Adele Muscolo

Earthworm humic matter produces auxin-like effects on Daucus carota cell growth and nitrate metabolism

Abstract While earthworms are known to improve plant growth by improving the structure of the soil, recent work has suggested that earthworms also produced humic substances endowed with hormone-like activity. Suspensions of Daucus carota (carrot) cells were treated with auxin derivatives (2,4-D=2,4-dichlorophenoxyacetic acid, IAA=indole-3-acetic acid and NAA=1-naphthylacetic acid) and a humic substance of low molecular weight (HEf), obtained from the faeces of the earthworms Nicodrilus caliginosus and Allolobophora rosea, which have auxin-like activity. HEf, at a concentration of 200 μg C l−l, caused an increase in carrot cell growth, determined by packed cell volumes, similar to that of 2,4-D, and morphological changes induced by HEf were similar to those induced by IAA. Humic matter and the tested auxin derivatives stimulated carrot cell glutamate dehydrogenase (GDH), glutamine synthetase (GS) and malic dehydrogenase (MDH) to various extents. When carrot cells were treated with HEf or IAA, GDH and MDH isoenzymes separated by isoelectrofocusing showed similar polymorphism. The addition of HEf or auxin derivatives to carrot cells caused an increase in free amino acids belonging to the oxaloacetate and α-ketoglutarate pathways. Our results showed that HEf affects nitrate metabolism, has auxin-like activity, was strongly acidic and had elevated peptide, carbohydrate and aliphatic C contents. Our work has confirmed that the effective materials in the HEf were highly acidic and of low molecular weight. We conclude that, in addition to the already well established modes of action, earthworms are important in humogenesis because their faeces contained humic substances that can influence plant growth via physiological effects.

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.

Auxin-like effect of humic substances extracted from faeces of Allolobophora caliginosa and A. rosea

Abstract Lef explants of Nicotiana plumbaginifolia were compared in cultures supplemented with IAA, inhibitors of IAA (TIBA = 2,3,5-triiodobenzoic acid and PCIB = 4-chlorophenoxy-isobutyric acid) and a humic substance (HEf) obtained from the faeces of yAllolobophora caliginosa and A. rosea . The results show that HEf at a concentration of 1 mg Cl −1 causes root development from leaf explants that appears to be similar to IAA-induced activity, while the control did not develop roots. Furthermore HEf induced longer roots than those grown in IAA with fewer hair roots. In the presence of the IAA inhibitors, the leaf explants were without roots. Humic matter, IAA and IAA-inhibitors stimulated peroxidase activity in N. plumbaginifolia . Also, when the Nicotiana tissues were treated with the humic fraction and IAA there was a minor polymorphism in the esterase isoenzymes. The presence of both TIBA and PCIB restored the esterase profile obtained from control tissues. The induced root-forming activity in leaf explants and the minor polymorphism with respect to the control in the esterase zymograms demonstrate that the humic substance exhibited auxin-like activity. HEf, a low molecular size fraction, was obtained from the faeces of Allolobophora caliginosa (Sav.) and A. rosea (Sav.) by disaggregating the humic material with acetic acid, confirmed the effectiveness of the combination of high acidity and low molecular size in influencing the biological activity of the plant system tested.

Effect of earthworm humic substances on esterase and peroxidase activity during growth of leaf explants of Nicotiana plumbaginifolia

SummaryLeaf explants of Nicotiana plumbaginifolia were compared in cultures supplemented with hormones or humic substances (extracted from faeces of Allolobophora caliginosa) of various molecular complexity and concentration. The results showed that the humic substances (F1, F2, and T) at the concentration of 1 mg C l-1 produced greater leaf explants than those grown in the control. Furthermore, humic fractions like gibberellic alone induced a rhizogenic activity in leaf explants. Quantitative differences were also observed in the peroxidase activity induced in Nicotiana plumbaginifolia by humic matter (F2, F2, and T). In addition, the Nicotiana sp. tissue treated with humic fractions revealed, in the esterase enzyme pattern, the appearance of the 2a band, which was attributable to indoleacetic acid, since its profile was consistent with those obtained from tissues treated with indoleacetic acid. These differences demonstrate that humic substances exhibited a hormone-like behaviour, but no evidence of a relationship between biological activities and chemical characteristics of humus substances was found.

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.

Effect of molecular complexity and acidity of earthworm faeces humic fractions on glutamate dehydrogenase, glutamine synthetase, and phosphoenolpyruvate carboxylase in Daucus carota α II cells

Carrot cells were grown in cultures supplemented with two hormones [2,4-dichlorophenoxyacetic acid (2,4-D) and 6-benzylaminopurine (6BAP)] and two humic fractions extracted from earthworm faeces, one with high acidity and a low apparent molecular size (<3500) and the other with low acidity and a large molecular size. 2,4-D stimulated growth through an effect on cell enlargement, while the strongly acidic humic fraction (0.2 mg l-1) and the weakly acidic fraction (1 mg l-1) were both less effective. With 4–16 h of pre-incubation, the highly acid humic fraction, mainly alone, induced the best increase in protein content; the effect of the weakly acid humic fraction and the hormones was generally less important. The two humic fractions also differed in their influence on glutamate dehydrogenase activity. After 2 h of pretreatment, the highly acidic fraction increased glutamate dehydrogenase activity, while the other fraction did not affect it. After 4–16 h of pre-incubation, the activity of this enzyme was still not influenced by these humic fractions. The presence of the two hormones did not interfere with the humic matter effects. Glutamine synthetase activity was not affected by a pre-incubation of up to 4 h with the two humic fractions, but it was stimulated after 8–16 h of pre-incubation. A 2,4-D+6BAP mixture stimulated glutamine synthetase activity (from +12 to +50%). Again, the presence of the hormones did not interfere with the effects induced by the humic fractions. After 16 h of pre-incubation, phosphoenolpyruvate carboxylase activity was increased by the highly acidic humic fraction (+93%) and by both humic fractions together (+34%). An explanation of the different incubation times necessary for the humic fractions to exert stimulatory effects on these enzymes is proposed here. The regulatory properties of the strongly acidic humic fraction appeared to depend on the combination of high acidity (expecially carboxylic C) with low molecular size.

Phenotypic and metabolic responses to drought and salinity of four contrasting lentil accessions

Highlight Automated imaging-based plant phenotyping combined with GC-MS-based metabolite profiling of four lentil accessions differing in their drought and salt tolerance shows common and specific responses and yields characteristic stress markers

Effect of saline water on seed germination and early seedling growth of the halophyte quinoa

The introduction of new crops with improved salinity stress tolerance could preserve water quality and protect soil resources from further degradation, providing extra sources of food for salinized areas. In this context, we tested the salinity tolerance of a variety of quinoa. Quinoa, a rich source of minerals, proteins and antioxidants, is considered a major alternative crop to meet food shortages in this century. Our study indicated that salinity tolerance of quinoa is largely conferred by a delicate balance between osmotic adjustment and ion accumulation. Salinity reduced productivity in terms of biomass, but increased the levels of antioxidant compounds, which are important health-protecting factors in food, thus providing economic benefit.

Salt tolerance traits increase the invasive success of Acacia longifolia in Portuguese coastal dunes.

Salt tolerance of two co-occurring legumes in coastal areas of Portugal, a native species--Ulex europaeus, and an invasive species--Acacia longifolia, was evaluated in relation to plant growth, ion content and antioxidant enzyme activities. Plants were submitted to four concentrations of NaCl (0, 50, 100 and 200 mM) for three months, under controlled conditions. The results showed that NaCl affects the growth of both species in different ways. Salt stress significantly reduced the plant height and the dry weight in Acacia longifolia whereas in U. europaeus the effect was not significant. Under salt stress, the root:shoot ratio (W(R):W(S)) and root mass ratio (W(R):W(RS)) increased as a result of increasing salinity in A. longifolia but the same was not observed in U. europaeus. In addition, salt stress caused a significant accumulation of Na+, especially in U. europaeus, and a decrease in K+ content and K+/Na+ ratio. The activities of antioxidant enzymes were higher in A. longifolia compared to U. europaeus. In A. longifolia, catalase (CAT, EC 1.11.1.6) and glutathione reductase (GR, EC 1.6.4.2.) activities increased significantly, while ascorbate peroxidase (APX, EC 1.11.1.11) and peroxidase (POX, EC 1.11.1.7) activities remained unchanged in comparison with the control. In U. europaeus, NaCl concentration significantly reduced APX activity but did not significantly affect CAT, GR and POX activities. Our results suggest that the invasive species copes better with salinity stress in part due to a higher rates of CAT and GR activities and a higher K+/Na+ ratio, which may represent an additional advantage when competing with native species in co-occurring salty habitats.