Inhibition of phospholipases influences the metabolism of wound-induced benzylisoquinoline alkaloids in Papaver somniferum L.

Benzylisoquinoline alkaloids (BIAs) are important secondary plant metabolites and include medicinally relevant drugs, such as morphine or codeine. As the de novo synthesis of BIA backbones is (still) unfeasible, to date the opium poppy plant Papaver somniferum L. represents the main source of BIAs. The formation of BIAs is induced in poppy plants by stress conditions, such as wounding or salt treatment; however, the details about regulatory processes controlling BIA formation in opium poppy are not well studied. Environmental stresses, such as wounding or salinization, are transduced in plants by phospholipid-based signaling pathways, which involve different classes of phospholipases. Here we investigate whether pharmacological inhibition of phospholipase A2 (PLA2, inhibited by aristolochic acid (AA)) or phospholipase D (PLD; inhibited by 5-fluoro-2-indolyl des-chlorohalopemide (FIPI)) in poppy plants influences wound-induced BIA accumulation and the expression of key biosynthetic genes. We show that inhibition of PLA2 results in increased morphinan biosynthesis concomitant with reduced production of BIAs of the papaverine branch, whereas inhibition of PLD results in increased production of BIAs of the noscapine branch. The data suggest that phospholipid-dependent signaling pathways contribute to the activation of morphine biosynthesis at the expense of the production of other BIAs in poppy plants. A better understanding of the effectors and the principles of regulation of alkaloid biosynthesis might be the basis for the future genetic modification of opium poppy to optimize BIA production.

Impact of galactoglucomannan oligosaccharides and Cd stress on maize root growth parameters, morphology, and structure.

Biologically active oligosaccharides, including galactoglucomannan oligosaccharides (GGMOs), affect plant growth and development. The impact of GGMOs is dependent on their concentration, and the plant species and plant parts affected. The aim of this article is to ascertain the effects of GGMOs, GGMOs + Cd2+, on growth parameters, morphology, and the structure of maize (Zea mays L.) roots. We undertook this research because, in monocots, the effect of these oligosaccharides is so far unknown. In our study, GGMOs stimulated primary root elongation, induction and elongation of lateral roots, and biomass production. Their effect was dependent on the concentration used. Simultaneously, GGMOs moderated the negative effect of Cd2+ on root elongation growth. Besides, GGMOs affected the primary root structure, proven in the earlier development of xylem and Casparian bands, but not of suberin lamellae (compared to the control). The presence of Cd2+ shifted the apoplasmic barriers closer to the root apex in comparison to samples treated with GGMOs + Cd2+. GGMOs do not inhibit Cd uptake into the root directly, but they moderate its effect, and therefore their influence at the structural and metabolic level seems possible. Their positive impact on plant vitality, even in contaminated conditions, strongly indicates their potential application in remediation technologies.

Cadmium impact, accumulation and detection in poplar callus cells.

Effect of cadmium cations and their interaction with silicon cations was determined in poplar calli and expressed as changes in callus growth, cell viability and cadmium cation accumulation. Cell viability throughout culture versus cadmium cation accumulation in cells is discussed. At the same time, the study sought appropriate methods for cadmium cation detection in callus cells and also in experiments with low plant material (e.g. protoplasts). Cadmium cations were determined by atomic absorption spectroscopy and using fluorescence microscopy with a specific cadmium cation fluorescent dye. The detection of cadmium cations in callus cells by the latter method appears suitable because the callus cells are surrounded by primary cell walls without auto-fluorescence and these values fit well with atomic absorption spectroscopy quantification. However, the visualisation method has some limits discussed below.

Impact of cadmium stress on two maize hybrids.

Some physiological parameters and composition of the root cell walls of two maize hybrids (monocots), the sensitive Novania and the tolerant Almansa were studied after treatment with cadmium cations. After 10 days of Cd2+ treatment (1 × 10-5 M and 5 × 10-5 M), plant growth inhibition, in the sensitive hybrid in particular, as well as a certain alteration in root structure and pigment content were observed. The Cd2+ accumulation was ten times higher in the roots than in the shoots. Chemical analyses and atomic absorption spectroscopy proved that Cd2+ modified the composition of the root cell walls by a significant increase in the content of alkali-soluble polysaccharide fractions, particularly in the tolerant hybrid. An increase in the content of phenolic compounds, mainly in the tolerant hybrid, and a decrease in protein content were observed in the presence of Cd2+ in the alkali fractions. The results indicate that the changes in the cell wall polysaccharide fractions and their proportion to lignin and cellulose are obviously involved in the tolerance and/or defence against Cd2+ of the maize hybrids studied.

Interaction of galactoglucomannan oligosaccharides with auxin involves changes in flavonoid accumulation.

Galactoglucomannan oligosaccharides (GGMOs) are signalling molecules originating from plant cell walls influencing plant growth and defence reactions. The present study focused on their interaction with exogenous IAA (indole-3-acetic acid). GGMOs acted as auxin antagonists and diminished the effect of IAA on Arabidopsis primary root growth. Their effect is associated with meristem enlargement and prolongation of the elongation zone. Reduction of the elongation zone was a consequence of the IAA action, but IAA did not affect the size of the meristem. In the absence of auxin, GGMOs stimulated root growth, meristem enlargement and elongation zone prolongation. It is assumed that the effect of GGMOs in the absence of exogenous auxin resulted from their interaction with the endogenous form. In the presence of auxin transport inhibitor GGMOs did not affect root growth. It is known that flavonoids are auxin transport modulators but this is the first study suggesting the role of flavonoids in GGMOs' signalling. The accumulation of flavonoids in the meristem and elongation zone decreased in GGMOs' treatments in comparison with the control. These oligosaccharides also diminished the effect of IAA on the flavonoids' elevation. The fact that GGMOs decreased the accumulation of flavonoids, known to be modulators of auxin transport, and the loss of GGMOs' activity in the presence of the auxin transport inhibitor indicates that the root growth stimulation caused by GGMOs could be related to changes in auxin transport, possibly mediated by flavonoids.

Galactoglucomannan oligosaccharides alleviate cadmium stress in Arabidopsis.

Our study focused on the mediatory role of galactoglucomannan oligosaccharides (GGMOs) in plant protection against cadmium stress, examined mainly on the primary root growth of Arabidopsis thaliana. The application of GGMOs diminished the negative effect of cadmium on root length, root growth dynamics and also on photosynthetic pigment content. We tested the hypothesis that the effect of GGMOs is associated with decreased cadmium accumulation or its modified distribution. Cadmium distribution was observed chronologically from the first day of plant culture and depended on the duration of cadmium treatment. First, cadmium was stored in the root and hypocotyl and later transported by xylem to the leaves and stored there in trichomes. The protective effect of GGMOs was not based on modified cadmium distribution or its decreased accumulation. In cadmium and GGMOs+cadmium-treated plants, the formation of suberin lamellae was shifted closer to the root apex compared to the control and GGMOs. No significant changes between cadmium and GGMOs+cadmium variants in suberin lamellae development corresponded with any differences in cadmium uptake. GGMOs also stimulated Arabidopsis root growth under non-stress conditions. In this case, suberin lamellae were developed more distantly from the root apex in comparison with the control. Faster solute and water transport could explain the faster plant growth induced by GGMOs. Our results suggest that, in cadmium-stressed plants, GGMOs' protective action is associated with the response at the metabolic level.

How do galactoglucomannan oligosaccharides regulate cell growth in epidermal and cortical tissues of mung bean seedlings?

Biologically active galactoglucomannan oligosaccharides (GGMOs) alone or in combination with IBA stimulate primary root elongation and inhibit hypocotyl elongation in mung bean (Vigna radiata (L.) Wilczek) seedlings. For a more detailed view of GGMOs effect in these processes, the present work is focused on cell growth in selected tissues (epidermis and primary cortex) and on xylem formation. The GGMOs effect on tissue level has not been studied so far. The results show that GGMOs-induced stimulation of primary root growth is mainly caused by enhancing cell elongation (and in less extent by cell production rate) in all tissues observed. Xylem elements were formed at longer distance from the root tip than in the control. In hypocotyl GGMOs reduced cell elongation. IBA in roots caused decrease of cell elongation and cell production rate and acceleration of xylem maturation; in hypocotyls IBA strongly stimulated cell elongation. Application of GGMOs with IBA resulted in increase of cell elongation, cell production rate and delay of xylem maturation in roots. In GGMOs + IBA treated hypocotyls, cell length was decreased to 50% compared to IBA. Based on our results it can be concluded that GGMOs induced elongation growth in mung bean seedlings was caused by increased cell production rate and cell elongation and was accompanied with delay of xylem maturation.

Interaction of galactoglucomannan oligosaccharides with auxin in mung bean primary root.

In the present paper timing of galactoglucomannan oligosaccharides (GGMOs) with exogenously added indole-3-butyric acid (IBA) action on early germination stage (24 h) and primary root elongation of mung bean (Vigna radiata (L.) Wilczek) has been studied. GGMOs inhibited primary root elongation induced by low concentration (10(-8) M) of IBA. This inhibition was considerably higher after preincubation with GGMOs compared with other timing experiments. The most intensive inhibition of elongation has been ascertained at the 10(-8) M concentration of GGMOs. On the other hand GGMOs stimulated this elongation inhibited by high IBA concentration (10(-4) M). This stimulation was the most intensive by simultaneous addition of IBA and GGMOs at the beginning of the experiment and subsequent seeds incubation in distilled water. Our results indicate competition between GGMOs and auxin. The root growth inhibition, induced by GGMOs and/or IBA, was accompanied by the increase of cell wall-associated peroxidase activity and by a higher number of peroxidase isoenzymes. The presence of different peroxidase isoenzymes in experiments with distinct treatment of GGMOs and IBA could indicate variations in the mechanism of interaction between GGMOs and IBA.