Maize Leaf Cells Research Articles

Uncovering the Infection Strategy of Phyllachora maydis During Maize Colonization: A Comprehensive Analysis.

Tar spot, a disease caused by the ascomycete fungal pathogen Phyllachora maydis, is considered one of the most significant yield-limiting diseases of maize (Zea mays) within the United States. P. maydis may also be found in association with other fungi, forming a disease complex that is thought to result in the characteristic fisheye lesions. Understanding how P. maydis colonizes maize leaf cells is essential for developing effective disease control strategies. Here, we used histological approaches to elucidate how P. maydis infects and multiplies within susceptible maize leaves. We collected tar spot-infected maize leaf samples from four different fields in northern Indiana at three different time points during the growing season. Samples were chemically fixed and paraffin-embedded for high-resolution light and scanning electron microscopy. We observed a consistent pattern of disease progression in independent leaf samples collected across different geographical regions. Each stroma contained a central pycnidium that produced asexual spores. Perithecia with sexual spores developed in the stomatal chambers adjacent to the pycnidium, and a cap of spores formed over the stroma. P. maydis reproductive structures formed around but not within the vasculature. We observed P. maydis associated with two additional fungi, one of which is likely a member of the Paraphaeosphaeria genus; the other is an unknown fungi. Our data provide fundamental insights into how this pathogen colonizes and spreads within maize leaves. This knowledge can inform new approaches to managing tar spot, which could help mitigate the significant economic losses caused by this disease.

Inhibition of Aspergillus flavus Growth and Aflatoxin Production in Zea mays L. Using Endophytic Aspergillus fumigatus.

Aspergillus flavus infection of vegetative tissues can affect the development and integrity of the plant and poses dangerous risks on human and animal health. Thus, safe and easily applied approaches are employed to inhibit A. flavus growth. To this end, the fungal endophyte, i.e., Aspergillus fumigatus, was used as a safe biocontrol agent to reduce the growth of A. flavus and its infection in maize seedlings. Interestingly, the safe endophytic A. fumigatus exhibited antifungal activity (e.g., 77% of growth inhibition) against A. flavus. It also reduced the creation of aflatoxins, particularly aflatoxin B1 (AFB1, 90.9%). At plant level, maize seedling growth, leaves and root anatomy and the changes in redox status were estimated. Infected seeds treated with A. fumigatus significantly improved the germination rate by 88.53%. The ultrastructure of the infected leaves showed severe disturbances in the internal structures, such as lack of differentiation in cells, cracking, and lysis in the cell wall and destruction in the nucleus semi-lysis of chloroplasts. Ultrastructure observations indicated that A. fumigatus treatment increased maize (leaf and root) cell wall thickness that consequentially reduced the invasion of the pathogenic A. flavus. It was also interesting that the infected seedlings recovered after being treated with A. fumigatus, as it was observed in growth characteristics and photosynthetic pigments. Moreover, infected maize plants showed increased oxidative stress (lipid peroxidation and H2O2), which was significantly mitigated by A. fumigatus treatment. This mitigation was at least partially explained by inducing the antioxidant defense system, i.e., increased phenols and proline levels (23.3 and 31.17%, respectively) and POD, PPO, SOD and CAT enzymes activity (29.50, 57.58, 32.14 and 29.52%, respectively). Overall, our study suggests that endophytic A. fumigatus treatment could be commercially used for the safe control of aflatoxins production and for inducing biotic stress tolerance of A. flavus-infected maize plants.

Low temperature caused modifications in the arrangement of cell wall pectins due to changes of osmotic potential of cells of maize leaves (Zea mays L.)

The cell wall emerged as one of the important structures in plant stress responses. To investigate the effect of cold on the cell wall properties, the content and localization of pectins and pectin methylesterase (PME) activity, were studied in two maize inbred lines characterized by different sensitivity to cold. Low temperature (14/12 °C) caused a reduction of pectin content and PME activity in leaves of chilling-sensitive maize line, especially after prolonged treatment (28 h and 7 days). Furthermore, immunocytohistological studies, using JIM5 and JIM7 antibodies, revealed a decrease of labeling of both low- and high-methylesterified pectins in this maize line. The osmotic potential, quantified by means of incipient plasmolysis was lower in several types of cells of chilling-sensitive maize line which was correlated with the accumulation of sucrose. These studies present new finding on the effect of cold stress on the cell wall properties in conjunction with changes in the osmotic potential of maize leaf cells.

Chloroplast transcription, untangling the Gordian Knot.

Chloroplast transcription, untangling the Gordian Knot.

Organellar genome copy number variation and integrity during moderate maturation of roots and leaves of maize seedlings.

Little information is available about organellar genome copy numbers and integrity in plant roots, although it was reported recently that the plastid and mitochondrial genomes were damaged under light, resulting in non-functional fragments in green seedling leaves in a maize line. In the present study, we investigated organellar genome copy numbers and integrity, after assessing the cellular ploidy, in seedling leaves and roots of two elite maize (Zea mays) cultivars using both long-fragment polymerase chain reaction (long-PCR) and real-time quantitative polymerase chain reaction (qPCR, a type of short-PCR). Since maize leaf and root cells are mainly diploid according to chromosome number counting and the literature, the DNA amount ratio between the organellar genomes and the nuclear genome could be used to estimate average organellar genome copy numbers per cell. In the present study, both long-PCR and qPCR analyses found that green leaves had dramatically more plastid DNA and less mitochondrial DNA than roots had in both cultivars. The similarity in results from long-PCR and qPCR suggests that green leaves and roots during moderate maturation have largely intact plastid and mitochondrial genomes. The high resolution of qPCR led to the detection of an increase in copies in the plastid genome and a decrease in copies in the analyzed mitochondrial sub-genomes during the moderate maturation of seedling leaves and roots. These results suggest that green seedling leaves and roots of these two maize cultivars during moderate maturation had essentially intact organellar genomes, an increased copy number of the plastid genome, and decreased copy numbers of certain mitochondrial sub-genomes.

Effect of zinc on maize leaf cell ultra-structure under different soil moistures

选择 土为供试土壤, 进行盆栽玉米试验, 设定0和5.0 mg·kg^-1两个锌处理, 按土壤饱和持水量的40%~45%和70%~75%在玉米的4叶1心期实施干旱和正常水分处理。生长50 d后, 测定不同土壤水分与锌供应状况下植株生物量和锌含量, 利用透射电子显微镜观察完全伸展新叶的超微结构变化, 以期揭示不同土壤水分供应下, 植物对施锌的响应机理。结果表明: 土壤水分供应充足条件下, 与不施锌相比, 施锌玉米地上部生物量和总干重分别增加78%和52%, 根系和地上部锌含量和锌吸收量增加较多; 而干旱条件下, 施锌对玉米生物量无显著影响。干旱条件下缺锌玉米叶片维管束鞘细胞中叶绿体结构基本保持完好, 淀粉粒和基质片层清晰可见, 但叶肉细胞中叶绿体膜受损, 基质片层结构出现皱缩, 基粒片层减少; 施锌玉米叶片维管束鞘细胞中叶绿体结构保持完好, 叶绿体周围的线粒体数目较多, 叶肉细胞中叶绿体中脂肪颗粒增多, 叶片维管束鞘细胞与叶肉细胞之间可见清晰的胞间连丝。土壤水分充足处理下, 缺锌叶片细胞膜出现皱缩, 维管束鞘细胞叶绿体淀粉粒增多, 片层结构受损, 严重时维管束鞘细胞中内溶物消失, 残存的叶绿体中仅有淀粉粒和少许片层; 叶肉细胞中叶绿体可见淀粉粒, 但片层结构少, 有些出现断裂、收缩。土壤水分充足条件下, 施锌玉米维管束鞘核叶肉细胞结构清晰, 叶绿体结构完整。结论认为: 锌对干旱胁迫下玉米叶片细胞结构的破坏有一定的缓解作用; 但土壤水分正常供应下, 缺锌导致细胞结构受损程度比干旱情况下更严重。

Effects of salinity on the transcriptome of growing maize leaf cells point at cell-age specificity in the involvement of the antioxidative response in cell growth restriction.

BackgroundSalinity inhibits growth and development of most plants. The response to salinity is complex and varies between plant organs and stages of development. It involves challenges of ion toxicities and deficiencies as well as osmotic and oxidative stresses. The range of functions affected by the stress is reflected in elaborate changes to the transcriptome. The mechanisms involved in the developmental-stage specificity of the inhibitory responses are not fully understood. The present study took advantage of the well characterized developmental progression that exists along the maize leaf, for identification of salinity induced, developmentally-associated changes to the transcriptome. Differential subtraction screening was conducted for cells of two developmental stages: from the center of the growth zone where the expansion rate is highest, and from older cells at a more distal location of the growing zone where the expansion rate is lower and the salinity restrictive effects are more pronounced. Real-Time PCR analysis was used for validation of the expression of selected genes.ResultsThe salinity-induced changes demonstrated an age-related response of the growing tissue, with elevation of salinity-damages with increased age. Growth reduction, similar to the elevation of percentage dry matter (%DM), and Na and Cl concentrations were more pronounced in the older cells. The differential subtraction screening identified genes encoding to proteins involved in antioxidant defense, electron transfer and energy, structural proteins, transcription factors and photosynthesis proteins. Of special interest is the higher induced expression of genes involved in antioxidant protection in the young compared to older cells, which was accompanied by suppressed levels of reactive oxygen species (H2O2 and O2-). This was coupled with heightened expression in the older cells of genes that enhance cell-wall rigidity, which points at reduced potential for cell expansion.ConclusionsThe results demonstrate a cell-age specificity in the salinity response of growing cells, and point at involvement of the antioxidative response in cell growth restriction. Processes involved in reactive oxygen species (ROS) scavenging are more pronounced in the young cells, while the higher growth sensitivity of older cells is suggested to involve effects on cell-wall rigidity and lower protein protection.

Salicylic acid induced alleviation of oxidative stress caused by clethodim in maize (Zea mays L.) leaves

Salicylic acid is used for regulation of oxidative stress in plants subjected to unfavorable environmental conditions. Application of herbicides for the purpose of weed killing can affect not only the weeds but also the main crop as well. Many herbicides have the ability to cause oxidative stress and further degradation of cell components. In this work, SA was used to alleviate the oxidative stress caused in response to clethodim herbicide in maize leaves. The results demonstrated that, spraying of clethodim caused yellowing of leaves and sometimes browning or drying of leaf tips with high clethodim doses. Contrary, leaves showed no injuries when treated with 1mM SA 3days prior clethodim application. Elevated amounts of H2O2 and MDA were detected in clethodim treated leaves compared with control indicating ROS formation and lipid peroxidation. Excessive ROS formation led to oxidative stress which followed by degradation of membranous structures. In SA treated leaves, the contents of H2O2 and MDA were more or less similar to the corresponding controls. A change in the antioxidant enzymes activities due to clethodim and SA treatment was noticed. For example, the activities of POD and APX were induced while SOD and CAT were more or less reduced in response to clethodim. SA treatment prior clethodim application could induce POD but inhibit CAT. Moreover, SOD and APX activities were adjusted to be similar to those of the control. Another mechanism of SA regulation of the oxidative stress occurred through the formation of antioxidants in the form of phenolic compounds. For that, spraying SA with or without clethodim could accumulate phenolic compounds greatly. The DPPH free radical scavenging assay for leaf extracts had confirmed a change in antioxidant status. Furthermore, SA could enhance accumulation of total proteins and free amino acids in clethodim and SA treated leaves compared with the control. This work was to provide evidence for the ability of SA to regulate clethodim herbicide detoxification through regulation of the antioxidant status of maize leaf cells.

Ultrastructural Changes in Maize Leaf Cells Infected with Maize Dwarf Mosaic Virus and Sugarcane Mosaic Virus

Plant viruses create many changes in the morphology of the plant cell once the infection process has begun. This paper describes and compares the ultrastructural changes induced in maize cells by two isolates of Maize dwarf mosaic virus (MDMV), Spanish (MDMV-Sp) and Polish (MDMV-P), and one isolate of Sugarcane mosaic virus (SCMV) at 10 and 42 days post-inoculation: the concentration and arrangement of virus particles, inclusion bodies associated with infection, and other cytological alterations. The most important difference between maize cells infected with MDMV isolates and with SCMV-P1 was in the form of cytoplasmic cylindrical inclusions. In cells infected with MDMV only typical inclusions such as pinwheels and scrolls were observed, but laminar aggregates were also present in SCMV-infected cells. No virus particles were found in plant cell organelles. Specific virion arrangements occurred in cells infected with MDMV-Sp and SCMV. The most interesting new finding was of specific amorphous inclusions in the cytoplasm of MDMV-Sp-infected cells, which clearly differentiated the two MDMV isolates studied.

Effect of cadmium ion excess over cell structure and functioning of Zea mays and Hordeum vulgare

Zea mays (maize) and Hordeum vulgare (barley) plants were analyzed in order to study the variation in response to Cadmium (Cd) toxicity based on development of leaf symptoms, effect in dry matter production, Cd uptake, lipid peroxidation and effect on cell ultrastructure in leaves and roots. Cd accumulation in roots of Z. mays and H. vulgare was 18–50 times higher than in the aerial parts. Malondialdehyde (MDA) content was more affected in the roots of both Z. mays and H. vulgare than in shoots (60 and 56–51 and 40%, respectively). At ultrastructural level, in Cd treated seedlings, a decline in the vacuolar content of barley roots cells and maize leaf cells was observed. Results corroborate that these gramineous crops can uptake and accumulate substantial amounts of Cd especially in roots. Therefore, H. vulgare and Z. mays could have a phytostabilization potential and thereafter could be tested in phytoremediation technologies.

Ultraweak photon emission from herbivory-injured maize plants

Following perception of herbivory or infection, plants exhibit a wide range of inducible responses. In this study, we found ultraweak photon emissions from maize leaves damaged by Helicoverpa armigera (Noctuidae). Interestingly, mechanically damaged maize leaves treated with caterpillar regurgitants emitted the same intensity and pattern of photon emissions as those from maize leaves damaged by caterpillars. Furthermore, two-dimensional imaging of the leaf section treated with the oral secretions clearly shows that photon emissions were observed specifically at the lip of the wound exposed to the secretions. These results suggest that the direct interaction between maize leaf cells and chemicals contained in caterpillar regurgitants triggers these photon emissions.

Regulation by light and metabolites of ferredoxin-dependent glutamate synthase in maize.

The regulation of Fd-glutamate synthase (Fd-GOGAT, EC 1.4.1.7) and NADH-glutamate synthase (NADH-GOGAT, EC 1.4.1.14) was investigated in maize (Zea mays L. cv. DEA) (1) during development starting from 7- to 11-day-old seedlings, (2) by treatment of 7-day-old etiolated leaves with intermittent light pulses to activate (red) and inactivate (far-red) phytochromes and (3) in 7-day-old green leaves grown under 16-h light/8-h dark cycles. Fd-GOGAT mRNA accumulated 4-fold, and the enzyme polypeptide (3-fold) and activity (3-fold) also increased in leaf cells, while NADH-GOGAT activity remained constantly low. Leaf-specific induction of Fd-GOGAT mRNA (3-fold) occurred in etiolated leaves by low fluence red light, and far-red light reversibly repressed the mRNA accumulation. Red/far-red reversible induction also occurred for Fd-GOGAT polypeptide (2-fold) and activity (2-fold), implicating the phytochrome-dependent induction of Fd-GOGAT. In contrast, NADH-GOGAT activity remained constant, irrespective of red/far-red light treatments. Fd-GOGAT showed diurnal changes under light/dark cycles with the maximum early in the morning and the minimum in the afternoon at the levels of mRNA, enzyme polypeptide and activity. Gln diurnally changed in parallel with Fd-GOGAT mRNA. The induction of Fd-GOGAT provides evidence that light and metabolites are the major signal for the Gln and Glu formation in maize leaf cells.

Analysis of cell wall hardening and cell wall enzymes of salt-stressed maize (Zea mays) leaves

It has been indicated that salinity inhibits maize (Zea mays L.) leaf growth and leaf cell expansion by increasing the apparent yield threshold of the cell wall. We tested whether this increase in the apparent yield threshold was a physical property of cell walls, using in vitro creep-type assays. Salinity had no significant effects on cell wall structural properties based upon several different in vitro assays. In support of these results, there were no differences between control and salt-stressed plants in their total apoplastic concentration of cell wall proteins, in the activity of apoplastic peroxidases or xyloglucan endotransglycosylase. We conclude that short-term salinity does not appear to inhibit maize leaf elongation by hardening the physical structure of the cell walls of the growing zone.

Engineered GFP as a vital reporter in plants

Background: The green-fluorescent protein (GFP) of the jellyfish Aequorea victoria has recently been used as a universal reporter in a broad range of heterologous living cells and organisms. Although successful in some plant transient expression assays based on strong promoters or high copy number viral vectors, further improvement of expression efficiency and fluorescent intensity are required for GFP to be useful as a marker in intact plants. Here, we report that an extensively modified GFP is a versatile and sensitive reporter in a variety of living plant cells and in transgenic plants.Results We show that a re-engineered GFP gene sequence, with the favored codons of highly expressed human proteins, gives 20-fold higher GFP expression in maize leaf cells than the original jellyfish GFP sequence. When combined with a mutation in the chromophore, the replacement of the serine at position 65 with a threonine, the new GFP sequence gives more than 100-fold brighter fluorescent signals upon excitation with 490 nm (blue) light, and swifter chromophore formation. We also show that this modified GFP has a broad use in various transient expression systems, and allows the easy detection of weak promoter activity, visualization of protein targeting into the nucleus and various plastids, and analysis of signal transduction pathways in living single cells and in transgenic plants.Conclusion The modified GFP is a simple and economical new tool for the direct visualization of promoter activities with a broad range of strength and cell specificity. It can be used to measure dynamic responses of signal transduction pathways, transfection efficiency, and subcellular localization of chimeric proteins, and should be suitable for many other applications in genetically modified living cells and tissues of higher plants. The data also suggest that the codon usage effect might be universal, allowing the design of recombinant proteins with high expression efficiency in evolutionarily distant species such as humans and maize.

Subcellular and immunocytochemical localization of the enzymes involved in ammonia assimilation in mesophyll and bundle-sheath cells of maize leaves

The cellular localization of the enzymes involved in primary nitrogen assimilation was investigated following separation of mesophyll protoplasts and bundle-sheath cells of maize (Zea mays L.) leaves. Determination of the enzymatic activities in the two types of cell revealed that nitrate and nitrite reductase are principally located in the mesophyll cells whereas glutamine synthetase (GS) and ferredoxin-dependent glutamate synthase (Fd-GOGAT) are present in both tissues with a preferential location in the bundle-sheath strands. In order to confirm the results obtained by this conventional biochemical method we have used an in-situ immunofluorescence technique to unambiguously localize GS and Fd-GOGAT at the cellular level. Thin-sectioned maize leaves treated with specific GS and Fd-GOGAT antisera followed by conjugation with fluorescein-isothiocyanate-labelled sheep anti-rabbit immunoglobulins clearly show that GS is equally distributed within the leaf whereas Fd-GOGAT is mostly present in the chloroplasts of the bundle-sheath cells. The cellular localization of nitrate reductase, nitrite reductase, GS-2 and Fd-GOGAT in maize leaf cell types strongly indicates that primary nitrogen assimilation functions in the mesophyll cells while photorespiratory nitrogen recycling is restricted to the bundle-sheath cells.

Effects of Nitrate and Ammonium on Gene Expression of Phosphoenolpyruvate Carboxylase and Nitrogen Metabolism in Maize Leaf Tissue during Recovery from Nitrogen Stress

We previously showed that the selective accumulation of phosphoenolpyruvate carboxylase (PEPC) in photosynthetically maturing maize (Zea mays L.) leaf cells induced by nitrate supply to nitrogen-starved plants was primarily a consequence of the level of its mRNA (B Sugiharto, K Miyata, H Nakamoto, H Sasakawa, T Sugiyama [1990] Plant Physiol 92: 963-969). To determine the specificity of inorganic nitrogen sources for the regulation of PEPC gene expression, nitrate (16 millimolar) or ammonium (6 millimolar) was supplied to plants grown previously in low nitrate (0.8 millimolar), and changes in the level of PEPC and its mRNA were measured in the basal region of the youngest, fully developed leaves of plants during recovery from nitrogen stress. The exogenous supply of nitrogen selectively increased the levels of protein and mRNA for PEPC. This increase was more pronounced in plants supplemented with ammonium than with nitrate. The accumulation of PEPC during nitrogen recovery increased in parallel with the increase in the activity of glutamine synthetase and/or ferredoxin-dependent glutamate synthase. Among the major amino acids, glutamine was the most influenced during recovery, and its level increased in parallel with the steady-state level of PEPC mRNA for 7 hours after nitrogen supply. The administration of glutamine (12 millimolar) to nitrogen-starved plants increased the steady-state level of PEPC mRNA 7 hours after administration, whereas 12 millimolar glutamate decreased the level of PEPC mRNA. The results indicate that glutamine and/or its metabolite(s) can be a positive control on the nitrogen-dependent regulation of PEPC gene expression in maize leaf cells.

Reversible effects of inhibitory diffusates from maize inoculated with Cochliobolus carbonum

The localized resistance of maize to Cochliobolus carbonum race 1 induced by a prior inoculation with the weakly virulent race 2 is associated with the release of inhibitory compounds from affected leaf cells into the infection court after penetration. In this study, diffusates containing this inhibitory material harvested from the inoculated leaf surface were found to inhibit conidial germination and accompanying metabolic and biosynthetic activities—oxygen uptake and uridine and leucine incorporation. Addition of carboxyl-containing compounds (amino acids or salts of organic acids) to the germination medium prevented and reversed these inhibitory effects. Similarly, in the host-pathogen interaction, these compounds prevented the action of the diffusates, abolished the induced resistance, and promoted disease development in both resistant and susceptible isolines of maize by race 2 of C. carbonum. In this respect, sodium acetate mimicked the phenotypic effect of the host-specific toxin produced by race 1, which is essential for pathogenicity of C. carbonum. In contrast to the toxin, however, the effect of sodium acetate was not genotype-specific, suggesting that the inhibitory compounds produced by maize leaf cells are components of a general resistance response whose activity is suppressed by acidic compounds and whose synthesis by susceptible genotypes is suppressed by HC-toxin.

Identification of a calmodulin‐stimulated (Ca2++ Mg2+)‐ATPase in a plasma membrane fraction isolated from maize (Zea mays) leaves

Plasma membranes were isolated from light‐grown, 14‐day‐old maize leaves (Zea mays L. cv. Golden Cross Bantam) using aqueous two‐phase partitioning. The plasma membrane (PM) fraction contained < 0.3% of the total chlorophyll, < 0.2% of the mitochondrial marker enzyme activity, minimal contamination by endomembranes and 34% of the total PM.A calmodulin‐stimulated (Ca2++ Mg2+)‐ATPase was identified in the PM‐enriched fraction. The Ca2++ calmodulin stimulation was dependent on Mg2+, saturated at ca 25 μM total Ca2+, had a pH maximum at 7.2 and was maximally stimulated by 600 nM bovine brain calmodulin. The stimulation was not greatly affected by the anion present and showed a divalent cation specificity of Ca2+ > Sr+2 ± Mn+2 > Co2+± Cu2+ > Ba2+. The napthalenesulfonamide W7, an antagonist of calmodulin action, completely inhibited the calmodulin stimulation at 175 μM, while the less active analogue W5 was ineffective at this concentration. La3+, an inhibitor of PM Ca2+ transport, showed a 50% inhibition of calmodulin‐stimulated ATPase activity at ca 200 μM. Taken as a whole, these data demonstrate the presence of a calmodulinstimulated, (Ca2++ Mg2+)‐ATPase on the cytoplasmic surface of the plasma membrane of maize leaf cells.

Étude ultrastructurale des modifications induites par Exserohilum turcicum chez le limbe de Zea mays – Effet du gène de résistance Ht-1

Ultrastructural changes induced by Exserohilum turcicum (Pass.) Leonard et Suggs in maize leaf cells are observed 24 to 72 h after inoculation, in a comparative study between two isogenic lines with or without the Ht-1 gene. In the susceptible plants (without Ht-1), the plasmalemma and the tonoplast of the mesophyll cells are the first cellular components altered, followed by disorganisation and alteration of organelles, which become scattered throughout the cell. Chloroplasts in particular seem to be very sensitive to the toxic action of the pathogen, which causes disruption of their envelope and grana. Bundle sheath cells are altered later and to a lesser extent than the mesophyll cells. In Ht-1 monogenic resistant inbred lines, cytoplasmic residues of prematurely dead cells surround healthy mesophyll cells protecting them and stimulating their activity and resulting in stabilization of the pathotoxic process 36 to 48 h after inoculation.

Differential expression of oxygen-evolving polypeptide genes in maize leaf cell types

Three polypeptides of 33 kD, 23 kD and 16 kD are released from maize photosystem II particles by alkaline Tris solution treatment and shown to cross-react with antisera to purified spinach oxygen-evolving (OE) polypeptides of 34 kD, 23 kD and 17 kD, respectively. They are not located exclusively in mesophyll cells but each is about 4 times more abundant in the thylakoid membranes of mesophyll than bundle sheath cells of etiolated, greening and green leaves. Three maize cDNA clones (OE33, OE23, OE16) have been identified by hybrid-selection, in vitro translation and immunoprecipitation with antisera against spinach OEs. Transcripts of all three genes are already detectable in both mesophyll and bundle sheath cells of etiolated leaves; however, they accumulate transiently and coordinately in mesophyll cells but remain at a constant low level in bundle sheath cells upon illumination of dark-grown maize seedlings. Moreover, the level of each protein increases in mesophyll cells following the accumulation of transcripts during greening and remains high in late greening and green leaves, despite the decline in each corresponding mRNA. The accumulation of all three OE proteins is also stimulated by light in bundle sheath cells without increases in their corresponding mRNAs. The preferential localization of these three proteins in mesophyll cells is due to both transcriptional and translational regulation.