MECHANICAL STRESS AND CELL WALL ORIENTATION IN PLANTS. I. PHOTOELASTIC DERIVATION OF PRINCIPAL STRESSES. WITH A DISCUSSION OF THE CONCEPT OF AXILLARITY AND THE SIGNIFICANCE OF THE “ARCUATE SHELL ZONE”

This study describes a further investigation into the meaning of patterns of cell wall orientation in plants and outlines a modified method for the generation of patterns of principal stresses in a two-dimensional model. Evidence from simple photoelastic models is presented which supports the concept that the initial location of a presumptive axillary bud primordium may be controlled by mechanical stress in the region of the leaf axil.     

DIFFERENTIATION,ORGANOGENESIS, AND THE TECTONICS OF CELL WALL ORIENTATION. II. SEPARATION OF STRESSES IN A TWO-DIMENSIONAL MODEL

This paper describes a polarographic technique for the separation of tension and compression stresses in a two-dimensional plastic model of a sectioned cotton ovule. Compression and tension stress trajectories in the model comprise two families of lines which are mutually perpendicular and which, in the “nucellar” region of the model, coincide with cell wall patterns seen in sectioned ovules. This arrangement of stresses is demonstrated, by direct manipulation of the model, to be dependent on the pressure of the integuments. The integuments insure that compressive stresses generated during the growth of the nucellus do not collapse the embryo sac but pass around it, leaving it as a compression-free space within the growing ovule.     

ORIENTATION OF THE PLANE OF CELL DIVISION IN FERN GAMETOPHYTES: THE ROLES OF CELL SHAPE AND STRESS

Apical cells of Onoclea sensibilis L. protonemata were measured to determine areas of new walls which were formed during both transverse and longitudinal cell division. Actual wall areas were compared with calculated areas of hypothetical walls oriented in the opposite sense (i.e., an actual transverse wall compared with a hypothetical longitudinal wall, and the reverse). Among 87 out of 90 cells which were analyzed the actual walls had the least area. Thus, the minimal area hypothesis of cell partitioning accurately predicts wall orientation in this instance, although it appears, on other grounds, that the hypothesis does not furnish a plausible mechanism for wall orientation. The application of Lintilhac's concept of the orientation of cell walls in response to anisotropic stresses in the cell was explored. Photographs of apical cells during deplasmolysis indicated that unequal stresses might be generated in apical cells as a result of the osmotic distension of the elastic protoplast. It is concluded that the primary factor which determines the plane of cell division in the apical cell, and the transition from one- to two-dimensional growth, is the local pattern of stress which exists at the position of the nucleus at the time of onset of cell division and wall formation. Calculations of some geometrical properties of idealized model cells are interpreted to mean that the accuracy of the minimal area hypothesis results from a coincidence of its predictions with predictions of Lintilhac's hypothesis, and no causal significance is attributed to wall areas.     

DIFFERENTIATION,ORGANOGENESIS, AND THE TECTONICS OF CELL WALL ORIENTATION. III. THEORETICAL CONSIDERATIONS OF CELL WALL MECHANICS

This paper is concerned with the relationship between cell wall orientation in dividing tissues and stress. An examination of the possible orientations of a cell-plate in a cell under axial stress reveals that only one orientation passing through the center of the cell can be completely free from shear stress, thus providing a favored plane for the positioning of an hypothetical, shear-sensitive, cell-plate precursor. From this principle of shear-free partitioning, and the three basic rules of stress behavior along free boundaries, it is possible to predict certain features of cell wall orientation along free edges and epidermal surfaces and in some simple apices. The possible significance of the widespread phenomenon of axillary induction of bud formation is discussed in terms of the generation of stresses at the base of the axillant leaf, and the general efficacy of mechanical stress as a spontaneously arising morphogenetic trigger is considered.     

几种植物细胞表面糖蛋白的电镜细胞化学及其与植物抗逆性的关系

1.无论是小麦、玉米或长豇豆的叶片组织,经钌红染色显示的糖蛋白均明显地定位于细胞间隙周围游离的细胞表面上,在细胞壁的外部形成一个糖蛋白层,厚度一般为50—100nm之间。紧贴细胞壁的部分比较致密,外部边缘比较松散,有些呈现为丝状。2.抗寒性强的冬小麦幼苗叶片细胞表面的糖蛋白比不抗寒的春小麦品种显得丰富;并且在低温锻炼中,前者细胞表面的糖蛋白层有增厚的趋势,而后者的糖蛋白层明显变薄、甚至完全消失。3.当长豇豆叶片感染花叶病或玉米叶片感染小斑病后,黄色病斑组织的细胞表面的糖蛋白向细胞间隙中脱落,直至糖蛋白层完全消失。病斑周围的绿色组织细胞表面的糖蛋白层,有些也发生减少,甚至完全消失;有些则增厚。抗小斑病的玉米品种的细胞表面的糖蛋白比不抗品种显得丰富。以上情况表明,细胞表面的糖蛋白与植物的抗病性和抗寒性存在密切关系。     

FINE-STRUCTURAL STUDY ON THE FORMATION OF THE GENERATIVE CELL WALL AND INTINE-3 LAYER IN A GROWING POLLEN GRAIN OF LILIUM LONGIFLORUM

At the end of mitosis in the lily pollen microspore, the fan-shaped cell plate gives rise to a cell wall delineating a hemispherical cell. At first, the cell wall of the newly formed generative cell and the intine-3 layer of the pollen grain wall are inseparable. Gradually, the wall of the generative cell near the pollen grain wall becomes thicker and wall segments are formed between the thickened zones, and these make a network system by which the generative cell becomes suspended and separated from the pollen grain wall. After the separation, the intine-3 layer is formed inside the intine 2. The generative cell wall and the intine-3 layer are formed by coated vesicles, polysaccharide particles and rough ER.     

EFFECTS OF ENVIRONMENTAL FACTORS ON MECHANICAL PROPERTIES OF THE CELL WALL IN RICE COLEOPTILES

Cell wall properties determined by the stress-relaxation technique were studied with coleoptiles of rice seedlings grown under different environmental conditions. The cell wall was simulated by a viscoelastic model consisting of either four or an infinite number of Maxwell components. Reciprocal of relaxation time for the first component in the former model (1/τ₁) and minimum and maximum relaxation times (T_o and T_m) in the latter, in addition to the stress/strain ratio, were parameters representing cell wall properties. Parameters changed depending on the ages and regions of the coleoptilles used and 011 the environmental conditions under which rice seedlings were grown. Effects on cell wall properties of aeration during submerged growth, excision of the coleoptile tip, and exposure to small doses of red and/or far-red light were examined. In most cases, high values of 1/τ₁ and of T_m and small values of T_o were consistent with the growth potentiality of cells, while the stress/strain ratio seemed to be a consequence of elongation growth.     

DEMONSTRATION OF A FIBRILLAR COMPONENT IN THE CELL WALL OF THE YEAST SACCHAROMYCES CEREVISIAE AND ITS CHEMICAL NATURE

The ultrastructure of isolated cell walls of Saccharomyces cerevisiae from the log and stationary phases of growth was studied after treatment with the following enzymes: purified endo-β-(1 → 3)-glucanase and endo-β-(1 → 6)-glucanase produced by Bacillus circulans; purified exo-β-glucanase and endo-β-(1 → 3)-glucanase produced by Schizosaccharomyces versatilis; commercial Pronase. While exo-β-glucanase from S. versatilis had no electron microscopically detectable effect on the walls, Pronase removed part of the external amorphous wall material disclosing an amorphous wall layer in which fibrils were indistinctly visible. Amorphous wall material was completely removed by the effect of either endo-β-(1 → 3)- or endo-β-(1 → 6)-glucanase of B. circulans or by a mixture of the two enzymes. As a result of these treatments a continuous fibrillar component appeared, composed of densely interwoven microfibrils resisting further action by both of the B. circulans enzymes. The fibrillar wall component was also demonstrated in untreated cell walls by electron microscopy after negative staining. Because of the complete disappearance of the fibrils following treatment with the S. versatilis endo-β-(1 → 3)-glucanase it can be concluded that this fibrillar component is composed of β-(1 → 3)-linked glucan. Bud scars were the only wall structures resistant to the effect of the latter enzyme.     

叶片组织结构特征对氯气、二氧化硫的抗性研究

为研究叶片组织结构和植物对大气污染的抗性关系,本文对75种植物叶片的解剖结构进行了观察,并测量了它们的形态指标。初步结论如下:(1)早生结构的叶片,表现为叶较厚、角质层厚等,对大气污染具较强的抗性;(2)具发达贮水组织的肉质叶,抗性较强;(3)阴生结构叶片,如叶较薄、纸质或柔软者,多是敏感植物;(4)在少数科中,如桑科、赤铁科,夹竹桃科等有不少种类属抗性植物;(5)在污染条件下,气孔开放度对植物的伤害有重要影响;(6)栅栏组织细胞层数,栅栏组织厚度和叶片厚度之比,对植物的敏感性没有直接相关关系;(7)叶片解剖结构特征,在评价植物对大气污染的抗性有其局限性。     

ON THE NATURE OF FORCES OPERATING IN BLOOD CLOTTING : II. THE CLOTTING OF FIBRINOGEN AS A TWO-STEP REACTION

It is found that clotting of fibrinogen by thrombin does not occur on the acid side of the isoelectric point of the fibrinogen. At such pH values, however, a primary reaction between thrombin and fibrinogen takes place, leading to the formation of profibrin, a compound of thrombin and fibrinogen. At pH values at which clotting is possible, fibrinogen is negatively, thrombin positively charged, whereas profibrin has a pattern of positive and negative charges. The primary reaction, the formation of profibrin by combination of thrombin and fibrinogen, is inhibited by urea but not by neutral salts. The combination of thrombin with fibrinogen most probably takes place by hydrogen bonds. The second reaction, the polymerisation of profibrin to fibrin, is inhibited by neutral salts in the same way as complex or autocomplex coacervates. It is caused therefore by electrostatic attraction between the positive and the negative charges of the profibrin.