SEASONAL CHANGES IN THE APICAL ZONATION AND ULTRASTRUCTURE OF COASTAL DOUGLAS FIR SEEDLINGS (PSEUDOTSUGA MENZIESII)

The apical meristems of one-year-old container-grown seedlings of coastal Douglas fir were studied in two years during embryonic shoot development, dormancy, and dormancy release by light and electron microscopy. Apical zonation was evident at all times but prominence of some zones varied. Vacuolation was an important zone-characteristic and was not an artifact created by lipid extraction. During late summer and fall the plasma membrane was relatively smooth, ER not abundant, nuclear membranes irregular, and lipid bodies sparse. Numerous autophagic vacuoles occurred in apical cells. These diminished after bud scale initiation was completed in September and reappeared again in midwinter. Maximum starch accumulation was in the fall then it decreased during the winter and remained low during cold storage. The number of lipid bodies gradually increased in late fall and was large in winter. A single night of –1 C caused an increase in the number of lipid bodies. Plastids contained electron-dense material which accumulated further under subfreezing temperatures and eventually appeared to be released during winter into the cytoplasm and arranged into small globules along the cisternae of the ER. Granular protein bodies were observed at this time as well as deposits of electron-dense material on the outer surface of the plasma membrane and in cell walls. During winter, the plasma membrane became convoluted, short cisternae of the ER abundant, the nuclear membranes evenly separated, and nucleolar components aggregated. At the end of dormancy, ribosomes and starch grains became very abundant. Most lipid bodies diminished by budbreak.     

PROTEIN SYNTHESIS AND THE CONTROL OF PLANT PROCESSES

Bonner , James . (California Inst. Technology, Pasadena.) Protein synthesis and the control of plant processes. Amer. Jour. Bot. 46(1) : 58-62. Illus. 1959.—Microsomal ribonucleoprotein particles which occur in the cytoplasm of plant, animal, and microbial cells alike, possess the function of protein synthesis, and appear to be responsible for the formation of many, perhaps all, of the soluble cytoplasmic proteins. To the process the microsome contributes information, arranging previously acyl-activated amino acid residues in the abundance and sequence characteristic of the specific enzyme being synthesized. The microsome consists of RNA and of protein. The latter appears to be a structural protein, common to microsomes and not directly related to the protein synthesized by the microsome. The amount of information contained in the RNA of a microsomal particle can be calculated to be sufficient for the synthesis of one or at the most a few species of protein molecules. There must therefore be within the cytoplasm of the cell many different species of microsomes, superficially alike, but each different species bearing in RNA code the information required for the assemblage of but one or a few kinds of protein molecules. Microsomes do not, so far as can be judged, possess the power to reproduce. On the contrary microsomal RNA, and possibly microsomal protein also, appear to be synthesized within the nucleus. Transfer of microsomes from nucleus to cytoplasm is therefore implied and is in fact suggested by a variety of indirect experiments. The transfer of nuclear information to the cytoplasm may well be mediated by the microsomes.     

HISTOLOGICAL ANALYSIS OF ADVENTITIOUS BUD FORMATION IN CULTURED DOUGLAS FIR COTYLEDON

Initiation of adventitious bud formation in vitro from Douglas fir cotyledons required both cytokinin and auxin at concentrations of 5 μM BAP and 5 nM NAA. Histological observations showed that these adventitious buds arose de novo from cells residing in hypodermal layers. Development of adventitious buds in culture was characterized by the sequential appearance of four anatomically distinguishable structures: 1) meristemoid, 2) bud primordium, 3) shoot apex with needle primordia, and 4) adventitious bud. The anatomical structure of tissue culture-produced buds was similar to that of vegetative buds produced on intact plants. Cultured cotyledons capable of producing adventitious buds (bud culture) were compared with bud-callus and callus cultures initiated by 5 μM BAP plus 5 μM NAA and 5μM NAA alone without BAP, respectively. Results showed that, during early stages of the culture period (i.e., prior to the appearance of meristemoid structure), cell division of bud culture was mainly located in hypodermal layers, whereas for the other culture types, bud-callus and callus cultures, cell division occurred randomly in all tissues.     

CHARACTERIZATION OF MEMBRANES OBTAINED FROM ELECTRIC ORGAN OF THE ELECTRIC EEL BY SUCROSE GRADIENT FRACTIONATION AND BY MICRODISSECTION

Abstract— Two membrane fractions were obtained from electric organ tissue of the electric eel by sucrose gradient centrifugation of tissue homogenates. Electron microscopic examination showed that both fractions contained mainly vesicular structures (microsacs). Both the light and heavy fractions had a-bungarotoxin-binding capacity and Na⁺-K⁺ ATPase activity, while only the light fraction had AChE activity. The polypeptide patterns of vesicles derived from both the light and heavy fractions were examined by SDS-polyacrylamide gel electrophoresis and found to be very similar. The ratio of protein to phospholipid in the light vesicles was much lower than in the heavy vesicles, but the relative amounts of individual phospholipids in the two fractions were similar. A marked difference in the permeability of the light and heavy vesicles was observed by measuring efflux of both [¹⁴C]sucrose and ²²Na⁺, and also by monitoring volume changes induced by changing the osmotic strength of the medium. All three methods showed the heavy vesicles to be much more permeable than the light ones. Only the light vesicles displayed increased sodium efflux in the presence of carbamylcholine. The AChE in the light fraction does not appear to be membrane-bound, but is rather a soluble enzyme, detached from the membrane during homogenization, which migrates on the gradient similarly to that of the light vesicles. This is supported by the fact that the bulk of the AChE is readily removed by washing the vesicles. Moreover, under the conditions employed in our sucrose gradient separations,‘native’14 S + 18 S AChE exists in the form of aggregates which migrate very similarly to the major peak of AChE activity of tissue homogenates. Separated innervated and non-innervated surfaces of isolated electroplax were obtained by microdissection. α-Bungarotoxin-binding capacity was observed only in the innervated membrane. About 80% of the AChE was in the innervated membrane, and about 70% of the Na⁺-K⁺ ATPase in the non-innervated membrane. The data presented indicate that the light and heavy vesicle fractions separated by sucrose gradient centrifugation are not derived exclusively from the innervated and non-innervated membranes respectively, as previously suggested by others, but contain membrane fragments from both sides of the electroplax. The separation of two populations on sucrose gradients may be explained both by the differences in permeability and in protein to phospholipid ratios.     

ELECTRIC TISSUE : RELATIONS BETWEEN THE STRUCTURE,ELECTRICAL CHARACTERISTICS,AND CHEMICAL PROCESSES OF ELECTRIC TISSUE

In the main electric organs of the electric eel, the cross-sectional area, the thickness of the electroplaxes, and certain electrical characteristics of the tissue vary widely between the anterior and posterior ends. However, a transverse layer of the organs one electroplax thick has certain characteristics which are roughly uniform along the organs. These are its volume, its maximum voltage, its maximum current per unit area, and the resistance of unit area at the peak of the discharge. Measurements of the voltage developed by a segment of the organs across different external resistances at different instants during the discharge are all rather well described by representing the segment, with the adjacent non-electric tissue, as a simple combination of E.M.F. and ohmic resistance. The internal resistance of the tissue varies during the discharge. Its E.M.F. appears to be practically constant, at least during the greater part of the discharge. Estimates made of the total electric energy show it about equal to the energy supplied by the decrease of phosphocreatine and the formation of lactic acid.     

香雪兰外植体形态学极性决定的体细胞胚胎发生

在含有２ｍｇ／ＬＩＡＡ和３ｍｇ／ＬＢＡＰ的改良Ｎ６培养基上,香雪兰（ＦｒｅｓｉａｒｅｆｒａｃｔａＫｌａｔ）花序外植体经直接体细胞胚胎发生途径再生出新的植株。在这一形态发生过程中,一个引人注意的现象是,所有的体细胞胚都出现在花序轴切段的原形态学下端（称为胚发生端,ＥＥ）,而在形态学上端（称为非胚胎发生端,ＮＥＥ）无体细胞胚形成。这一形态发生的极性与地心引力的方向和外植体在培养基上的放置位置无关。在培养的早期,仅于胚发生端观察到了起始细胞的分裂。ＳＤＳ聚丙烯酰胺凝胶电泳结果表明,在培养了１ｄ的外植体的胚发生端出现了两个特殊的多肽成分,而在非胚发生端则未检测到这两种多肽。高效液相色谱分析表明,培养前外植体切段两端的内源激素（ＩＡＡ）的含量无显著差别。但经过一段时间的培养,胚发生端的ＩＡＡ含量明显高于非胚发生端的ＩＡＡ含量,表明内源激素在体细胞胚胎发生的诱导过程中起着关键的作用。在香雪兰体细胞胚胎发生诱导的过程中,由于花序轴切段两端在分子水平和生理水平上均存在差异,使这一系统有可能成为研究体细胞胚胎发生机理的有用实验材料。     

CONTROL OF INTERCALARY GROWTH IN THE SCAPE OF GERBERA BY AUXIN AND GIBBERELLIC ACID

With the inflorescence removed, intercalary growth can be maintained in the scape of Gerbera jamesonii by application of gibberellic acid (GA, gibberellin A₃) or indole-3-acetic acid (IAA); the latter usually promotes more rapid and greater elongation than the former because of a greater effect on older tissues. Simultaneous application of the two substances, even when both are at optimal levels, promotes more rapid elongation than either substance alone; in fact, the rate of elongation may equal that of the intact scape. In decapitated scapes (receptacle and involucral bracts removed with the inflorescence), GA and IAA promote cell elongation with reduced or no cell division. In deflowered scapes (receptacle and involucral bracts intact) both GA and IAA promote cell division, as well as cell elongation, so that the pattern of scape elongation is nearly the same as that for intact scapes. Apparently the bracts and receptacle contribute something required for cell division which acts in concert with GA and IAA. Deflowered and decapitated scapes elongate at nearly the same rates initially; thus the rate of elongation does not depend on cell division. The ultimate length of the scape is dependent on cell number and, hence, cell division, since deflowered scapes attain greater lengths than those that are decapitated.