ABSTRACFPhospholipid polar head group and fatty acid composition were determined for plasma membrne enriched fractions from developing soybean root (Glycine max [L.1 Meff. cult. Wells II). Plasma membrane vesicles were isolated from meristematic and mature sections of four-day-old dark grown soybean roots at pH 7.8 and in the presence of 5 miflimolar ethylenediaminetetraacetate, 5 millimolar ethyleneglycol-bis (l-aminoethyl (27), and protein composition (5) with development. These changes may reflect alterations in membrane composition associated with differentiation of the average cell in the representative root segment and/or aging effects which may be common to all cells.The inability to prepare highly enriched fractions of plasma membranes from plants in quantities sufficient for analysis has hindered efforts to characterize plasma membrane composition. In a previous communication (28) we reported the isolation of a highly enriched plasma membrane fraction. Comparisons of isolated vesicles stained with the phosphotungstic acid-chromic acid procedure, specific for the plasma membrane, with vesicles stained with the general membrane stain uranyl acetate-lead citrate indicated these preparations were approximately 75% pure (2). Additional electron microscope studies with concana-

A protein spin label and lipid spin probes were used to study the temperature-dependent motion of protein and lipid, respectively, in barley (Hordeum vulgare L. cv Conquest) root plasma membrane-enriched microsomes. Using membranes from seedlings grown at 20°C, the temperature-dependence of the relative motion of membrane surface spin probes and a spin label covalently attached to membrane proteins suggested abrupt changes in the lipid and protein mobilities at about 12°C. Spin probe spin-spin exchange broadening and fluorescent probe eximer formation indicated apparent temperature-induced alterations in probe lateral diffusion within the membrane at about 12 to 14°C. The results suggest the presence of temperature-induced quasicrystalline lipid clusters which may influence the activity of membrane-bound enzymes. (19,25).Gaffney and Lin (7) (pH 6.5) in the dark at 20 ± 1°C. Roots of 5-d-old seedlings were collected and a plasma membrane-enriched microsome fraction isolated by the aqueous two-phase partition method of Kjellbom and Larsson (13) with the following modifications. The homogenization solution consisted of 0.25 mM sorbitol, 10% (w/v) soluble PVP, 5 mM thiourea, 2.5 mM EDTA, 2.5 mm EGTA, 2 mm SHAM', 2 mM potassium metabisulfite and 0.5 mM PMSF in 25 mM Hepes-KOH buffer (pH 7.6). The upper phase of the final two-phase partition was diluted with 0.5 M sorbitol, 10% (w/v) glycerol, 5 mM EDTA, and 0.5 mm PMSF in 10 mM Mes-KOH buffer (pH 6.5)

impacts of climate change, provided a bridge of understanding from the basic physics and chemistry of the climate system to the important scientific results of the IPCC assessments, especially those relevant to decisionmakers. In addition, MacCracken eloquently articulated the underlying reasoning needed to build an intuitive understanding of the IPCC conclusions and their implications for humanity. This paper presents a discussion of the 2008 A&WMA Critical Review by invited panelists and others who chose to comment. It includes written submissions and presentation of transcripts that were, in a few instances, edited for conciseness, to minimize redundancy, and to provide supporting and instructional citations. Substantial deviations from the intent of a discussant are unintentional and can be addressed in a follow-up letter to the journal. The invited discussants are listed below. • Dr. Mark Jacobson is the director of the Atmosphere and Energy Program and professor of civil and environmental engineering at Stanford University. He holds a B.S. in civil engineering (Stanford, 1988), an A.B. in economics (Stanford, 1988), an M.S. in environmental engineering (Stanford, 1988), an M.S. in atmospheric sciences (UCLA, 1991), and a Ph.D. in atmospheric sciences (UCLA, 1991). His work relates primarily to the development and application of numerical models to understand better the effects of air pollutants on climate and air quality and to the analysis and impacts of energy systems.

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