Adam Woźny

Lead deposited in the cell wall of Funaria hygrometrica protonemata is not stable – A remobilization can occur

The hypothesis that lead (Pb) can be uptake or remobilized from the cell wall (CW) by internalization withlow-esterified pectins (up to 40%--JIM5-P), was studied in tip-growing apical cell of Funaria hygrometrica protonemata. Treatment 4h with 1mM PbCl(2) caused marked vesicular traffic intensification and the common internalization of JIM5-P from the CW. Lead bound to JIM5-P was internalized from the CW, together with this compound and entered the protoplast. It showed that Pb deposited in CW is not as safe for plant cell as previously believed. However, pulse-chase experiments (recovering 4 h and 24 h) indicated that CW and its thickenings can function as the final sequestration compartments. In Pb deposition sites, a callose layer occurred. It was localized from the protoplast site, next to Pb deposits separating sequestrated to CW and its thickenings Pb from plasma membrane almost certainly protecting the plant cell from its returning into the protoplast.

Is callose a barrier for lead ions entering Lemna minor L. root cells

Plants have developed a range of strategies for resisting environmental stresses. One of the most common is the synthesis and deposition of callose, which functions as a barrier against stress factor penetration. The aim of our study was to examine whether callose forms an efficient barrier against Pb penetration in the roots of Lemna minor L. exposed to this metal. The obtained results showed that Pb induced callose synthesis in L. minor roots, but it was not deposited regularly in all tissues and cells. Callose occurred mainly in the protoderm and in the centre of the root tip (procambial central cylinder). Moreover, continuous callose bands, which could form an efficient barrier for Pb penetration, were formed only in the newly formed and anticlinal cell walls (CWs); while in other CWs, callose formed only small clusters or incomplete bands. Such an arrangement of callose within root CWs inefficiently protected the protoplast from Pb penetration. As a result, Pb was commonly present inside the root cells. In the light of the results, the barrier role of callose against metal ion penetration appears to be less obvious than previously believed. It was indicated that induction of callose synthesis is not enough for a successful blockade of the stress factor penetration. Furthermore, it would appear that the pattern of callose distribution has an important role in this defence strategy.

Effect of Cytokinins and Antibiotics on Chloroplast Development in Cotyledons of Cucumis sativus

Summary A description is given of changes which occured under the influence of cytokinins, chloramphenicol (CAP), eyeloheximide (CXD) and their combinations in chlorophyll synthesis and development of chloroplast structure in palisade parenchyma cells of cucumber cotyledons. Cytokinins distinctly promoted chlorophyll synthesis and chloroplast development, and the antibiotics inhibited these processes. The inhibiting activity of CXD was several times higher than that of CAP. Kinetin applied simultaneously with CAP only partially overcame its inhibitory effect, whereas in the case of CXD the overcoming was complete. It is suggested that the promotion by cytokinins of chloroplast development in cucumber cotyledons results mainly from their effect on protein synthesis occurring in the cytoplasm.

Effect of Pb(NO3)2 on poplar tissue culture and the ultrastructural localization of lead in culture cells

Abstract In tissue cultures of Populus maximowiczii Henry, Pb(NO 3 ) 2 had a restraining effect on fresh weight increase and anthocyanin content. In ultrastructural research Pb deposits of various size were mainly present in the intercellular spaces, cell walls (mainly in the region of the middle lamella), in the paramural bodies and in the vacuoles. Small deposits of this metal were also observed in the endoplasmic reticulum (ER), dictyosomes and dictyosome derivated vesicles.

The effect of 3-Indolylacetic acid on the differentiation of plastids in callus culture ofCichorium intybus L.

SummaryThe effect of 3-indolylacetic acid (IAA) on structure of plastids in cells of callus developing on the phloem explants of chicory roots was investigated. In the absence of IAA the proplastids in the initial expiant developed into typical chloroplasts. The presence of increasing IAA concentrations in the medium resulted in a gradual reduction of the thylakoid system accompanied by an increasing starch content of the plastids. Depending on the IAA concentration used, various types of plastids from typical chloroplasts to typical amyloplasts were found. A possible relationship between auxins and sugar metabolism is indicated.

Pb-Induced Avoidance-Like Chloroplast Movements in Fronds of Lemna trisulca L.

Lead ions are particularly dangerous to the photosynthetic apparatus, but little is known about the effects of trace metals, including Pb, on regulation of chloroplast redistribution. In this study a new effect of lead on chloroplast distribution patterns and movements was demonstrated in mesophyll cells of a small-sized aquatic angiosperm Lemna trisulca L. (star duckweed). An analysis of confocal microscopy images of L. trisulca fronds treated with lead (15 μM Pb2+, 24 h) in darkness or in weak white light revealed an enhanced accumulation of chloroplasts in the profile position along the anticlinal cell walls, in comparison to untreated plants. The rearrangement of chloroplasts in their response to lead ions in darkness was similar to the avoidance response of chloroplasts in plants treated with strong white light. Transmission electron microscopy X-ray microanalysis showed that intracellular chloroplast arrangement was independent of the location of Pb deposits, suggesting that lead causes redistribution of chloroplasts, which looks like a light-induced avoidance response, but is not a real avoidance response to the metal. Furthermore, a similar redistribution of chloroplasts in L. trisulca cells in darkness was observed also under the influence of exogenously applied hydrogen peroxide (H2O2). In addition, we detected an enhanced accumulation of endogenous H2O2 after treatment of plants with lead. Interestingly, H2O2-specific scavenger catalase partly abolished the Pb-induced chloroplast response. These results suggest that H2O2 can be involved in the avoidance-like movement of chloroplasts induced by lead. Analysis of photometric measurements revealed also strong inhibition (but not complete) of blue-light-induced chloroplast movements by lead. This inhibition may result from disturbances in the actin cytoskeleton, as we observed fragmentation and disappearance of actin filaments around chloroplasts. Results of this study show that the mechanisms of the toxic effect of lead on chloroplasts can include disturbances in their movement and distribution pattern.

Effects of Cadmium on the Host-Pathogen System II. Alterations of Potato Tuber and Phytophthora infestans Relations

Summary The influence of cadmium on the resistance of potato leaves ( Solanum tuberosum L.) to Phytophthora infestans was examined in two potato cultivars characterized by different levels of resistance to the pathogen. The effect of reduction of pathogen growth in leaves of susceptible cv. Bintje depended on the concentration of the toxic metal in the investigated material. At the concentration of 75 µg g -1 fw, the number of infected shoots, leaves and leaflets of an individual shoot decreased significantly. The rate of fungal growth and colonization reduced 4 fold. The high resistance of leaves of the cv. Bzura did not change in the presence of cadmium. These leaves seemed to possess higher tolerance to this metal. Macroscopic observations were confirmed in the study of ultrastructure of these systems e.g. the materials contained numerous hyphae and haustoria which displayed varying degrees of degeneration.

Pectinous cell wall thickenings formation – A common defense strategy of plants to cope with Pb

Lead, one of the most abundant and hazardous trace metals affecting living organisms, has been commonly detected in plant cell walls including some tolerant plants, mining ecotypes and hyperaccumulators. We have previously shown that in tip growing Funaria sp. protonemata cell wall is remodeled in response to lead by formation of thickenings rich in low-methylesterified pectins (pectin epitope JIM5 - JIM5-P) able to bind metal ions, which accumulate large amounts of Pb. Hence, it leads to the increase of cell wall capacity for Pb compartmentalization. Here we show that diverse plant species belonging to different phyla (Arabidopsis, hybrid aspen, star duckweed), form similar cell wall thickenings in response to Pb. These thickenings are formed in tip growing cells such as the root hairs, and in diffuse growing cells such as meristematic and root cap columella cells of root apices in hybrid aspen and Arabidopsis and in mesophyll cells in star duckweed fronds. Notably, all analyzed cell wall thickenings were abundant in JIM5-P and accumulated high amounts of Pb. In addition, the co-localization of JIM5-P and Pb commonly occurred in these cells. Hence, cell wall thickenings formed the extra compartment for Pb accumulation. In this way plant cells increased cell wall capacity for compartmentalization of this toxic metal, protecting protoplast from its toxicity. As cell wall thickenings occurred in diverse plant species and cell types differing in the type of growth we may conclude that pectinous cell wall thickenings formation is a widespread defense strategy of plants to cope with Pb. Moreover, detection of natural defense strategy, increasing plant cell walls capacity for metal accumulation, reveals a promising direction for enhancing plant efficiency in phytoremediation.

Induction by Auxin of Polyribosomes and Granular Endoplasmic Reticulum in the Callus Tissue of Cichorium intybus

Summary The effect of 3-indolylacetic acid (IAA) on RNA synthesis, polyribosome distribution and fine structure in callus developing on explants of chicory root cultured in vitro was investigated. The 32 P experiments followed by MAK chromatography showed that auxin-induced increase in RNA synthesis mainly concerned the ribosomal fraction which probably also comprised the mRNA. The ultracentrifugation of ribosomes indicated a promotion by IAA of the transformation of monoribosomes into polyribosome configurations, and the electron microscope observations demonstrated in IAA-treated material a remarkable development of the granular endoplasmic reticulum and an increase in the number of ribosomes, mainly in form of polyribosomes.

Cycloheximide Induced Changes in the Development of Chloroplasts in Ceratodon purpureus

Summary The effect of cycloheximide on ultrastructure of differentiating chloroplasts in the moss Ceratodon purpureus after transferring from darkness to light was investigated. In the abscence of cycloheximide the amyloplasts developed into chloroamyloplasts or typical chloroplasts. Depending on the concentration of the inhibitor, development of plastids was gradually retarded till complete inhibition with cycloheximide at 10 mg/l.