Nuclear genetic control of variation in simazine tolerance in oilseed brassicas

Summary Brassica napus is a natural allotetraploid derived from the diploid species B. rapa L. (syn. campestris L.) and B. oleracea L. Somatic hybrids synthesized from highly heterozygous lines of these two diploid species were evaluated for fertility. The hybrids were obtained from two fusion experiments which differed in the B. rapa full-sibling parent used as the source of protoplasts. Both B. rapa siblings were lelf-incompatible (SI) yet contained different S-alleles; the B. oleracea species parent was self-compatible (SC). Eight tetraploid hybrids examined had very high female and male fertility; eight hybrids with higher ploidy had low fertility. Hybrids derived from one B. rapa sibling were self-incompatible, whereas those derived from the other B. rapa sibling were fully self-compatible. These data suggest that the different S-alleles of each B. rapa sibling displayed varying penetrance relative to the SC of the B. oleracea parent when combined in B. napus.Abbreviations SC self-compatibility - SI self-incompatibility     

Nuclear genetic control of variation in simazine tolerance in oilseed brassicas

Summary Substantial variation in tolerance to the triazine herbicide simazine was observed among a wide range of Brassica napus cultivars grown in a hydroponic screening system. None of these cultivars was as tolerant of are simazine treatment as the Canadian cultivar Triton which carries cytoplasmic gene(s) which confer a high level of resistance through their modification of chloroplast membranes to which triazine herbicides normally bind. A field study showed that the most tolerant cultivar Haya had a significantly higher yield than Triton in both handweeded plots and plots treated with 1000 ml/ha simazine. This finding supported other observations that the yield potential of cultivars such as Triton is substantially reduced because of the impairment of photosynthesis by cytoplasmic gene(s) for triazine resistance. A slight reduction in the yield of Haya with an increase in simazine concentration from 500 to 1000 ml/ha suggested that further increases in simazine concentration required for optimal weed control are likely to have a detrimental effect on the yield of Haya and other tolerant cultivars. Genetic analyses of variation in simazine tolerance in populations derived from crosses among cultivars representative of the range in tolerance indicated that the narrow-sense heritability of tolerance was of sufficient magnitude to allow for isolation of genotypes tolerant of higher simazine concentrations. These could be utilized in developing high yielding cultivars in areas of southern Australia where simazine treatment is necessary for effective weed control in Canola crops.     

Characterization of a salt-independent pectin methylesterase purified from valencia orange peel

The pectin methylesterase (PME; EC 3.1.1.11) present in a commercial orange peel enzyme preparation was characterized to establish its identity among the multiple PME isozymes present in Valencia orange (Citrus sinensis L.) peel. We show the commercial enzyme corresponds to the major peak 2 PME previously separated by heparin-Sepharose chromatography (Cameron et al., J. Food Sci. 1998, 63, 253). Both PMEs have comparable elution profiles on cation-exchange and hydrophobic-interaction perfusion chromatography columns, molecular weights (ca. 34 kDa) and pI (pH 9.2), and biochemical properties, including a broad pH activity range and activity in the absence of added cations. An identical partial amino terminal peptide sequence was also obtained for the PMEs, which further demonstrated a structural identity with other plant PMEs. The biochemical and structural properties readily distinguish this Valencia orange PME from salt-dependent isozymes and further suggest that it is an ortholog to the salt-independent fruit-specific isozyme of tomato. This work provides a well-defined, enzymatically homogeneous, salt-independent (type 1) plant PME isozyme that is suitable for studying details of the enzyme's mode of action and for use in modifying methylester patterns for studying the structure-functional property relationships in pectin.     

Separation and characterization of a salt-dependent pectin methylesterase from Citrus sinensis var. Valencia fruit tissue

A pectin methylesterase (PME) from sweet orange fruit rag tissue, which does not destabilize citrus juice cloud, has been characterized. It is a salt-dependent PME (type II) and exhibits optimal activity between 0.1 and 0.2 M NaCl at pH 7.5. The pH optimum shifted to a more alkaline range as the salt molarity decreased (pH 8.5-9.5 at 50 mM NaCl). It has an apparent molecular mass of 32.4 kDa as determined by gel filtration chromatography, an apparent molecular mass of 33.5 kDa as determined by denaturing electrophoresis, and a pI of 10.1 and exhibits a single activity band after isoelectric focusing (IEF). It has a K(m) of 0.0487 mg/mL and a V(max) of 4.2378 nkat/mg of protein on 59% DE citrus pectin. Deblocking the N-terminus revealed a partial peptide composed of SVTPNV. De-esterification of non-calcium-sensitive pectin by 6.5% increased the calcium-sensitive pectin ratio (CSPR) from 0.045 +/- 0.011 to 0.829 +/- 0.033 but had little, if any, effect on pectin molecular weight. These properties indicate this enzyme will be useful for studying the PME mode of action as it relates to juice cloud destabilization.     

Pyrimidinones: inducers of NK cell activity and antitumor immunity

We have shown that pyrimidinone molecule, 2 amino-5-iodo-6-phenyl-4-pyrimidinone (AIPP) after regional administration, displayed both prophylactic and therapeutic effect on ascitic mammary adenocarcinoma, ACA-755. The antitumor effect was mediated by natural killer (NK) cells, since depletion of this lymphocyte population resulted in abrogation of AIPP-induced tumor resistance. This observation confirms the role of NK cells in antitumor immunity and suggests that AIPP may be therapeutically beneficial also in man.     

Effects of level of feed intake on pancreatic exocrine secretions during the early postweaning period in piglets

The objective of this study was to determine the influence of the level of feed intake and a 2-d feed restriction period on the postweaning adaptation of pancreatic exocrine secretions. At 33 d of age, 18 piglets fitted with 2 permanent catheters (for pancreatic juice collection and reintroduction) were weaned and allocated to 1 of the following 2 dietary treatments for 5 d: restricted feed allocation (restricted) or gradually increasing feed allocation (control). Pancreatic juice was collected daily during both basal and prandial periods. The basal period was defined as the period from 1400 to 1700 h (i.e., 5 to 8 h after the morning meal), whereas the prandial period was defined as the period from 30 min before to 60 min after the morning meal (given at 0900). Digestive enzyme activities and antibacterial activity were determined. Pancreatic protein secretion was 44% less (P < 0.05) in restricted piglets than in control piglets during the basal period. Trypsin secretion was affected by feed-restriction of piglets. The meal did not affect protein and trypsin secretions in restricted piglets, whereas at d 3 postweaning, protein and trypsin secretions and trypsin specific activity in control piglets were 9-, 105-, and 25-fold greater (P < 0.001) during the first 30 min after the meal than before the meal. Lipase and amylase secretions were not affected by variations in feed intake. The secretion of antibacterial activity in restricted piglets was greater (P < 0.05) than that of control piglets only at d 5. The extended feed restriction period increased the basal secretion of antibacterial activity (P = 0.09) and postprandial secretion of amylase (P = 0.05). In conclusion, a low level of feed intake during the early postweaning period decreased pancreatic protein and trypsin secretions, whereas a 2-d feed restriction period enhanced secretions of amylase and antibacterial activity. In addition, our results indicate that during periods of dietary adaptation, such as at weaning, measurements of enzyme activities in the tissue do not accurately reflect the enzyme secretion.