Seedlings Zea Mays Research Articles

Enhanced ethylene production by primary roots of Zea mays L. in response to sub‐ambient partial pressures of oxygen

ABSTRACTEthylene production by primary roots of 72–h‐old intact seedlings of Zea mays L. cv. LG11 was studied under ambient and sub‐ambient oxygen partial pressures (pO2) using a gas flow‐through system linked to a photoacoustic laser detector. Despite precautions to minimize physical perturbation to seedlings while setting‐up, ethylene production in air was faster during the first 6h than later, in association with a small temporary swelling of the roots. When roots were switched from air (20–8kPa O2) to 3 or 5kPa O2 after 6h, ethylene production increased within 2—3 h. When, the roots were returned to air 16 h later, ethylene production decreased within 2—3 h. The presence of 10kPa CO2 did not interfere with the effect of 3kPa O2. Transferring roots from air to 12–5kPa did not change ethylene production, while a reduction to 1 kPa O2 induced a small increase. The extra ethylene formed in 3 and 5 kPa O2 was associated with plagiotropism, swelling, root hair production, and after 72 h, increased amounts of intercellular space (aerenchyma) in the root cortex. Root extension was also slowed down, but the pattern of response to oxygen shortage did not always match that of ethylene production. On return to air, subsequent growth patterns became normal within a few hours. In the complete absence of oxygen, no ethylene production was detected, even when anaerobic roots were returned to air after 16 h.

Hypoxic and Anoxic Induction of Alcohol Dehydrogenase in Roots and Shoots of Seedlings of Zea mays (Adh Transcripts and Enzyme Activity).

Alcohol dehydrogenase (ADH) is one of a number of enzymes of glycolysis and fermentation known to be synthesized preferentially under low O2 conditions. We examined levels of Adh1 transcripts and of ADH activity in 5-mm root tips, root axes (the remainder of the seminal root), and shoots of maize (Zea mays L. cv TX 5855) seedlings. Seedlings with roots averaging about 60-mm long were transferred from fully aerobic conditions (solutions sparged with 40% [v/v] O2) to anaerobic (O2-free) conditions, or to an intermediate O2 concentration. There was no prior acclimation to low O2. In root tips, anoxia induced Adh1 transcripts and enzyme activity at 6 h, but this was followed by a rapid decline so that at 12 to 18 h neither were detectable and the root tips were dead. In contrast, higher levels of Adh1 transcripts and enzyme activity were maintained for at least 48 h in root axes and shoots. When induction at 6 h was measured over a wide range of O2 concentrations, a peak in ADH activity occurred in all tissues at 4% (v/v) O2. Maximum levels of transcripts, however, were in the range of 0 to 4% O2, depending on the tissue. The time course of hypoxic induction (at 4% O2) in root tips showed a peak in transcript levels at 6 h, whereas ADH activity continued to rise throughout the 24-h experiment. These results show that in root tips, ADH induction by anoxia was small and transient relative to induction by hypoxia.

Studies on the growth and indole-3-acetic acid and abscisic acid content of Zea mays seedlings grown in microgravity.

Measurements were made of the fresh weight, dry weight, dry weight-fresh weight ratio, free and conjugated indole-3-acetic acid, and free and conjugated abscisic acid in seedlings of Zea mays grown in darkness in microgravity and on earth. Imbibition of the dry kernels was 17 h prior to launch. Growth was for 5 d at ambient orbiter temperature and at a chronic accelerational force of the order of 3 x 10(-5) times earth gravity. Weights and hormone content of the microgravity seedlings were, with minor exceptions, not statistically different from seedlings grown in normal gravity. The tissues of the shuttle-grown plants appeared normal and the seedlings differed only in the lack of orientation of roots and shoots. These findings, based upon 5 d of growth in microgravity, cannot be extrapolated to growth in microgravity for weeks, months, and years, as might occur on a space station. Nonetheless, it is encouraging, for prospects of bioregeneration of the atmosphere and food production in a space station, that no pronounced differences in the parameters measured were apparent during the 5 d of plant seedling growth in microgravity.

Identification of Δ 5,7-sterol-Δ 7-reductase in higher plant microsomes

A microsomal preparation from seedlings of Zea mays catalyzed the NADPH dependent reduction of the delta 7-bond of delta 5,7-cholestadienol (1) giving the first in vitro evidence for the intermediacy of delta 5,7-sterols in plant sterol biosynthesis. Using a GC assay developed to detect the cholesterol (2) produced, the properties of the microsomal enzyme have been established with respect to cofactor requirements and kinetics. The potent in vitro inhibition of the plant delta 5,7-sterol-delta 7-reductase by the ammonium-ion containing fungicides, tridemorph2 (3), fenpropimorph (4) and AY 9944 (5) was demonstrated. The high affinities observed for these derivatives, especially for (4) (I50 = 8 x 10(-8) M, I50/Km = 2 x 10(-4)), are in full accordance with the previously proposed cationic mechanism involved in this reduction reaction.

DC-Electric Fields Affect the Growth Direction and StatocytePolarity of Root Tips ( Lepidium sativum)

Summary Main roots of 20 h old Lepidium sativum seedlings (garden cress) were used to investigate the effect ofweak DC-electric fields on the growth direction of the root tip and the polarity of statocytes of the root cap. When DC-electric fields of 1 - 3 V/cm were applied for 3 h at right angles to Lepidium roots growing downward in well stirred low salt medium of pH 6 the root tips grew towards the cathode as a result of differential flank growth in the distal elongation zone. A pH value of 5 caused curvature towards the anode due to differential flank growth in the proximal elongation zone. In the statocytes of the root cap, the proximally located cell nucleus always migrated towards the anode and the distal ER towards the cathode. Both the electrotropic growth of the root tip and the displacement of the cell organelles in the statocytes were fully reversible within 3 and 1 h, respectively, after shutting off the electric field. Some comparative studies on main roots of approximately 48 h old seedlings of Zea mays (corn) showedan electrotropic curvature towards the cathode in an electric field of 0.5 V/cm. The curvature was maintained, and frequently even enhanced for up to 24 h after shut-off of the electric field. Field strengths exceeding 0.5 V/cm induced a curvature towards the anode. (So far, the response of corn root statocytes to electric fields has not been investigated.)

Cytoplasmic calcium levels in protoplasts from the cap and elongation zone of maize roots.

Calcium has been implicated as a key component in the signal transduction process of root gravitropism. We measured cytoplasmic free calcium in protoplasts isolated from the elongation zone and cap of primary roots of light-grown, vertically oriented seedlings of Zea mays L. Protoplasts were loaded with the penta-potassium salts of fura-2 and indo-1 by incubation in acidic solutions of these calcium indicators. Loading increased with decreasing pH but the pH dependence was stronger for indo-1 than for fura-2. In the case of fura-2, loading was enhanced only at the lowest pH (4.5) tested. Dyes loaded in this manner were distributed predominantly in the cytoplasm as indicated by fluorescence patterns. As an alternative method of loading, protoplasts were incubated with the acetoxymethylesters of fura-2 and indo-1. Protoplasts loaded by this method exhibited fluorescence both in the cytoplasm and in association with various organelles. Cytoplasmic calcium levels measured using spectrofluorometry, were found to be 160 +/- 40 nM and 257 +/- 27 nM, respectively, in populations of protoplasts from the root cap and elongation zone. Cytoplasmic free calcium did not increase upon addition of calcium to the incubation medium, indicating that the passive permeability to calcium was low.

Microtubule organization and morphogenesis of stomata in caffeine-affected seedlings ofZea mays

Treatment ofZea mays seedlings with a 5 mM caffeine solution inhibits cytokinesis in guard cell mother cells (GMCs), producing unicellular, binucleate aberrant stomata (a-stomata). Ventral wall (VW) strips of limited length, which usually meet the wall portions of GMCs adjoining the cortical zone of the preprophase microtubule band (PMB), are laid down in many a-stomata.

Apoplastic domains and sub-domains in the shoots of etiolated corn seedlings

Light Green, an apoplastic probe, was applied to the cut mesocotyl base or to the cut coleoptile apex of etiolated seedlings of Zea mays L. cv. Silver Queen. Probe transport was measured and its tissue distribution determined. In the mesocotyl, there is an apoplastic barrier between cortex and stele. This barrier creates two apoplastic domains which are non-communicating. A kinetic barrier exists between the apoplast of the mesocotyl stele and that of the coleoptile. This kinetic barrier is not absolute and there is limited communication between the apoplasts of the two regions. This kinetic barrier effectively creates two sub-domains. In the coleoptile, there is communication between the apoplast of the vascular strands and that of the surrounding cortical tissue. No apoplastic communication was observed between the coleoptile cortex and the mesocotyl cortex. Thus, the apoplastic space of the coleoptile cortex is a sub-domain of the integrated coleoptile domain and is separate from that of the apoplastic domain of the mesocotyl cortex.

Apoplastic domains and sub‐domains in the shoots of etiolated corn seedlings

Light Green, an apoplastic probe, was applied to the cut mesocotyl base or to the cut coleoptile apex of etiolated seedlings of Zea mays L. cv. Silver Queen. Probe transport was measured and its tissue distribution determined. In the mesocotyl, there is an apoplastic barrier between cortex and stele. This barrier creates two apoplastic domains which are non-communicating. A kinetic barrier exists between the apoplast of the mesocotyl stele and that of the coleoptile. This kinetic barrier is not absolute and there is limited communication between the apoplasts of the two regions. This kinetic barrier effectively creates two sub-domains. In the coleoptile, there is communication between the apoplast of the vascular strands and that of the surrounding cortical tissue. No apoplastic communication was observed between the coleoptile cortex and the mesocotyl cortex. Thus, the apoplastic space of the coleoptile cortex is a sub-domain of the integrated coleoptile domain and is separate from that of the apoplastic domain of the mesocotyl cortex.

Changes in the Sugar Content of the Leaf Sheath of Dwarf Maize Seedlings Associated with Gibberellin-Induced Growth

Changes in the time in sugar and starch content of the first leaf sheath were compared among normal, d5, and GA1-treated (1μg/plant) d5 seedlings of Zea mays L., from which endosperms had been removed. The patterns of changes in the levels of these carbohydrates were more or less similar to one another among the three groups of seedlings. Generally, the levels decreased toward the time of maturation of the leaf sheath except for the level of sucrose which showed a sharp increase followed by a decrease. There was an inverse relationship over time between growth and levels of glucose and fructose. Although treatment with GA1 resulted in a decrease in sucrose content, it had practically no significant effect on the levels of the other sugars. In the leaf sheath of d5, growth is probably not limited by the levels of these sugars, and GA-induced elongation does not seem to have any significant correlation with the changes in the levels of sugars.

The effect of the etched (et) mutation on the amylolytic enzyme activities in germinating kernels and seedlings of Zea mays

The etched (et) mutation in maize causes distinct depressions and structural gaps in the endosperm and also gives rise to virescent seedlings, α- and β-Amylase activities were observed to be higher in et (+) et (+) kernels and seedlings as compared to that of the et et mutant. The total amylase and β-amylase trends during germination also differed between normal and mutant kernels and seedlings (it increases in the wildtype and decreases in et et). On the contrary, the overall α-amylase trend was found to be similar in both genotypes (slight decrease during germination). The native gel electrophoresis of crude enzyme extracts did not reveal any qualitative differences in α and β amylases during germination. The germinating et et kernels initially showed lower levels of starch compared with the wild type kernels, whereas no such difference was found at later stages of germination. It is concluded that et gene associated endosperm lesions lead to an impairment of starch degradation in germinating kernels resulting in virescent seedlings.

Metabolic Dependence of Na + Efflux from Roots of Intact Maize Seedlings

Summary The mechanism of Na+ efflux from roots was investigated using intact seedlings of Zea mays L. cv. Pioneer 3906. 22Na+ efflux was independent of external Na+ but stimulated by K+. Low temperature (4°C) and the Ca2+ chelator, ethyleneglycol-bis-(β-aminoethyl ether) N,N1,N1-tetraacetic acid (EGTA), increased 22Na+ efflux. The protonophore and uncoupler, carbonylcyanide-3-chlorophenylhydrazone (CCCP), and the sulfhydryl reagent, N-ethylmaleimide (NEM), did not affect 22Na+ efflux during the initial 60 minutes. Except for Na+, which transiently depolarized the membrane potential, a permanent depolarization was observed with all treatments, causing a change in the electro-chemical driving force for Na+. The data allowed to distinguish between two cytoplasmic Na+ efflux components: an active component depending on metabolic energy and a passive one driven by the electro-chemical potential difference for Na+. Since both components counteract each other when metabolism is inhibited (e.g. by CCCP or NEM), metabolic dependence of Na+ efflux from maize roots can only by estimated indirectly taking into account the change in the electro-chemical potential difference for Na+.

Effect of inoculation with Azotobacter chroococcum on nitrogenase activity of Zea mays roots grown in agricultural soils under aseptic and non-sterile conditions

Inoculated and non-inoculated seedlings of Zea mays were grown in agricultural soils under aseptic and non-sterile conditions. Acetylene reduction activity and microbial counts were determined after 7 and 30 days of growth. Irrespective of the soil type Azotobacter spp. were commonly isolated under maize cultivation. Inoculation of agricultural soils with a suspension of A. chroococcum led to an increase in Azotobacter numbers, although this effect diminished with time. Nitrogenase activity was detected on maize roots and increased in response to the inoculation with A. chroococcum, showing that this associative growth could be of primary importance for the plant. The results of assays for acetylene reduction activity indicated that the nitrogenase activity was associated only with the root systems.

Effects of N, P, and K Deficiencies on Light-dependent Anthocyanin Formation in Zea mays L. Seedlings

The effects of mineral nutrient deficiencies on light-dependent anthocyanin formation in seedlings of Zea mays L., cv. Golden Bantam were investigated. Anthocyanin accumulation in roots and shoots was significantly higher in seedlings grown on N or P deficient than on K deficient or complete nutrient solutions. However, less ethylene was produced by seedlings grown on N or P deficient solutions than by those grown on K deficient or complete nutrient media. Absorption of ethylene by permanganate or inhibition of ethylene production or action by C O 2+ or Ag + ions brought about increased anthocyanin production in roots and shoots of seedlings grown on complete and N, P, and K deficient nutrient solutions, respectively, above the anthocyanin levels found in these organs of the control plants. Elimination of differences in anthocyanin production among seedlings grown on complete, N, or K deficient nutrient solutions in the presence of permanganate or C O 2+ ions indicates that ethylene may act in a core of responses caused by N or K deficiencies. However, other factors in addition to decreased ethylene formation appear to be involved regarding higher anthocyanin production under P deficiency.

GC-MS identification of GA20-13-O-glucoside formed from GA20 in normal plants and dwarf-1 mutants ofZea mays L.

After feeding GA20 to excised seedlings ofZea mays L. normals (N) and dwarf-1 mutants (d1), GA20-13-O-glucoside (9) was identified by HPLC and by GC-MS of its permethylated derivative. The glucosylation rate of GA20 was found to be higher in the dwarf-1 mutant (26%) than in the normal plant (3.6%). This article includes a GC-MS study in which diagnostic fragments from the spectra of permethylated synthetic GA glucosides have been selected that proved to be useful for the identification of permethylated GA glucosides.

Effects of growth regulators on light‐dependent anthocyanin production in Zea mays seedlings

Rengel, Z. and Kordan, H. A. 1987. Effects of growth regulators on light‐dependent anthocyanin production in Zea mays seedlings.The effects of ethylene, indolyl‐ and naphthylacetic acids, zeatin, benzyladenine, gib‐berellic acid and triiodobenzoic acid on anthocyanin production in seedlings of Zea mays L. cv. Golden Bantam were investigated. Endogenously produced and exogen‐ously supplied ethylene, as well as the other growth regulators tested markedly suppressed anthocyanin formation. Except for triiodobenzoic acid, the other growth regulators stimulated ethylene production, the amounts produced in the light being larger than those in the dark. Absorption of ethylene by permanganate as well as inhibition of ethylene production or action by Co2+ or Ag+ increased anthocyanin formation in maize seedlings above the level found in the control plants. The inhibiting effect of auxins and cytokinins on anthocyanin production was reversed by Co2+ or Ag+. In contrast, decreased anthocyanin formation caused by gibberellic acid or triiodobenzoic acid seemed unrelated to ethylene and could not be alleviated by Co2+ or Ag+.

Influence of Microgravity on Root-Cap Regeneration and the Structure of Columella Cells in Zea mays

We launched imbibed seeds and seedlings of Zea mays into outer space aboard the space shuttle Columbia to determine the influence of microgravity on 1) root-cap regeneration, and 2) the distribution of amyloplasts and endoplasmic reticulum (ER) in the putative statocytes (i.e., columella cells) of roots. Decapped roots grown on Earth completely regenerated their caps within 4.8 days after decapping, while those grown in microgravity did not regenerate caps. In Earth-grown seedlings, the ER was localized primarily along the periphery of columella cells, and amyloplasts sedimented in response to gravity to the lower sides of the cells. Seeds germinated on Earth and subsequently launched into outer space had a distribution of ER in columella cells similar to that of Earth-grown controls, but amyloplasts were distributed throughout the cells. Seeds germinated in outer space were characterized by the presence of spherical and ellipsoidal masses of ER and randomly distributed amyloplasts in their columella cells. These results indicate that 1) gravity is necessary for regeneration of the root cap, 2) columella cells can maintain their characteristic distribution of ER in microgravity only if they are exposed previously to gravity, and 3) gravity is necessary to distribute the ER in columella cells of this cultivar of Z. mays.

INFLUENCE OF MICROGRAVITY ON ROOT‐CAP REGENERATION AND THE STRUCTURE OF COLUMELLA CELLS IN ZEA MAYS

We launched imbibed seeds and seedlings of Zea mays into outer space aboard the space shuttle Columbia to determine the influence of microgravity on 1) root-cap regeneration, and 2) the distribution of amyloplasts and endoplasmic reticulum (ER) in the putative statocytes (i.e., columella cells) of roots. Decapped roots grown on Earth completely regenerated their caps within 4.8 days after decapping, while those grown in microgravity did not regenerate caps. In Earth-grown seedlings, the ER was localized primarily along the periphery of columella cells, and amyloplasts sedimented in response to gravity to the lower sides of the cells. Seeds germinated on Earth and subsequently launched into outer space had a distribution of ER in columella cells similar to that of Earth-grown controls, but amyloplasts were distributed throughout the cells. Seeds germinated in outer space were characterized by the presence of spherical and ellipsoidal masses of ER and randomly distributed amyloplasts in their columella cells. These results indicate that 1) gravity is necessary for regeneration of the root cap, 2) columella cells can maintain their characteristic distribution of ER in microgravity only if they are exposed previously to gravity, and 3) gravity is necessary to distribute the ER in columella cells of this cultivar of Z. mays.

Effects of S-Ethyl-N,N-Dipropylthiocarbamate (EPTC) on Normal and Dwarf Seedlings of Zea mays L.

Gibberellin-deficient dwarf 1 maize mutant seedlings are at least ten times more sensitive to EPTC (S-ethyl-N,N-dipropylthiocarbamate) phytotoxicity than normal maize. Levels of reduced glutathione and the enzymes cytosolic and microsomal glutathione S-transferase (important in the detoxication of the herbicide) are not significantly different in dwarf and normal maize. Our data suggest that EPTC phytotoxicity is related to alterations in gibberellin metabolism in maize plants.

Exogenous Cytokinins Cause Cell Separation and Cell Expansion in the Root Tip Cortex of Zea mays

Root tips, entire roots, and entire seedlings of Zea mays were cultured in a modified B5 medium containing kinetin, zeatin, or 6-benzylaminopurine at either 0.46 or 4.65 μM. After 6 days, the diameter of the root tips in all three cytokinin-containing media was ca. fourfold that of the controls. Fluorescence microscopic analyses of the cytokinin-treated roots showed expansion and partial isolation of cortical cells. Files of cells were separated by intercellular spaces parallel to the root axis. Electron microscopic observations indicated that the cell isolation resulted from dissolution of the middle lamellae. Ethylene was not involved in cell expansion and cell isolation. Cytokinin-induced separation of the cortical cells probably resulted from the intensification of localized cell wall loosening in the growing root.