14CO2 Fixation, Translocation, and Carbon Metabolism in Rapidly Expanding Leaves ofPopulus deltoides

To examine ¹⁴CO₂ fixation, potential translocation, and carbonflow among leaf chemical fractions of young developing leaves,the shoot tip of 24-leaf cottonwood (Populus deltoides Bartr.ex. Marsh) plants were cut off under water, placed in artificialxylem sap, and treated with ¹⁴CO₂ in continuous and pulse-chaseexperiments. Additional leaves on whole plants were spot treatedon the lamina tip to follow export from the tip only. The analysedleaves ranged in age from leaf plastochron index(LPI) –5to 3, the spot treated leaves from LPI 2 to 5. After 30 minfixation, the specific activity in the lamina tip increasedlinearly with leaf age from LPI –5 to 1 (0.5 to 4.5 kBqmg^–1). Specific activity in the lower lamina increasedslowly with leaf age and did not reach 500 kBq mg^–1 untilLPI –1. Total ¹⁴CO₂ fixed in the lower lamina exceededthat fixed in the tip by LPI –2 because of the large amountof tissue present in the lower lamina. Although the lamina tipfixed high levels of ¹⁴CO₂, pulse-chase studies coupled withautoradiography indicated no vein loading or translocation fromthe tip until about LPI 4 or 5. The ¹⁴C fixed in both tip andlower lamina was incorporated at the site of fixation and wasnot distributed to younger tissue or translocated from the lamina.Although the percentage distribution (¹⁴C in each chemical fractioncompared with the total in all fractions) of ¹⁴C among certainchemical fractions, e.g. sugars, amino acids and proteins, indicatedthat the mesophyll of the tip was more mature than the lowerlamina, physiologically both leaf sectors were immature basedon the expected ¹⁴C distribution in mature tissue. Informationfrom this and other studies indicates that the extreme tip ofa developing cottonwood leaf first begins to export photosynthateabout LPI 4 or 5 on a 24-leaf plant. The first photosynthatetranslocated may be incorporated into the vascular tissues andmesophyll directly below the tip. However, as the tip continuesto mature photosynthate is translocated past the immature lowerlamina into the petiole and out of the leaf. Populus deltoides Bartr. ex. Marsh, eastern cottonwood, translocation, leaf development, ¹⁴C fixation, carbon metabolism     

Photosystem II and Hypoxic Quiescence in Alligatorweed

Stem cuttings of alligatorweed [Alternanthera philoxeroides (Mart.) Griseb.] were subjected to various light and chemical inhibitor treatments to obtain information about the physiological nature of the hypoxic quiescence induced by dark submergence. White or red light at 40 μE m^?2 s^?1 stimulated growth from submerged stem cuttings but far-red at 5 μE M^?2 s^?1 did not. Photo-system II inhibitors, such as 3-(3,4-dichlorophenyl) 1,1-dimethylurea (DCMU) at 1.4 × 10^?5M or 2-chloro-4,6-bis(ethylamino)-s-triazine (simazine) at 10^?5M, completely inhibited the growth that normally occurs in a submerged state under continuous white light at 40 μE m^?2 s^?1. These concentrations of DCMU or simazine did not reduce nonphotosynthetic growth from underwater nodes of emersed stem cuttings partially exposed to air in the light for 1 week. Hydrogen peroxide at 50 mg/1 added every other day partially relieved the simazine-induced inhibition of growth from submerged, illuminated cuttings. These data indicated that sprouting and early growth of submerged, illuminated alligatorweed depended on the oxygen produced by photosystem II to support respiration and to overcome hypoxic quiescence.     

Northern Bobwhites and Postfire Succession

ABSTRACT Our study evaluated the effects of prescribed fire on northern bobwhites (Colinus virginianus) occupying native rangelands in Rolling Plains of Texas, USA, during 2002 and 2003. Prescribed fires were conducted during February of 1996, 1998, and 2000; pastures with no recent treatment history served as controls. We quantified bobwhite densities from line transects using distance sampling. We used a repeated-measures analysis of variance to test for treatment-year differences in bobwhite densities. We measured postfire herbaceous and woody vegetation attributes and evaluated vegetation relationships to bobwhite density using simple linear regression. We found significant between-year differences in fall bobwhite densities (F = 13.05, df = 3, P = 0.036) but no differences among treatments or controls. Fall bobwhite densities were inversely related to visual obstruction (r² = 0.179, df = 15, P = 0.058) and positively associated with increasing heterogeneity of grass cover (r² = 0.416, df = 15, P = 0.004). Our results suggest prescribed fire at large spatial scales may be a neutral practice for managing bobwhite habitat on semiarid rangelands.     

Effects of Rain on Palm Springs Ground Squirrel Occupancy in the Sonoran Desert

ABSTRACT Long-term monitoring programs must use informative yet cost-effective methods. Occupancy estimates that incorporate detection probabilities are used with increasing frequency to describe species status and make management recommendations. Estimating changes in the occupancy of points over time in response to management actions or environmental changes may be especially useful for management of the Palm Springs round-tailed ground squirrel (Spermophilus tereticaudus chlorus), a subspecies covered under the Coachella Valley Multiple Species Habitat Conservation Plan and Natural Community Conservation Plan. In 2002 and 2003, we estimated occupancy and detection probability of ground squirrels across lands modeled as ground squirrel habitat by the Scientific Advisory Committee for the Habitat Conservation Plan and tested a priori hypotheses about how occupancy varied among vegetation and substrate types. In the 2003 study, we asked whether these associations were affected by winter rains after the 2002 drought year. Occupancy in 2003 was estimated at 0.99 (SE = 0.01) in Western honey mesquite (Prosopis glandulosa) on dunes and hummocks, and occupancy of the remaining modeled habitat was best described by distance to mesquite, with the occupancy probability decreasing with increasing distance from mesquite on dunes or hummocks. The best-supported model in 2002 described the distribution of ground squirrels as a function of only vegetation and substrate type. However, the best-supported models in 2003 suggested that distance to mesquite was a component of the occupancy of non-mesquite vegetation. Mesquite seems to provide high-quality habitat that can support ground squirrels at high occupancy probabilities that may breed successfully every year. In contrast, other vegetation types provide low-quality habitat that can only support ground squirrels at low occupancy probabilities that may only breed occasionally. Mesquite could be an essential refugium during drought years, and the 4 best-supported models in 2003 suggest that restoration of mesquite beginning near currently occupied mesquite patches could be critical for maintaining ground squirrel populations on the preserves.     

REGIONAL AND SUBCELLULAR DISTRIBUTION OF PROTEIN CARBOXYMETHYLASE IN BRAIN AND OTHER TISSUES

Protein carboxymethylase, an enzyme that transfcrs the methyl group of S-adenosyl-L-methionine to carboxyl groups of proteins and endogenous acceptor proteins were examined in nerve and endocrine tissues. The highest protein carboxymethylase activity was found in the brain, followed by the testis, pituitary and heart. On the other hand, the tissue with the highest level of endogenous substrate(s) was the pituitary. The nearly identical specific activity ratio for two different protein substrates in all tissues examined, suggests that one enzyme is responsible for carboxymethylase activity in different tissues. The subcellular distribution of the enzyme in brain showed a high concentration in the soluble fraction, presumably representative of the enzyme in the cytosol of cell bodies. Considerable enzyme activity was also found in brain synaptosomes which was increased by osmotic lysis. Protein carboxymethylase was shown to accumulate proximally to a ligation of the rat sciatic nerve. A possible physiological role for protein carboxymethylase in neuronal function is discussed.     

The Respiratory Transition from Water to Air Breathing During Amphibian Metamorphosis

SYNOPSIS. Profound developmental changes occur in the morphologyand physiology of the respiratory system of amphibians duringthe transition from strictly aquatic to dual aquatic-aerialbreathing. This developmental transition usually involves modificationsin ventilatory mechanisms and/or respiratory surfaces {e.g.,degeneration of gills, ventilation of functional lungs). Boththe first appearance of obligate air breathing and the subsequentdependence upon it by amphibian larvae are sensitive to a varietyof environmental stressors during critical developmental periods.These stressors include oxygen availability, ambient temperature,the risk of predation and mode of feeding.