear until late in development. The ability to germinate was correlated with decreasing moisture content in the endosperm at the time of removal; premature drying of immature kernels resulted in greatly increased germination following imbibition. Excised embryos germinated precociously when removed from the endosperm as early as 25 DAP. Such germination could be prevented by treatment with 10^-5 M ABA or by lowering the solute potential (_s) of the medium with 0.3 M mannitol. Treatment of excised embryos with ABA led to internal ABA concentrations comparable to those in embryos in which germination was inhibited in situ. Mannitol treatment did not have this effect, although water-deficit stress of excised embryos resulted in substantial ABA production. Germinated vp-1 embryos were less sensitive to growth inhibition by ABA or mannitol than germinating wild-type embryos. The vp-1 seedlings were not wilty and their transpiration rates were reduced in response to ABA or water shortage.Abbreviations and symbols ABA abscisic acid - DAP days after pollination - FW fresh weight - vp-1 viviparous genotype - _s solute potential     

Influence of Temperature Stress on in Vitro Fertilization and Heat Shock Protein Synthesis in Maize (Zea mays L.) Reproductive Tissues

This study was conducted to investigate the response of maize (Zea mays) male and female mature reproductive tissues to temperature stress. We have tested the fertilization abilities of the stressed spikelets and pollen using in vitro pollination-fertilization to determine their respective tolerance to stress. The synthesis of heat shock proteins (HSPs) was also analyzed in male and female tissues using electrophoresis of ³⁵S-labeled proteins and fluorography, to establish a relationship between the physiological and molecular responses. Pollen, spikelets, and pollinated spikelets were exposed to selected temperatures (4, 28, 32, 36, or 40°C) and tested using an in vitro fertilization system. The fertilization rate is highly reduced when pollinated spikelets are exposed to temperatures over 36°C. When pollen and spikelets are exposed separately to temperature stress, the female tissues appear resistant to 4 hours of cold stress (4°C) or heat stress (40°C). Under heat shock conditions, the synthesis of a typical set of HSPs is induced in the female tissues. In contrast, the mature pollen is sensitive to heat stress and is responsible for the failure of fertilization at high temperatures. At the molecular level, no heat shock response is detected in the mature pollen.     

Water Deficit and Inflorescence Development in Zea mays L.

A water deficit imposed during the period of terminal male inflorescenceinitiation and early development reduced both the growth rateand the mature size of that organ in Zea mays (cv. Iochief).Growth and development of the axillary shoots, the potentialfemale inflorescences, was inhibited during the episode of waterdeficit but promoted thereafter. As a result, plants which hadbeen subjected to a water deficit at that period produced 2–3mature cobs and relatively large axillary shoots at the lowernodes, whereas plants supplied with water throughout produceda single mature cob and relatively small axillary shoots. A water deficit imposed during other growth phases did not producethis response and, moreover, a further period of deficit imposedlater in development, following a deficit at the sensitive stage,inhibited the enlargement of the axillary shoots invoked bythe earlier deficit. It did not, however, inhibit the enhancedfloral development of those axillary shoots nor reverse theinhibition of tassel growth. The data are discussed in relation to correlative inhibitionin Zea mays.     

The phytochrome system in light-grown Zea mays L.

The phytochrome system is analyzed in light-grown maize (Zea mays L.) plants, which were prevented from greening by application of the herbicide SAN 9789. The dark kinetics of phytochrome are not different in the first, second or third leaf. It is concluded that in light-grown maize plants phytochrome levels are regulated by P_r formation and P_fr and P_r destruction, rather than by P_frP_r dark reversion. P_r undergoes destruction after it has been cycled through P_fr. The consequences of this P_r destruction on the phytochrome system are discussed.Abbreviations SAN 9789 4-chloro-5-(methylamino)-2-(,,-trifluoro-m-tolyl)-3(2H) pyridazinone - P_fr far-red absorbing form of phytochrome - P_r red absorbing form of phytochrome - P_tot P_fr+P_r     

Two novel meiotic restitution mechanisms in haploid maize (Zea mays L.)

Two original mechanisms of nuclear restitution related to different processes of meiotic division of pollen mother cells (PMCs) have been found in male meiosis of the lines of maize haploids no. 2903 and no. 2904. The first mechanism, which is characteristic of haploid no. 2903, consists in spindle deformation (bend) in the conventional metaphase-anaphase I. This leads to asymmetric incomplete cytokinesis with daughter cell membranes in the form of incisions on the mother cell membrane. As a result, the chromosomes of the daughter nuclei are combined into a common spindle during the second meiotic division, and a dyad of haploid microspores is formed at the tetrad stage. The frequency of this abnormality is about 50%. The second restitution mechanism, which has been observed in PMCs of haploid no. 2904, results from disturbance of the fusion of membrane vesicles (plastosomes) at the moment of formation of daughter cell membranes and completion of cytokinesis in the first meiotic division. This type of cell division yields a binuclear monad. In the second meiotic division, the chromosomes of the daughter nuclei form a common spindle, and meiosis results in a dyad of haploid microspores. The frequency of this abnormality is as high as 15%. As a result, haploid lines no. 2903 and no. 2904 partly restore fertility.     

Abscisic Acid Refines the Synthesis of Chloroplast Proteins in Maize (Zea mays) in Response to Drought and Light

To better understand abscisic acid (ABA) regulation of the synthesis of chloroplast proteins in maize (Zea mays L.) in response to drought and light, we compared leaf proteome differences between maize ABA-deficient mutant vp5 and corresponding wild-type Vp5 green and etiolated seedlings exposed to drought stress. Proteins extracted from the leaves of Vp5 and vp5 seedlings were used for two-dimensional electrophoresis (2-DE) and subsequent matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) mass spectrometry (MS). After Coomassie brilliant blue staining, approximately 450 protein spots were reproducibly detected on 2-DE gels. A total of 36 differentially expressed protein spots in response to drought and light were identified using MALDI-TOF MS and their subcellular localization was determined based on the annotation of reviewed accession in UniProt Knowledgebase and the software prediction. As a result, corresponding 13 proteins of the 24 differentially expressed protein spots were definitely localized in chloroplasts and their expression was in an ABA-dependent way, including 6 up-regulated by both drought and light, 5 up-regulated by drought but down-regulated by light, 5 up-regulated by light but down-regulated by drought; 5 proteins down-regulated by drought were mainly those involved in photosynthesis and ATP synthesis. Thus, the results in the present study supported the vital role of ABA in regulating the synthesis of drought- and/or light-induced proteins in maize chloroplasts and would facilitate the functional characterization of ABA-induced chloroplast proteins in C₄ plants.     

Heat Shock Proteins and Circadian Rhythms

Significant circadian rhythms in heat shock gene expression were observed in a prokaryotic species (Synechocystis). In eukaryotes, in contrast, several heat shock genes (constitutive and inducible) were shown to be constantly expressed. A few cases of circadian expression of heat shock proteins (HSPs), however, have been reported. Significant circadian changes of thermotolerance were observed in yeast and several plant species. Higher thermo-tolerance can be attributed to a higher abundance of HSPs, but also to other adaptive mechanisms. Zeitgeber effects of temperature changes can be explained on the basis of their direct effects on the state variables of the clock gene (per, frq) expression and its negative feedback loop. Effects of increased HSP concentrations, as observed after heat shock, but also after light and serotonin (5HT), appear possible, in particular with respect to nuclear localization of the clock (PER) protein, but these effects have not been documented yet. Thus, the role of HSPs in the circadian clock system is little understood and, from our point of view, deserves more attention. (Chronobiology International, 13(4), 239-250, 1996)     

Ethylene Release from Leaves of Xanthium strumarium L. and Zea mays L.

The release of ethylene into sealed Erlenmeyer flasks by intactleaves and leaf discs of Xanthium strumarium L. a C₃ plant andZea mays L. a C₄ plant were compared both in white light andin darkness. The effects of the presence or absence of addedCO₂ (in the form of sodium bicarbonate) the photosynthetic inhibitor3-[3,4-dichlorophenyl]-l, l-dimethyl urea (DCMU) and 1-aminocyclopropane-1-carboxylicacid (ACC), the precursor of ethylene in higher plants, werealso investigated. The rate of ethylene release from leaf tissue of Xanthium inthe absence of added CO₂ was markedly reduced in the light (i.e.at the CO₂ compensation point). Treatments that would enhancethe CO₂ availability to the tissue (i.e. added bicarbonate,darkness, treatment with DCMU) allowed higher levels of ethylenerelease. Incubation of the tissue with ACC considerably enhancedthe release of ethylene compared to that from the correspondingcontrol tissue without ACC. However, the pattern of ethylenerelease induced by the various treatments was similar with orwithout added ACC. When tissue, in the absence of added CO₂, was transferred fromlight to darkness, and back to light for 90 min periods, theethylene release rates Increased during the interposed darkperiod but resumed the lower rate during the final light period.The addition of CO₂ in the light resulted in a similar rateof ethylene release to that found in the dark. The overall pattern of ethylene release from Zea leaf tissuesubjected to light and dark in the presence or absence of addedCO₂ was similar to that of Xanthium. However, two or three timesmore ethylene was released from maize leaves in the light whenCO² was added compared to that generated in the dark. This isin marked contrast to Xanthium, where, under the light conditionsused, the ethylene release rate in the dark equalled or exceededthat occurring in the light, even in the presence of high levelsof CO₂. A very low rate of ethylene release was observed atthe CO₂ compensation point of maize. A speculative model is presented to explain how photosyntheticactivity might act as a key factor in regulating ethylene evolutionfrom leaf tissue in these experiments. It invokes the conceptof an inhibition by CO₂ of ethylene retention or breakdown thuspermitting more ethylene to be released from the leaves.