Photosynthetic characteristics in plant breeding: targets, options and limitations

Přírodovědecká fakult

KALCIT-BARYTOVÉ KONKRECE Z TĚŠAN, OKR. BRNO-VENKOV: NÁLEZ, DATA A MOŽNÉ DŮSLEDKY

Unique calcite-barite concretions from Těšany (district Brno-country) have been found and studied in detail. These concretions and large limestone boulders are considered to represent material from the Jurassic period and present the only material and opportunity to improve knowledge about these unussual rocks in the studied area. EPMA has been used to constrain complex mineralogy. Results in this study are supplemented by LA-ICP-MS microanalysis. The increased precision is related to combination of different methods (PL, CL and BSE imaging) to distinguish compositionaly different calcites as a separate groups investigated by scans of multi-point analyses. Based on microtextural observations and chemical analyses 3 calcite groups are distinguish. This study provides new information for widespread sulphates (5–20 %) and fi ne-grained quartz (5–35 %) too

Contents of endogenous brassinosteroids and the response to drought and/or exogenously applied 24-epibrassinolide in two different maize leaves

Exogenously applied brassinosteroids (BRs) improve plant response to drought. However, many important aspects of this process, such as the potential differences caused by different developmental stages of analyzed organs at the beginning of drought, or by BR application before or during drought, remain still unexplored. The same applies for the response of different endogenous BRs belonging to the C27, C28-and C29- structural groups to drought and/or exogenous BRs. This study examines the physiological response of two different leaves (younger and older) of maize plants exposed to drought and treated with 24-epibrassinolide (epiBL), together with the contents of several C27, C28-and C29-BRs. Two timepoints of epiBL application (prior to and during drought) were utilized to ascertain how this could affect plant drought response and the contents of endogenous BRs. Marked differences in the contents of individual BRs between younger and older maize leaves were found: the younger leaves diverted their BR biosynthesis from C28-BRs to C29-BRs, probably at the very early biosynthetic steps, as the levels of C28-BR precursors were very low in these leaves, whereas C29-BR levels vere extremely high. Drought also apparently negatively affected contents of C28-BRs (particularly in the older leaves) and C29-BRs (particularly in the younger leaves) but not C27-BRs. The response of these two types of leaves to the combination of drought exposure and the application of exogenous epiBL differed in some aspects. The older leaves showed accelerated senescence under such conditions reflected in their reduced chlorophyll content and diminished efficiency of the primary photosynthetic processes. In contrast, the younger leaves of well-watered plants showed at first a reduction of proline levels in response to epiBL treatment, whereas in drought-stressed, epiBL pre-treated plants they were subsequently characterized by elevated amounts of proline. The contents of C29- and C27-BRs in plants treated with exogenous epiBL depended on the length of time between this treatment and the BR analysis regardless of plant water supply; they were more pronounced in plants subjected to the later epiBL treatment. The application of epiBL before or during drought did not result in any differences of plant response to this stressor

The Physiology and Proteomics of Drought Tolerance in Maize: Early Stomatal Closure as a Cause of Lower Tolerance to Short-Term Dehydration?

Understanding the response of a crop to drought is the first step in the breeding of tolerant genotypes. In our study, two maize (Zea mays L.) genotypes with contrasting sensitivity to dehydration were subjected to moderate drought conditions. The subsequent analysis of their physiological parameters revealed a decreased stomatal conductance accompanied by a slighter decrease in the relative water content in the sensitive genotype. In contrast, the tolerant genotype maintained open stomata and active photosynthesis, even under dehydration conditions. Drought-induced changes in the leaf proteome were analyzed by two independent approaches, 2D gel electrophoresis and iTRAQ analysis, which provided compatible but only partially overlapping results. Drought caused the up-regulation of protective and stress-related proteins (mainly chaperones and dehydrins) in both genotypes. The differences in the levels of various detoxification proteins corresponded well with the observed changes in the activities of antioxidant enzymes. The number and levels of up-regulated protective proteins were generally lower in the sensitive genotype, implying a reduced level of proteosynthesis, which was also indicated by specific changes in the components of the translation machinery. Based on these results, we propose that the hypersensitive early stomatal closure in the sensitive genotype leads to the inhibition of photosynthesis and, subsequently, to a less efficient synthesis of the protective/detoxification proteins that are associated with drought tolerance

Physiological and fitness differences between cytotypes vary with stress in a grassland perennial herb.

Understanding the consequences of polyploidization is a major step towards assessing the importance of this mode of speciation. Most previous studies comparing different cytotypes, however, did so only within a single environment and considered only one group of traits. To take a step further, we need to explore multiple environments and a wide range of traits. The aim of this study was to assess response of diploid and autotetraploid individuals of Knautia arvensis (Dipsacaceae) to two stress conditions, shade or drought.We studied eleven photosynthetic, morphological and fitness parameters of the plants over three years in a common garden under ambient conditions and two types of stress.The results indicate strong differences in performance and physiology between cytotypes in ambient conditions. Interestingly, higher fitness in diploids contrasted with more efficient photosynthesis in tetraploids in ambient conditions. However, stress, especially drought, strongly reduced fitness and disrupted function of the photosystems in both cytotypes reducing the between cytotype differences. The results indicate that drought stress reduced function of the photosynthetic processes in both cytotypes but particularly in tetraploids, while fitness reduction was stronger in diploids.The photosynthesis related traits show higher plasticity in polyploids as theoretically expected, while the fitness related traits show higher plasticity in diploids especially in response to drought. This suggests that between cytotype comparisons need to consider multiple traits and multiple environments to understand the breath of possible responses of different cytotypes to stress. They also show that integrating results based on different traits is not straightforward and call for better mechanistic understanding of the relationships between species photosynthetic activity and fitness. Still, considering multiple environments and multiple species traits is crucial for understanding the drivers of niche differentiation between cytotypes in future studies

Photos of stomata.

<p>Stomata of A) diploid and B) tetraploid individual of <i>K</i>. <i>arvensis</i>.</p

Summary of differences between cytotypes, treatments and traits.

<p>Differences between diploid (2x) and tetraploid (4x) plants growing in different treatments (shade, drought and control) in A) values of the effective quantum yield of photosystem II photochemistry in light-adapted leaves (Qy) of, B) performance index for energy conservation from Photosystem II antenna to the reduction of Q_B (PI_ABS) measured in dark-adapted leaves, C) performance index for energy conservation from Photosystem II antenna to the reduction of Photosystem I end electron acceptors (PI_TOTAL) measured in dark-adapted leaves, D) chlorophyll a content, E) specific leaf mass (SLM), F) cumulative number of flowering stalks and G) cumulative number of flower heads. The graphs show means and standard errors of the mean (SE). Columns sharing the same letter are not significantly different (P > 0.05).</p

Summary of the effects of ploidy level and treatment on the different traits.

<p>The effect of ploidy level, treatment and their interaction on effective quantum yield of photosystem II photochemistry in light-adapted leaves (Qy), performance index for energy conservation from Photosystem II antenna to the reduction of Photosystem I end electron acceptors (PI_TOTAL)_, performance index for energy conservation from Photosystem II antenna to the reduction of Q_B (PI_ABS)_, content of chlorophylls a and b and total carotenoids, specific leaf mass (SLM), cumulative number of flower heads and flowering stalks over 2012 and 2013 and plant height in 2013 measured in diploid and tetraploid plants growing in different treatments (shade, drought and control). Significant values (P < 0.05) are shown in bold. 2x or 4x next to ploidy level indicates that diploids (2x) have significantly higher values of the respective parameter than tetraploids and the other way round. Letters next to treatment indicate which plants (C-control, S-shaded, D-drought-stressed) have significantly higher values of the respective parameter. Effect of population is only shown in S6 Table. Results marked by * are significant even after sequential Bonferroni correction.</p

Map of the populations.

<p>Locations of the diploid (crosses) and tetraploid (circles) study populations in the Czech Republic, Europe.</p