A root observation and sampling chamber (rhizotron) for pot studies

Summary A plant root observation chamber (rhizotron) was designed to examine soil-grown roots under a stereomicroscope and to sample roots and soil during the growth period of a pot study. The mini-rhizotrons are inexpensive to construct and are suitable for replicated, multitreatment experiments. Illustrative data on root hair and lateral development are presented for seedlings of four crop species.Vermont Agric. Exp. Stn. Journal Article No 572.     

外电场诱导叶肉原生质体融合

应用一交变电场(正弦波,500KHz,175—225V/cm),分别将裸大麦(正常或正常与黄化)、蚕豆、烟草的叶肉原生质体在一定间隔、平行的两电极间排列成串。再附加单个的方波脉冲(10—40μs,800V/cm,因不同的材料而异),以诱导相邻原生质体局部接触区发生质膜的可逆击穿而形成融合。上述正弦波和方波脉冲均由自制的细胞融合仪发生。在本实验条件下,融合率可达50%以上,并探讨了方波脉冲讯号以及其它有关的条件对于融合率的影响。     

Alterations in the structure of the electrical double layer adjacent to a charged membrane arising from electromagnetically induced changes in the activity of membrane bound enzymes

Electromagnetic fields of very low amplitude have been reported to influence a number of cellular functions. Many of these effects have a high degree of frequency specificity. Herein it is suggested that some of these reported results could be explained by a fieldinduced alteration in the enzymic activity of integral membrane proteins. It is shown that such a field-induced transition from an initial nonequilibrium steady-state to a final nonequilibrium steady-state can lead to an alteration in the concentration profiles of those charged species in the cell's ambient electrolyte that comprise the so-called electrical double layer. Examples of variations in the concentration profiles of those ions that react with a membrane-bound enzyme, as well as nonreacting ionic species, are given. The modulation of such effects by systematic variations in extracellular pH and ionic strength is discussed.     

Personal reflections on the nature of intelligence in humans and machines

Computers, the human mind, and social systems have common problems of inadequate memory and insufficient data manipulation speed. In each of these domains, information compression techniques have evolved to reduce storage and processing needs. Among the techniques for information compression, coding of information in procedures stands out as exceptionally powerful. Procedural information coding also gives rise to behavior that may be defined as intelligent. It is found in the human mind, in machines and in social systems. Its use in human thought is aided by language development which promotes regular review of abstract procedures. A practical consequence of better understanding of procedural information coding is the possibility of training people to exhibit greater mental capacity, a controversial possibility. This paper explores the impact of data processing resource limitations, data compression and procedural thinking in men and machines.     

Thermodynamics of the charge recombination in photosystem II

The temperature dependence of the electric field-induced chlorophyll luminescence in photosystem II was studied in Tris-washed, osmotically swollen spinach chloroplasts (blebs). The system II reaction centers were brought in the state Z⁺P⁺-Q_A ^-Q_B ^- by preillumination and the charge recombination to the state Z⁺PQ_AQ_B ^- was measured at various temperatures and electrical field strengths. It was found that the activation enthalpy of this back reaction was 0.16 eV in the absence of an electrical field and diminished with increasing field strength. It is argued that this energy is the enthalpy difference between the states IQ_A ^- and I^-Q_A and accounts for about half of the free energy difference between these states. The redox state of Q_B does not influence this free energy difference within 150 s after the photoreduction of Q_A. The consequences for the interpretation of thermodynamic properties of Q_A are discussed.Abbreviations DCMU 3(3,4-dichlorophenyl)-1,1-dimethylurea - I intermediary electron acceptor - Mops 3-(N-morpholino)propanesulphonic acid - P (P₆₈₀) primary electron donor - PS II photosystem II - Q_A and Q_B first and second quinone electron acceptors - Tricine N-tris(hydroxymethyl)methylglycine - Tris tris-(hydroxymethyl)aminomethane - Z secondary electron donor Dedicated to Professor L.N.M. Duysens on the occasion of his retirement     

Habitat choice of some field-inhabiting carabid beetles (Coleoptera: Carabidae) studied by recapture of marked individuals

ABSTRACT.

• 1 Habitat choice of some field-inhabiting carabid beetles was studied in the field, and included the adult-overwintering Bembidion lampros Herbst, Pterostichus cupreus L. and Agonum dorsale Pontoppidan, and the larval-overwintering Trechus secalis Paykull, Pterostichus melanarius Illiger, P.niger Schaller and Harpalus rufipes De Geer. These were compared to the forest-inhabiting and adult-overwintering species, Carabus nemoralis Müller.
• 2 Marked beetles were released in the centre of a circular enclosure which was placed on the edge between a cereal field and a wood. The direction of movement in this circle was compared with that in a control circle placed entirely in the cereal field.
• 3 In the field/wood circle, adult-overwinterers and the larval-overwin-terer H.rufipes choose to move into the cereal field. The majority of T.secalis. P.melanarius and C.nemoralis, however, moved into the wood, while P.niger exhibited no preference.
• 4 In the field circle, adult-overwinterers moved towards the more sun-exposed parts of the circle, whereas the movements of larval-overwin-terers were random.
• 5 Some species-specific characteristics considered important for habitat choice by these carabid beetles, and the relevance of these characteristics for their dispersal behaviour are discussed.

     

麻黄碱抑制小鼠输精管电场刺激致收缩的机制

麻黄碱(10 nmol/L~(-0.1) mmol/L)对电场刺激所致输精管收缩的浓度依赖性抑制作用可被育亨宾(0.1 μmol/L)减弱。去甲肾上腺素(0.1 nmol/L~(-10)μmol/L )和酪胺(0.1 μmol/L~(-0.1) mmol/L)也有类似麻黄碱的作用,去氧肾上腺素则缺乏此种作用。利血平处理和可卡因(10 μmol/L)可减弱麻黄碱和酪胺的抑制效应,但能增敏去甲肾上腺素的作用。高 Ca~( )和4-氨基吡啶(50 μmol/L)明显减弱甚至取消麻黄碱对电场刺激的抑制效应。以上结果提示麻黄碱抑制电场刺激所引起的输精管收缩。至少部分通过促进神经末梢释放去甲肾上腺素间接作用,后者激动突触前α_2-肾上腺素受体,从而抑制去甲肾上腺素的进一步释放。麻黄碱和其释放的去甲肾上腺素的作用,又可能与阻遏 Ca~( )内流有关。