Contents of total and individual brassinosteroids (BRs) in two maize genotypes (2023 and CE704).

<p>Plants were either subjected to normal watering (control; grey columns) or to 14 days of withholding water (stress; black columns). Mean values ± SEM are shown (n = 3). Asterisks indicate significant (<i>p</i>≤0.05; *) or highly significant (<i>p</i>≤0.01; **) differences between mean values according to Tukey's tests made separately for each genotype (in case of the differences between control and stress treatment) or for each treatment (in case of the differences between both genotypes). BL … brassinolide, CS … castasterone, DS … dolichosterone, FM … leaf fresh mass, TY … typhasterol.</p

The contents of proline, H₂O₂, malondialdehyde (MDA), the antioxidant activities and the index of membrane injury in two maize genotypes (2023 and CE704).

<p>Plants were either subjected to normal watering (control; grey columns) or to 14 days of withholding water (stress; black columns). Mean values ± SEM are shown (n = 6 for the contents of MDA, n = 4 for the other parameters). Asterisks indicate significant (<i>p</i>≤0.05; *) or highly significant (<i>p</i>≤0.01; **) differences between mean values according to Tukey's tests made separately for each genotype (in case of the differences between control and stress treatment) or for each treatment (in case of the differences between both genotypes).AsA … ascorbate, APX … ascorbate peroxidase, CAT … catalase, FM … leaf fresh mass.</p

The difference kinetics and the relative variable fluorescences calculated from OJIP analysis of two maize genotypes (2023 and CE704).

<p>The difference kinetics ΔW_OJ (<b>A</b>) reveals the K-band; ΔW_OK (<b>B</b>) reveals the L-band. Only the part between the I and P points of the OJIP curve is shown for the relative variable fluorescence W_OI (<b>C</b>). The normalization of OJIP curve between the I and P points with the maximum amplitude fixed as 1 is shown as the relative variable fluorescence W_IP (<b>D</b>). Plants were subjected either to normal watering (control) or to 14 days of withholding water (stress). ΔW_OJ and ΔW_OK were calculated from the comparisons of the stressed and control plants; the latter are represented by the zero point of the respective y axes in graphs <b>A</b> and <b>B</b>. Mean values (n = 8) are shown. r.u. … relative units.</p

Drought-tolerant and drought-sensitive genotypes of maize (<i>Zea mays</i> L.) differ in contents of endogenous brassinosteroids and their drought-induced changes

<div><p>The contents of endogenous brassinosteroids (BRs) together with various aspects of plant morphology, water management, photosynthesis and protection against cell damage were assessed in two maize genotypes that differed in their drought sensitivity. The presence of 28-norbrassinolide in rather high quantities (1–2 pg mg^-1 fresh mass) in the leaves of monocot plants is reported for the first time. The intraspecific variability in the presence/content of the individual BRs in drought-stressed plants is also described for the first time. The drought-resistant genotype was characterised by a significantly higher content of total endogenous BRs (particularly typhasterol and 28-norbrassinolide) compared with the drought-sensitive genotype. On the other hand, the drought-sensitive genotype showed higher levels of 28-norcastasterone. Both genotypes also differed in the drought-induced reduction/elevation of the levels of 28-norbrassinolide, 28-norcastasterone, 28-homocastasterone and 28-homodolichosterone. The differences observed between both genotypes in the endogenous BR content are probably correlated with their different degrees of drought sensitivity, which was demonstrated at various levels of plant morphology, physiology and biochemistry.</p></div

Selected parameters of plant morphology in two maize genotypes (2023 and CE704).

<p>Plants were either subjected to normal watering (control; grey columns) or to 14 days of withholding water (stress; black columns). Mean values ± SEM are shown (n = 8). Asterisks indicate significant (<i>p</i>≤0.05; *) or highly significant (<i>p</i>≤0.01; **) differences between mean values according to Tukey's tests made separately for each genotype (in case of the differences between control and stress treatment) or for each treatment (in case of the differences between both genotypes).</p

Selected parameters of gas exchange, the osmotic potential and the contents of chlorophylls and carotenoids in leaves of two maize genotypes (2023 and CE704).

<p>Plants were either subjected to normal watering (control; grey columns) or to 14 days of withholding water (stress; black columns). Mean values ± SEM are shown (n = 8 for gas exchange and the contents of photosynthetic pigments, n = 12 for osmotic potential). Asterisks indicate significant (<i>p</i>≤0.05; *) or highly significant (<i>p</i>≤0.01; **) differences between mean values according to Tukey's tests made separately for each genotype (in case of the differences between control and stress treatment) or for each treatment (in case of the differences between both genotypes).</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 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

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

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