Activity, cloning, and expression of an isoamylase-type starch-debranching enzyme from banana fruit

Unripe bananas have a high content of starch (almost 20%) that is metabolized during fruit ripening with a concomitant synthesis of soluble sugars. Since starch granules are composed of amylose and amylopectin, several enzymes have to be involved in its mobilization during banana ripening, with a necessary participation of one starch-debranching enzyme (DBE) to hydrolyze the alpha-1,6-branches of amylopectin. Banana DBE seems to be an isoamylase-type enzyme, as indicated by substrate specificity and the cloning of a 1575 bp cDNA, similar to the isoamylase sequences from potato, Arabdopsis, and maize. The assays for DBE indicated only minor changes in activity during ripening, and the results of the northern and western blots with antiserum against the recombinant banana isoamylase were in agreement with the steady-state level of activity, since no significant changes in gene expression were observed. The high activity on beta-limit dextrin and the similarity to the potato isoform 3 suggest that during banana ripening the hydrolysis of alpha-1,6-linkage of amylopectin results from the activity of a pre-existing isoamylase-type debranching enzyme in coordination with other amylolitic enzymes. To the best of our knowledge, this is the first evaluation of activity and expression of a DBE from a fruit.     

Partial chemical composition,free soluble sugars and unavailable carbohydrates in the embryonic axis and seed coat ofPhaseolus vulgaris L. (Canario group)

Four varieties of common bean were examined, but there were no significant differences among them. Crude protein content (46.7% and 49.0%) was the main constituent in embryonic axes. The average values of ash, crude fiber and ether extract were 4.2%, 3.7% and 3.0% respectively. Starch was approximately three times more abundant (7.5%) than cellulose (2.7%). Hemicellulose B values were lower (5.5%) than hemicellulose A (9.2%). The mean value of the pectic substances in embryonic axes was 12.3%. The free ethanol-soluble sugars ranged from 2.9% to 4.9%. Verbascose, stachyose, raffinose, sucrose, and galactose were identified and quantified in embryonic axes. Seed coat flour contained cellulose (30.6%), ether extract (0.4%), ash (2.8%), and protein (5.4%). Free ribose, mannose, arabinose, and galactose were present in seed coats in amounts ranging from 0.009% to 0.031%.     

Actinobacteria-enhanced plant growth, nutrient acquisition, and crop protection: Advances in soil, plant, and microbial multifactorial interactions

Agricultural areas of land are deteriorating every day owing to population increase, rapid urbanization, and industrialization. To feed today’s huge populations, increased crop production is required from smaller areas, which warrants the continuous application of high doses of inorganic fertilizers to agricultural land. These cause damage to soil health and, therefore, nutrient imbalance conditions in arable soils. Under these conditions, the benefits of microbial inoculants (such as Actinobacteria) as replacements for harmful chemicals and promoting ecofriendly sustainable farming practices have been made clear through recent technological advances. There are multifunctional traits involved in the production of different types of bioactive compounds responsible for plant growth promotion, and the biocontrol of phytopathogens has reduced the use of chemical fertilizers and pesticides. There are some well-known groups of nitrogen-fixing Actinobacteria, such as Frankia, which undergo mutualism with plants and offer enhanced symbiotic trade-offs.In addition to nitrogen fixation, increasing availability of major plant nutrients in soil due to the solubilization of immobilized forms of phosphorus and potassium compounds, production of phytohormones, such as indole-3-acetic acid, indole-3-pyruvic acid, gibberellins, and cytokinins, improving organic matter decomposition by releasing cellulases, xylanase, glucanases, lipases, and proteases, and suppression of soil-borne pathogens by the production of siderophores, ammonia, hydrogen cyanide, and chitinase are important features of Actinobacteria useful for combating biotic and abiotic stresses in plants.The positive influence of Actinobacteria on soil fertility and plant health has motivated us to compile this review of important findings associated with sustaining plant productivity in the long run.     

Improvement of dietary fiber,ferulic acid and calcium contents in pan bread enriched with nejayote food additive from white maize (Zea mays)

Nejayote is the wastewater from the alkaline-cooking of maize and its solids are rich in dietary fiber (45.3%), calcium (5.7%) and ferulic acid (219 mg/100 g). Nejayote solids were used to develop a food additive (NS) consisting of 80% nejayote solids and 20% gluten. NS was incorporated at 3, 6 or 9%, in wheat flour to increase the dietary fiber, calcium, phenolics and antioxidant capacity of breads. The addition of 9% NS did not affect overall baking performance and bread quality but increased dietary fiber up to 54% in composite breads. Moreover, enriched breads contained about 745 times more free ferulic acid and increased approximately 70% their antioxidant capacity. Two slices of bread (64 g) supplemented with 9% of NS provided 29% of the recommended calcium intake. Thus, the NS could be used as a value-added food-ingredient for the preparation of composite bakery-products with improved dietary fiber, calcium, nutraceuticals and antioxidant properties.     

Resistance of Selected Potato Genotypes to the Potato Psyllid (Hemiptera: Triozidae)

The characterization of resistance of selected potato, Solanum tuberosum L., breeding clones to the potato psyllid, Bactericera cockerelli (Sulc) (Hemiptera: Triozidae) was investigated. Antixenosis was assessed in choice tests in which a single plant of each genotype was placed inside a rearing cage, where 60 female psyllid adults were released and the number of adults and eggs on each genotype was counted 24 h later. Antibiosis was evaluated in no-choice tests in which adults (five males and five females) were confined in a cage fixed to the upper side of leaves. After 4 h of exposure, adults were removed and the number of eggs counted. The developmental time and survival of offspring were recorded until all insects became adults. All the resistant genotypes showed strong antibiotic effects to B. cockerelli. These results show promise for incorporation into an IPM program against B. cockerelli.     

Structural collapse prevents beta-carotene loss in a supercooled polymeric matrix

The kinetics of degradation and surface color changes of beta-carotene encapsulated in a polymeric matrix (PVP-40) and its relationship with physical changes (manifested as structural collapse) of the matrix were studied during storage of samples at several water activities at constant temperature. The degradation rate constants obtained decreased with an increase in the relative humidity (RH) of the storage atmosphere. Beta-carotene losses were observed mainly at RHs below the glass transition temperature (Tg) of the corresponding systems, and the lower degradation constant rates were observed under conditions where the matrices were fully plasticized (i.e., rubbery) and collapsed (RH, 64 and 75%). An inverse correlation was observed between collapse and degradation rate constants. The results presented here indicated that the molecular mobility of the matrix is not rate limiting for the degradation of beta-carotene. Factors such as microstructure and porosity of the polymeric matrix may be more important as modifiers of kinetic reactions. Surface color was not a sensitive indicator of beta-carotene retention, because it was mostly affected by the degree of matrix hydration and collapse phenomena.     

Stay-green phenotype slows the carotenogenic process in Capsicum annuum (L.) fruits

Stay-green mutants have been very useful for elucidating the chlorophyll catabolism pathway in higher plants. In the present study the possible relationship between the retention/catabolism of chlorophylls and the carotenogenic process taking place in ripening Capsicum annuum (L.) fruits has been investigated. Phytylated, dephytylated and oxidized chlorophyll derivatives, and total and individual carotenoids were analyzed over the whole ripening period. In general terms, the biosynthesis of carotenoid pigments taking place during the ripening of C. annuum fruits is identical in both red and stay-green lines, so that the carotenogenic process is independent of the retention of chlorophylls. However, it has been found that the carotenogenesis is slowed in the stay-green lines. Therefore, although the catabolism of chlorophylls and biosynthesis of carotenoids seem to be separate processes, the fact that they are taking place in the chloroplast/chromoplast suggests that some kind of interaction between the two processes may occur at different levels. Plastids corresponding to the wild genotype (red color fruit phenotype) show high plastoglobuli density and thylakoids are almost absent, whereas in the case of stay-green phenotype, thylakoids and plastoglobuli coexist in the same plastid (chlorochromoplasts). The role of carotenoid pigments on the physiological mechanism for protecting the preserved thylakoid structures is discussed.     

Spatio-temporal distribution of pyrethroids in soil in Mediterranean paddy fields

Journal of Soils and Sediments - The demand of rice by the increase in population in many countries has intensified the application of pesticides and the use of poor quality water to irrigate...