Acclimation to fluctuating light environment with short (lasting 20 s, at 650 or 1,250 μmol photons m−2 s−1, every 6 or 12 min) or long (for 40 min at 650 μmol photons m−2 s−1, once a day at midday) sunflecks was studied in Arabidopsis thaliana. The sunfleck treatments were applied in the background daytime light intensity of 50 μmol photons m−2 s−1. In order to distinguish the effects of sunflecks from those of increased daily irradiance, constant light treatments at 85 and 120 μmol photons m−2 s−1, which gave the same photosynthetically active radiation (PAR) per day as the different sunfleck treatments, were also included in the experiments. The increased daily total PAR in the two higher constant light treatments enhanced photosystem II electron transport and starch accumulation in mature leaves and promoted expansion of young leaves in Columbia-0 plants during the 7-day treatments. Compared to the plants remaining under 50 μmol photons m−2 s−1, application of long sunflecks caused upregulation of electron transport without affecting carbon gain in the form of starch accumulation and leaf growth or the capacity of non-photochemical quenching (NPQ). Mature leaves showed marked enhancement of the NPQ capacity under the conditions with short sunflecks, which preceded recovery and upregulation of electron transport, demonstrating the initial priority of photoprotection. The distinct acclimatory responses to constant PAR, long sunflecks, and different combinations of short sunflecks are consistent with acclimatory adjustment of the processes in photoprotection and carbon gain, depending on the duration, frequency, and intensity of light fluctuations. While the responses of leaf expansion to short sunflecks differed among the seven Arabidopsis accessions examined, all plants showed NPQ upregulation, suggesting limited ability of this species to utilize short sunflecks. The increase in the NPQ capacity was accompanied by reduced chlorophyll contents, higher levels of the xanthophyll-cycle pigments, faster light-induced de-epoxidation of violaxanthin to zeaxanthin and antheraxanthin, increased amounts of PsbS protein, as well as enhanced activity of superoxide dismutase. These acclimatory mechanisms, involving reorganization of pigment–protein complexes and upregulation of other photoprotective reactions, are probably essential for Arabidopsis plants to cope with photo-oxidative stress induced by short sunflecks without suffering from severe photoinhibition and lipid peroxidation.

Flowering time (FTi) control is well examined in the long-day plant Arabidopsis (Arabidopsis thaliana), and increasing knowledge is available for the short-day plant rice (Oryza sativa). In contrast, little is known in the day-neutral and agronomically important crop plant maize (Zea mays). To learn more about FTi and to identify novel regulators in this species, we first compared the time points of floral transition of almost 30 maize inbred lines and show that tropical lines exhibit a delay in flowering transition of more than 3 weeks under long-day conditions compared with European flint lines adapted to temperate climate zones. We further analyzed the leaf transcriptomes of four lines that exhibit strong differences in flowering transition to identify new key players of the flowering control network in maize. We found strong differences among regulated genes between these lines and thus assume that the regulation of FTi is very complex in maize. Especially genes encoding MADS box transcriptional regulators are up-regulated in leaves during the meristem transition. ZmMADS1 was selected for functional studies. We demonstrate that it represents a functional ortholog of the central FTi integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) of Arabidopsis. RNA interference-mediated down-regulation of ZmMADS1 resulted in a delay of FTi in maize, while strong overexpression caused an early-flowering phenotype, indicating its role as a flowering activator. Taken together, we report that ZmMADS1 represents a positive FTi regulator that shares an evolutionarily conserved function with SOC1 and may now serve as an ideal stating point to study the integration and variation of FTi pathways also in maize.Flowering time (FTi) in crops is an important agronomical trait critical for harvesting date, biomass yield, crop rotation schemes, and terminal drought avoidance (Jung and Müller, 2009;Bendix et al., 2015). For flowering, the shoot apical meristem (SAM) has to change from vegetative to generative growth, a process called the floral transition. This process is controlled by various key players representing components of different signaling pathways triggered by both external and endogenous factors. The main environmental influence on FTi is derived from photoperiods or daylength as well as temperature. Unlike Arabidopsis (Arabidopsis thaliana) and some winter-annual crops like wheat (Triticum aestivum) and barley (Hordeum vulgare) that require vernalization by cold temperature periods for floral induction, this does not seem to play an essential role for flowering in maize (Zea mays). Furthermore, during thousands of years of breeding history, cultivated temperate maize is thought to have lost its photoperiod sensitivity and is well adapted to growth under longday (LD) conditions. Tropical lines flower under shortday (SD) conditions and depend on photoperiods to flower (Colasanti and Coneva, 2009). Especially in temperate maize lines, endogenous signals related to the developmental stage of the plant appear to play t...

BackgroundMaize is a major crop plant, grown for human and animal nutrition, as well as a renewable resource for bioenergy. When looking at the problems of limited fossil fuels, the growth of the world’s population or the world’s climate change, it is important to find ways to increase the yield and biomass of maize and to study how it reacts to specific abiotic and biotic stress situations. Within the OPTIMAS systems biology project maize plants were grown under a large set of controlled stress conditions, phenotypically characterised and plant material was harvested to analyse the effect of specific environmental conditions or developmental stages. Transcriptomic, metabolomic, ionomic and proteomic parameters were measured from the same plant material allowing the comparison of results across different omics domains. A data warehouse was developed to store experimental data as well as analysis results of the performed experiments.DescriptionThe OPTIMAS Data Warehouse (OPTIMAS-DW) is a comprehensive data collection for maize and integrates data from different data domains such as transcriptomics, metabolomics, ionomics, proteomics and phenomics. Within the OPTIMAS project, a 44K oligo chip was designed and annotated to describe the functions of the selected unigenes. Several treatment- and plant growth stage experiments were performed and measured data were filled into data templates and imported into the data warehouse by a Java based import tool. A web interface allows users to browse through all stored experiment data in OPTIMAS-DW including all data domains. Furthermore, the user can filter the data to extract information of particular interest. All data can be exported into different file formats for further data analysis and visualisation. The data analysis integrates data from different data domains and enables the user to find answers to different systems biology questions. Finally, maize specific pathway information is provided.ConclusionsWith OPTIMAS-DW a data warehouse for maize was established, which is able to handle different data domains, comprises several analysis results that will support researchers within their work and supports systems biological research in particular. The system is available at http://www.optimas-bioenergy.org/optimas_dw.