The morphology and biomass characteristics of drought-stressed maize genotypes.

<p>The number of fully developed leaves (<b><i>A</i></b>), the plant height (<b><i>B</i></b>), the total area of the photosynthetically active leaves (<b><i>C</i></b>), the leaf area ratio (LAR) (<b><i>D</i></b>), the shoot fresh mass (FM) (<b><i>E</i></b>), the shoot dry mass (DM) (<b><i>F</i></b>), the root fresh mass (<b><i>G</i></b>) and the root dry mass (<b><i>H</i></b>) of maize inbred lines 2023 (23) and CE704 (04) and their F1 hybrids 2023×CE704 (23×04) and CE704×2023 (04×23) subjected to 10 days of drought (solid bars) or normally watered (hatched bars). Means ± SD (n = 20) are shown. The letters <i>A-C</i> denote the statistical significance of the differences between genotypes under control conditions, the letters <i>a-c</i> denote the statistical significance of the differences between genotypes under drought conditions (only those marked with different letters differ significantly at p ≤ 0.05). Asterisks indicate significant differences between control and drought-stressed plants of the respective genotype (p ≤ 0.05).</p

The disadvantages of being a hybrid during drought: A combined analysis of plant morphology, physiology and leaf proteome in maize

<div><p>A comparative analysis of various parameters that characterize plant morphology, growth, water status, photosynthesis, cell damage, and antioxidative and osmoprotective systems together with an iTRAQ analysis of the leaf proteome was performed in two inbred lines of maize (<i>Zea mays</i> L.) differing in drought susceptibility and their reciprocal F1 hybrids. The aim of this study was to dissect the parent-hybrid relationships to better understand the mechanisms of the heterotic effect and its potential association with the stress response. The results clearly showed that the four examined genotypes have completely different strategies for coping with limited water availability and that the inherent properties of the F1 hybrids, <i>i</i>.<i>e</i>. positive heterosis in morphological parameters (or, more generally, a larger plant body) becomes a distinct disadvantage when the water supply is limited. However, although a greater loss of photosynthetic efficiency was an inherent disadvantage, the precise causes and consequences of the original predisposition towards faster growth and biomass accumulation differed even between reciprocal hybrids. Both maternal and paternal parents could be imitated by their progeny in some aspects of the drought response (<i>e</i>.<i>g</i>., the absence of general protein down-regulation, changes in the levels of some carbon fixation or other photosynthetic proteins). Nevertheless, other features (<i>e</i>.<i>g</i>., dehydrin or light-harvesting protein contents, reduced chloroplast proteosynthesis) were quite unique to a particular hybrid. Our study also confirmed that the strategy for leaving stomata open even when the water supply is limited (coupled to a smaller body size and some other physiological properties), observed in one of our inbred lines, is associated with drought-resistance not only during mild drought (as we showed previously) but also during more severe drought conditions.</p></div

The chlorophyll <i>a</i> fluorescence kinetics (O-J-I-P) measured in dark-adapted leaves of drought-stressed maize genotypes.

<p>Direct transients (<b><i>A</i></b>), the relative variable fluorescence and the difference kinetics W_OI = (F_t-F₀)/(F_I-F₀) and ΔW_OI = (W_{OI Stress}-W_{OI Control}) (<b><i>B</i></b>), W_OJ = (F_t-F₀)/(F_J-F₀) and ΔW_OJ = (W_{OJ Stress}-W_{OJ Control}) (<b><i>C</i></b>), W_OK = (F_t-F₀)/(F_K-F₀) and ΔW_OK = (W_{OK Stress}-W_{OK Control}) (<b><i>D</i></b>), W_IP = (F_t-F_I)/(F_P-F_I) (<b><i>E</i></b>) and the part of W_OI between 30 and 300 ms (<b><i>F</i></b>) in leaves of maize inbred lines 2023 and CE704 and their F1 hybrids 2023×CE704 and CE704×2023 subjected to 10 days of drought (Stress) or normally watered (Control). The relative variable fluorescence is plotted on left vertical axes using open symbols, the difference kinetics is plotted on right vertical axes using solid symbols. F_t represents the fluorescence intensity measured at any time during the recording period, F_I the fluorescence intensity at the I-step, F_J the fluorescence intensity at the J-step, F_K the fluorescence intensity at the K-step, F_P the maximum fluorescence intensity, and F₀ the initial fluorescence intensity. Mean values (n = 20) are shown for each genotype/water treatment combination.</p

Mid-parent heterosis in selected morphological, physiological and biochemical parameters of drought-stressed maize.

<p>Mid-parent heterosis in selected morphological, physiological and biochemical parameters of drought-stressed maize.</p

Five proteins that showed the highest negative uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 after 10 days of drought.

<p>Five proteins that showed the highest negative uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 after 10 days of drought.</p

Five proteins that showed the highest positive uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 under conditions of normal water supply.

<p>Five proteins that showed the highest positive uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 under conditions of normal water supply.</p

The functional classification of proteins from maize leaves with different responses in parental lines and F1 hybrids.

<p>The number of proteins with higher or lower level in F1 hybrids (as compared to parental lines) identified by an iTRAQ method in leaves of normally watered (C) or drought-stressed (S) plants of maize is shown; only those proteins whose levels differred between the respective hybrid and its parental line by at least two fold were included. 23: drought-sensitive parental inbred line 2023, 04: drought-tolerant parental inbred line CE704, 23×04: 2023×CE704 hybrid, 04×23: CE704×2023 hybrid. ET: proteins of the photosynthetic light-harvesting, electron-transport chain and chlorophyll synthesis; SM: proteins participating in photosynthetic carbon fixation and saccharide metabolism; MT: membrane proteins participating in transport and energetics; 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 signalling; PT: proteases and their inhibitors; GE: proteins participating in gene expression and its regulation; MS: miscellaneous proteins.</p

Five proteins that showed the highest positive uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 after 10 days of drought.

<p>Five proteins that showed the highest positive uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 after 10 days of drought.</p

Five proteins that showed the highest negative uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 under conditions of normal water supply.

<p>Five proteins that showed the highest negative uniparental heterosis in maize F1 hybrids 2023×CE704 or CE704×2023 under conditions of normal water supply.</p

The cell membrane injury, the activities/contents of antioxidants and the proline content in leaves of drought-stressed maize genotypes.

<p>The cell membrane injury (MI) (<b><i>A</i></b>), the content of proline (<b><i>B</i></b>), the activities of superoxide dismutase (SOD) (<b><i>C</i></b>), catalase (CAT) (<b><i>D</i></b>), ascorbate peroxidase (APX) (<b><i>E</i></b>), glutathione reductase (GR) (<b><i>F</i></b>), the percentage of reduced ascorbate (RSA) (<b><i>G</i></b>) and the percentage of reduced glutathione (RSG) (<b><i>H</i></b>) in leaves of maize inbred lines 2023 (23) and CE704 (04) and their F1 hybrids 2023×CE704 (23×04) and CE704×2023 (04×23) subjected to 10 days of drought (solid bars) or normally watered (hatched bars). Means ± SD (n = 5 for MI, 10 for the proline content, 8 for the activities of antioxidant enzymes, 4 for RSA and 3 for RSG) are shown. The letters <i>A-D</i> denote the statistical significance of the differences between genotypes under control conditions, the letters <i>a-d</i> denote the statistical significance of the differences between genotypes under drought conditions (only those marked with different letters differ significantly at p ≤ 0.05). Asterisks indicate significant differences between control and drought-stressed plants of the respective genotype (p ≤ 0.05).</p