S. Suzanne Nielsen

Biological effects of plant lectins on the cowpea weevil.

Abstract Plant lectins have been implicated as antibiosis factors against insects, particularly the cowpea weevil, Callosobruchus maculatus . In the present investigation, 17 plant lectins were screened in an artificial seed system to determine if biological activity toward C. maculatus is widespread among lectins. Five of the 17 plant lectins screened caused a significant delay in C. maculatus developmental time at dietary levels of 0.2 and 1.0% (w/w). These lectins could be classed into one of two groups: lectins with specificity for N -acetylgalactosamine/galactose (GalNAc/Gal) and lectins with specificity for N -acetylglucosamine (GlcNAc). The GalNAc/Gal lectins included osage orange lectin and peanut agglutinin. A dose-response analysis of peanut agglutinin indicated that for every 0.1% increase in dose there was a 0.49 day delay in developmental time. The GlcNAc lectins included potato lectin, jimson weed lectin and wheat germ agglutinin (WGA). The most potent lectin was WGA; the dose-response analysis indicated that for every 0.1% increase in dose there was a 1.47 day delay in developmental time. Additionally, for every 0.1% increase in WGA there was a 2.79% increase in mortality. The results of this investigation indicate that there exists in C. maculatus physiological/biochemical systems vulnerable to selected plant lectins. The genes coding for the effective plant lectins could, in principle, serve as antibiosis factors to use in host plant resistance programs designed to bring resistance into cowpea through recombinant DNA technologies.

Differential Expression of Soybean Cysteine Proteinase Inhibitor Genes during Development and in Response to Wounding and Methyl Jasmonate

Three cysteine proteinase inhibitor cDNA clones (pL1, pR1, and pN2) have been isolated from a soybean (Glycine max L. Merr.) embryo library. The proteins encoded by the clones are between 60 and 70% identical and contain the consensus QxVxG motif and W residue in the appropriate spatial context for interaction with the cysteine proteinase papain. L1, R1, and N2 mRNAs were differentially expressed in different organs of plants (juvenile and mature) and seedlings, although N2 mRNA was constitutive only in flowers. R1 and N2 transcripts were induced by wounding or methyl jasmonate (M-JA) treatment in local and systemic leaves coincident with increased papain inhibitory activity, indicating a role for R1 and N2 in plant defense. The L1 transcript was constitutively expressed in leaves and was induced slightly by M-JA treatment in roots. Unlike the chymotrypsin/trypsin proteinase inhibitor II gene (H. Pena-Cortes, J. Fisahn, L. Willmitzer [1995] Proc Natl Acad Sci USA 92: 4106–4113), expression of the soybean genes was only marginally induced by abscisic acid and only in certain tissues. Norbornadiene, a competitive inhibitor of ethylene binding, abolished the wounding or M-JA induction of R1 and N2 mRNAs but not the accumulation of the wound-inducible vspA transcript. Presumably, ethylene binding to its receptor is involved in the wound inducibility of R1 and N2 but not vspA mRNAs. Bacterial recombinant L1 and R1 proteins, expressed as glutathione S-transferase fusion proteins, exhibited substantial inhibitory activities against vicilin peptidohydrolase, the major thiol endopeptidase in mung bean seedlings. Recombinant R1 protein had much greater cysteine proteinase inhibitor activity than recombinant L1 protein, consistent with the wound inducibility of the R1 gene and its presumed role in plant defense.

Two Wound-Inducible Soybean Cysteine Proteinase Inhibitors Have Greater Insect Digestive Proteinase Inhibitory Activities than a Constitutive Homolog

Diverse functions for three soybean (Glycine max L. Merr.) cysteine proteinase inhibitors (CysPIs) are inferred from unique characteristics of differential regulation of gene expression and inhibitory activities against specific Cys proteinases. Based on northern blot analyses, we found that the expression in leaves of one soybean CysPI gene (L1) was constitutive and the other two (N2 and R1) were induced by wounding or methyl jasmonate treatment. Induction of N2 and R1 transcript levels in leaves occurred coincidentally with increased papain inhibitory activity. Analyses of kinetic data from bacterial recombinant CysPI proteins indicated that soybean CysPIs are noncompetitive inhibitors of papain. The inhibition constants against papain of the CysPIs encoded by the wound and methyl jasmonate-inducible genes (57 and 21 nM for N2 and R1, respectively) were 500 to 1000 times lower than the inhibition constant of L1 (19,000 nM). N2 and R1 had substantially greater inhibitory activities than L1 against gut cysteine proteinases of the third-instar larvae of western corn rootworm and Colorado potato beetle. Cysteine proteinases were the predominant digestive proteolytic enzymes in the guts of these insects at this developmental stage. N2 and R1 were more inhibitory than the epoxide trans-epoxysuccinyl-L-leucylamide-(4-guanidino)butane (E-64) against western corn rootworm gut proteinases (50% inhibition concentration = 50, 200, and 7000 nM for N2, R1, and E-64, respectively). However, N2 and R1 were less effective than E-64 against the gut proteinases of Colorado potato beetle. These results indicate that the wound-inducible soybean CysPIs, N2 and R1, function in host plant defense against insect predation, and that substantial variation in CysPI activity against insect digestive proteinases exists among plant CysPI proteins.

Determination of Moisture Content

The moisture (or total solids) content of foods is important to food manufacturers for a variety of reasons. Moisture is an important factor in food quality, preservation, and resistance to deterioration. Determination of moisture content also is necessary to calculate the content of other food constituents on a uniform basis (i.e., dry weight basis). The dry matter that remains after moisture analysis is commonly referred to as total solids.

Invited review: Plasmin protease in milk: Current knowledge and relevance to dairy industry

Plasmin is by far the predominant and most completely studied endogenous protease in bovine milk. Plasmin-induced proteolysis can have either beneficial or detrimental effects on the texture and flavor of dairy products, depending on the extent of hydrolysis and type of dairy product. In cheese, the breakdown of protein can help develop desirable flavors and texture during ripening, whereas in pasteurized milk and ultra-high-temperature milk, proteolysis causes undesirable gelation. Plasmin is part of a complex protease-protease inhibitor system in milk that consists of active and inactive forms of the enzyme, activators, and inhibitors. Considerable research has been done to isolate and characterize components of the plasmin system, determine how they interact, develop and compare quantitation methods, and determine how they are affected by cow characteristics, processing conditions, other milk components, storage conditions, and bacterial proteases. Considerable research has focused on enhancing or minimizing the activity of plasmin system components. The intent has been to control protease activity in casein and whey fractions, depending on the final food or ingredient application. Controlling the activity of plasmin has a great potential to improve dairy product quality and reduce their processing costs.

Phenol-Sulfuric Acid Method for Total Carbohydrates

The phenol-sulfuric acid method is a simple and rapid colorimetric method to determine total carbohydrates in a sample. The method detects virtually all classes of carbohydrates, including mono-, di-, oligo-, and polysaccharides. Although the method detects almost all carbohydrates, the absorptivity of the different carbohydrates varies. Thus, unless a sample is known to contain only one carbohydrate, the results must be expressed arbitrarily in terms of one carbohydrate.

Impact of the hard-to-cook phenomenon on phenolic antioxidants in dry beans (Phaseolus vulgaris).

Epidemiological studies have established a link between consumption of dry beans and lower incidence of degenerative diseases. This relationship is attributed in part to properties of natural antioxidants present in beans. The objective of this study was to determine if the hard-to-cook (HTC) phenomenon in beans had a negative effect on the content of free and bound phenolic antioxidants and antioxidant capacity. Folin-Ciocalteu, Trolox equivalent antioxidant capacity, and HPLC methods were used to quantify the content of phenolic acids and antioxidant capacity. Results showed that the HTC phenomenon did not equally affect the content and antioxidant capacity of phenolic acids in different bean cultivars. Black beans were most affected, the contents of free and acid hydrolyzable phenolic acids being reduced by 35 and 36%, respectively, and the antioxidant activity by 18 and 25%, respectively. This study showed that the HTC phenomenon affected a potential nutritive characteristic of dry beans.

Physical and chemical attributes of cowpea lines resistant and susceptible to Callosobruchus maculatus (F.) (Coleoptera: Bruchidae)

Abstract Fifteen lines of cowpeas, Vigna unguiculata (L.) Walpers, were analyzed for physical and chemical characteristics to study their relationship with resistance to Callosobruchus maculatus (F.). No significant differences were found (P

Excess nutrients in hydroponic solutions alter nutrient content of rice, wheat, and potato

Environment has significant effects on the nutrient content of field-grown crop plants. Little is known, however, about compositional changes caused by controlled environments in which plants receive only artificial radiation and soilless, hydroponic culture. This knowledge is essential for developing a safe, nutritious diet in a Controlled Ecological Life-Support System (CELSS). Three crops that are candidates for inclusion in a CELSS (rice, wheat, and white potato) were grown both in the field and in controlled environments where the hydroponic nutrient solution, photosynthetic photon flux (PPF), and CO2 level were manipulated to achieve rapid growth rates. Plants were harvested at maturity, separated into discrete parts, and dried prior to analysis. Plant materials were analyzed for proximate composition (protein, fat, ash, and carbohydrate), total nitrogen (N), nitrate, minerals, and amino-acid composition. The effect of environment on nutrient content varied by crop and plant part. Total N and nonprotein N (NPN) contents of plant biomass generally increased under controlled-environment conditions compared to field conditions, especially for leafy plant parts and roots. Nitrate levels were increased in hydroponically-grown vegetative tissues, but nitrate was excluded from grains and tubers. Mineral content changes in plant tissue included increased phosphorus and decreased levels of certain micronutrient elements under controlled-environment conditions. These findings suggest that cultivar selection, genetic manipulation, and environmental control could be important to obtain highly nutritious biomass in a CELSS.

Evaluation of Cyanothece sp. ATCC 51142 as a candidate for inclusion in a CELSS

Controlled ecological life support systems (CELSS) have been proposed to make long-duration manned space flights more cost-effective. Higher plants will presumably provide food and a breathable atmosphere for the crew. It has been suggested that imbalances between the CO2/O2 gas exchange ratios of the heterotrophic and autotrophic components of the system will inevitably lead to an unstable system, and the loss of O2 from the atmosphere. Ratio imbalances may be corrected by including a second autotroph with an appropriate CO2/O2 gas exchange ratio. Cyanothece sp. ATCC 51142 is a large unicellular N2-fixing cyanobacterium, exhibiting high growth rates under diverse physiological conditions. A rat-feeding study showed the biomass to be edible. Furthermore, it may have a CO2/O2 gas exchange ratio that theoretically can compensate for ratio imbalances. It is suggested that Cyanothece spp. could fulfill several roles in a CELSS: supplementing atmosphere recycling, generating fixed N from the air, providing a balanced protein supplement, and protecting a CELSS in case of catastrophic crop failure.