Renato A. Moreira

Proline accumulation and glutamine synthetase activity are increased by salt-induced proteolysis in cashew leaves

In this study cashew (Anacardium occidentale) plants were exposed to a short- and long-term exposure to NaCl in order to establish the importance of the salt-induced proteolysis and the glutamine synthetase activity on the proline accumulation. The cashew leaf showed a prominent proline accumulation in response to salt stress. In contrast, the root tissue had no significant changes in proline content even after the drastic injury caused by salinity on the whole plant. The leaf proline accumulation was correlated to protease activity, accumulation of free amino acid and ammonia, and decrease of both total protein and chlorophyll contents. The leaf GS activity was increased by the salt stress whereas in the roots it was slightly lowered. Although the several amino acids in the soluble pool of leaf tissue have showed an intense increment in its concentrations in the salt-treated plants, proline was the unique to show a proportional increment from 50 to 100 mol m-3 NaCl exposure (16.37 to 34.35 mmol kg-1 DM, respectively). Although the leaf glutamate concentration increased in the leaves of the salt-stressed cashew plants, as compared to control, its relative contribution to the total amino acid decreased significantly in stressed leaves when compared to other amino acids. In addition, when the leaf discs were incubated with NaCl in the presence of exogenous precursors (Glu, Gln, Orn or Arg) involved in the proline synthesis pathways, the glutamate was unique in inducing a significant enhancement of the proline accumulation compared to those discs with precursor in the absence of NaCl. These results, together with the salt-induced increase in the GS activity, suggest an increase in the de novo synthesis of proline probably associated with the increase of the concentration of glutamate. Moreover, the prominent salt-induced proline accumulation in the leaves was associated with the higher salt-sensitivity in terms of proteolysis and salt-induced senescence as compared to the roots. In conclusion, the leaf-proline accumulation was due, at least in part, to the increase in the salt-induced proteolysis associated with the increments in the GS activity and hence the increase in the concentration of glutamate precursor in the soluble amino acid pool.

Compositional and nutritional attributes of seeds from the multiple purpose tree Moringa oleifera Lamarck

Moringa oleifera Lam is a multipurpose tree cultivated to use as a vegetable, for spice, for cooking and cosmetic oil and as a medicinal plant. Owing to the use of its seeds as food and as a clarifying agent of turbid water some nutritional and antinutritional characteristics were studied. The mature seeds contained 332.5 g crude protein, 412.0 g crude fat, 211.2 g carbohydrate and 44.3 g ash per kg dry matter. The essential amino acid profile compared with the FAO/WHO/UNU scoring pattern requirements for different age groups showed deficiency of lysine, threonine and valine. The content of methionine + cysteine (43.6 g kg−1 protein), however, was exceptionally higher and close to that of human milk, chicken egg and cows milk. The seed extract agglutinated rabbit erythrocytes but did not show trypsin inhibitor and urease activities. Feeding rats with a diet containing the seed meal showed loss of appetite, impaired growth, lower NPU and enlargement of stomach, small intestine, caecum + colon, liver, pancreas, kidneys, heart and lungs and atrophy of thymus and spleen in comparison with rats fed on an egg-white diet. The results indicated that consumption of M oleifera raw mature seeds should be viewed with some caution until suitable processing methods are developed to abolish the yet unknown adverse factors.

Functional polysaccharides as edible coatings for cheese.

The objective of the present study was to apply the polysaccharides from different nontraditional sources for cheese coatings. Chitosan, galactomannan from Gleditsia triacanthos, and agar from Glacilaria birdiae were tested, with different formulations and with the addition of plasticizer and corn oil. The surface properties of the cheese and the wetting capacity of the coatings on the cheese were determined. The three best solutions for each polysaccharide were chosen, further films were cast, and permeability to water vapor, oxygen, and carbon dioxide was determined, along with opacity. The solutions of G. triacanthos (formulation: 1.5% of galactomannan, 2.0% of glycerol, and 0.5% of oil) presented the best properties to coat the cheese: -38.76 mN x m(-1) for wettability; 3.24 x 10(-11) (g x (m x s x Pa)(-1)) for water vapor permeability; 0.94 x 10(-15) and 15.35 x 10(-15) (g x m(Pa x s x m(2))(-1)) for oxygen and carbon dioxide permeabilities, respectively; and opacity values of 5.27%. The O(2) consumption and CO(2) production rates of the cheese with and without coating were evaluated, showing a decrease of the respiration rates when the coating was applied. The uncoated cheese had an extensive mold growth at the surface when compared with the coated cheese. The results show that these coatings can be applied as an alternative to synthetic coatings.

Composition, toxic and antinutritional factors of newly developed cultivars of Brazilian soybean (Glycine max)

Five different recently released Brazilian soybean cultivars (Bays, BR-10, Rio Balsas, Serido and Tropical) were compared for their proximate analyses and presence of antinutritional or toxic factors. As expected, the seeds are rich in proteins, varying from 360·7 to 485·4 g kg−1 flour, and they also have a high amount of fat (from 183·0 to 215·3 g kg−1 flour). Crude extracts from seeds of Bays, BR-10, Serido and Tropical were highly toxic to mice within 1–12 h, depending on the administration route (intraperitoneal, intramuscular or subcutaneous) and dose used while Rio Balsas was not. These acute effects were very similar to those produced by the soytoxin, a neurotoxin that has been recently purified from the commercial soybean sold in Brazil. The amount of trypsin inhibited in the presence of crude extracts ranged from 28·5 to 62·5 g kg−1 flour. Urease was also present and the seed lectin agglutinated preferentially rabbit erythrocytes. A heat treatment at 92°C for 1 min destroyed completely the toxic activity while the haemagglutinating and trypsin inhibitor activities were abolished within 5 min. At these conditions urease was still active. Due to its high protein content, lack of soytoxin, and low levels of trypsin inhibitor, lectin, and urease it is suggested that Rio Balsas could be an alternative for breeding programmes aimed to improve the nutritional quality of soybeans. ©1997 SCI

Plant lectins, chemical and biological aspects

Lectins, carbohydrate-binding proteins of non-immune origin, that agglutinate cells or precipitate polysaccharides and glycoconjugates, are well distributed in nature, mainly in the Plant Kingdom. The great majority of the plant lectins are present in seed cotyledons where they are found in the cytoplasm or in the protein bodies, although they have also been found in roots, stems and leaves. Due to their peculiar properties, the lectins are used as a tool both for analytical and preparative purposes in biochemistry, cellular biology, immunology and related areas. In agriculture and medicine the use of lectins greatly improved in the last few years. The lectins, with few exceptions, are glycoproteins, need divalent cations to display full activity and are, in general, oligomers with variable molecular weight. Although the studies on lectins have completed a century, their role in nature is yet unknown. Several hypotheses on their physiological functions have been suggested. Thus, lectins could play important roles in defense against pathogens, plant-microorganism symbiosis, cell organization, embryo morphogenesis, phagocytosis, cell wall elongation, pollen recognition and as reserve proteins. A brief review on the general properties and roles of the lectins is given.

Composition and nutritional properties of seeds from Pachira aquatica Aubl, Sterculia striata St Hil et Naud and Terminalia catappa Linn.

Abstract The seeds of three wild plants (Pachira aquatica, Sterculia striata and Terminalia catappa) were analyzed to establish their chemical compositions and nutritional properties in order to investigate the possibility of using them for human and/or animal consumption. Proximate analyses showed that they have high amounts of protein and oil. However, they are deficient in various essential amino acids but P. aquatica seeds have tryptophan, threonine and phenylalanine + tyrosine contents higher than those reported for human milk, chicken egg and cows milk. Haemagglutinating and trypsin inhibitor activities were found to be present in the seeds of P. aquatica and T. catappa but absent in S. striata. Coincidentally the rats fed on S. striata diet gained slightly in weight and presented alterations in the key internal organs which were less drastic throughout the 10-day test period. On the other hand, the rats fed on T. catappa diet maintained their body weight but suffered from stomah, small intestine and pancreas hypertrophy as well as spleen atrophy. Five out of six rats fed on P. aquatica diet died within 6–8 days. The remaining rat experienced enlargement of the stomach, liver, pancreas, kidneys, heart and lungs and had spleen atrophy when compared with the same organs of rats fed on egg-white diet. Hypertrophy of the pancreas and kidneys was very marked and these organs nearly doubled in dry weight in comparison with those of the egg-white control group, demonstrating that the raw seed of P. aquatica are highly toxic when fed to rats even at a meal protein concentration half that of S. striata or T. catappa, which were better tolerated by the experimental animals.

Visualization of proteinase inhibitors in SDS-polyacrylamide gels.

Abstract A simple and sensitive method was developed to distinguish between low (ca. 10,000 daltons) and high (over 10,000 daltons) molecular weight proteinase inhibitors in crude extracts of seeds. The activity of trypsin and chymotrypsin inhibitors could easily be detected in SDS-polyacrylamide gels by using acetyl- dl -phenylalanine-β-naphthyl ester as substrate for the enzymes.

Cashew-tree (Anacardium occidentale L.) exudate gum: a novel bioligand tool

The potential of bioaffinity as a tool for the study of biological-recognition mechanisms is gaining increasing value. The search continues for alternative products that can be obtained from renewable sources, such as the bark exudate gum from the cashew tree (Anacardium occidentale L.), which grows wild in many tropical and subtropical countries. Its potential use as a chromatographic matrix and/or for bioaffinity ligand for proteins (lectins) has been investigated. The crude gum was cross-linked in order to obtain a kind of chromatographic matrix (gel). To evaluate the gums ability to retain glycoproteins (lectins), affinity chromatography was performed and, in addition, the reological behaviour of the gum was characterized.The potential of bioaffinity as a tool for the study of biological‐recognition mechanisms is gaining increasing value. The search continues for alternative products that can be obtained from renewable sources, such as the bark exudate gum from the cashew tree (Anacardium occidentale L.), which grows wild in many tropical and subtropical countries. Its potential use as a chromatographic matrix and/or for bioaffinity ligand for proteins (lectins) has been investigated. The crude gum was cross‐linked in order to obtain a kind of chromatographic matrix (gel). To evaluate the gums ability to retain glycoproteins (lectins), affinity chromatography was performed and, in addition, the reological behaviour of the gum was characterized.

Comparison of the amino acid sequences of the lectins from seeds of Dioclea lehmanni and Canavalia maritima

The amino acid sequences of the major lectins from the seeds of Dioclea lehmanni and Canavalia maritima were determined by DABITC/PITC microsequence analysis of peptides derived from the proteins by enzymatic digestions with trypsin, chymotrypsin and the protease from S. aureus V8. These sequences were found to be very similar to those of the lectins from Dioclea grandiflora and Canavalia ensiformis (Con A). The D. lehmanni lectin was unusual amongst legume lectins in that it contained a single Cys.

Isolation and characterization of Dioclea altissima var. megacarpa seed lectin

Abstract A lectin was isolated from Dioclea altissima var. megacarpa seeds by affinity chromatography on Sephadex G-50 column. The lectin showed carbohydrate specificity for d -mannose/ d -glucose, and divalent metal cations (Ca 2+ and Mn 2+ are required for full activity. It contained no covalently bound carbohydrate and had an amino acid composition characterised by large contents of aspartic acid and serine. The activation energy of the heat denaturing process was 106.9 kJ mol −1 . The lectin presented three protein bands in SDS-PAGE, with M r of 26 000, 15 000 and 9000, respectively, and showed immunological identity and the same N-terminal sequence as other lectins already isolated from the sub-tribe Diocleinae .