Measurement of expansin activity and plant cell wall creep by using a commercial texture analyzer

Background: Expansins play an important role in cell wall metabolism and fruit softening. Determination of expansin activity is a challenging problem since it depends on measuring cell wall properties by using ad hoc extensometers, a fact that has strongly restricted its study. Then, the objective of the work was to adapt a methodology to measure cell wall creep and expansin activity using a commercial texture meter, equipped with miniature tensile grips and an ad hoc cuvette of easy construction. Results: It was possible to measure hypocotyls acid growth and expansin activity in a reliable and reproducible way, using a commercial texture meter, common equipment found in laboratories of food science or postharvest technology. Expansin activity was detected in protein extracts from cucumber hypocotyls, tomato and strawberry fruits, and statistical differences in expansin activity were found in both fruit models at different ripening stages. Conclusions: The possibility of measuring expansin activity following this adapted protocol with a commercial texture meter could contribute to ease and increase the analysis of expansin in different systems, leading to a better understanding of the properties of these proteins under different experimental conditions.

Role of pectin from cucumber (Cucumis sativus) in modulation of protein kinase C activity and regulation of glycogen metabolism in rats.

The regulatory role of protein kinase C (PKC) in glycogen metabolism in pectin fed rats was investigated. Administration of pectin (5 g/kg body wt/day) from cucumber (Cucumis sativius L.) led to inhibitory effects on PKC activity in the liver of rats. In the brain and pancreas, PKC activity was significantly higher in pectin-treated rats as compared to the control group. Level of blood glucose was significantly lowered and the level of glycogen in the liver was significantly increased in pectin-administered rats. Glycogen synthase activity was enhanced, while glycogen phosphorylase enzyme showed inhibition in pectin-treated rats. Results indicated that pectin administration might have caused an increase in the secretion of the insulin, which, in turn, had a stimulatory effect on the PKC activity in the pancreas. The decreased PKC activity in the liver and increased PKC activity in the brain and pancreas on pectin administration indicated enhanced glycogenesis and reduced glycogenolysis.

Involvement of oxyradicals in promotion/inhibition of expansion growth in cucumber cotyledons.

Cytokinin-induced expansion growth of cucumber cotyledons and its interaction with UV-B (280-320 nm) was studied with reference to oxyradicals. UV-B radiation enhanced the level of oxyradicals in the cotyledons measured by EPR spectroscopy. Cytokinin promoted expansion growth was inhibited by UV-B radiation. Cytokinins reduced the level of oxyradicals in dark grown cotyledons, while promoting growth. Overproduction of oxyradicals by UV-B could not be fully accounted for the inhibition of growth of cotyledons, since quenching of radicals by cytokinins did not fully restore inhibition of growth.

Age dependent alterations in photosystem II acceptor side in Cucumis sativus cotyledonary leaf thylakoids: analysis of binding characteristics of herbicide [14C]-atrazine.

Senescence induced temporal changes in photosystems can be conveniently studied in cotyledonary leaves. We monitored the protein, chlorophyll and electron transport activities in Cucumis sativus cv Poinsette cotyledonary leaves and observed that by 20th day, there was a 50%, 41% and 30-33% decline in the chlorophyll, protein and photosystem II activity respectively when compared to 6th day cotyledonary leaves taken as control. We investigated the changes in photosystem II activity (O2 evolution) as a function of light intensity. The photosystem II functional antenna decreased by 27% and the functional photosystem II units decreased by 30% in 20-day old cotyledonary leaf thylakoids. The herbicide [14C]-atrazine binding assay to monitor specific binding of the herbicide to the acceptor side of photosystem II reaction centre protein, D1, showed an increase in the affinity for atrazine towards D1 protein and decrease in the QB binding sites in 20th day leaf thylakoids when compared to 6th day leaf thylakoids. The western blot analysis also suggested a decrease in steady state levels of D1 protein in 20th day cotyledonary leaf thylakoids as compared to 6th day sample which is in agreement with [14C]-atrazine binding assay and light saturation kinetics.

Effect of spent wheat straw on growth, growth hormones, metabolism and rhizosphere of cucumis sativus

The effect of wheat straw added to the soil as a raw straw [rs] and spent straw [ss] form [after being treated by oyster mushroom, Pleurotus floridanus] on the growth of cucumber plants [Cucumis sativus] was studied. In addition to microbial biomass of the rhizosphere and soil chemical properties. The response of cucumber plants treated with either [rs] or [ss] at concentration 1.0 percent and 0.2 percent respectively exhibited the best growth. There were an increase in fresh weight, dry weight, number of leaves, leaf area, photosynthetic pigments, main growth regulators [auxins, gibberellins and cytokinins] and some metabolites [carbohydrates, nitrogenous compounds, nucleic acid] and some minerals [K, Na and Ca] than in control plants, whereas the highest concentration [2.0 percent] of both types of straw suppressed these parameters. The analyses of either raw or spent straw revealed that, they contained considerable amounts of carbon, nitrogen, minerals and hormones. This lead to a change in the chemical composition as well as the microbial biomass in the soil. On the other hand, spent straw contained higher values of phenolic compounds than in raw straw as a result of lignin decomposition by Pleurotus floridanus which resulted to decrease the growth of cucumber. This was related to the stimulation in IAA oxidase