Quantum yield and rate of formation of the carotenoid triplet state in photosynthetic structures

The formation of the triplet state of carotenoids (detected by an absorption peak at 515 nm) and the photo-oxidation of the primary donor of Photosystem II, P-680 (detected by an absorption increase at 820 nm) have been measured by flash absorption spectroscopy in chloroplasts in which the oxygen evolution was inhibited by treatment with Tris. The amount of each transient form has been followed versus excitation flash intensity (at 590 or 694 nm). At low excitation energy the quantum yield of triplet formation (with the Photosystem II reaction center in the state Q⁻) is about 30% that of P-680 photo-oxidation. The yield of carotenoid triplet formation is higher in the state Q⁻ than in the state Q, in nearly the same proportion as chlorophyll a fluorescence. It is concluded that, for excited chlorophyll a, the relative rates of intersystem crossing to the triplet state and of fluorescence emission are the same in vivo as in organic solvent. At high flash intensity the signal of P-680⁺ completely saturates, whereas that of carotenoid triplet continues to increase.

The rate of triplet-triplet energy transfer from chlorophyll a to carotenoids has been derived from the rise time of the absorption change at 515 nm, in chloroplasts and in several light-harvesting pigment-protein complexes. In all cases the rate is very high, around 8 · 10⁷ s⁻¹ at 294 K. It is about 2–3 times slower at 5 K. The transitory formation of chlorophyll triplet has been verified in two pigment-protein complexes, at 5 K.     

Central place foraging in the Eastern chipmunk, Tamias striatus

Orians & Pearson (1979) considered the optimal foraging strategies of ‘central place foragers’, animals that repeatedly return with their food to a fixed location. We tested some of their predictions on eastern chipmunks, Tamias striatus. The rate of cheek pouch loading declines as the pouches fill; thus the optimal load size may vary, depending on the time required to travel between the feeding site and burrow. This ‘travel time’ may also affect the choice of feeding site. A method was developed to test this, and preliminary results confirm the hypothesis. Methodological and theoretical implications of these empirical results are discussed.     

Respiration of the air breathing fishPiabucina festae

Summary Piabucina festae, a Central American stream fish, breathes air frequently, even in air saturated water, however, is not an obligate air breather. Without access to air, it can maintain routine by aquatic respiration down to aP _wO₂ of about 70 Torr which is its critical O₂ tension (P _cO₂, Fig. 5). Aerial respiration averages 10% of total in air saturated water and 70% in hypoxic water (Fig. 4). At lowP _wO₂ air breathing is more frequent (Fig. 1), and more O₂ is utilized from each air breath (Table 3), and tidal volume may increase (Fig. 7). Vascularized respiratory compartments or cells (Fig. 6), located in the second chamber of the physostomus gas bladder, function for aerial respiration. In ventilation air is gulped and forced through a large pneumatic duct into the gas bladder, excess gas is then released through opercula. Inspiration always precedes expiration and tidal volume is small, keeping gas bladderP _{O 2} low (Table 4). Major differences in the air breathing physiology ofP. festae and other species are its higherP _cO₂, a low aerial in normoxic water, even though air gulps are frequent, and its pattern of inhalation prior to expiration. The interrelationship and optimization of the three gas bladder functions (buoyancy, sound reception, and air breathing) inP. festae is discussed. Aerial respiration may have evolved secondarily to the gas bladder's function in buoyancy control.     

Sesquiterpenes of thalloid liverworts of the genera Conocephalum,Lunularia, Metzgeria and Riccardia

Thalloid liverworts of orders Metzgeriales and Marchantiales elaborate essential oils distinguishable from those of the Jungermanniales by the absence of β-barbatene and anastreptene. Riccardia sinuata elaborates a novel tricyclic exomethylene sesquiterpene of as yet undetermined structure. Conocephalum conicum elaborates cadinene-type sesquiterpenes. β-Cadinene from the latter species is clearly enantiomeric to the same product from vascular plants.     

Interaction of methotrexate with polycationic carriers

Binding parameters were measured for the $\text{in vitro}$ interaction of methotrexate with poly-L-lysine and diethylaminoethyl dextran. The complexes were found to have apparent affinity constants of 2590 and 440 M^?1 respectively at 37°, ionic strength 0.02. For hypotonic solutions containing therapeutic concentrations of methotrexate, this results in 87% binding of the drug to poly-L-lysine and 74% to diethylaminoethyl dextran. While the binding decreased to about 50% upon increasing ionic strength to physiologic levels, sufficient drug-carrying capacity was retained at isotonicity to support the potential utility of such complexes as tissue-specific drug carriers.