Measurement of the Water Potential of Intact Plant Tissues1

A modified design of a thermocouple psychrometer is describedwhich utilizes the Peltier effect for producing an exceedinglysmall wet-bulb thermometer. The thermocouple assembly has beenreduced to miniature dimensions and the thermocouple chamberconsists of a silver cylinder (volume 0.06 cm³) whose base isformed by the material under observation. This makes it possibleto measure water potentials over limited surfaces of intactplant tissues, e.g. germinating pea seeds (Pisum sativum L.).The apparatus is capable of measuring water potentials downto a magnitude of about –6,000 joules/kg.³     

Regulators of Cell Division in Plant Tissues

The cytokinins, 6-benzylaminopurine and kinetin, markedly enhanced the yield of both free and membrane-bound 80S ribosomes per unit weight of radish (Raphanus sativus) cotyledon tissue. The response was observed only after the induction of growth by cytokinin; during the lag period preceding cytokinin-induced growth, ribosome yields from both control and cytokinin-treated cotyledons were below detectable levels. Mannitol depressed both growth and ribosome yield to the same degree. The enhanced ribosome yield appeared to be an indirect effect of cytokinin and was probably a consequence of cytokinin-induced growth. The effect of 6-benzylaminopurine on ribosome yield was not reflected in enhanced levels of cytoplasmic ribosomal RNA, while recently synthesized ribosomes were found to be more readily recovered from cytokinin-treated tissue than from control tissue. It was concluded that cytokinin-enhanced ribosome yield resulted from enhanced ribosome recovery or extractability and that ribosome yield is an unreliable indication of ribosome level in plant tissue.     

Regulators of Cell Division in Plant Tissues

Procedures were devised for purification of the cytokinins in the milk of mature coconuts (Cocos nucifera fruits). One cytokinin isolated in crystalline form was unequivocally identified as 9-β-D-ribofuranosylzeatin. This compound appeared to account for a large proportion of the cytokinin activity in n-butanol extracts of coconut milk. The activity which was not extracted by n-butanol was largely due to unidentified compounds which could be partially purified by adsorption onto and elution from charcoal.     

Freezing-Sectioning of Plant Tissues1

An improved and simple method is described by which serial 10µ frozen sections of plant tissues may be obtained. Thevalue of this method for use in plant histochemistry is discussed.     

植物细胞壁松弛因子

植物细胞壁的松弛是细胞伸长必需的一个生理过程,发生于植物生长发育的各个阶段。研究发现参与细胞壁松弛的因子有多种,主要包括膨胀素（expansin）、木葡聚糖内转糖苷酶/水解酶（XTH）、糖基水解酶和羟基自由基（·OH）四大类。本文主要对这些细胞壁松弛因子的结构特征、作用机制及其在植物生理过程中的作用等方面的研究进展进行综述。     

The Autoradiographic Detection of Ions in Plant Tissues1

The autoradiographic techniques for the examination of the subcellularlocalization of ions in plant cells have been assessed. It hasbeen shown that the use of a controlled-temperature freezing-sectioningtechnique, together with low-temperature, stripping-film autoradiography,may provide a more suitable method than is at present availablefor studies on ion uptake and movement in plant cells.     

Preparation of Freeze-dried Powders of Plant Tissues1

Apparatus is described for the preparation of freeze-dried powdersfrom plant tissues. Tissue samples were ground in a high-speedmixer under liquid nitrogen. The resulting frozen powder wasdried at — 25° C. using anhydrous calcium chlorideat — 25° C. as the desiccant.     

Studies in the Respiratory and Carbohydrate Metabolism of Plant Tissues1

Oxygen at pressures of 2 and 3 atmospheres caused an initialincrease in CO₂ output of strawberry leaves followed by a decrease.In oxygen at 2 atmospheres, but not in oxygen at 3 atmospheres,the increase in CO₂ output could be attributed to an increasein glucose-6-phosphate and in fructose diphosphate; in oxygenat 3 atmospheres the increase may be due to an increased accessibilityof substrates and enzymes or to other causes. The decline inCO₂ output in oxygen at both 2 and 3 atmospheres was associatedwith large decreases in glucose-6-phosphate and 3-phosphoglycerate,probably due to a large decrease in adenosine triphosphate relatedto a ‘block’ of the tricarboxylic acid cycle.     

Regulators of Cell Division in Plant Tissues VUI. The Cytokinins of the Apple Fruit

The cytokinin activities of extracts of organs developed from the apple fruit bud were compared using the carrot phloem bioassay, and the identity of the cytokinins in the apple fruitlet was investigated. The activity of apple fruitlet extracts was slightly greater than the activity of pedicel extracts, and considerably greater than the activities of extracts of other organs. Extracts of the developing seeds of fruitlets were much more active than extracts of fruitlet flesh. Apple fruitlet extracts contained three principal cytokinins. One was identified as a 6-(substituted amino)purine and was either zeatin or some very closely related compound. The two other cytokinins exhibited the chromatographic behaviour of zeatin riboside and zeatin ribotide. A cytokinin extracted from vegetative apple shoots was chromatographically indistinguishable from zeatin.     

细胞周期因子与植物根系发育

植物根系的发育是一个非常复杂且被精确调控的过程,受到多种信号的调控,其中对细胞分裂水平调控的研究已经成为细胞生物学研究的热点之一.文章介绍了植物细胞周期因子和植物根系发育相关的细胞周期调控机制以及根系细胞周期激素调节的研究进展.     

The Effect of L-Methionine on the Respiration of Plant Tissues1

The respiration of washed disks of storage tissue has been foundto be inhibited by L-methionine. The inhibitory effect of methionineappears to be exerted on the Krebs cycle and the inhibitionis reversed by dinitrophenol. The possibility that the increasedrespiration which occurs after washing disks of storage tissueis due to loss of methionine has been raised, and briefly discussedin relation to the tentative suggestion that methionine is acoupling agent between oxidation and phosphorylation.     

影响T-DNA转移的寄主植物细胞因子

在农杆菌介导的植物遗传转化过程中,寄主细胞因子参与农杆菌细胞与寄主细胞的识别与附着、毒性基因的表达以及T-DNA的跨膜运输和整合等过程.文章就这几方面的研究进展进行了综述.     

Plant Growth Regulators in Citriculture: Factors Regulating Endogenous Levels in Citrus Tissues

Since the review on endogenous growth substances of citrus tissues by Goldschmidt in 1976 (HortScience, 11: 95-99), much information regarding this topic has been published in a wide array of journals. The present review provides a comprehensive overview of published information on endogenous levels of the five classes of plant growth substances (i.e., auxins, cytokinins, gibberellins, ethylene, and abscisic acid), plus polyamines and other endogenous substances that appear to have a role in regulating citrus growth and development. It is the first in a three-part series that next examines hormonal regulation of physiological processes in citrus followed by review of current uses and commercial applications of plant growth regulators in citrus production. In this article, a brief history of the detection and characterization of each class of plant growth substances is given. Following this, variation in endogenous levels associated with different organs (and/or tissues), stages of development, species, cultivars, cultural practices, and environmental factors is reviewed. For each class, current knowledge regarding biosynthesis, metabolism and transport in citrus tissues is summarized. The concluding section deals with future research directions.     

Freeze-Sectioning of Plant Tissues

Techniques are described for freeze-sectioning a wide range of both fresh and fixed plant tissues. Gelatin-antifreeze media are used to support but not infiltrate the tissue during sectioning. At cryostat temperatures of -10 to -15 C, 15% gelatin (w/v) containing 0.8% dimethyl sulfoxide (DMSO), or 1.5% ethanediol (ethylene glycol), or 2% glycerol is used. Lower concentrations of gelatin and higher concentrations of antifreezes are required for sectioning at -24 C. Petri plates of media are stored at 2 C, and used by simply melting a hole in the medium. Fresh tissues can be placed directly in the hole, or prefrozen at temperature of liquid nitrogen, or equilibrated in antifreeze solution, before freeze-sectioning in the gelatin antifreeze medium. Many plant tissues have highly vacuolated cells and need equilibration in antifreeze solutions prior to freeze-sectioning. Fixed tissues are rehydrated and washed in water or buffer for 15-24 hr before equilibrating in a 10% solution of either DMSO, ethanediol or glycerol (named in order of rapidity of equilibration). Pretreatment in 10% DMSO is usually for 1-6 hr at 2 C for histochemical studies; or in 10% ethanediol or glycerol for 15-24 hr at either room temperature or 37 C for morphological studies. These methods permit serial cryostat sections free from freezing and thawing artifacts to be cut as thin as 2 μ.     

Resistance to Water Loss from the Mesophyll Cell Surface in Plant Leaves

A method is described for the accurate measurement of the apparentresistance to water loss from the mesophyll cell walls of plantleaves (r_w), and for studying the mechanism underlying thisresistance. The method for distinguishing possible mechanismsinvolves a comparison of the calculated values of r_w at differentrates of evaporation. The value of r_w remained below 50 s m^–1at relative water contents greater than 11 ± 3% and 7± 2% for Pelargonium hortorum Bailey and Vicia faba L.respectively. Therefore r_w is relatively insignificant at normalphysiological water contents in these species. When r_w did increaseit was not sensitive to evaporation rate, suggesting that alowering of the vapour pressure at the evaporating sites wasnot involved. This contrasted with the results for cellulosefilter paper, where r_w was more sensitive to evaporative flux.     

Thermal and Ionic Factors in the Ultraviolet Photolysis of Plant Cell Membranes

The exposure of red beet root tissue to ultraviolet (254 nm) at 2 × 10⁶ erg × cm^?2× min^?1 (0.2 J × cm^?2× min^?1) causes release of betacyanin after a 20 minute induction period. Ultraviolet-photolysis is temperature-sensitive having a thermal threshold at about 10°C. Reduction in pigment release was effected by chlorides of Mg, Ca and Sr, but not by Li, Na or K. This effect was marked but not complete, even at 40 mM concentration. It is concluded that photolysis is indirect, and involves a lytic factor, possibly an oxidant, derived from an original photochemical product.     

Electroosmotic Phenomena in Plant Tissues

The effect of a direct electric current on electrolyte transport through plant tissues was studied by applying it to 10-mm segments of the mesocotyls of etiolated maize seedlings, similar segments of one-year linden shoots with the normal conducting system and without vascular bundles, and isolated elements of the xylem and cell wall segments. At current densities of 9–38 A/mm² (10–20 V), electrolyte solutions in plant tissues always moved toward the cathode. The results suggest that electroosmosis is one of the factors responsible for changes in solution transport through the conductive plant tissues that occur under the effect of electric current.     

Ethanolamine Metabolism in Plant Tissues

Ethanolamine is readily metabolized by oat, pea, wheat, apple and carrot tissue preparations. Ethanolamine-1,2 (14)C was incorporated into the lipid fraction, and (14)C activity was distributed in the organic acid, sugar, acid volatile, carbon dioxide and insoluble residue fractions. The distribution varied with the particular tissue. Incorporation into the lipid fraction occurred in tissue homogenates in the absence of ATP by a Ca(++) activated system similar to that reported for animal preparations. The initial step in ethanolamine oxidation involves an amine oxidase. Glycolaldehyde and glyoxylic acid are metabolic intermediates, the former in the conversion of ethanolamine to carbon dioxide. No evidence was obtained for the operation of an ethanolamine transaminase or for the involvement of phosphorylated intermediates in the conversion of ethanolamine to carbon dioxide.