Calcium variously mediates the effect of cytokinin on chlorophyll and LHCPII accumulation during greening in barley leaves and cucumber cotyledons

Abstract During greening, excised etiolated barley leaves and cucumber cotyledons that were depleted of exogenous Ca2+ by a chelating agent (ethylene glycol-bis (beta aminoethyl ether)-N,N,N`N`-tetraacetic acid, EGTA) showed ∼50% reduced chlorophyll (Chl) accumulation and ∼30% accumulation of apoprotein of the light-harvesting chlorophyll a/b-binding protein complex of photosystem II (LHCPII). The Ca2+ channel blocker lanthanum chloride (LaCl3) applied to cucumber cotyledons reduced LHCPII accumulation more than EGTA did. In both plant mate-rials, cytokinins enhanced chlorophyll accumulation by 50-60% and this effect was completely canceled by EGTA application. Hormones significantly increased LHCPII accumulation but EGTA application reduced that effect in barley leaves by ∼30% and in cucumber cotyledons by ∼80%. A similar effect was observed in LaCl3-treated cotyledons. CaCl2 application boosted chlorophyll accumulation in both plant materials. CaCl2 applied together with cytokinin reduced the hormonal effect on chlorophyll accumulation by ∼38% in barley leaves and 23% in cucumber cotyledons, but almost totally inhibited cytokinin-stimulated LHCPII accumulation. Our results indicate that calcium variously mediates the effect of cytokinin on chlorophyll and LHCPII accumulation. Cytokinin-induced enhancement of chlorophyll accumulation seems totally dependent on the exogenous pool of Ca2+, while Ca2+-dependent and Ca2+-independent pathways are involved in the hormonal effect on LHCPII accumulation. The effect of cytokinin on the increase of light-induced LHCPII accumulation appears to be sensitive to exogenously applied Ca2+, which almost totally blocked the hormonal effect. Our results give indirect evidence that the responses to cytokinin and light act on different events leading to Chl and LHCPII accumulation.</jats:p

Effect of kinetin on nucleic acid synthesis in senescing and young leaves in Brassica oleracea L. var. gongylodes L.

In detached kohlrabi leaves senescing in the dark, the decrease in chlorophyll to was more pronounced than in chlorophyll a. The retardation by kinetin of the chlorophyll loss was also markedly stronger in the case of chlorophyll b. Using the fractionation of nucleic acids on polyacrylamide gels it has been shown that during leaf senescence the level of all RNA species decreased, whereas the amount of DNA was more or less constant. In the presence of kinetin, the loss of RNA was inhibited and the incorporation of precursor into the cytoplasmic rRNA as well as into low molecular weight RNA species was supported. Chloroplast rRNA synthesis has not been detected in mature leaves and kinetin showed no effect in this respect. In young expanding leaves detached and kept in light, the synthesis of cytoplasmic rRNA was strongly stimulated by kinetin, whereas in the case of Chloroplast rRNA only an inhibitory effect of kinetin could be found. The results suggest that the cytokinins are primarily involved in processes of the synthesis of cytoplasmic rRNA and low molecular RNA fractions, and in this way affect the development of plastids, in particular the course of their senescence

Ultrastructural study of chloroplasts isolated by various fractionation methods

The chloroplasts of kohlrabi and barley leaves isolated in conventional media and examined in electron microscope showed considerable impairements of their structure. The damages were not eliminated if the centrifugation number was limited and the tonicity of the medium was reduced gradually throughout the fixation and dehydration procedure. A good yield (about 90%) of structurally intact kohlrabi chloroplasts was obtained when they were isolated from leaves pre-fixed and homogenized in medium containing glutaraldehyde

The role of cytokinins in the development and metabolism of barley leaves. I. The effect of cytokinins on leaf senescence

The loss of chlorophyll during dark-induced ageing of barley leaves was prevented to a similar extent by kinetin and the natural cytokinin, 6-Δ2-iso-pentenylarninopurine (2iP). A concentration of 400 μM appeared to be optimal in both cases. In the presence of 2iP the structure of mesophyll cells in dark-incubated leaves was maintained unchanged. A distinct correlation has been found between the retardation by 2iP of the chlorophyll loss, the rate of S2P-incorporation into nucleic acids and the maintaining of the RNase activity at a low level. The importance of the RNA synthesis and the rate of its de-gradation in the cytokinin action in barley leaf senescence will be subjected to future experiments

The role of cytokinins in the development and metabolism of barley leaves. I. The effect of cytokinins on leaf senescence

The loss of chlorophyll during dark-induced ageing of barley leaves was prevented to a similar extent by kinetin and the natural cytokinin, 6-Δ2-iso-pentenylarninopurine (2iP). A concentration of 400 μM appeared to be optimal in both cases. In the presence of 2iP the structure of mesophyll cells in dark-incubated leaves was maintained unchanged. A distinct correlation has been found between the retardation by 2iP of the chlorophyll loss, the rate of S2P-incorporation into nucleic acids and the maintaining of the RNase activity at a low level. The importance of the RNA synthesis and the rate of its de-gradation in the cytokinin action in barley leaf senescence will be subjected to future experiments

The structure of bitumen modified with SBS copolymer and synthetic wax

W pracy przedstawiono wyniki badań struktury asfaltu modyfikowanego kopolimerem SBS i woskiem syntetycznym. Do asfaltu drogowego 35/50 dodawano kopolimer styren-butadien-styren (SBS) w ilości 1-4% mas. oraz 0,5% mas. wosku syntetycznego. Dokonano oceny ilościowej i jakościowej struktury otrzymanych układów trójskładnikowych za pośrednictwem mikroskopii optycznej z przystawką fluorescencyjną. Na podstawie jakościowych i ilościowych badań mikroskopowych określono homogeniczność kompozycji asfaltowo-polimerowych, a także wielkość cząstek polimeru w asfalcie.This work shows the results of studies on the structure of modified bitumen with SBS copolymer and synthetic wax. The styrene-butadiene-styrene (SBS) copolymer in the amount of 1-4 wt% and 0.5 wt% of synthetic wax were added to the road bitumen 35/50. For the obtained bitumen-polymer compositions, quality and quantity evaluation of structure by fluorescence microscopy were carried out. On the base of quality and quantity microscopic tests can determine the homogeneity of the bitumen-polymer compositions, and particle size of the polymer in the bitumen

Modified halloysite as a filler for epoxy resins

The modification methods of halloysite and further applications of the modified mineral as a filler for epoxy resins have been presented. The advantage of ultrasound treatment prior to chemical modification with an organic compound in order to obtain a hybrid filler was confirmed. The analysis of the composites obtained with the use of the modified halloysite (3–5 wt.% range) as a filler for epoxy resins indicates an improved interphase interaction and mechanical properties in comparison to the composites based on neat halloysite