Inducing salt tolerance in maize (Zea mays L.) through seed priming with chloride salts: Growth and ion transport at early growth stages

The study was conducted to determine whether salt tolerance could be induced in maize at germination stage by soaking of seeds for 8 h in distilled water or in 200 meq·L⁻¹ of NaCl, KCl, CaCl₂·2H₂O. Both primed and un-primed seeds were subjected for 14 days to 0, 100 or 200 mol·m⁻³ NaCl under controlled conditions. Although all priming agents were effective in alleviating adverse effects of salt stress on maize at germination stage, CaCl₂·2H₂O proved to be more effective since the seeds primed with this salt had significantly higher final germination, rate of germination and fresh and dry weights of plumules and radicles than those treated with other salts or distilled water. Concentration of Na⁺, K⁺ and Ca²⁺ increased significantly in all parts of germinating seeds of maize seeds primed with NaCl, KCl, or CaCl₂·2H₂O, respectively. In addition, seeds primed with CaCl₂·2H₂O were the highest in Cl⁻ accumulation in all parts of the germinating seeds, followed by seeds treated with NaCl and KCl. Most of the Ca²⁺ was retained in seeds and mesocotyl, because of which, transport of this ion to plumules and radicles was low.     

Membrane stabilization by abscisic acid under cold aids proline in alleviating chilling injury in maize (Zea mays L.) cultured cells

Previous studies of maize suspension‐cultured cells showed that abscisic acid (ABA) treatment at warm temperatures improved the tolerance of cells to subsequent chilling. In the present study, it is shown that both ABA‐treated and untreated maize cells accumulated proline in response to chilling. However, ABA‐treated cells displayed less lipid peroxidation during chilling, and thus, unlike untreated cells, were able to retain the accumulated proline intracellularly. Proline application experiments indicate that an intracellular proline level higher than 2 µmole (g FW)^?1 prior to chilling was needed to meaningfully reduce chilling‐enhanced lipid peroxidation and significantly improve chilling tolerance. The results suggest that total proline accumulation in ABA‐treated as well as untreated cells during chilling was enough to potentially improve chilling tolerance, but proline leakage rendered the control cells unable to benefit from the endogenous synthesis of proline in relation to the alleviation of chilling injury. Proline participated in chilling tolerance improvement in ABA‐treated maize cells, as evidenced by: (1) the inhibition of proline accumulation by l ‐methionine‐d , l ‐sulphoximine (MSO), an inhibitor of glutamine synthetase, reduced ABA‐improved chilling tolerance, and (2) the addition of glutamine into the medium prevented the MSO‐induced reduction in chilling tolerance. The revised relationship between proline accumulation and membrane stability at cold is discussed in the light of these current findings.     

Biochemical composition of maize (Zea mays L.) pollen

Summary Pollen grains containing either the Wx, wx, Su ₁, su ₁, Sh ₂ or sh ₂ alleles were stored at 0, 1, 2, 3, 4 and 5 days at 2 °C. After each storage period, a portion of pollen from each genotype was analyzed for free amino acid content. Over all genotypes, storage significantly altered the content of all 16 amino acids measured. With increasing storage, a relatively consistent increase in aspartic acid, isoleucine, leucine, phenylalanine, ethanolanine, aminobutyric acid, NH₃ and lysine was found. A relatively consistent decrease in glutamic acid, proline, glycine and alanine occurred with increasing storage. No consistent response to storage was obtained with threonine-serine, valine, histidine and the unknown. Apparently, storage or stage of viability loss has a pronounced effect on amino acid metabolism in maize pollen grains. The experiment was designed so that comparisons free of genetic background effects could be made between alleles at each locus. Significant allele X storage interactions at each locus were found as follows: at the waxy locus, aspartic acid, glycine, alanine and ethanolanine; at the sugary locus, aspartic acid, alanine, ethanolanine and aminobutyric acid; and at the shrunken locus, aspartic acid, alanine, valine, leucine and ethanolanine. Amino acid metabolism is apparently influenced by the action of the alleles at these loci. The differences between the loci in the amino acids affected indicate the different areas of amino acid metabolism are influenced by each locus.Journal Series Paper No. 4425, Florida Agricultural Experiment Station.     

Biochemical composition of maize (Zea mays L.) pollen

Summary Mean percentages of sugars, water-soluble polysaccharides, starch, total carbohydrates and lipids were 40.1, 7.4, 28.6, 76.1, and 1.8 respectively. Differences among the mutants were found only for water-soluble polysaccharides with both wx and sh ₂ decreasing the percentage a small but significant amount. In terms of the various carbohydrates measured, no correlation was found between the expression of these mutants in the pollen and the kernel.

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Zusammenfassung Die Untersuchung des Kohlenhydrat- und Lipid-Gehaltes im Pollen der Endosperm-Mutanten waxy, shrunken und sugary vom Mais ergab einen gemittelten Gehalt an Zucker von 40,1%, wasserlöslichen Polysacchariden 7,4%, Stärke 28,6, Gesamtkohlenhydraten 76,1% und Lipiden 1,8%.Unterschiede zwischen den Mutanten wurden lediglich hinsichtlich der wasserlöslichen Polysaccharide gefunden, und zwar bei wx und sh ₂, die einen signifikant niedrigeren Gehalt aufwiesen.Hinsichtlich der verschiedenen analysierten Kohlenhydrate wurde keine Korrelation zwischen der Expression der Mutanten im Pollen und in den Karyopsen gefunden.

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Herrn Professor Dr. J. Straub (Köln-Vogelsang) zu seinem 60. Geburtstag gewidmet.

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Journal Series Paper No. 3621, Florida Agricultural Experiment Station.     

Synergistic effect of antioxidant system and osmolyte in hydrogen sulfide and salicylic acid crosstalk-induced heat tolerance in maize (Zea mays L.) seedlings

Salicylic acid (SA), is a plant hormone with multifunction that is involved in plant growth, development and the acquisition of stress tolerance. Hydrogen sulfide (H₂S) is emerging similar functions, but crosstalk between SA and H₂S in the acquisition of heat tolerance is not clear. Our recent study firstly reported that SA treatment enhanced the activity of L-cysteine desulfhydrase (L-DES), a key enzyme in H₂S biosynthesis, followed by induced endogenous H₂S accumulation, which in turn improved the heat tolerance of maize seedlings.¹ In addition, NaHS, a H₂S donor, enhanced SA-induced heat tolerance, while its biosynthesis inhibitor DL-propargylglycine (PAG) and scavenger hydroxylamine (HT) weakened SA-induced heat tolerance. Also, NaHS had no significant effect on SA accumulation and its biosynthesis enzymes phenylalanine ammonia lyase (PAL) and benzoic-acid-2-hydroxylase (BA2H) activities, as well as significant difference was not observed in NaHS-induced heat tolerance of maize seedlings by SA biosynthesis inhibitors paclobutrazol (PAC) and 2-aminoindan-2-phosph- onic acid (AIP) treatment.¹ Further study displayed that SA induced osmolytes (proline, betaine and trehalose) accumulation and enhancement in activity of antioxidant system in maize seedlings. These results showed that antioxidant system and osmolyte play a synergistic role in SA and H₂S crosstalk-induced heat tolerance of maize seedlings.     

Biochemical composition of maize (Zea mays L.) pollen

Summary Proline was the most abundant amino acid with a mean value of 186.28 moles/mg dry pollen. The other amino acids tested were below 33 moles/mg dry pollen. The mutant wx significantly increased aspartic acid, valine, histidine and an unknown but significantly decreased aminobutyric acid. The mutant sh ₂ significantly increased glutamic acid, proline, lysine, histidine and an unknown but significantly decreased aspartic acid and aminobutyric acid. The effect of su ₁ was altered by the genetic background involved. In one genetic background, su ₁ did not significantly increase any amino acid but significantly decreased alanine and aminobutyric acid. However, in a distinctly different background, su ₁ significantly increased aminobutyric acid but significantly decreased aspartic acid and glutamic acid. Apparently the genetic background is capable of producing major shifts in the amino acid pattern in addition to the action of these mutants.The fatty acids, palmitic and linolenic were the most common with percentages of 54.1 and 34.4 respectively. The mutants tested did not affect the fatty acid distribution.

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Zusammenfassung Prolin war die am reichlichsten vorkommende Aminosäure mit einem mittleren Gehalt von 186,28 Mikromol per mg trockenen Pollen. Die anderen Aminosäuren erreichten weniger als 33 Mikrogramm per mg trockenen Pollen.Die Mutante wx zeigte einen signifikant erhöhten Gehalt an Asparaginsäure, Valin, Histidin, sowie einer nicht identifizierten Komponente, während der Gehalt an -Aminobuttersäure signifikant erniedrigt war. Die Mutante sh ₂ ist gekennzeichnet durch einen signifikant erhöhten Gehalt an Glutaminsäure, Prolin, Lysin, Histidin, sowie einer unbekannten Fraktion; der Gehalt an Asparaginsäure und -Aminobuttersäure war dagegen signifikant erniedrigt. Die Wirkung des mutierten Gens su ₁ wurde durch das übrige Genom, in dem es sich befand, geändert. In dem einen genetischen Milieu verursachte su ₁ keine signifikante Erhöhung des Gehaltes irgend einer Aminosäure, während der Gehalt an Alanin und -Aminobuttersäure signifikant erniedrigt war. In einem anderen genetischen Milieu jedoch zeigte su ₁ eine signifikante Erhöhung der -Aminobuttersäure; Asparaginsäure und Glutaminsäure waren signifikant erniedrigt.Offensichtlich ist das übrige Genom zusätzlich zu der Wirkung der genannten Mutanten in der Lage, wesentliche Verschiebungen im Verteilungsmuster der Aminosäuren zu verursachen.Von den Fettsäuren wurden am häufigsten Palmitin- und Linolen-Säure mit einem Gehalt von 54,1 bzw. 34,4% gefunden. Die untersuchten Endosperm-Mutanten zeigten keinen Einfluß auf die Fettsäureverteilung im Pollen.

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Journal Series Paper No. 3468, Florida Agricultural Experiment Station.     

Biochemical characterization of a new maize (Zea mays L.) peptide growth factor

Coordination of cell growth and cell division is very important for living organisms in order for these to develop harmonically. The present research is concerned with the purification and characterization of a new peptide hormone, namely ZmIGF (Zea mays insulin-like growth factor), which regulates growth and cell division in maize tissues. ZmIGF is a peptide of 5.7 kDa, as determined by mass spectroscopy. It was isolated either from maize embryonic axes of 48-h germinated seeds or from embryogenic callus and purified through several chromatographic procedures to obtain a single peak as shown by Reverse Phase High-Performance Liquid Chromatography (RP-HPLC). This peptide exhibits a well defined α-helix structure by circular dichroism analysis, similar to that reported for Insulin or for Insulin-like growth factor (IGF-1). Further, ZmIGF seems to perform, in maize, a similar function to that reported for insulin or peptides from the IGF family in animals. Indeed, maize tissues stimulated either by ZmIGF or insulin showed to induce selective synthesis of ribosomal proteins as well as of DNA. Taken together, the previously mentioned data strongly suggest that plants contain a peptide hormone of the IGF family, highly conserved through evolution that regulates growth and development.     

The response of maize (Zea mays L.) plant assisted with bacterial consortium and fertilizer under oily sludge

The objective of this study was to evaluate the role of PGPR consortium and fertilizer alone and in combination on the physiology of maize grown under oily sludge stress environment as well on the soil nutrient status. Consortium was prepared from Bacillus cereus (Acc KR232400), Bacillus altitudinis (Acc KF859970), Comamonas (Delftia) belonging to family Comamonadacea (Acc KF859971) and Stenotrophomonasmaltophilia (Acc KF859973). The experiment was conducted in pots with complete randomized design with four replicates and kept in field. Oily sludge was mixed in ml and Ammonium nitrate and Diammonium phosphate (DAP) were added at 70 ug/g and 7ug/g at sowing. The plant was harvested at 21 d for estimation of protein, proline and antioxidant enzymes superoxide dismutase (SOD) and peroxidase (POD). To study the degradation, total petroleum hydrocarbon was extracted by soxhelt extraction and extract was analyzed by GC-FID at different period after incubation. Combined application of consortium and fertilizer enhanced the germination %, protein and, proline content by 90,130 and 99% higher than untreated maize plants. Bioavailability of macro and micro nutrient was also enhanced with consortium and fertilizer in oily sludge. The consortium and fertilizer in combined treatment decreased the superoxide dismutase (SOD), peroxidase dismutase (POD) of the maize leaves grown in oily sludge. Degradation of total petroleum hydrocarbon (TPHs) was 59% higher in combined application of consortium and fertilizer than untreated maize at 3 d. The bacterial consortium can enhanced the maize tolerance to oily sludge and enhanced degradation of total petroleum hydrocarbon (TPHs). The maize can be considered as tolerant plant species to remediate oily sludge contaminated soils.     

Hematoxylin staining as a phenotypic index for aluminum tolerance selection in tropical maize (Zea mays L.)

Hematoxylin staining is an early indicator of Aluminum (Al) toxicity effects on the apices of young, developing roots grown in nutrient solution. In this work, the potential of this technique as a reliable and reproducible phenotypic index for Al tolerance in tropical maize genotypes was assessed, with its performance systematically compared to two other parameters widely used in breeding programs – relative seminal-root length (RSRL) and net seminal-root length (NSRL). Seeding roots from contrasting genotypes for Al sensitivity stained remarkably different after 24- and 48-h and 7-day exposures to 222 μM Al in nutrient solution, with the Al-dye complex being detected in both the outer (epidermis) and inner (cortex) portions of the roots from the sensitive cultivar. Hematoxylin staining was compared to the RSRL and NSRL parameters using 20 families from the third generation of selfing (S3) following the cross between two contrasting inbred lines that had been previously classified by the RSRL index in an independent procedure. The coloration technique showed the highest capacity to discriminate among tolerant and sensitive genotypes and displayed significant correlation coefficients to the other two indexes. Evaluation of the results from diallel crosses involving nine inbred lines proved that hematoxylin staining was also particularly adequate for identifying expressive hybrid vigor, as demonstrated by the general (GCA) and specific (SCA) combining ability estimates obtained by using the three indexes simultaneously. Hence, hematoxylin staining of Al-stressed root apices appears to be a powerful tool to assist in Al-tolerance selection in tropical maize breeding programs. Received: 21 January 1999 / Accepted: 1 February 1999     

Subcellular localization of glutelin-2 in maize (Zea mays L.) endosperm

Accumulation of the 28 KD protein of the glutelin-(G2) fraction was followed in developing maize endosperm, using sodium dodecylsulphate polyacrylamide gel electrophoresis (SDS-PAGE) and peak integration of scanned gels. 28 KD glutelin-2 could already be observed from 15 days after pollination and its accumulates reached a plateau during the second half of the development period. The process of biosynthesis of 28 KD glutelin-2 and zeins occurs in a parallel way. Subcellular fractions obtained from linear sucrose gradient centrifugation of developing maize endosperms were analyzed by SDS-PAGE and immunoblotting using a serum reacting against glutelin-2 and 14 KD Z2. Glutelin-2 was found to be present in the protein bodies when subcellular fractionation was carried out without dithiothreitol (DTT). The presence of a reducing agent causes the elution of glutelin-2 from protein bodies. Immunocytochemical labelling using the protein A-colloidal gold technique in protein bodies incubated with anti-G2 IgG revealed that G2 is located mainly in the periphery of protein bodies. These results are interpreted as indicating a structural role for glutelins in protein bodies.     

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.     

Free proline accumulation in maize (Zea mays L.) subjected to prolonged waterlogging

Summary Free proline accumulation was measured in two maize genotypes (Ganga-2 and D747) subjected to waterlogging for three weeks at the knee high stage. The initial content of free proline was same in both the genotypes (0.1 micromole per gram fresh weight of leaves). The free proline content increased in both the genotypes when the plants were subjected to waterlogging. However, Ganga-2 accumulated more free proline than D747. Ganga-2 appeared to be more waterlogging tolerant than D-747.     

Genomic prediction of seedling root length in maize (Zea mays L.)

Genotypes with extreme phenotypes are valuable for studying ‘difficult’ quantitative traits. Genomic prediction (GP) might allow the identification of such extremes by phenotyping a training population of limited size and predicting genotypes with extreme phenotypes in large sequences of germplasm collections. We tested this approach employing seedling root traits in maize and the extensively genotyped Ames Panel. A training population made up of 384 inbred lines from the Ames Panel was phenotyped by extracting root traits from images using the software program aria . A ridge regression best linear unbiased prediction strategy was used to train a GP model. Genomic estimated breeding values for the trait ‘total root length’ (TRL) were predicted for 2431 inbred lines, which had previously been genotyped by sequencing. Selections were made for 100 extreme TRL lines and those with the predicted longest or shortest TRL were validated for TRL and other root traits. The two predicted extreme groups with regard to TRL were significantly different (P = 0.0001). The difference in predicted means for TRL between groups was 145.1 cm and 118.7 cm for observed means, which were significantly different (P = 0.001). The accuracy of predicting the rank between 1 and 200 of the validation population based on TRL (longest to shortest) was determined using a Spearman correlation to be ρ = 0.55. Taken together, our results support the idea that GP may be a useful approach for identifying the most informative genotypes in sequenced germplasm collections to facilitate experiments for quantitative inherited traits.     

冬玉米对氮肥的吸收利用和需求

在不同施氮量下 ,研究了冬玉米对氮肥的吸收利用 ,结果表明 :(1 )冬玉米地上各部分中氮的累积随着用氮量的增加而增加 ,花丝期前的吸收量均多于后期 ,但高氮区的前期吸氮比大于低氮区 ;(2 )营养体氮的转移率随施氮量的增加而降低 ,但绝对量依然是高氮处理大于低氮处理 ,其中雄穗的转移率最高 ,叶的转移量最大 ;(3 )氮肥利用率随施氮量的增加而提高 ,但氮的生产力下降。根据试验结果 ,在肥力好的土地上种植冬玉米以 1 80～ 2 70 kg N/hm2比较适宜     

Toxicological aspects of pendimethalin induced activities of certain oxidising and hydrolytic enzymes in the germinating seedlings of maize (Zea mays L.)

Maize (Zea mays L.) variety NAC-6002 grains were exposed to a range of field relevant concentrations (0.5, 1.0, 2.5, 5.0 and 10.0 ppm) of formulated grade of pendimethalin. The seedlings were maintained in Hogaland and Arnon's nutrient media for up to 15 days to study the toxicity of pendimethalin on germination and activities of certain oxidizing and hydrolytic enzymes using embryonic axis and endosperms of 4, 6, 8, 10 and 15-day-old germinating maize seedlings. The percent germination, length of radicle and plumule decreased significantly with increasing pendimethalin concentrations. The α-amylase activity in the treated seedlings decreased with increasing concentration of pendimethalin in both endosperm and embryonic axis of maize seedling, when compared with control in all the days of observations. The catalase, peroxidase and polyphenoloxidase activity was high in both cotyledons and embryonic axis of treated sets at all time intervals of seedling during early growth over the period of 15 day when compared to control. However, catalase and peroxidase activity was decreased and polyphenoloxidase activity was higher in treated seedlings at higher pendimethalin concentrations. The present study therefore indicates that herbicidical stress brings constraints in the physiological events of seed germination and enzyme activity.     

Root cortical aerenchyma improves the drought tolerance of maize (Zea mays L.)

Root cortical aerenchyma (RCA) reduces root respiration in maize by converting living cortical tissue to air volume. We hypothesized that RCA increases drought tolerance by reducing root metabolic costs, permitting greater root growth and water acquisition from drying soil. To test this hypothesis, recombinant inbred lines with high and low RCA were observed under water stress in the field and in soil mesocosms in a greenhouse. In the field, lines with high RCA had 30% more shoot biomass at flowering compared with lines with low RCA under water stress. Root length density in deep soil was significantly greater in the high RCA lines compared with the low RCA lines. Mid‐day leaf relative water content in the high RCA lines was 10% greater than in the low RCA lines under water stress. The high RCA lines averaged eight times the yield of the low RCA lines under water stress. In mesocosms, high RCA lines had less seminal root respiration, deeper rooting, and greater shoot biomass compared with low RCA lines under water stress. These results support the hypothesis that RCA is beneficial for drought tolerance in maize by reducing the metabolic cost of soil exploration.     

牛磺酸对小麦幼苗生长的生理效应

采用牛磺酸溶液培育小麦幼苗,测定10、100、500、1 000、5 000 mg/L的牛磺酸对小麦幼苗的光合作用PS Ⅱ光化学效率、细胞膜相对透性和膜脂过氧化以及生长的影响.结果表明,与对照组相比,适宜浓度的牛磺酸处理可促进小麦幼苗的生长,使其根长、株高、单株幼苗的干重和鲜重增加,并在一定程度上提高叶片的光化学效率,降低细胞膜相对透性和膜脂过氧化产物的含量;最适处理浓度约为500 mg/L.说明牛磺酸对小麦幼苗细胞膜有一定的保护作用.     

Biochemical characterization of elongase activity in corn (Zea mays L.) roots

Chemical analysis of 4-day-old corn (Zea mays L.) root cell walls revealed that the lipophilic biopolymer suberin forms an important constituent of rhizodermal and hypodermal cell walls. Identified aliphatic monomers had chain lengths ranging from C16 to C26 and they belonged to 5 substance classes (omega-hydroxycarboxylic acids, 1,omega-dicarboxylic acids, 2-hydroxycarboxylic acids, carboxylic acids and alcohols) by which suberin is characterized. Biochemical experiments proved the occurrence of elongase activities in corn roots. Highest enzymatic activities were found in corn root microsomes, and major products synthesized by root elongases were elongated fatty acids with chain lengths ranging from C20 to C24. Preferred substrates of root elongases were acyl-CoAs of the chain length C18 and C20, whereas monounsaturated acyl-CoAs (C16:1 and C18:1) and acyl-CoAs of lower (C12-C16) and higher chain lengths (C22-C24) were rarely elongated. Elongase activities significantly decreased over the length (40 cm) of 10-day-old corn roots going from the young tip to the older base of the root. Thus, results presented here show the presence and activity of elongases in roots of plants.     

Biochemical and molecular characterization of corn (Zea mays L.) root elongases

Root surfaces are protected against the soil environment by the deposition of lignin and suberin. In order to obtain more insight into the regulation of root suberin biosynthesis, elongases from primary roots of corn (Zea mays L.) seedlings were characterized. Elongase activities (acyl-CoA and ATP-dependent) were located in the microsomal fraction of the root cells. C(20), C(22) and C(24) fatty acids were detected as primary products of elongases. Preferred substrates of the acyl-CoA elongases were C(18:0)-CoA and C(20:0)-CoA. Applying a molecular approach, using PCR and degenerate primers derived from the sequences of known leaf and seed 3-ketoacyl-CoA synthases (KCSs), catalysing the first step of very-long-chain fatty acid synthesis, the cDNA of a putative root KCS was obtained showing high homology to known leaf and seed KCSs at the DNA and amino acid levels. Thus, our approach provides the first direct evidence for the presence and the activity of root elongases in Z. mays. Ongoing research is focusing on the molecular analysis and the regulation of KCS expression in roots in reaction to different environmental stimuli.