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1.
The cell surface is a mechanobiological unit that encompasses the plasma membrane, its interacting proteins, and the complex underlying cytoskeleton. Recently, attention has been directed to the mechanics of the plasma membrane, and in particular membrane tension, which has been linked to diverse cellular processes such as cell migration and membrane trafficking. However, how tension across the plasma membrane is regulated and propagated is still not completely understood. Here, we review recent efforts to study the interplay between membrane tension and the cytoskeletal machinery and how they control cell form and function. We focus on factors that have been proposed to affect the propagation of membrane tension and as such could determine whether it can act as a global or local regulator of cell behavior. Finally, we discuss the limitations of the available tool kit as new approaches that reveal its dynamics in cells are needed to decipher how membrane tension regulates diverse cellular processes. 相似文献
2.
The function of the epidermis in auxinmediated elongation growth of maize (Zea mays L.) coleoptile segments was investigated. The following results were obtained: i) In the intact organ, there is a strong tissue tension produced by the expanding force of the inner tissues which is balanced by the contracting force of the outer epidermal wall. The compression imposed by the stretched outer epidermal wall upon the inner tissues gives rise to a wall-pressure difference which can be transformed into a water-potential difference between inner tissues and external medium (water) by removal of the outer epidermal wall. ii) Peeled segments fail to respond to auxin with normal growth. The plastic extensibility of the inner-tissue cell walls (measured with a constant-load extensiometer using living segments) is not influenced by auxin (or abscisic acid) in peeled or nonpeeled segments. It is concluded that auxin induces (and abscisic acid inhibits) elongation of the intact segment by increasing (decreasing) the extensibility specifically in the outer epidermal wall. In addition, tissue tension (and therewith the pressure acting on the outer epidermal wall) is maintained at a constant level over several hours of auxin-mediated growth, indicating that the inner cells also contribute actively to organ elongation. However, this contribution does not involve an increase of cell-wall extensibility, but a continuous shifting of the potential extension threshold (i.e., the length to which the inner tissues would extend by water uptake after peeling) ahead of the actual segment length. Thus, steady growth involves the coordinated action of wall loosening in the epidermis and regeneration of tissue tension by the inner tissues. iii) Electron micrographs show the accumulation of striking osmiophilic material (particles of approx. 0.3 m diameter) specifically at the plasma membrane/cell-wall interface of the outer epidermal wall of auxin-treated segments. iv) Peeled segments fail to respond to auxin with proton excretion. This is in contrast to fusicoccin-induced proton excretion and growth which can also be readily demonstrated in the absence of the epidermis. However, peeled and nonpeeled segments show the same sensitivity to protons with regard to the induction of acid-mediated in-vivo elongation and cell-wall extensibility. The observed threshold at pH 4.5–5.0 is too low to be compatible with a second messenger function of protons also in the growth response of the inner tissues. Organ growth is described in terms of a physical model which takes into account tissue tension and extensibility of the outer epidermal wall as the decisive growth parameters. This model states that the wall pressure increment, produced by tissue tension in the outer epidermal wall, rather than the pressure acting on the inner-tissue walls, is the driving force of growth.Abbreviations and symbols
E
el, E
pl
elastic and plastic in-vitro cell-wall extensibility, respectively
-
E
tot
E
el+E
pl
- FC
fusicoccin
- IAA
indole-3-acetic acid
- IT
inner tissue
- ITW
inner-tissue walls
- OEW
outer epidermal wall
-
osmotic pressure
-
P
wall pressure
-
water potential 相似文献
3.
Genetical and ecological differentiation across a hybrid zone 总被引:1,自引:0,他引:1
ABSTRACT.
- 1 There is a narrow hybrid zone between two chromosomal races of the grasshopper Podisma pedestris (L.) in the French Alps.
- 2 There are no gross differences in habitat across the zone, and a multivariate analysis of the vegetation composition detected no significant transition either.
- 3 The hatch and development rates of Podisma in hybrid populations were lower than those found in matched habitat types outside the zone.
- 4 The simplest explanation for the persistence of the parapatric distribution of the two races is that hybrid disadvantage is maintaining a tension zone between them.
4.
冷冻液温和季节对鼠尾过冷点的影响 总被引:3,自引:0,他引:3
为研究动物对寒冷的适应性,将鼠尾置于冷液浸冻,发现在一定条件下鼠尾组织可发生过冷现象。实验表明,鼠尾组织的过冷点和冷冻液温有关,同一季节冷冻液温越低过冷点越高;而不同季节相同冷冻条件下,冬季鼠尾组织的过冷点明显低于春季。 动物肢体组织的过冷特性是动物的抗寒冷特性,它和组织自身的物理化学性质有关。理沦证明,过冷度(△T)和表面张力(O)、摩尔质量(M),冰点(Ti)、密度(p)、摩尔凝固热(△H)及冰胚临界半径(rk)有关,其关系式为△T=26MTi/p△Hrk. 相似文献
5.
A. M. BORLAND H. GRIFFITHS C. MAXWELL M. C. FORDHAM M. S. J. BROADMEADOW 《Plant, cell & environment》1996,19(6):655-664
The interrelationships between the induction of CAM and the turnover of malate and citrate in the dicotyledenous tree Clusia minor were compared with seasonal changes in rainfall, leaf water status, PFD and photoinhibitory responses during the transition from wet to dry season in Trinidad. Over a period of 8 weeks, as rainfall declined from a maximum observed around week 3, leaf xylem tensions measured at dusk and dawn reflected the concurrent reduction in day-time carbon gain and an increase in the diel turnover of malate (exposed leaves) and citrate (shaded leaves). Clear seasonal trends were observed in the turnover of malate and citrate during the transition from wet to dry season. In contrast to the declining back-ground concentrations of citrate during the wet-dry season transition, malate accumulation was markedly enhanced and the ratio of malalc:citrate accumulated overnight increased as the dry season advanced. Photo-inhibitory responses, assessed by chlorophyll fluorescence, indicated that photochemistry was largely determined by the diurnal course of PFD incident on leaves, regardless of the magnitude of internal CO2 release from malate and citrate decarboxylation. In the long term, photochemical efficiency in both shaded and exposed leaves appeared to decline as the dry season progressed. Although there was a clear linear relationship between integrated PFD and overnight accumulation of malate, no such correlation was found for citrate. However, citrate breakdown during the day showed a much closer correlation with PFD as compared to malate, with levels of citrate measured at dusk declining in response to higher daily light intensities. Moreover, enhanced citrate decarboxylation during the day was strongly correlated with increased CAM and overnight accumulation of both malate and citrate. 相似文献
6.
Dissolved oxygen tension and oxygen uptake rate are critical parameters in animal cell culture. However, only scarce information of such variables is available for insect cell culture. In this work, the effect of dissolved oxygen tension (DOT) and the utility of on-line oxygen uptake rate (OUR) measurements in monitoring Spodoptera frugiperda (Sf9) cultures were determined. Sf9 cells were grown at constant dissolved oxygen tensions in the range of 0 to 30%. Sf9 metabolism was affected only at DOT below 10%, as no significant differences on specific growth rate, cell concentration, amino acid consumption/production nor carbohydrates consumption rates were found at DOT between 10 and 30%. The specific growth rate and specific oxygen uptake rate followed typical Monod kinetics with respect to DOT. The calculated max and
max were 0.033 h-1 and 3.82×10-10 mole cell-1h-1, respectively, and the corresponding saturation constants were 1.91 and 1.57%, respectively. In all aerated cultures, lactate was consumed only after glucose and fructose had been exhausted. The yield of lactate increased with decreasing DOT. It is proposed, that an apparent DOT in non-instrumented cultures can be inferred from the lactate yield of bioreactors as a function of DOT. Such a concept, can be a useful and important tool for determining the average dissolved oxygen tension in non-instrumented cultures. It was shown that the dynamic behavior of OUR can be correlated with monosaccharide (fructose and glucose) depletion and viable cell concentration. Accordingly, OUR can have two important applications in insect cell culture: for on-line estimation of viable cells, and as a possible feed-back control variable in automatic strategies of nutrient addition.Abbreviations DOT
Dissolved oxygen tension
- OUR
Oxygen uptake rate
-
specific oxygen uptake rate
-
specific growth rate
- Xv
viable cell concentration
- CL, C*, and
oxygen concentrations in liquid phase, in equilibrium with gas phase, and medium molar concentration, respectively
- H
Henry's constant
- KLa
volumetric oxygen transfer coefficient
- PT
total pressure
-
oxygen partial pressure
-
oxygen molar fraction
- i
discrete element 相似文献
7.
Oxidation of glucose to 2,5-diketogluconic acid by Erwinia herbicola was inhibited at 100% dissolved O2 tension (DOT) relative to air at 1 atm. Gluconic acid accumulation, however, increased under this condition. The negative influence of the high DOT is attributed to a 10-fold decrease in 2-ketogluconate dehydrogenase activity.The authors are with the Department of Biotechnology, Regional Research Laboratory, Canal Road, Jammu Tawi-180001, India 相似文献
8.
低氧低二氧化碳对大鼠脑血流的调节作用 总被引:1,自引:0,他引:1
低氧下脑血流与急性高原病有关,许多研究已证明,低氧不适应者的CBF明显高于低氧适应者,而高原世居者则低于海平正常值。低氧下低动脉血二氧化碳分压有对抗低氧扩血管及降低CBF的作用。因此研究低氧下低PaCO2对CBF的调节作用对于研究急性高原病的防治及其机理分析具有重要意义。本项研究目的:(1)揭示低氧下低PaCO2与CBF之间的关系;(2)通过增加通气量使PaCO2下降至合适水平,以保护脑血流维持在 相似文献
9.
Nobuakira Takeda Akira Tanamura Takaaki Iwai Mitsutoshi Kato Kenji Noma Makoto Nagano 《Molecular and cellular biochemistry》1993,129(2):139-143
The effects of captopril, an angiotensin-converting enzyme inhibitor, on congestive heart failure (CHF) were investigated in animal and clinical studies. Congestive heart failure was induced in rats by a combination of pressure and volume overload. Cardiac pressure overload was induced by constricting one renal artery (Goldblatt rat) and volume overload was induced by aorto-caval fistula. Captopril (100 mg/kg/day) was then administered for 14 weeks. Isometric contraction was assessed using isolated left ventricular papillary muscles. The maximum developed tension and the maximum rate of increase in tension (dT/dtmax) were decreased in untreated rats with CHF and improved in captopriltreated rats. The left ventricular myosin isoenzyme pattern was shifted towards V3 in untreated rats with CHF, and was shifted back towards V1 in the captopril-treated rats. In the clinical study, captopril (37.5–75 mg/day) was administered to patients with cardiomyopathy for 12 months. There was no effect on left ventricular mass in hypertrophic cardiomyopathy, although systolic anterior motion of the mitral valve disappeared in one patient. In dilated cardiomyopathy, however, left ventricular mass tended to decrease. These results indicate that captopril has a beneficial effect in congestive heart failure. 相似文献
10.
Shigemichi Iha Kunzo Orita Tomoko Kannoh Toshihiko Utsumi Eisuke F. Sato Masayasu Inoue Kozo Utsumi 《Free radical research》1996,25(6):489-498
Effect of nitric oxide (NO) on the respiratory burst of neutrophils was examined under different oxygen tensions. Phorbol myristate acetate (PMA) stimulated oxygen consumption and superoxide (O2-) generation in neutrophils by a mechanism which was inhibited reversibly by NO. The inhibitory effect of NO increased significantly with a decrease in oxygen tension in the medium. The inhibitory effect of NO was suppressed in medium containing oxyhemoglobin (HbO2), a NO scavenging agent. In contrast, 3-morpholinosydnonimine (SIN-1), a compound that rapidly generates peroxynitrite (ONOO-) from the released NO and O2-, slightly stimulated the PMA-induced respiratory burst. These results suggested that NO, but not ONOO, might reversibly inhibit superoxide generation by neutrophils especially at physiologically low oxygen tensions thereby decreasing oxygen toxicity particularly in and around hypoxic tissues. 相似文献