Seedling de-etiolation is one of the key stages of the plant life cycle, characterized by a strong rearrangement of the plant development and metabolism. The conversion of dark accumulated protochlorophyllide to chlorophyll in etioplasts of de-etiolating plants is taking place in order of ns to µs after seedlings illumination, leading to detectable increase of chlorophyll levels in order of minutes after de-etiolation initiation. The highly complex chlorophyll biosynthesis integrates number of regulatory events including light and hormonal signaling, thus making de-etiolation an ideal model to study the underlying molecular mechanisms. Here we introduce the iReenCAM, a novel tool designed for non-invasive fluorescence-based quantitation of early stages of chlorophyll biosynthesis during de-etiolation with high spatial and temporal resolution. iReenCAM comprises customized HW configuration and optimized SW packages, allowing synchronized automated measurement and analysis of the acquired fluorescence image data. Using the system and carefully optimized protocol, we show tight correlation between the iReenCAM monitored fluorescence and HPLC measured chlorophyll accumulation during first 4h of seedling de-etiolation in wild type Arabidopsis and mutants with disturbed chlorophyll biosynthesis. Using the approach, we demonstrate negative effect of exogenously applied cytokinins and ethylene on chlorophyll biosynthesis during early de-etiolation. Accordingly, we identify type-B response regulators, the cytokinin-responsive transcriptional activators ARR1 and ARR12 as negative regulators of early chlorophyll biosynthesis, while contrasting response was observed in case of EIN2 and EIN3, the components of canonical ethylene signaling cascade. Knowing that, we propose the use of iReenCAM as a new phenotyping tool, suitable for quantitative and robust characterization of the highly dynamic response of seedling de-etiolation.

• Keywords
• Arabidopsis, chlorophyll biosynthesis, cytokinins, de-etiolation, ethylene, fluorescence, iReenCAM,
• Publication type
• Journal Article MeSH

Plants are sessile organisms forced to adapt to environmental variations recurring in a day-night cycle. Extensive research has uncovered the transcriptional control of plants' inner clock and has revealed at least some part of the intricate and elaborate regulatory mechanisms that govern plant diel responses and provide adaptation to the ever-changing environment. Here, we analyzed the proteome of the Arabidopsis thaliana mutant genotypes collected in the middle of the day and the middle of the night, including four mutants in the phytochrome (phyA, phyB, phyC, and phyD) and the circadian clock protein LHY. Our approach provided a novel insight into the diel regulations, identifying 640 significant changes in the night-day protein abundance. The comparison with previous studies confirmed that a large portion of identified proteins was a known target of diurnal regulation. However, more than 300 were novel oscillations hidden under standard growth chamber conditions or not manifested in the wild type. Our results indicated a prominent role for ROS metabolism and phytohormone cytokinin in the observed regulations, and the consecutive analyses confirmed that. The cytokinin signaling significantly increased at night, and in the mutants, the hydrogen peroxide content was lower, and the night-day variation seemed to be lost in the phyD genotype. Furthermore, regulations in the lhy and phyB mutants were partially similar to those found in the catalase mutant cat2, indicating shared ROS-mediated signaling pathways. Our data also shed light on the role of the relatively poorly characterized Phytochrome D, pointing to its connection to glutathione metabolism and the regulation of glutathione S-transferases.

• Keywords
• cytokinin, diurnal, glutathione metabolism, light, peroxide, phytochrome, signaling,
• MeSH
• Apoproteins metabolism   MeSH
• Arabidopsis * metabolism   MeSH
• Cytokinins metabolism   MeSH
• Phytochrome B metabolism   MeSH
• Phytochrome * genetics   metabolism   MeSH
• Glutathione metabolism   MeSH
• Arabidopsis Proteins * genetics   metabolism   MeSH
• Proteome genetics   metabolism   MeSH
• Reactive Oxygen Species metabolism   MeSH
• Publication type
• Journal Article MeSH
• Names of Substances
• Apoproteins MeSH
• Cytokinins MeSH
• Phytochrome B MeSH
• Phytochrome * MeSH
• Glutathione MeSH
• PHYD protein, Arabidopsis MeSH Browser
• Arabidopsis Proteins * MeSH
• Proteome MeSH
• Reactive Oxygen Species MeSH

Plants growing in any particular geographical location are exposed to variable and diverse environmental conditions throughout their lifespan. The multifactorial environmental pressure resulted into evolution of plant adaptation and survival strategies requiring ability to integrate multiple signals that combine to yield specific responses. These adaptive responses enable plants to maintain their growth and development while acquiring tolerance to a variety of environmental conditions. An essential signaling cascade that incorporates a wide range of exogenous as well as endogenous stimuli is multistep phosphorelay (MSP). MSP mediates the signaling of essential plant hormones that balance growth, development, and environmental adaptation. Nevertheless, the mechanisms by which specific signals are recognized by a commonly-occurring pathway are not yet clearly understood. Here we summarize our knowledge on the latest model of multistep phosphorelay signaling in plants and the molecular mechanisms underlying the integration of multiple inputs including both hormonal (cytokinins, ethylene and abscisic acid) and environmental (light and temperature) signals into a common pathway. We provide an overview of abiotic stress responses mediated via MSP signaling that are both hormone-dependent and independent. We highlight the mutual interactions of key players such as sensor kinases of various substrate specificities including their downstream targets. These constitute a tightly interconnected signaling network, enabling timely adaptation by the plant to an ever-changing environment. Finally, we propose possible future directions in stress-oriented research on MSP signaling and highlight its potential importance for targeted crop breeding.

• Keywords
• Arabidopsis, abiotic stress, abscisic acid, cytokinin, ethylene, light signaling, multistep phosphorelay (MSP), temperature,
• Publication type
• Journal Article MeSH
• Review MeSH

Cytokinin is a multifaceted plant hormone that plays major roles not only in diverse plant growth and development processes, but also stress responses. We summarize knowledge of the roles of its metabolism, transport, and signalling in responses to changes in levels of both macronutrients (nitrogen, phosphorus, potassium, sulphur) and micronutrients (boron, iron, silicon, selenium). We comment on cytokinin's effects on plants' xenobiotic resistance, and its interactions with light, temperature, drought, and salinity signals. Further, we have compiled a list of abiotic stress-related genes and demonstrate that their expression patterns overlap with those of cytokinin metabolism and signalling genes.

• Keywords
• abiotic stress, cytokinin, drought, nutrient, stress tolerance, temperature,
• MeSH
• Acclimatization MeSH
• Circadian Clocks MeSH
• Cytokinins metabolism   MeSH
• Stress, Physiological * MeSH
• Plant Physiological Phenomena * MeSH
• Droughts MeSH
• Gene Expression Regulation, Plant MeSH
• Plants genetics   metabolism   MeSH
• Salinity MeSH
• Signal Transduction * MeSH
• Light MeSH
• Temperature MeSH
• Plant Development MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Cytokinins MeSH