Five most up-regulated and down-regulated proteins in drought-stressed maize plants of 2023 and CE704 genotypes, as revealed by the iTRAQ analysis.

<p>The number in the column “CE704”, resp. “2023”, represents the n-fold increase or decrease in the protein content after 6 days of drought, derived from the ratio S_CE704/C_CE704 (resp. S₂₀₂₃/C₂₀₂₃) in case of the increased protein content and from the formula: –1/(S_CE704/C_CE704) (resp. –1/[S₂₀₂₃/C₂₀₂₃]) in case of the decreased protein content. ETC  =  electron transport chain; ZM  =  <i>Zea mays</i> L.</p

The differences in leaf proteins observed either between the genotypes or between control (C) and drought-stressed (S) plants of 2023 and CE704 maize genotypes, as evaluated by the 2D-electrophoresis method.

<p>AT  =  <i>Arabidopsis thaliana</i> (L.) Heynh.; ETC  =  electron transport chain; OEC  =  oxygen evolving complex of photosystem II; OS  =  <i>Oryza sativa</i> L.; LE  =  <i>Lycopersicon esculentum</i> Mill.; TA  =  <i>Triticum aestivum</i> L.; ZM  =  <i>Zea mays</i> L. The following symbols indicate the quantity of individual spots: –  =  absence, +/−  =  very weak intensity, +  =  medium intensity, ++  =  high intensity.</p

The functional classification of differentially expressed drought-related proteins from maize leaves.

<p>The number of proteins identified by the iTRAQ method in two maize genotypes (2023 and CE704) with up-regulated (<b><i>A</i></b>) or down-regulated (<b><i>B</i></b>) levels is shown; only those proteins whose levels changed due to drought in at least one genotype by at least twofold were included. ET: proteins of the photosynthetic electron-transport chain and chlorophyll synthesis; SM: proteins participating in photosynthetic carbon fixation and saccharide metabolism; MT: membrane proteins participating in transport; LM: proteins participating in lipid metabolism; AM: proteins participating in amino acid metabolism; DX: detoxification proteins; ST: stress proteins; DH: dehydrins; CP: chaperones; SG: proteins involved in cell signaling; PT: proteases and their inhibitors; GE: proteins participating in gene expression and its regulation; MS: miscellaneous proteins.</p

The gas exchange and water use characteristics of the leaves of drought-stressed maize genotypes.

<p>The net photosynthetic rate (P_N) (<b><i>A</i></b>), intercellular CO₂ concentration (c_i) (<b><i>B</i></b>), net transpiration rate (E) (<b><i>C</i></b>), stomatal conductance (g_S) (<b><i>D</i></b>), water use efficiency (WUE) (<b><i>E</i></b>) and relative water content (RWC) (<b><i>F</i></b>) in the leaves of two maize genotypes (2023 and CE704) that were subjected to 6 days of drought (solid bars) or normally watered (hatched bars). The means ± SD (n  = 18) are shown. The letters <i>a-c</i> denote the statistical significance (as determined by the Tukey-Kramer test) of the differences between genotypes/water treatments (only those marked with different letters differ significantly at p≤0.05).</p

Five proteins with the strongest contrast in the response to drought between 2023 and CE704 maize genotypes.

<p>The number in the column “CE704”, resp. “2023”, represents the n-fold increase or decrease in the protein content after 6 days of drought, derived from the ratio S_CE704/C_CE704 (resp. S₂₀₂₃/C₂₀₂₃) in case of the increased protein content and from the formula: –1/(S_CE704/C_CE704) (resp. –1/[S₂₀₂₃/C₂₀₂₃]) in case of the decreased protein content. The number in the column “Contrast” represents the difference between genotypes according to the ratio (S_CE704/C_CE704)/(S₂₀₂₃/C₂₀₂₃) in case of the higher protein up-regulation in the CE704 genotype/higher protein down-regulation in the 2023 genotype (upper part of the table). For the opposite situation (lower part of the table), the formula: –1/([S_CE704/C_CE704]/[S₂₀₂₃/C₂₀₂₃]) was used. AT  =  <i>Arabidopsis thaliana</i> (L.) Heynh.; ETC  =  electron transport chain; ZM  =  <i>Zea mays</i> L.</p

Phenotypic representation of drought-stressed and control plants of two maize genotypes.

<p>2023: sensitive genotype; CE704: tolerant genotype.</p

The 2D gels showing the leaf proteomes of drought-stressed and control plants of two maize genotypes.

<p>S: drought-stressed; C: control; 2023: sensitive genotype; CE704: tolerant genotype. Only selected regions of the gels are shown; the frames mark the differences in the representation of two isoforms of the heat-shock protein HSP26 (spots nos. 4 and 5) in the drought-stressed plants of both genotypes. The protein spots that are differentially represented between genotypes and water treatments are marked by arrows and the respective numbers (1–11; N … unidentified protein) refer to the notation used in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0038017#pone-0038017-t003" target="_blank">Table 3</a>.</p