Photosynthesis of Arid and Subtropical Succulent Plants

The hypothesis of Crassulacean acid metabolism (CAM) is that it is a physiological adaptation to arid or otherwise dry habitats. Stomata are closed during the day and open at night when the evaporative demand is low. Thus exogenous CO2 is fixed at night with relatively little water loss. CAM is typically found in succulents occurring in desert and dry Mediterranean regions, but not in the cold deserts of Asia. Recently, it has become known that many arid tropical succulent plants are CAM as well, particularly those growing epiphytically. The vegetation of St. John, U.S. Virgin Islands, ranges from desertlike cacti at the windward, dry eastern side of the island to near tropical rainforest at the higher elevations. Native CAM plants are found in families Agavaceae, Bromeliaceae, Cactaceae, Clusiaceae, Orchidaceae, Piperaceae and Vitaceae. Exotic CAM species are in the families Aizoaceae, Crassulaceae, and Liliaceae. The distribution of these plants is entirely consistent with the hypothesis of CAM being an adaptation to arid habitats. All species in the Agavaceae and Cactaceae are CAM. All of the Bromeliaceae with the exception of the terrestrial Pitcairnia and the epiphytic Catopsis are CAM. The epiphytic and dry habitat orchids occurring in the genera Epidendrum, Oncidium, Vanilla, and Tetramicra are CAM. Of three species of Cissus, only the species occurring in the most arid zones, C. trifoliata, is CAM. Clusia rosea is enigmatic in that it is epiphytic when young and a rooted tree when mature. It is the only known genus of true dicotyledonous trees to have CAM. Two of the most serious exotic weeds naturalized in arid scrub areas are CAM, Sansevieria trifasciata and Bryophyllum pinnatum

Crassulacean acid metabolism in the Gesneriaceae

The occurrence of the Crassulacean acid metabolism (CAM) was studied in four epiphytic species of the Gesneriaceae: two neotropical species, Codonanthe crassifolia and Columnea linearis, and two paleotropical species, Aoschynanthus pulcher and Saintpaulia ionantha. Gas exchange parameters, enzymology, and leaf anatomy, including mesophyll succulence and rel­ ative percent of the mesophyll volume occupied by airspace, were studied for each species. Codonanthe crassifolia was the only species to show nocturnal CO2 uptake and a diurnal organic acid fluctuation. According to these results, Codonanthe crassifolia shows CAM-cycling under well-watered conditions and when subjected to drought, it switches to CAM-idling. Other characteristics, such as leaf anatomy, mesophyll succulence, and PEP carboxylase and NADP malic enzyme activity, indicate attributes of the CAM pathway. All other species tested showed C3 photosynthesis. The most C3-like species is Columnea linearis, according to the criteria tested in this investigation. The other two species show mesophyll succulence and relative percent of the leaf volume occupied by airspace within the CAM range, but no other characters of the CAM pathway. The leaf structure of certain genera of the Gesneriaceae and of the genus Peperomia in the Piperaceae are similar, both having an upper succulent, multiple epidermis, a medium palisade of one or a few cell layers, and a lower, succulent spongy parenchyma not too unlike CAM photosynthetic tissue. We report ecophysiological similarities between these two distantly related families. Thus, the occurrence of CAM-cycling may be more common among epiphytic species than is currently known

The Effect of Wind on Transpiration and Evaporation Through Multiperforate Septa

Diffusion of water vapor through single-pore membranes with pores 100 to 800 μ in diameter and multipore membranes with pores 2.5 to 20 μ in diameter was studied as a function of wind velocity. The results of these studies are compared with data obtained with transpiring leaves in wind. It was found that wind had relatively little effect on small pores as compared with large pores and free water surfaces. The primary response of stomates or small, isolated pores to wind was simply an increase in the diffusion gradient. In general, the wind-to-still-air diffusion ratios determined with the use of small pores, either isolated or as a part of a multipore system, were less than 2, while the ratio for open surface evaporation in 1,000 feet per minute wind exceeded 15. The relatively small response of transpiration to wind is tenable, considering the epidermis as a multiperforate septum

Adhesive Contact to a Coated Elastic Substrate

We show how the quasi-analytic method developed to solve linear elastic contacts to coated substrates (Perriot A. and Barthel E. {\em J. Mat. Res.}, {\bf 2004}, {\em 19}, 600) may be extended to adhesive contacts. Substrate inhomogeneity lifts accidental degeneracies and highlights the general structure of the adhesive contact theory. We explicit the variation of the contact variables due to substrate inhomogeneity. The relation to other approaches based on Finite Element analysis is discussed

Gravin Orchestrates Protein Kinase A and β2-Adrenergic Receptor Signaling Critical for Synaptic Plasticity and Memory

A kinase-anchoring proteins (AKAPs) organize compartmentalized pools of protein kinase A (PKA) to enable localized signaling events within neurons. However, it is unclear which of the many expressed AKAPs in neurons target PKA to signaling complexes important for long-lasting forms of synaptic plasticity and memory storage. In the forebrain, the anchoring protein gravin recruits a signaling complex containing PKA, PKC, calmodulin, and PDE4D (phosphodiesterase 4D) to the β2-adrenergic receptor. Here, we show that mice lacking the α-isoform of gravin have deficits in PKA-dependent long-lasting forms of hippocampal synaptic plasticity including β2-adrenergic receptor-mediated plasticity, and selective impairments of long-term memory storage. Furthermore, both hippocampal β2-adrenergic receptor phosphorylation by PKA, and learning-induced activation of ERK in the CA1 region of the hippocampus are attenuated in mice lacking gravin-α. We conclude that gravin compartmentalizes a significant pool of PKA that regulates learning-induced β2-adrenergic receptor signaling and ERK activation in the hippocampus in vivo, thereby organizing molecular interactions between glutamatergic and noradrenergic signaling pathways for long-lasting synaptic plasticity, and memory storage