植物生活史对策的进化

植物生活史对策的进化班勇（中国林业科学院林业研究所,北京１０００９１）ＥｖｏｌｕｔｉｏｎｏｆＬｉｆｅＨｉｓｔｏｒｙＳｔｒａｔｅｇｙｉｎＰｌａｎｔｓ￥ＢａｎＹｏｎｇ（ＲｅｓｅａｒｃｈＩｎｓｔｉｔｕｔｅｏｆＦｏｒｅｓｔｒｙ,ＣｈｉｎｅｓｅＡｃａｄｅｍｙｏ...     

Seasonal changes of osmotic pressure, symplasmic water content and tissue elasticity in the blades of dune grasses growing in situ along the coast of Oregon

Abstract Midday water potentials of blades of the dune grasses Ammophila arenaria (L.) Link and Elymus mollis Trin. ex Spreng. growing in situ declined over the summer growing period, indicating a trend of increasing water stress. An analysis of the water relations characteristics of these blades using pressure-volume techniques demonstrated that both species increased bulk osmotic pressure at full hydration () and, therefore, bulk turgor as an acclimation response. In A. arenaria, however, the increase of osmotic pressure (+ 0.35 MPa) was entirely the result of decreasing symplasmic water content. The increase of osmotic pressure (+ 0.54 MPa) observed in E. mollis blades was due to solute accumulation (72% of Δ) and to a lesser degree, decreased symplasmic water content (28% of Δ). Osmotic adjustment in E. mollis blades was accompanied by a significant decrease in tissue elasticity (_max went from 12 to 19 MPa). The elastic properties of A. arenaria blades remained constant over the same period and had a maximum modulus (10 MPa) that was always less than that of E. mollis, As estimated from Höfler plots, these seasonal adjustments of osmotic pressure and differences in tissue elasticity enabled plants in situ to maintain turgor pressure in the range of 0.5–0.6 MPa at the lowest water potentials of mid-August. Laboratorygrown plants exhibited the species-specific differences in osmotic pressure, turgor pressure, and tissue elasticity observed in field plants. Although certain alterations of leaf structure were expected to coincide with the observed changes and species-specific differences in symplasmic water content and tissue elasticity, these could not be detected by measurements of specific leaf weight or the ratio of dry matter to saturated water content.     

Interactions between two sheets of a bilayer membrane and its internal lateral pressure

We have modelled a phospholipid bilayer as two monolayer sheets which interact with each other by a coupling which depends upon the states of the lipid hydrocarbon chains in each sheet. We make use of a model (Georgallas and Pink 1982a) and its parameters, already used to study monolayer phase changes at the LC-LE transition, in order to study the lipid main transition. Although the monolayer coexistence curve can be calculated exactly, we have made use of high-temperature series expansions to calculate the critical point of the bilayer. We also present the results of computer simulations on triangular lattices for the pressure-area isotherms. We find: (i) the interaction between the sheets of a DPPC bilayer is about 1.5–2% of the maximum interaction within the plane of each sheet; (ii) the internal lateral pressure of a DPPC bilayer is about 30.5 dyne/cm; (iii) the bilayer transition enthalpy depends sensitively upon the coupling between the sheets. Should this coupling vary from sample to sample (due, possibly, to its preparation) then very different values of transition enthalpy may be measured. (iv) We present a rough rule-of-thumb for estimating the internal lateral pressure of a bilayer from a knowledge of the corresponding monolayer pressure-area isotherms.Abbreviations LC-LE liquid condensed — liquid expanded - DPPC dipalmitoylphosphatidylcholine - Q transition enthalpy Work supported in part by the Natural Sciences and Engineering Research Council of Canada     

Parallel bioassay of litorin and phyllolitorins on smooth muscle preparations

Phyllolitorin and Leu8-phyllolitorin, two nonapeptide amides from the skin of the South American frog Phyllomedusa sauvagei, are representatives of a novel bombesin subfamily, characterized by the occurrence in their molecule of a serine residue substituting the usual histidine residue at position 3 from the C-terminus. In parallel bioassay on ten different smooth muscle preparations and rat blood pressure, phyllolitorin and Leu8-phyllolitorin were virtually equiactive, but the two peptides appeared remarkably less potent that litorin in all test preparations, except the rat urinary bladder. The shape of contractions produced by the phyllolitorins and promptness of cessation of their action upon washing seem to indicate a looser binding of these peptides to their receptors and/or a more rapid inactivation, in comparison to litorin.     

Homeoviscous theory under pressure. I. The fatty acid composition of Tetrahymena pyriformis NT-1 grown at high pressure

Tetrahymena was grown at up to 260 atm to see if the bilayer-ordering effect of pressure increased the proportion of unsaturated fatty acids in the membrane lipids. Both whole cells and microsomes showed no such change in their fatty acid composition. The most striking effect was seen in the former which showed a pressure-dependent increase in the proportion of C16:0 in relation to C16:Δ9. Homeoviscous adaptation to pressure does not appear to occur in this cell.     

Identification of cellular prosomatostatin and nonsomatostatin peptides derived from its amino terminus

Rat prosomatostatin was isolated from a somatostatin-producing cell line and was partially microsequenced. This indicated the amino terminal structure of cellular prosomatostatin and implied a 92-amino acid sequence for the somatostatin precursor. Based on the structure for cellular prosomatostatin, a peptide was synthesized and used to develop a radioimmunoassay directed toward the amino terminal portion of prosomatostatin. This assay has revealed two peptides containing the amino-terminal portion of prosomatostatin in a somatostatin-secreting CA-77 rat medullary thyroid carcinoma cell line. These two peptides - MW 4000 and 8000 daltons - lack somatostatin immunoreactivity. Thus, processing of prosomatostatin occurs both at the amino and carboxyl regions. These results open the way for elucidation of the structure, function and metabolism of non-somatostatin peptides derived from the amino terminus of prosomatostatin.     

Evidence for intracellular formation of angiotensins: coexistence of renin and angiotensin-converting enzyme in Leydig cells of rat testis

Leydig cells were purified from rat testes by discontinuous metrizamide density gradient and were shown to contain renin (EC 3.4.99.1), angiotensin-converting enzyme (dipeptidyl carboxypeptidase, (EC 3.4.15.1), and the peptide hormone angiotensins I, II and III as determined by the combined HPLC and radioimmunoassay. In germinal cells only angiotensin II (AII) was found at a significant level. These findings provide evidence for intracellular formation of AII in testicular cells and demonstrate that an intracellular renin-angiotensin system exists in normal non-transformed cells.     

Action of sauvagine on the mesenteric vascular bed of the dog

Sauvagine, a linear peptide of 40 amino acids, produced hypotension when administered intravenously to anesthetized dogs. Diastolic pressure was always more affected than systolic pressure. Aortic blood flow and venous return both increased to the same extent. The mechanism of the hypotensive response was mainly, if not exclusively, due to dilatation of the superior and inferior mesenteric arteries. Intravenous infusion of sauvagine in doses ranging from 3 to 10 ng · kg^?1 · min^?1 produced a dose-related increased of mesenteric blood flow up to 400% control values. Mucosal-submucosal blood flow of ileum and colon was increased, while blood flow in muscle was unaffected or slight decreased. The mesenteric vasodilator response was not prevented by adrenergic or muscarinic receptor blockade. The hypotensive response was more marked and sustained in dibenamine-propranolol treated dogs.     

Sucrose biosynthesis in Dunaliella

Four independent kinds of observations indicate that the cell wall regenerated by oat (Avena sativa L.) and corn (Zea mays L.) protoplasts in culture is less well developed than that regenerated by tobacco (Nicotiana tabacum L.) protoplasts. Following wall regeneration the cereal protoplasts remained susceptible to osmotic shock upon transfer to water, showed great enlargement, stained poorly with calcofluor white, and maintained a positive internal electrical potential. The development of a negative membrane potential by tobacco protoplasts in culture often occurred simultaneously with the onset of cell division. Since division was observed only in protoplasts which had regenerated good cell walls and had re-established negative membrane potentials it is suggested that culture conditions which favor these two processes should improve protoplast viability.