Biography:

In the past S.P. Webb has collaborated on articles with T.G. Owens and B.D. Scott. One of their most recent publications is Research ArticleAntenna structure and excitation dynamics in photosystem I. II. Studies with mutants of Chlamydomonas reinhardtii lacking photosystem II. Which was published in journal Biophysical Journal.

More information about S.P. Webb research including statistics on their citations can be found on their Copernicus Academic profile page.

S.P. Webb's Articles: (3)

Research ArticleAntenna structure and excitation dynamics in photosystem I. II. Studies with mutants of Chlamydomonas reinhardtii lacking photosystem II

Using time-resolved single photon counting, fluorescence decay in photosystem I (PS I) was analyzed in mutant strains of Chlamydomonas reinhardtii that lack photosystem II. Two strains are compared: one with a wild-type PS I core antenna (120 chlorophyll a/P700) and a second showing an apparent reduction in core antenna size (60 chlorophyll a/P700). These data were calculated from the lifetimes of core antenna excited states (75 and 45 ps, respectively) and from pigment stoichiometries. Fluorescence decay in wild type PS I is composed of two components: a fast 75-ps decay that represents the photochemically limited lifetime of excited states in the core antenna, and a minor (less than 10%) 300–800 ps component that has spectral characteristics of both peripheral and core antenna pigments. Temporal and spectral properties of the fast PS I decay indicate that (a) excitations are nearly equilibrated among the range of spectral forms present in the PS I core antenna, (b) an average excitation visits a representative distribution of core antenna spectral forms on all pigment-binding subunits regardless of the origin of the excitation, (c) reduction in core antenna size does not alter the range of antenna spectral forms present, and (d) transfer from peripheral antennae to the PS I core complex is rapid (less than 5 ps).

Influence of body fat content on digestible energy requirements of exercising horses in temperate and hot environments*

SummarySix mature horses were used to determine the energy requirements of exercising horses during different seasons and in different body conditions. Horses were conditioned to work 7.2 km in 30 min 5 d/wk and fed to either a fleshy or moderate body condition during both hot (temperature mean 32.4 C, with a 23.9–36.1 C range) and temperate (temperature mean 17.4 C, with a 3.9–27.8 C range) seasons. Horses were fed average quality Bermuda grass hay at .75% of body weight sufficient concentrate to maintain body weight and condition. During each combination of body condition and season when body weight, condition and feed intake were stable for 14 d horses were declared at energy equilibrium and a digestion trial was conducted. Horses in fleshy body condition (7.5) required 2.3 kg/d more total feed than horses in moderate (5.2) body condition. When expressed in terms of digestible energy (DE) intake, fleshy horses required 11.12 kcal/kgBW/d more than horses in moderate flesh. When DE for maintenance (DEM) was calculated as the difference between DE intake and DE for work (DEW), DEM for horses in fleshy condition exceeded that of horses in moderate condition by 11.3 kcal/kgBW/d (P<.01). Seasonal effects on feed and DE intake were not as apparent as the effect of body condition. These data indicate that body condition is a significant consideration when estimating DE requirements for the performance horse in all seasons and that optimum body condition for the performance horse may vary according to ambient temperature and humidity at the time of performance.

Growth and feed utilization by yearling horses fed added dietary fat

SummaryTwenty-four yearlings were used to evaluate the efficacy of feeding feed-grade fat to growing horses. All horses were started on trial at 13-months-of-age and were fed for 112 days. The experimental diets, containing similar nutrient-to-calorie ratios, were: 1) control (no added fat; 2) 5% added fat and; 3) 10% added fat. There was a trend for yearlings fed the 10% added fat diet to grow faster and eat less feed than those on the control diet. Data from this study indicate that feed-grade fat can be safely fed to growing horses. Feeding fat to yearlings stimulated growth and efficiency of feed utilization initially, but these effects were not maintained as the yearlings grew toward maturity.

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