Tihana Teklić

A novel hydrogen sulfide donor causes stomatal opening and reduces nitric oxide accumulation

Effects of hydrogen sulfide (H(2)S) on plant physiology have been previously studied, but such studies have relied on the use of NaSH as a method for supplying H(2)S to tissues. Now new compounds which give a less severe H(2)S shock and a more prolonged exposure to H(2)S have been developed. Here the effects of one such compound, GYY4137, has been investigated to determine its effects on stomatal closure in Arabidopsis thaliana. It was found that both NaSH and GYY4137 caused stomatal opening in the light and prevented stomatal closure in the dark. Nitric oxide (NO) has been well established as a mediator of stomatal movements and here it was found that both NaSH and GYY4137 reduced the accumulation of NO in guard cells, perhaps suggesting a mode of action for H(2)S in this system. GYY4137, and future related compounds, will be important tools to unravel the effects of plant exposure to H(2)S and to determine how H(2)S may fit into plant cell signalling pathways.

Hydrogen sulfide: environmental factor or signalling molecule?

Hydrogen sulfide (H₂S) has traditionally been thought of as a phytotoxin, having deleterious effects on the plant growth and survival. It is now recognized that plants have enzymes which generate H₂S, cysteine desulfhydrase, and remove it, O-acetylserine lyase. Therefore, it has been suggested that H₂S is considered as a signalling molecule, alongside small reactive compounds such as hydrogen peroxide (H₂O₂) and nitric oxide (NO). Exposure of plants to low of H₂S, for example from H₂S donors, is revealing that many physiological effects are seen. H₂S seems to have effects on stomatal apertures. Intracellular effects include increases in glutathione levels, alterations of enzyme activities and influences on NO and H₂O₂ metabolism. Work in animals has shown that H₂S may have direct effects on thiol modifications of cysteine groups, work that will no doubt inform future studies in plants. It appears therefore, that instead of thinking of H₂S as a phytotoxin, it needs to be considered as a signalling molecule that interacts with reactive oxygen species and NO metabolism, as well as having direct effects on the activity of proteins. The future may see H₂S being used to modulate plant physiology in the field or to protect crops from postharvest spoilage.

Hydrogen sulfide effects on stomatal apertures.

Hydrogen sulfide (H2S) has recently been reported to be a signaling molecule in plants. It has been well established that is has such roles in animals and it has been suggested that it is included into the group of gasotransmitters. We have recently shown that hydrogen sulfide causes stomatal opening in the model plant Arabidopsis thaliana. H2S can be supplied to the plant tissues from donors such as sodium hydrosulfide (NaSH) or more recently from slow release H2S donor molecules such as GYY4137. Both give similar effects, that is, they cause stomatal opening. Furthermore both H2S donors reduced the accumulation of nitric oxide (NO) induced by abscisic acid (ABA) treatment of leaf tissues. Here similar work has been repeated in a crop plant, Capsium anuum, and similar data has been obtained, suggesting that such effects of hydrogen sulfide on plants is not confined to model species.

The relationship of proline content and metabolism on the productivity of maize plants

The free proline content in maize ear-leaves, silk and pollen were analyzed in field grown plants which had matured to the pollination stage. Using maize hybrids PR34F02, PR35P12 and PR36B08 field trials were set up at two locations in eastern Croatia in two different years. Two enzymes of proline metabolism were analyzed in the same leaf samples and specific activities of synthetase (P5CS) and proline dehydrogenase (PDH). Plant productivity was evaluated at harvest by the estimation of total and fully developed grain number per ear and per plant, the mean single grain mass, and the mass of grain per plant. The year in which the plants were grown had a very significant effect on the free proline content in the leaf and pollen, as well as on the enzyme activities assayed. The differences between the plants from the two localities were very significant in all tested parameters of plant grain productivity. There was a significant genotype effect on proline content and P5CS total activity in leaf and on all the productivity parameters. Some of the correlations established suggest that the rate of proline synthesis and degradation in maize ear-leaf at pollination might contribute to the final grain production of the maize plant. Multiple regression analyses was used to further analyze the relationship between proline and grain productivity, but it is clear that future work should include other environmental conditions, plant species and organs such as roots.

Hydrogen sulphide and signalling in plants

The electronic version of this article is the definitive one. It is located here: http://www.cabi.org/cabreviews

Relationships among Chloroplast Pigments Concentration and Chlorophyllmeter Readings in Soybean under Influence of Foliar Magnesium Application

The influence of foliar magnesium (Mg) application before flowering on chloroplast pigment indices was investigated in a 2‐year field experiment with five soybean cultivars. Acetone extraction of pigments (chlorophyll a and b, total chlorophylls, and carotenoids as well as their ratios) was compared to chlorophyll meter (SPAD‐502) readings. The untreated plants showed significant influence of cultivar on pigment concentrations, and pigment ratios were year‐dependant. Foliar fertilization with Mg influenced chlorophyll concentration mostly in the year 2004, and carotenoids were not altered by Mg treatment. Cultivar differences prevailed in the next year when Mg treatment was less effective. The interactions among year, cultivar, and Mg application were showed to be significant for a particular parameter. The SPAD‐502 readings significantly correlated with pigment concentrations only in the untreated plants in 2005. However, the foliar treatment influenced significantly SPAD readings in 2004, through the interaction with cultivar in once‐treated plants and as a single factor in twice‐treated plants. Grain yield was under significant positive influence of leaf Mg concentration in both years, and one treatment with Epsom salt was enough for significant grain yield increase.

Heavy Metal-Induced Oxidative Stress in Plants: Response of the Antioxidative System

Heavy metals (HMs) are among the most important environmental pollutants, particularly in areas with strong anthropogenic pressure. For plants, high levels of HMs are extremely toxic since they may act in several different modes: by the direct inhibition of plant growth and biosynthetic pathways or through the production of reactive oxygen species (ROS). Certain metals generate ROS due to their involvement in redox reactions like Fenton and/or Haber–Weiss reactions, while metals without redox capacity enhance ROS production by reducing the antioxidant glutathione pool, activating calcium-dependent systems and influencing iron-mediated processes. ROS production affects lipids, proteins, and DNA and consequently leads to cell death. In response, plants are equipped with complex enzymatic and nonenzymatic mechanisms involved in antioxidative defense to neutralize HM toxicity, and the main components of these mechanisms will be reviewed in this chapter.

MODEL FOR OPTIMIZING FERTILIZATION OF SUGAR BEET, WHEAT, AND MAIZE GROWN ON PSEUDOGLEY SOILS

ABSTRACT The selected pseudogley soils from Eastern Croatia were analyzed by the electro-ultrafiltration (EUF) method and by the standard soil analyses. Functional dependency was established among parameters of plant nutrient availability. The experimental computer model for the determination of nitrogen, phosphorus and potassium fertilization rates for sugar beet, wheat and maize was developed. The major feature of this model is the application of mathematical functions to adjust crop nutrient demand using (i) the soil nutrient content determined by the EUF method, (ii) the nutrient interactions, and (iii) other factors determining soil fertility. A model was supplemented with the concept of the nutrient potential as a valuable indicator of nutrient availability. The model allows determining optimal fertilization for a range of crops quickly and precisely.

Detection of Thiol Modifications by Hydrogen Sulfide

Hydrogen sulfide (H2S) is an important gasotransmitter in both animals and plants. Many physiological events, including responses to stress, have been suggested to involve H2S, at least in part. On the other hand, numerous responses have been reported following treatment with H2S, including changes in the levels of antioxidants and the activities of transcription factors. Therefore, it is important to understand and unravel the events that are taking place downstream of H2S in signaling pathways. H2S is known to interact with other reactive signaling molecules such as reactive oxygen species (ROS) and nitric oxide (NO). One of the mechanisms by which ROS and NO have effects in a cell is the modification of thiol groups on proteins, by oxidation or S-nitrosylation, respectively. Recently, it has been reported that H2S can also modify thiols. Here we report a method for the determination of thiol modifications on proteins following the treatment with biological samples with H2S donors. Here, the nematode Caenorhabditis elegans is used as a model system but this method can be used for samples from other animals or plants.

THE EFFECTS OF LIGHT REGIME AND SUBSTRATE ON FLOWER PRODUCTIVITY AND LEAF MINERAL COMPOSITION IN TWO GERBERA CULTIVARS

This research evaluates the influence of light regime and substrate composition on the flower productivity and leaf macronutrient content of two gerbera cultivars (‘Ruby Red’ and ‘Vino’) grown in a greenhouse. A special emphasis was given to macro-element ratios in gerbera leaf. The results confirm positive influence of supplemental lighting on flower yield in both gerbera cultivars. Also, mixed substrate (coco fiber + rice husks) resulted with higher flower yield. Cultivar ‘Vino’ showed better productivity and significantly lower concentration of nitrogen (N), potassium (K), and magnesium (Mg) as compared to ‘Ruby Red’. The total flower productivity per plant correlated with some of the tested macronutrients in gerbera leaf (N, K, Mg) only in natural light conditions. Among all calculated leaf nutrient ratios, only P/Mg was significantly and positively correlated to flower yield, based on data from both light variants.