The influence of acid on astringency of alum and phenolic compounds

Astringency of aqueous solutions of phenolic compounds (grape seed tannins, tannic acid, catechin and gallic acid) increased upon addition of citric acid, whereas the astringency of alum was reduced. Astringency of alum was decreased equivalently by addition of equi-sour levels of lactic acid, citric acid or hydrochloric acid. The difference between alum and the phenolic compounds is speculated to result from chemical modifications affecting binding of the astringents with oral proteins rather than cognitive differences. Chelation of the aluminum ion in alum by acids reduces its availability for interacting with salivary proteins or epithelial proteins. In contrast, the increased astringency produced upon acidification of phenolic compounds is speculated to result from the pH driven increase in the affinity of the phenols for binding with proteins. These results suggest that alum cannot be used interchangeably with phenolic astringents in psychophysical studies.      

The Partitioning of Nitrate Assimilation Between Root and Shoot of a Range of Temperate Cereals and Pasture Grasses

Nitrate reductase activity (NRA, in vivo assay) and nitrate(NO^-₃) content of root and shoot and NO^-₃ and reduced nitrogencontent of xylem sap were measured in five temperate cerealssupplied with a range of NO^-₃ concentrations (0·1–20mol m^–3) and three temperate pasture grasses suppliedwith 0·5 or 5 0 mol m^–3 NO^-₃ For one cereal (Hordeumvulgare L ), in vitro NRA was also determined The effect ofexternal NO^-₃ concentration on the partitioning of NO^-₃ assimilationbetween root and shoot was assessed All measurements indicatedthat the root was the major site of NO3 assimilation in Avenasatwa L, Hordeum vulgare L, Secale cereale L, Tnticum aestivumL and x Triticosecale Wittm supplied with 0·1 to 1·0mol m^–3 NO^-₃ and that for all cereals, shoot assimilationincreased in importance as applied NO^-₃ concentration increasedfrom 1.0 to 20 mol m^–3 At 5.0–20 mol m^–3 NO3,the data indicated that the shoot played an important if notmajor role in NO^-₃ assimilation in all cereals studied Measurementson Lolium multiflorum Lam and L perenne L indicated that theroot was the main site of NO^-₃ assimilation at 0.5 mol m^–3NO^-₃ but shoot assimilation was predominant at 5.0 mol m^–3NO^-₃ Both NRA distribution data and xylem sap analysis indicatedthat shoot assimilation was predominant in Dactylis glomerataL supplied with 0.5 or 5.0 mol m^–3 NO^-₃ Avena sativa L., oats, Hordeum vulgare L., barley, Secale cereale L., rye, x Triticosecale Wittm., triticale, Triticum aestivum L., wheat, Dactylis glomerata L., cocksfoot, Lolium multiflorum Lam., Italian ryegrass, Lolium perenne L., perennial ryegrass, nitrate, nitrate assimilation, nitrate reductase activity, xylem sap     

History of Shiny Cowbird Molothrus bonariensis brood parasitism in Trinidad and Tobago

In attempting to evaluate the evolutionary stability of the reproductive strategies of an avian brood parasite, it is important to know whether or not the observed levels of parasitism on host species have changed through time and whether or not new host species are being used in the region under study. In this regard, the islands of Trinidad and Tobago provide an excellent opportunity because they are ornithologically well known and the expansion of the parasitic Shiny Cowbird Molothrus bonariensis into the West Indian region is thought to have originated from Trinidad and Tobago. On the whole, host choice has remained remarkably stable over the past 50–60 years. The three hosts (House Wren Troglodytes aedon, Red-breasted Blackbird Leistes militaris and Yellow-hooded Blackbird Agelaius icterocephalus) known to be heavily parasitized historically remain heavily parasitized today. Only one instance of parasitism of a new host (Tropical Kingbird Tyrannus melancholicus) is recorded. In the case of one intensively studied host, the Yellow-hooded Blackbird, cowbird parasitism had a minimal negative effect on the host's reproductive success. Reproductive equilibrium in this study seemed to be maintained by behavioural adaptations of host and parasite to each other. The stable pattern of host choice by Shiny Cowbirds in Trinidad and Tobago may not develop elsewhere in the West Indian region. Before the cowbird's expansion in the West Indies, potential hosts had no prior experience of brood parasites. Consequently, the island bird populations are unlikely to have evolved defensive strategies and thus may be more vulnerable to reproductive failure as a result of cowbird parasitism, precluding the development of a stable system at this point in time.     

Emergence of temperate pasture grases from different sowing depths: importance of seed weight, coleoptiele plus mesocotyl length and shoot strength

Inter-specific relationships between mean seed weight, coleoptile + mesocotyl (sub-coleoptile internode) length and width, shoot strength and emergence from different sowing depths were examined for timothy (Phleum pratense L., mean seed weight 0.33-0.48 mg depending on seed line), cocksfoot (Dactylis glomerata L., 0.65-0.78 mg), perennial ryegrass (Lolium perenne L., 1.71-2.19 mg), tall fescue (Festuca arundinucea Schreb., 1.73–2.60 mg), annual ryegrass (Lolium multiflorum Lam., 5.10-5.20 mg) and prairie grass (Bromus willdenowü Kunth., 10.5–12.2 mg). Across species at 10,30 and 60 mm sowing depths in the field and 10, 15 and 30 mm sowing depths under controlled environment conditions, there was a significant (P < 0.05) positive correlation between emergence % and mean seed weight. Across species at 10–30 mm sowing depth under controlled environment conditions, emergence % was not significantly correlated with coleoptile + mesocotyl length but there were significant positive correlations between emergence % and coleoptile and mesocotyl width: shoot strength increased with increased coleoptile width across species. For seed lines of timothy of different mean seed weight (0.21-0.81 mg), emergence %, coleoptile + mesocotyl length and coleoptile and mesocotyl width increased with increased seed weight at 10 and 15 mm sowing depth. Shoot strength increased with increased coleoptile width for timothy. For emerged and non-emerged cocksfoot and timothy seedlings regardless of seed weight, mean coleoptile + mesocotyl length was > 10 mm at 10 mm sowing depth. It is concluded that at 10–30 mm sowing depth, increased emergence % with increased seed weight across species is not due to increased coleoptile + mesocotyl length. It is proposed that increased emergence % with increased seed weight across species at 10–30 mm sowing depths and across seed lines of timothy at 10 mm sowing depth is primarily due to increased coleoptile and mesocotyl width resulting in increased shoot strength and hence an increased ability to penetrate the substrate.     

Influence of pregnancy on the thermal biology of the lizard, Sceloporus jarrovi: why do pregnant females exhibit low body temperatures?

1. Selected body temperatures of female lizards, Sceloporus jarrovi , were measured on a photothermal gradient during late pregnancy and again when postpartum, and pregnant females were subjected to one of three fluctuating temperature regimes that simulated body temperatures of (1) pregnant females, (2) postpartum females or (3) allowed normal thermoregulation.
2. Overall, females selected lower body temperatures when pregnant (mean = 32·0°C) than when postpartum (mean = 33·5°C).
3. Females regulated body temperature more precisely when pregnant than when postpartum as judged by their smaller variances in body temperature throughout the day.
4. When pregnant, females selected a lower mean maximum body temperature (mean: pregnant = 32·8°C; postpartum = 34·5°C) than when postpartum, but selected mean minimum body temperatures did not differ.
5. None of the experimental temperature treatments was detrimental to pregnant females. Female body length increased during pregnancy but the rate of increase did not differ among treatments. Moreover, length-adjusted body mass of postpartum females did not differ among treatments.
6. Pregnant females that experienced postpartum body temperatures produced neonates that were smaller in body mass and length than pregnant females that experienced pregnant body temperatures and females that were allowed to thermoregulate.
7. For neonates resulting from the postpartum body temperature treatment, the disparity in the body length, but not mass, was still observed at 9 days of age, although survival and growth of neonates was high and did not differ among treatments.
8. The results demonstrate that pregnant females could maintain higher postpartum body temperatures without compromising their physical condition, but select relatively low body temperatures, presumably to avoid decrements in offspring fitness.     

水稻涝害生理及其与水稻生产的关系

概述了水稻涝害生理、影响水稻涝害的因素以及涝害与水稻生产的关系,提出了减轻涝害的途径与灾后的补救措施。