Impact of lignin structure and cell wall reticulation on maize cell wall degradability

In this study, eight maize recombinant inbred lines were selected to assess both the impact of lignin structure and the impact of cell wall reticulation by p-hydroxycinnamic acids on cell wall degradability independently of the main "lignin content" factor. These recombinant lines and their parents were analyzed for in vitro degradability, cell wall residue content, esterified and etherified p-hydroxycinnamic acid content, and lignin content and structure. Lignin structure and esterified p-coumaric acid content showed significantly high correlation with in vitro degradability (r=-0.82 and r=-0.72, respectively). A multiple regression analysis showed that more than 80% of cell wall degradability variations within these 10 lines (eight recombinant inbred lines and their two parents) were explained by a regression model including two main explanatory factors: lignin content and estimated proportion of syringyl lignin units esterified by p-coumaric acid. This study revealed new biochemical parameters of interest to improve cell wall degradability and promote lignocellulose valorization.     

Effects of dietary energy levels on plasma leptin in sheep

This experiment investigates the changes in the plasma leptin levels of sheep fed a diet of three energy levels (low, moderate and high). Four mature wethers were used for this experiment. For the first 4 weeks, the sheep were fed diets to provide 1.2 times the maintenance metabolizable energy requirements, low energy levels (LE). During the second 4 weeks, the sheep were fed diets to provide 1.5 times the maintenance metabolizable energy requirements, moderate energy levels (ME). During third 4‐week period, the sheep were fed a diet to provide 1.8 times the maintenance metabolizable energy requirements, high energy levels (HE). Body weight was determined every week. Blood samples were collected prior to the morning meal at 3 days intervals throughout the experiment, and plasma leptin, insulin and nonesterified fatty acid (NEFA) concentrations were assayed. Body weight decreased in week 1 after the start of the experiment, it continued to decrease during the LE feeding, but it gradually increased until the end of HE period. Similarly, plasma leptin concentration decreased during LE feeding, but increased during the HE feeding. Additionally, positive correlation was obtained between leptin and insulin or glucose concentrations, whereas no clear relationship with circulating NEFA was observed. In conclusion, it was suggested that plasma leptin concentrations were affected by the metabolizable energy in feed.     

Seasonal differences in the field performance of micropropagated potato under a short growing season in Quebec

Field performance comparisons between ex vitro plantlet-derived (EVPD) plants and seed tuber-derived (STD) plants ofRusset Burbank were conducted for two consecutive years under a short growing season in Quebec. The EVPD plants produced more potential seed tubers than STD plants although total tuber biomass of EVPD plants was less than that of STD plants. The frequency and weight distributions of tubers formed by the two types of propagates were different. The EVPD plants produced significantly more small sized tubers and fewer large sized tubers than the STD plants. Average tuber weight was less for EVPD than STD plants for each of five size categories. No significant differences were found in the fresh and dry weight of plants, leaves and stems at harvest time. However, plant height and growth habit differed between the two types of propagates. The EVPD plants had a unique appearance. They produced a single stem with extensive axillary bud development. The EVPD plants were apparently more susceptible to early water stress in the field than STD plants, probably due to an earlier production of stolons. No differences were found between ex vitro plantlet- or microtuber-derived plants, in plant growth or yield characteristics.     

Microtuber dormancy in three potato cultivars

Microtuber size, media growth regulators, incubation period, as well as bud maturity and endogenous abscisic acid content of microtubers were evaluated for their effects on length of dormant period of Kennebec, Russet Burbank and Superior microtubers. The dormant period of microtubers was found to be cultivar-specific and a significant correlation was observed betweenin vitro andin vivo dormant periods. Smaller microtubers (≤250 mg) had longer dormant periods than did those greater than 250 mg. Dormant periods were unaffected by addition of coumarin or 2-(chloroethyl)-trimethylammoniumchloride and 6-benzylaminopurine to the culture media or incubation period (28 and 56 days). Developmental age had no effect on individual buds ability to break dormancy and elongate. A positive correlation was observed between tissue levels of abscisic acid and microtuber dormant periods.