Antioxidative response in variegated Pelargonium zonale leaves and generation of extracellular H2O2 in (peri)vascular tissue induced by sunlight and paraquat.

In this study we exposed variegated leaves of Pelargonium zonale to strong sunlight (>1100µmolm-2s-1 of photosynthetically active radiation) with and without paraquat (Pq), with the aim to elucidate the mechanisms of H2O2 regulation in green and white tissues with respect to the photosynthetically-dependent generation of reactive oxygen species (ROS). Sunlight induced marked accumulation of H2O2 in the apoplast of vascular and (peri)vascular tissues only in green sectors. This effect was enhanced by the addition of Pq. In the presence of diphenyl iodide, an NADPH oxidase inhibitor, H2O2 accumulation was abolished. Distinct light-induced responses were observed: in photosynthetic cells, sunlight rapidly provoked ascorbate (Asc) biosynthesis and an increase of glutathione reductase (GR) and catalase activities, while in non-photosynthetic cells, early up-regulation of soluble ascorbate peroxidase, dehydroascorbate reductase (DHAR) and GR activities was observed. Paraquat addition stimulated DHAR and GR activities in green sectors, while in white sectors activities of monodehydroascorbate reductase, DHAR and class III peroxidases, as well as Asc content rapidly increased. Differential antioxidative responses in the two tissues in the frame of their contrasting metabolisms, and the possible role of (peri)vascular H2O2 in signaling were discussed.

Performance of rose scented geranium (Pelargonium graveolens) in heavy metal polluted soil vis-à-vis phytoaccumulation of metals.

An investigation was carried out to evaluate the effect of heavy metal toxicity on growth, herb, oil yield and quality and metal accumulation in rose scented geranium (Pelargonium graveolens) grown in heavy metal enriched soils. Four heavy metals (Cd, Ni, Cr, and Pb) each at two levels (10 and 20 mg kg-1 soil) were tested on geranium. Results indicated that Cr concentration in soil at 20 mg kg-1 reduced leaves, stem and root yield by 70, 83, and 45%, respectively, over control. Root growth was significantly affected in Cr stressed soil. Nickel, Cr, and Cd concentration and accumulation in plant increased with higher application of these metals. Chromium, nickel and cadmium uptake was observed to be higher in leaves than in stem and roots. Essential oil constituents were generally not significantly affected by heavy metals except Pb at 10 and 20 ppm, which significantly increased the content of citronellol and Ni at 20 ppm increased the content of geraniol. Looking in to the higher accumulation of toxic metals by geranium and the minimal impact of heavy metals on quality of essential oil, geranium can be commercially cultivated in heavy metal polluted soil for production of high value essential oil.

Characterisation of antioxidants in photosynthetic and non-photosynthetic leaf tissues of variegated Pelargonium zonale plants.

Hydrogen peroxide is an important signalling molecule, involved in regulation of numerous metabolic processes in plants. The most important sources of H2 O2 in photosynthetically active cells are chloroplasts and peroxisomes. Here we employed variegated Pelargonium zonale to characterise and compare enzymatic and non-enzymatic components of the antioxidative system in autotrophic and heterotrophic leaf tissues at (sub)cellular level under optimal growth conditions. The results revealed that both leaf tissues had specific strategies to regulate H2 O2 levels. In photosynthetic cells, the redox regulatory system was based on ascorbate, and on the activities of thylakoid-bound ascorbate peroxidase (tAPX) and catalase. In this leaf tissue, ascorbate was predominantly localised in the nucleus, peroxisomes, plastids and mitochondria. On the other hand, non-photosynthetic cells contained higher glutathione content, mostly located in mitochondria. The enzymatic antioxidative system in non-photosynthetic cells relied on the ascorbate-glutathione cycle and both Mn and Cu/Zn superoxide dismutase. Interestingly, higher content of ascorbate and glutathione, and higher activities of APX in the cytosol of non-photosynthetic leaf cells compared to the photosynthetic ones, suggest the importance of this compartment in H2 O2 regulation. Together, these results imply different regulation of processes linked with H2 O2 signalling at subcellular level. Thus, we propose green-white variegated leaves as an excellent system for examination of redox signal transduction and redox communication between two cell types, autotrophic and heterotrophic, within the same organ.

The high potential of Pelargonium roseum plant for phytoremediation of heavy metals.

The major objective of this investigation was to evaluate the potential of scented geraniums, Pelargonium roseum, to uptake and accumulate heavy metals nickel (Ni), cadmium (Cd), or lead (Pb). For this, plants were grown in an artificial soil system and exposed to a range of metal concentrations over a 14-day treatment period. Then, metals from the entire biomass were extracted. The results showed that scented geranium plants accumulated in excess of 20,055 mg of Ni kg(-1) dry weight (DW) of root and 10,889 mg of Ni kg(-1) DW of shoot, and in excess of 86,566 mg of Pb kg(-1) DW for roots and 4,416 mg of Pb kg(-1) DW for shoots within 14 days. Also, the uptake and accumulation of cadmium in roots of scented geranium plants increased with the exposure at low (250, 500 mg L(-1)) and medium level (750 mg L(-1)) followed by a decline at the highest level (1,000 mg L(-1)). The highest accumulation in roots (31,267 mg kg(-1) DW) was observed in 750 mg L(-1) cadmium treatment. In the shoots of scented geraniums, the highest amount of metal accumulation (1,957 mg kg(-1) DW) was detected at 750 and 1,000 mg L(-1) of cadmium in the culture solution. Finally, since the high concentrations of Ni or Pb accumulated in shoots of scented geranium has far exceeded 0.1 % DW and for Cd has far exceeded 0.01 % DW, P. roseum is a new hyperaccumulator species for these metals and can be used in phytoremediation industry.

Droplet evaporation and spread on waxy and hairy leaves associated with type and concentration of adjuvants.

BACKGROUND: Adjuvants can improve pesticide application efficiency and effectiveness. However, quantifications of the adjuvant-amended pesticide droplet actions on foliage, which could affect application efficiencies, are largely unknown. RESULTS: Droplet evaporation rates and spread on waxy or hairy leaves varied greatly with the adjuvant types tested. On waxy leaves, the wetted areas of droplets containing crop oil concentrate (COC) were significantly smaller than those containing modified seed oil (MSO), non-ionic surfactant (NIS) or oil surfactant blend (OSB), whereas the evaporation rates of COC-amended droplets were significantly higher. On hairy leaves, COC-amended droplets remained on top of the hairs without wetting the epidermis. When the relative concentration was 1.50, the wetted area of droplets with NIS was 9.2 times lower than that with MSO and 6.1 times lower than that with OSB. The wetted area increased as the adjuvant concentration increased. MSO- or OSB-amended droplets spread extensively on the hairy leaf surface until they were completely dried. CONCLUSION: These results demonstrated that the proper concentration of MSO, NIS or OSB in spray mixtures improved the homogeneity of spray coverage on both waxy and hairy leaf surfaces and could reduce pesticide use. This article is a US Government work and is in the public domain in the USA.

Casparian bands occur in the periderm of Pelargonium hortorum stem and root.

BACKGROUND AND AIMS: Casparian bands are characteristic of the endodermis and exodermis of roots, but also occur infrequently in other plant organs, for example stems and leaves. To date, these structures have not been detected in phellem cells of a periderm. The aim of this study was to determine whether Casparian bands occur in phellem cells using tests that are known to detect Casparian bands in cells that also contain suberin lamellae. Both natural periderm and wound-induced structures were examined in shoots and roots. METHODS: Using Pelargonium hortorum as a candidate species, the following tests were conducted: (1) staining with berberine and counterstaining with aniline blue, (2) mounting sections in concentrated sulphuric acid and (3) investigating the permeability of the walls with berberine as an apoplastic, fluorescent tracer. KEY RESULTS: (1) Berberine-aniline blue staining revealed a modification in the radial and transverse walls of mature phellem cells in both stems and roots. Three days after wounding through to the cortex of stems, the boundary zone cells (pre-existing, living cells nearest the wound) had developed vividly stained primary walls. By 17 d, staining of mature phellem cells of wound-induced periderm was similar to that of natural periderm. (2) Mature native phellem cells of stems resisted acid digestion. (3) Berberine was excluded from the anticlinal (radial and transverse) walls of mature phellem cells in stems and roots, and from the wound-induced boundary zone. CONCLUSIONS: Casparian bands are present in mature phellem cells in both stems and roots of P. hortorum. It is proposed that Casparian bands act to retard water loss and pathogen entry through the primary cell walls of the phellem cells, thus contributing to the main functions of the periderm.

Twospotted spider mite population level, distribution, and damage on ivy geranium in response to different nitrogen and phosphorus fertilization regimes.

The influence of plant nutrition on arthropod pests has often been studied by comparing plants provided suboptimal nutrients with those provided sufficient or luxurious nutrients, but such results have limited applicability to commercially produced crops because nitrogen (N) and phosphorus (P) are almost never limiting in greenhouse production. We conducted a series of experiments with ivy geranium, Pelargonium peltatum (L.) L'Hr. ex Aiton 'Amethyst 96' to determine the response of twospotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), to six combinations of N (8 or 24 mM) and P (0.32, 0.64, or 1.28 mM) that reflected commercial production practices. All six combinations resulted in saleable plants when plants were free of spider mites, but tissue N and P concentrations among fertilizer combinations were different. On mite-infested plants, no difference in mite numbers or plant damage was found in response to N fertilization rates. Phosphorus had no effect on mite population level until week 8, at which time plants fertilized with 0.64 mM P had slightly more mites than plants fertilized with 0.32 mM. However, overall quality and dry weight of plants fertilized by 0.32 mM P was lower than that of 0.64 and 1.28 mM, which suggests that ivy geranium plants fertilized with the higher P rates may better compensate for mite feeding damage. Positive correlations were found between within-plant distribution of mites and the corresponding tissue N and P concentrations in three foliage strata, suggesting that tissue nutrient content may influence mite selection of feeding sites.

Thidiazuron-induced morphogenetic response in petiole cultures of Pelargonium x hortorum and Pelargonium x domesticum and its histological analysis.

The possibility of inducing somatic embryogenesis in petiole cultures of two cultivars of Pelargonium x hortorum and of one cultivar of Pelargonium x domesticum using thidiazuron (TDZ) was investigated. Petioles were cultivated on a modified Murashige and Skoog medium with different concentrations and application periods of TDZ. Regeneration was achieved with all TDZ treatments for all cultivars and was highly variable. Shoots of different shapes and somatic embryo-like structures were observed. Histological examination revealed that no somatic embryos were formed, and regenerants had to be classified as shoots and shoot-like or leaf-like structures. The importance of these results on the classification of regeneration induced by TDZ in these species and on the propagation of these pelargoniums is discussed.