Regulation of Assimilatory Sulfate Reduction by Cadmium in Zea mays L

Plants cultivated with Cd can produce large amounts of phytochelatins. Since these compounds contain much cysteine, these plants should have an increased rate of assimilatory sulfate reduction, the biosynthetic pathway leading to cysteine. To test this prediction, the effect of Cd on growth, sulfate assimilation in vivo and extractable activity of two enzymes of sulfate reduction, ATP-sulfurylase (EC 2.7.7.4) and adenosine 5′-phosphosulfate sulfotransferase were measured in maize (Zea mays L.) seedlings. For comparison, nitrate reductase activity was determined. In 9-day-old cultures, the increase in fresh and dry weight was significantly inhibited by 50 micromolar and more Cd in the roots and by 100 and 200 micromolar in the shoots. Seedlings cultivated with 50 micromolar Cd for 5 days incorporated more label from ³⁵SO₄²⁻ into higher molecular weight compounds than did controls, indicating that the predicted increase in the rate of assimilatory sulfate reduction took place. Consistent with this finding, an increased level of the extractable activity of both ATP-sulfurylase and adenosine 5′-phosphosulfate sulfotransferase was measured in the roots of these plants at 50 micromolar Cd and at higher concentrations. This effect was reversible after removal of Cd from the nutrient solution. In the leaves, a significant positive effect of Cd was detected at 5 micromolar for ATP-sulfurylase and at 5 and 20 micromolar for adenosine 5′-phosphosulfate sulfotransferase. At higher Cd concentrations, both enzyme activities were at levels below the control. Nitrate reductase (EC 1.6.6.1) activity decreased at 50 micromolar or more Cd in the roots and was similarly affected as ATP-sulfurylase activity in the primary leaves.     

Intercellular Localization of Assimilatory Sulfate Reduction in Leaves of Zea mays and Triticum aestivum

The intercellular distribution of assimilatory sulfate reduction enzymes between mesophyll and bundle sheath cells was analyzed in maize (Zea mays L.) and wheat (Triticum aestivum L.) leaves. In maize, a C₄ plant, 96 to 100% of adenosine 5′-phosphosulfate sulfotransferase and 92 to 100% of ATP sulfurylase activity (EC 2.7.7.4) was detected in the bundle sheath cells. Sulfite reductase (EC 1.8.7.1) and O-acetyl-l-serine sulfhydrylase (EC 4.2.99.8) were found in both bundle sheath and mesophyll cell types. In wheat, a C₃ species, ATP sulfurylase and adenosine 5′-phosphosulfate sulfotransferase were found at equivalent activities in both mesophyll and bundle sheath cells. Leaves of etiolated maize plants contained appreciable ATP sulfurylase activity but only trace adenosine 5′-phosphosulfate sulfotransferase activity. Both enzyme activities increased in the bundle sheath cells during greening but remained at negligible levels in mesophyll cells. In leaves of maize grown without addition of a sulfur source for 12 d, the specific activity of adenosine 5′-phosphosulfate sulfotransferase and ATP sulfurylase in the bundle sheath cells was higher than in the controls. In the mesophyll cells, however, both enzyme activities remained undetectable. The intercellular distribution of enzymes would indicate that the first two steps of sulfur assimilation are restricted to the bundle sheath cells of C₄ plants, and this restriction is independent of ontogeny and the sulfur nutritional status of the plants.     

Influence of Chilling Stress on the Intercellular Distribution of Assimilatory Sulfate Reduction and Thiols in Zea mays

Abstract: The effect of chilling on the intercellular distribution of mRNAs for enzymes of assimilatory sulfate reduction, the activity of adenosine 5'-phosphosulfate reductase (APR), and the level of glutathione was analysed in leaves and roots of maize ( Zea mays L). At 25 °C the mRNAs for APR, ATP sulfurylase, and sulfite reductase accumulated in bundle-sheath only, whereas the mRNA for O-acetylserine sulfhydrylase was also detected in mesophyll cells. Glutathione was predominantly detected in mesophyll cells; however, oxidized glutathione was equally distributed between the two cell types. Chilling at 12 °C induced oxidative stress which resulted in increased concentrations of oxidized glutathione in both cell types and a prominent increase of APR mRNA and activity in bundle-sheath cells. After chilling, mRNAs for APR and sulfite reductase, as well as low APR activity, were detected in mesophyll cells. In roots, APR mRNA and activity were at higher levels in root tips than in the mature root and were greatly increased after chilling. These results demonstrate that chilling stress affected the levels and the intercellular distribution of mRNAs for enzymes of sulfate assimilation.     

Regulation of Sulfate Assimilation in Plants : XIII. Assimilatory Sulfate Reduction during Ontogenesis of Primary Leaves of Phaseolus vulgaris L

The correlation between the extractable activities of three key enzymes of assimilatory sulfate reduction and the in vivo incorporation of ³⁵SO₄²⁻ into amino acids, proteins, and sulfolipids was investigated from greening to senescence in primary leaves of beans (Phaseolus vulgaris L.). The total extractable activity of ATP sulfurylase (EC 2.7.7.4) and of adenosine 5′-phosphosulfate sulfotransferase reached a maximum in the leaves of approximately 7- and 11-day-old seedlings, respectively. During senescence, there was a decrease in both enzyme activities. After approximately 17 days, no appreciable activities remained. In contrast, total O-acetyl-l-serine sulfhydrylase (EC 4.3.99.8) activity decreased to only approximately 50% of the maximal value during the same period. The in vivo incorporation of ³⁵SO₄²⁻ into amino acid and protein fractions showed a time-course similar to that of the total extractable adenosine 5′-phosphosulfate sulfotransferase activity. Both cysteine and sulfate markedly decreased during senescence. The total extractable activity of ribulosebisphosphate carboxylase (EC 4.1.1.39) was maximal in the primary leaves of 13-day-old seedlings, and approximately 40% of this value was still detectable after 17 days. Taken together with results from the literature, these results show that assimilatory sulfate reduction in primary leaves of P. vulgaris L. stops before CO₂ and nitrate assimilation.     

Assimilatory Sulfate Reduction by the Hemoflagellate Leishmania tarentolae1

SYNOPSIS. Continuous growth of one cell line (UCI variant) of Leishmania tarentolae was achieved in the absence of organic sulfur. These cells were able to use sodium sulfate, and, to a limited extent, sodium sulfite as their sole sulfur source and could utilize methionine sulfoxide in place of L-methionine. A related cell line (RU variant) was unable to grow in organic sulfate-free media nor could these cells utilize methionine sulfoxide. UCI promastigotes incorporated significant amounts of ³⁵S sodium sulfate; killed cells did not take up the label. ³⁵S incorporation was inhibited by sodium molybdate (5 × 10^?4 M), sodium arsenite (5 × 10^?4 M), 2,4-dinitrophenol (1 × 10^?4 M), or KCN (5 × 10^?4 M). RU promastigotes did not incorporate significant amounts of ³⁵S sodium sulfate. Thin layer chromatographs of protein hydrolysates from UCI cells incubated in ³⁵S sodium sulfate revealed several radio opaque spots, one of which had chromatographic properties of cystine. UCI variants of L. tarentolae were therefore capable of assimilatory sulfate reduction whereas RU cells lacked this ability.     

Regulation of phosphoenolpyruvate carboxylase of Zea mays by metabolites

Crude preparations of phosphoenolpyruvate carboxylase obtained from aetiolated seedlings of Zea mays are unstable but can be stabilized with glycerol. At the pH optimum of 8.3, the K(m) value for phosphoenolpyruvate is 80mum. When assayed at 30 degrees C, the enzyme shows normal Michaelis-Menten kinetics, but when assayed at 45 degrees C sigmoid kinetics are exhibited. At pH7.0 the enzyme is inhibited by a number of dicarboxylic acids and by glutamate and aspartate. d and l forms of the hydroxy acids and amino acids are inhibitory and the kinetics approximate to simple non-competitive inhibition. The same compounds produce less inhibition at pH7.6 than at pH7.0 and the kinetics of inhibition are more complex. The enzyme is activated by P(i), by SO(4) (2-) and by a number of sugar phosphates. Maximum activation occurs at acid pH values, where enzyme activity is lowest. The enzyme is activated by AMP and inhibited by ADP and ATP so that the response to energy charge is of the R type and is thus at variance with Atkinson's (1968) concept of energy charge. The physiological significance of the response to metabolites is discussed.     

Regulation of Nitrate Reductase Activity in Corn (Zea mays L.) Seedlings by Endogenous Metabolites

Primary and secondary metabolites of inorganic nitrogen metabolism were evaluated as inhibitors of nitrate reductase (EC 1.6.6.1) induction in green leaf tissue of corn seedlings. Nitrite, nitropropionic acid, ammonium ions, and amino acids were not effective as inhibitors of nitrate reductase activity or synthesis. Increasing α-amino nitrogen and protein content of intact corn seedlings by culture techniques significantly enhanced rather than decreased the potential for induction of nitrate reductase activity in excised seedlings.     

Rapid and Reversible High-Affinity Binding of the Dinitroaniline Herbicide Oryzalin to Tubulin from Zea mays L

Oryzalin, a dinitroaniline herbicide, was previously reported to bind to plant tubulin with a moderate strengthe interaction (dissociation constant [Kd] = 8.4 [mu]M) that appeared inconsistent with the nanomolar concentrations of drug that cause the loss of microtubules, inhibit mitosis, and produce herbicidal effects in plants (L.C. Morejohn, T.E. Bureau, J. Mole-Bajer, A.S. Bajer, D.E. Fosket [1987] Planta 172: 252-264). To characterize further the mechanism of action of oryzalin, both kinetic and quasi-equilibrium ligand-binding methods were used to examine the interaction of [14C]-oryzalin with tubulin from cultured cells of maize (Zea mays L. cv Black Mexican Sweet). Oryzalin binds to maize tubulin dimer via a rapid and pH-dependent interaction to form a tubulin-oryzalin complex. Both the tubulin-oryzalin binding strength and stoichiometry are underestimated substantially when measured by kinetic binding methods, because the tubulin-oryzalin complex dissociates rapidly into unliganded tubulin and free oryzalin. Also, an uncharacterized factor(s) that is co-isolated with maize tubulin was found to noncompetitively inhibit oryzalin binding to the dimer. Quasi-equilibrium binding measurements of the tubulin-oryzalin complex using purified maize dimer afforded a Kd of 95 nM (pH 6.9; 23[deg]C) and an estimated maximum molar binding stoichiometry of 0.5. No binding of oryzalin to pure bovine brain tubulin was detected by equilibrium dialysis, and oryzalin has no discernible effect on microtubules in mouse 3T3 fibroblasts, indicating an absence of the oryzalin-binding site on mammalian tubulin. Oryzalin binds to pure taxol-stabilized maize microtubules in a polymer mass- and number-dependent manner, although polymerized tubulin has a much lower oryzalin-binding capacity than unpolymerized tubulin. Much more oryzalin is incorporated into polyment during taxol-induced assembly of pure maize tubulin, and half-maximal inhibition of the rapid phase of taxol-induced polymerization of 5 [mu]M tubulin is obtained with 700 [mu]M oryzalin. The data are consistent with a molecular mechanism whereby oryzalin binds rapidly, reversibly, and with high affinity to the plant tubulin dimer to form a tubulin-oryzalin complex that, at concentrations substoichiometric to tubulin, copolymerizes with unliganded tubulin and slows further assembly. Because half-maximal inhibition of maize callus growth is produced by 37 nM oryzalin, the herbicidal effects of oryzalin appear to result from a substoichiometric poisoning of microtubules.     

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.     

Regulation of flower development in cultured ears of maize (Zea mays L.)

Summary Young ears of maize were cultured in two different liquid media containing either kinetin (KN) or kinetin + gibberellic acid (KN + GA₃) in order to manipulate stamen and gynoecium development. In KN medium, stamens developed and gynoecia aborted in the flowers of the cultured immature ears. In the KN + GA₃ medium, however, ovaries with silks developed and stamens aborted. These differential morphological events were recorded with SEM photomicrographs at regular intervals after excision of ear inflorescences. In addition, the mitotic activity in the developing or aborting organs was determined over a 75-h period. It increased from 6% to 14% in developing organs (i.e. stamens in KN medium, and gynoecia in KN + GA₃ medium) and gradually decreased to 1% in the degenerating organs (i.e. gynoecia in KN medium, and stamens in KN + GA₃ medium) by 45 h of culture. The mitotic activity reached zero in degenerating flower organs by 75 h of culture. Whether these differential sensitivities to the exogenously applied members of these two plant growth regulator classes are unique to our in vitro system or reflect a more general control feature of in vivo inflorescences must await further clarification.     

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     

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     

Regulation of IBA synthetase from maize (Zea mays L.) by drought stress and ABA

The rate of indole-3-butyric acid (IBA) synthesis in maize seedlingsis dependent on the culture conditions of the plants. When theseedlings were grown on filter paper soaked with different amountsof water, the activity of IBA synthetase differed strongly.High amounts of water (150 and 200 ml per bowl) inhibited IBAsynthesis completely in vitro, whereas 30 and 50 ml water perbowl increased the activity dramatically. Under conditions whereIBA synthetase was inhibited (150 ml H₂O), an increase of enzymeactivity was observed when abscisic acid (ABA) was exogenouslyadded in concentrations between 510^–4 to 510^–7M. Under ‘drought’ conditions (50 ml H₂O per bowl)the same ABA concentrations were inhibitory. Jasmonic acid andsalicylic acid also enhanced IBA synthetase activity to someextent, whereas indole-3-acetic acid (IAA) and kinetin had noeffect. Activity could also be enhanced by osmotic stress (NaCIand sorbitol), but not under temperature stress. In accompanyinginvestigations the endogenous contents of IAA, IBA, and ABAunder the different culture conditions have been determinedas well as the energy charge of the seedlings. Similar observationshave been made with Amaranthus, wheat and pea seedlings Key words: Abscisic acid, Amaranthus paniculatus, drought stress, inole-3-butyric acid biosynthesis, Pisum sativum, Triticum aestivum, Zea mays     

Herbicide effects on phenolic metabolism in maize (Zea mays L.)and soybean (Glycine max L.) seedling

The activities of phenylalanine ammonia lyase [PAL; EC 4.3.1.5 [EC] ]and chalcone isomerase [Cl; EC 5.5.1.5 [EC] ] as well as the contentsof anthocyanin and total soluble hydroxyphenolic compounds wereinvestigated in maize (Zea mays L.) and soybean (Glycine maxL.) seedlings 120 h after treatment with the field dose of fiveherbicides from different groups (trifluralin, fluometuron,atrazine, alachlor, and rimsulfuron) having varied modes ofaction. The fresh weight of both species was greatly decreasedby trifluralin followed by fluometuron and atrazine. The dryweight was, in general, only slightly decreased by all the herbicideswith the largest response with trifluralin. On the other hand,the activities of PAL and Cl were greatly enhanced in both speciesby alachlor and rimsulfuron, but decreased by trifluralin. Fluometuroninduced decreases in PAL activity of maize only and decreasedCl activity of maize and soybean seedlings. Moreover, hydroxyphenoliccompounds were increased in both species by alachlor and rimsulfuronand decreased by trifluralin and atrazine. Similarly, anthocyanincontent was increased in both seedlings by alachlor and rimsulfuron,but decreased by trifluralin and fluometuron, whereas atrazinedecreased the anthocyanin content in maize only. The presentresults indicate that stress is maintained by the differentherbicides and confirm the controlling action of PAL and Clon the production of anthocyanin and phenolic compounds duringthe induced state of stress. In addition, dry weight reductionappeared to coincide with the changes in the parameters of secondarymetabolism, suggesting a regulatory role of secondary metabolismon seedling growth. Key words: Herbicides, phenylalanine ammonia lyase, chalcone isomerase, anthocyanin, hydroxyphenolics     

Cytogenetic studies of chromosome replication in Zea mays L.: Regulation of homologue synchrony

Maize stocks with or without additional heterochromatin (a B chromosome or abnormal chromosome 10), and a stock heteromorphic for a reciprocal translocation, were used in a study of homologue synchrony of replication. Batches of attached primary roots were pulse labelled with ³H-TdR and sampled at hourly intervals during the S period (at 18° C). Silver grain counts over each chromosome arm from 25 cells at each collection period were submitted to analyses. Qualitative synchrony (concordance) was tested between chromosome arms using a χ² test. Quantitative synchrony was tested with an I-divergence test. Results from these tests in the control experiments were consistent with the hypothesis of meta-synchrony of homologue replication. The addition of heterochromatin in the form of a B chromosome or an abnormal 10 chromosome increased asynchrony two-fold. The insertion of a heteromorphic translocation into the genome produced a similar though less pronounced effect.     

Regulation of ACC-Dependent Ethylene Production by Excised Leaves from Normal and Albino Zea mays L. Seedlings

Dunlap, J. R. 1988. Regulation of ACC-dependent ethylene productionby excised leaves from normal and albino Zea mays L. seedlings.—J.exp. Bot. 39: 1079–1089. Albino corn (Zea mays L.) seedlings lacking natural leaf pigmentswere obtained by germinating seeds treated with fluridone, aninhibitor of carotenoid biosynthesis. Basal rates of ethyleneproduction were less than 2.0 nl g^–1 fr. wt h^–1in both treated (albino) and untreated (normal) leaves but increasedby 10- to 20-fold in the presence of added ACC. ACC-dependentethylene production (ADEP) was inhibited by cobalt or cyanideions and stimulated by NaHCO₃, CO₂ and light. ADEP in both tissueswas stimulated by glucose, fructose, galactose and sucrose.The accumulation of respiratory CO₂ did not account for thecarbohydrate response. The decline in the ADEP characteristicof albino leaf tissue was slowed by incubation in the presenceof sucrose. IAA and ABA stimulated ADEP in normal leaves butinhibited ADEP in albino leaves. Sucrose-stimulated ADEP wasinhibited in albino leaf tissue treated with IAA or ABA indicatinga possible role for the chloroplast in carbohydrate-facilitatedADEP. However, results from this study suggest that chloroplastsperform a function in the regulation of ethylene productionby leaf tissue that extends beyond merely influencing internallevels of CO₂. In the absence of detectable ACC, EFE was responsiblefor the entire series of responses expressed in regulation ofethylene biosynthesis by corn seedling leaf tissue. Key words: Corn, ethylene, sugars, phytohormones     

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     

Epistasis in maize (Zea mays L.)

Summary Three flint and three dent maize (Zea mays L.) inbred lines, their possible F₁ crosses, F₂ and backcross progenies, and all possible three-way crosses were evaluated in a three-year experiment for yield, ear moisture, and plant height. The purpose was to estimate genetic parameters in European breeding materials from (i) generation means analysis, (ii) diallel analysis of generation means, and (iii) analysis of F₁ and three-way cross hybrids. Method (i) was based on the F-metric model and methods (ii) and (iii) on the Eberhart-Gardner (1966) genetic model; both models extended for heterotic maternal effects.Differences among generation means for yield and plant height were mainly attributable to dominance effects. Epistatic effects were significantly different from zero in a few crosses and considerably reduced heterosis in both traits. Additive x additive and domiance x dominance effects for yield were consistently positive and negative, respectively. Significant maternal effects were established to the advantage of generations with a heterozygous seed parent. In the diallel analysis, mean squares for dominance effects were greater than for additive effects for yield and plant height but smaller for ear moisture. Though significant for yield and plant height, epistatic variation was small compared to additive and dominance variation. Estimates of additive x additive epistasis for yield were significantly negative in 11 of 15 crosses, suggesting that advantageous gene combinations in the lines had been disrupted by recombination in the segregating generations. The analysis of hybrids supported the above findings regarding the analysis of variance. However, the estimates of additive x additive epistasis for yield were considerably smaller and only minimally correlated with those from the diallel analysis. Use of noninbred materials as opposed to materials with different levels of inbreeding is considered the main reason for the discrepancies in the results.     

Nitrate Reductase Activity in Maize (Zea mays L.) Leaves: I. Regulation by Nitrate Flux

The roles that leaf nitrate content and nitrate flux play in regulating the levels of nitrate reductase activity (NRA) were investigated in 8- to 14-day old maize (Zea mays L.) plants containing high nitrate levels while other environmental and endogenous factors were constant. The nitrate flux of intact plants was measured from the product of the transpiration rate and the concentration of nitrate in the xylem. NRA decreased when the seedlings were deprived of nitrate. The nitrate flux and the leaf nitrate content also decreased. When nitrate was resupplied to the roots, all three parameters increased.     

Etioplast Development in Dark-grown Leaves of Zea mays L

The ultrastructure of etioplasts and the acyl lipid and the fatty acid composition of sequential 2-centimeter sections cut from the base (youngest) to the top (oldest) of nonilluminated 5-day-old etiolated leaves of Zea mays L., and the acyl lipid and fatty acid composition of the etioplasts isolated from them have been investigated. There is a 2.5-fold increase in the size of the plastids from the base to the tip of the leaf, and an increase both in the size of the prolamellar body and in the length of lamellae attached to it. The etioplasts in the bundle sheath and mesophyll cells of the older, but not the younger leaf tissue, are morphologically distinct. The monogalactosyl and digalactosyldiglycerides, phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol were the only detectable acyl lipids in the isolated etioplast fractions. Together with phosphatidylethanolamine these were also the major acyl lipids in the whole leaf sections. With increasing age of the leaf tissue, increases occurred in two of the major plastid lipids, monogalactosyldiglyceride and phosphatidylglycerol, while the levels of essentially nonplastid lipids remained constant or declined slightly. The monogalactosyldiglyceride to digalactosyldiglyceride ratio increased from 0.4 to 1.1 in the tissue sections of increasing age and from 0.7 to 1.2 in the etioplasts isolated from them. Similarly, the galactolipid to phospholipid ratio increased from 0.8 to 1.4 in the tissue and from 0.5 to 4.5 in the isolated plastids. In the latter, the proportions of phosphatidylglycerol (as a per cent of total phospholipid) increased from 20 to 41% with increasing age of plastids.

Linolenic acid was the major fatty acid in the total lipid of each of the etioplast fractions, but it was only the major fatty acid in the total lipid of the oldest leaf tissue. Its proportion in both total lipid extracts and individual lipids increased with age. The trans Δ³ hexadecenoic acid was absent from all lipids. The protochlorophyllide content of the tissue increased with age. The results are discussed in relation to the use of illuminated etiolated leaves for studying chloroplast development.