Plants in the forest canopy: some reflections on current research and future direction

Plants are one of the sessile components of the forest canopy, and consequently quantitative studies of plant components are more widely available than for some of their mobile counterparts. From a global perspective, several exciting and innovative canopy access tools have been designed over the past few decades that have facilitated the expansion our understanding of canopy plants. These include a network of canopy cranes, the development of the French luge (or sled), and the construction of walkways and platforms for access into different levels of the canopy on a permanent basis. At the recent international forest canopy conference in Sarasota, Florida (Forest Canopies 1998: Global Perspectives, November 4–8, 1998), many canopy plant studies were presented that illustrated the achievements in this field. As co-chair at this event, I present here some reflections based on my observations of the development of canopy research between the first and second international conferences. A selection of case studies from the conference presentations are cited in this review, including: tree crown respiration studies from the crane in Panama; epiphyte ecology from walkways in Peru; insect-plant relationships in tree crowns of the USA using platforms; experimental studies of epiphytes in cloud forests using single rope techniques; and epiphyte diversity surveys in Africa. Ideas for the future are also mentioned such as the novel concept of canopy farming of orchids in Costa Rica, the linking of canopy processes to forest floor activities, and the construction of canopy walkways to provide a sustainable forest economy instead of the conventional practice of logging. The integration of research with sustainable use of forests provides a conservation theme for future canopy studies. Such new approaches to studies of canopy plants are important, as scientists increasingly play a role in global conservation policies.     

The institutional official and postapproval monitoring: the view from 10,000 feet

The role of the institutional official (IO) in ensuring a high-quality program of laboratory animal care and use has received relatively little attention in the literature compared to that of the institutional animal care and use committee (IACUC) or attending veterinarian. Yet the IO is critical to institutional effectiveness. Often not a scientist, especially at colleges and universities, the IO is an executive who bears ultimate responsibility for the care and use of laboratory animals. An IO operates largely through delegation to the IACUC and the institutional veterinarian, yet must maintain a clear view of the program from the executive level--the "view from 10,000 feet." To do so, the IO must bring four critical leadership qualities to the position: (1) vision, (2) a commitment to quality and integrity, (3) strong planning and resource development, and (4) accountability to the laboratory animal program. The IO's ability to act on these qualities and to evaluate the effectiveness of the resulting program requires reliance on a strong program of postapproval monitoring (PAM). Summary data from PAM, based on metrics carefully defined by the IO in consultation with the IACUC and the institutional veterinarian, provide the feedback necessary to guide executive decisions and allow the IO to place the needs of the program of laboratory animal care and use successfully into the larger context of the mission of the institution.     

Effects of temperature on slow and fast inactivation of rat skeletal muscle Na+ channels

Patch-clampstudies of mammalian skeletal muscleNa⁺ channels are commonly done atsubphysiological temperatures, usually room temperature. However, atsubphysiological temperatures, mostNa⁺ channels are inactivated atthe cell resting potential. This study examined the effects oftemperature on fast and slow inactivation ofNa⁺ channels to determine iftemperature changed the fraction of Na⁺ channels that were excitableat resting potential. The loose patch voltage clamp recordedNa⁺ currents(I_Na) in vitroat 19, 25, 31, and 37°C from the sarcolemma of rat type IIbfast-twitch omohyoid skeletal muscle fibers. Temperature affected thefraction of Na⁺ channels that wereexcitable at the resting potential. At 19°C, only 30% of channelswere excitable at the resting potential. In contrast, at 37°C, 93%of Na⁺ channels were excitable atthe resting potential. Temperature did not alter the resting potentialor the voltage dependencies of activation or fast inactivation.I_Na available atthe resting potential increased with temperature because thesteady-state voltage dependence of slow inactivation shifted in adepolarizing direction with increasing temperature. The membranepotential at which half of the Na⁺channels were in the slow inactivated state was shifted by +16 mV at37°C compared with 19°C. Consequently, the low availability ofexcitable Na⁺ channels atsubphysiological temperatures resulted from channels being in the slow,inactivated state at the resting potential.

     

Isolation and preliminary characterization of a plasmid mutant derepressed for conjugal transfer in Staphylococcus aureus

The plasmid pCRG1600 is a 52.9-kb self-transmissible plasmid coding for resistance to aminoglycoside and β-lactam antibiotics in Staphylococcus aureus. When transferred by transduction, plasmid deletion mutants affecting one or more antibiotic-resistance genes were readily obtained. Of these, one derivative (pCRG1690) was found to exhibit a conjugal transfer frequency ca. 100-fold higher than that of the wild-type plasmid. A preliminary physical-genetic map of pCRG1600 located tra in a 14.6-kb region within the 16.9-kb XbaI-A fragment. An 8.5-kb deletion to the left of tra in pCRG1690 was specifically associated with the increased conjugal transferability of the plasmid. Thus, pCRG1690 appears similar to plasmids derepressed for conjugal transfer (drd) in gram-negative bacterial species.