Maria Sidari

Effects of salinity on growth, carbohydrate metabolism and nutritive properties of kikuyu grass (Pennisetum clandestinum Hochst)

Abstract The objective of this study was to investigate the effect of salinity on growth, nutritive properties and carbohydrate metabolism of Pennisetum clandestinum Hochst. Salt stress was induced by adding NaCl at different concentrations to the nutrient solution: 0, 50, 100, 150 and 200 mM. After 15 days under such stress, plants were actively growing up to 100 mM NaCl. Salinity affected root length more than leaf length. The invertase activity significantly enhanced in leaves and decreased in roots of kikuyu grass at 150 and 200 mM NaCl. In plants exposed to highest salt conditions, we observed an accumulation of hexoses and a lower activity of glucokinase (GK), phosphoglucoisomerase (GPI) and pyruvate kinase (PK). The glucose-6-phosphate dehydrogenase (G6PDH) decreased increasing salt concentration, showing at 200 mM NaCl the strongest reduction. The phosphoenolpyruvate carboxykinase (PEPCK) activity slightly and progressively increased in a concentration-dependent manner. Exposure of kikuyu grass to 150 and 200 mM NaCl caused an increase of NADP+-specific isocitrate dehydrogenase (IDH) activity in leaves and roots. The nutritive properties of kikuyu decreased in grass treated with 150 mM and even more with 200 mM NaCl. These data indicate that kikuyu is a grass tolerant to salinity up to 100 mM, suggesting its possible utilization in saline land where the survival of other fodder species is markedly reduced.

The effect of phenols on respiratory enzymes in seed germination

Low molecular weight phenolic compounds were identified in two soilswith different vegetative cover, Fagus sylvatica, L. andPinus laricio, Poiret, spp. calabrica, and were tested atdifferent concentrations on seed germination of Pinuslaricio, and on respiratory and oxidative pentose phosphate pathwayenzymes involved in the first steps of seed germination. The data obtained showthat there are marked differences in the phenolic acid composition of the twoinvestigated soils. All the phenolic compounds bioassayed inhibited seedgermination and those extracted from Pinus laricio soilwere particularly inhibitory. We also found that the non-germination of seedsisstrongly correlated to the inhibition of the activities of enzymes ofglycolysisand the oxidative pentose phosphate pathway.

A review of the roles of forest canopy gaps

Treefall gap, canopy opening caused by the death of one or more trees, is the dominant form of disturbance in many forest systems worldwide. Gaps play an important role in forest ecology helping to preserve bio- and pedo-diversity, influencing nutrient cycles, and maintaining the complex structure of the late-successional forests. Over the last 30 years, numerous reviews have been written describing gap dynamics. Here we synthesize current understanding on gap dynamics relating to tree regeneration with particular emphasis on gap characteristics considered critical to develop ecologically sustainable forest management systems and to conserve native biodiversity. Specifically, we addressed the question: how do gaps influence forest structure? From the literature reviewed, the size of gaps induces important changes in factors such as light intensity, soil humidity and soil biological properties that influence tree species regeneration and differ in gaps of different sizes. Shadetolerant species can colonize small gaps; shade-intolerant species need large gaps for successful regeneration. Additionally, gap dynamics differ between temperate, boreal, and tropical forests, showing the importance of climate differences in driving forest regeneration. This review summarizes information of use to forest managers who design cutting regimes that mimic natural disturbances and who must consider forest structure, forest climate, and the role of natural disturbance in their designs.

Coumarin inhibits the growth of carrot (Daucus carota L. cv. Saint Valery) cells in suspension culture

We used a carrot (Daucus carota L. cv. Saint Valery) cell suspension culture as a simplified model system to study the effects of the allelochemical compound coumarin (1,2 benzopyrone) on cell growth and utilisation of exogenous nitrate, ammonium and carbohydrates. Exposure to micromolar levels of coumarin caused severe inhibition of cell growth starting from the second day of culture onwards. At the same time, the presence of 50 mumol/L coumarin caused accumulation of free amino acids and of ammonium in the cultured cells, and stimulated their glutamine synthetase, glutamate dehydrogenase, glucose-6-phosphate dehydrogenase and phosphoenolpyruvate carboxylase activities. Malate dehydrogenase, on the other hand, was inhibited under the same conditions. These effects were interpreted in terms of the stimulation of protein catabolism and/or interference with protein biosynthesis induced by coumarin. This could have led to a series of compensatory changes in the activities of enzymes linking nitrogen and carbon metabolism. Because coumarin seemed to abolish the exponential phase and to accelerate the onset of the stationary phase of cell growth, we hypothesise that such allelochemical compounds may act in nature as an inhibitor of the cell cycle and/or as a senescence-promoting substance.

Effect of PEG-induced drought stress on seed germination of four lentil genotypes

Seeds of four lentil genotypes (Castelluccio, Eston, Pantelleria, and Ustica) were subjected to five levels (0, 10, 15, 18, and 21%) of polyethylene glycol (PEG-6000). Germination percentage, root length, tissue water content (WC), α- and β-amylases, α-glucosidase activities, and osmolyte content were evaluated at 24, 48, and 72 h after starting the germination test. Water stress reduced seed germination percentage, root length, and seedling WC in all cultivars to different extent. The increase in proline content and total soluble sugars was greater for Eston and Castelluccio compared to the other genotypes. The activity of the enzymes involved in the germination process decreased in all cultivars; the activities of α-amylase and α-glucosidase were most negatively affected by osmotic stress, mainly in the drought sensitive Ustica and Pantelleria. Overall, Eston and Castelluccio were able to express greater drought tolerance and consequently could be used as a valuable resource for breeding programs.

Effect of nitrate and humic substances of different molecular size on kinetic parameters of nitrate uptake in wheat seedlings

The kinetic parameters of nitrate uptake (Imax, Km and Cmin) were evaluated in young seedlings of Triticum durum L., cv. Appulo, exposed to nitrate and/or to soil-extracted humic acids (HAs) of different molecular weight. The uptake was enhanced after induction at low levels of nitrate (50 μM KNO3), while it was inhibited after induction at higher concentrations (2000 μM). The kinetic parameters of uptake were selectively influenced by pre-treatment with HAs: total (TE) and, at a greater extent, low (LMS,  3500 Da)-treated plants. An additive effect was shown when nitrate and humic substances were provided simultaneously: the uptake rate was enhanced in TE- and LMS-treated plants, but was strongly delayed in HMS-treated plants. Removal of nitrate and/or humic fractions de-induced the system and NO3— uptake rate decreased. Exposure to HAs was not able to induce nitrate reductase activity in root and leaf tissues. Inhibitors of protein synthesis p-fluorophenylalanine and cycloheximide reversed the positive effect of LMS fraction on nitrate uptake. This would support the hypothesis of a promoting effect of HAs on the molecular expression of proteins of the nitrate transport system. Wirkung von Nitrat und Humusstoffen unterschiedlicher Molekulgrose auf kinetische Parameter der Nitrataufnahme bei Weizenkeimpflanzen Die kinetischen Charakteristika der Nitrataufnahme von Hartweizenkeimpflanzen wurden nach Behandlung mit Nitratlosung ohne und mit Humusstoffen unterschiedlicher Molekulgrose ermittelt. Bereits bei dem niedrigsten Nitratangebot wurde die Nitrataufnahme induziert, wohingegen sie bei 2000 μM KNO3 nach Erreichen des Induktionsmaximums gehemmt wurde. Humusstoffe mit geringer Molekulgrose erhohten die Nitrataufnahmerate und die Effizienz des Transportsystems, erkennbar durch niedrige kM- und Cmin-Werte. Die Kombination von Nitrat und niedermolekularen Humusstoffen erhohte ebenfalls die Nitrataufnahme, wohingegen Pflanzen, die mit hochmolekularen Verbindungen behandelt wurden, Nitrat verzogert aufnahmen. Die Entfernung von Nitrat und/oder Humusstoffen de-induzierte die Nitrataufnahme, wobei die Nitrataufnahme auf ein Niveau fiel, das niedriger als das Ausgangsniveau war. Die Behandlung mit Humusstoffen allein hat keine Nitratreduktaseaktivitat in der Wurzel oder im Blattgewebe induziert. Hemmstoffe der Proteinbiosynthese kehrten den positiven Effekt niedermolekularer Humusstoffe um. Die Ergebnisse werden hinsichtlich einer Interaktion von Humusstoffen und der Expression des Nitrattransportproteins diskutiert.

Tolerance of kikuyu grass to long term salt stress is associated with induction of antioxidant defences

The response of the antioxidant system to long term (15 d) salt stress (50, 100, 200 mM NaCl) was studied in kikuyu (Pennisetum clandestinum, Hochst.), a perennial grass with a well developed root system (often used as an erosion controlling ground cover) and with high nutritive properties as pasture. The activities of peroxidase, catalase, ascorbate peroxidase, ascorbate-free radical reductase, glutathione reductase and dehydroascorbate reductase enzymes involved in the detoxification from reactive oxygen species were investigated. The growth of kikuyu grass was inhibited at 200 mM NaCl. Salinity affected root length more than leaf length. Lower activities of catalase, ascorbate-free radical reductase, and dehydroascorbate reductase enzymes were observed in stressed plants. The tolerance of kikuyu grass to salt stress (up to 100 mM) appears to be related to up-regulation of ascorbate peroxidase, peroxidase and glutathione reductase enzymes.

The Effects Of Humic Substances On Pinus Callus Are Reversed By 2,4-Dichlorophenoxyacetic Acid

The reversal of humic matter-induced inhibition of callus growth and metabolism by 2,4-dichlorophenoxyacetic acid (2,4-D) was studied in Pinus laricio. Two forest humic fractions (relative molecular mass (Mr) > 3500), derived from soil under Fagus sylvatica (Fs) and Abies alba (Aa) plantation, were used. Pinus laricio callus was grown for a subculture period (4 weeks) on Basal Murashige and Skoog (MS) medium plus forest humic matters (Fs or Aa), at a concentration of 1 mg C/l, and then was transferred, for an additional four weeks, to a MS medium culture without humic matter, but with different hormones: indole-3-acetic acid (IAA, 2 mg/1) or 2,4-dichlorophenoxyacetic acid (2,4-D, 0.5 mg/1) and/or 6-benzylaminopurine (BAP, 0.25 mg/1). Growth of calluse, glucose, fructose, and sucrose contents, and activities of soluble and bound invertases, glucokinase, phosphoglucose isomerase, aldolase, and pyruvate kinase were monitored. The results show a negative effect of humic fractions on callus growth, due to decreased utilization of glucose and fructose, and decreased activities of glycolytic enzymes. The effects are reversible. Substitution of humic fractions with 2,4-D+BAP or 2,4-D is followed by an increase of glycolytic enzyme activities and, consequently, by the utilization of glucose and fructose that induces a restart of growth. In contrast, the inhibitory effects of humic fractions persist when they are substituted with BAP alone, indicating that only the auxin 2,4-D is capable of reversing the negative effects. A possible competitive action on the auxin-binding site between 2,4-D and the chemical structures in the forest humic fractions is suggested.

Influence of Acidity on Growth and Biochemistry of Pennisetum clandestinum

Hydroponics were used to study the impact of acidity on growth, nutritive properties and metabolic changes in kikuyu grass (Pennisetum clandestinum Hochst). Four treatments (pH 6.0, 5.0, 4.0, and 3.0) were compared for effects on biomass, leaf and root length, crude protein, amino acid content and key enzymes of sugar metabolism. Reduction in biomass, root and leaf length, amino acid contents, glucose-6-phosphate dehydrogenase (G6PDH) and pyruvate kinase (PK) content was observed only at pH 3.0, in association with increased leaf proline content. Kikuyu grass is able to grow normally under mild acidity (down to at least pH 4.0).

Biological effects of water-soluble soil phenol and soil humic extracts on plant systems

The aim of this research was to extract, with a sequential method, HS free from water-soluble phenols (HS-WP) and water-soluble phenols free from humic substances (WP-HS), and to evaluate and to compare the biological effects of these two extracts to humic substances (HS) and water-soluble phenols (WP) traditionally extracted. In each extract we determined the concentration of low molecular weight organic acids, soluble carbohydrates, fatty acids, phenolic acids and total proteins. We tested the biological activity of each soil extract and of the single identified compounds on different plant organs (Pinus laricio callus, Daucus carota cells, and Pinus laricio, Pinus halepensis, Lens culinaris and Cichorium intybus seeds). The results showed that eliminating from HS the WP fraction, and from WP the HS fraction we obtained extracts chemically different from HS as such, and WP as such. HS and HS-WP increased callus and cell growth and also root elongation of the different species used; in contrast, WP and WP-HS had negative effects inhibiting callus and cell growth and seed germination percentage of coniferous, herbaceous and leguminous species. The negative effects can be ascribed to the presence of phenolic acids in the extracts while the positive biological activity can be attributed to the presence of tartaric acid, and fatty acids. In conclusion, this study helps to discriminate the effects of humic substances against phenolic compounds extracted from soils explaining the different and in some way contradictory biological behaviour of these two main fractions of SOM.