On the Ordered Development of Plants 1. An Hypothesis

It is hypothesized that each growing-point on a plant requiresa minimum flux of assimilate for growth to continue, and thatthis flux differs for different types of growing point. Thissimple concept provides cohesive explanation of the observedpatterns of plant development during both vegetative and reproductivegrowth. It also provides a qualitative explanation of the effectsof the aerial and rooting environments on shoot and root morphology.Some implications of the hypothesis are discussed. Development, morphology, root, shoot, branch, tiller, pod, grain     

On the Ordered Development of Plants 2. Self-thinning in Plant Communities

It is shown that the hypothesis that a growing point on a vegetativeplant requires a minimum rate of supply of assimilate to continuegrowth can quantitatively describe self-thinning in communitiesof Trifolium subterraneum. The hypothesis can also be used toexplain the different relationships observed between mean plantweight and plant density when plants are grown in full daylight,70 per cent shade, and transferred between the two light environments.The implications of the hypothesis to self-thinning in naturalplant communities are discussed. Self-thinning, assimilate, plant development     

On the Ordered Development of Plants 3. Branching by the Grain Legume Cyamopsis tetragonoloba(Guar)

Two selections of guar (Cyamopsis tetragonoloba (L.) Taub.)with contrasting branching patterns were grown at three plantdensities at two times of the year. The numbers of growing vegetativemeristems (branches and main stems) per unit ground area atthe start of reproductive growth were linearly related to theamount of the incident light energy intercepted by the differentcrops of each selection. The data were consistent with the hypothesisthat each vegetative meristem required a minimum assimilateflux to continue growth and, further, that meristems on thehighly branching selection required approximately one-quarterof the assimilate flux required by vegetative meristems on therelatively non-branching selection. The effect of increasingplant density in reducing branching by individual plants ofa particular selection was also consistent with this hypothesis. The hypothesis accounted quantitatively for the observed three-dimensionaldistribution of vegetative meristems through the volumes ofcrop canopies at each of the three plant densities. The implicationsof this analysis to the field performance of crops comprisingplants with different branching patterns are discussed. Cyamopsis tetragonoloba, guar, branching, grain legume, crop, morphology     

Vacuolar Lucifer Yellow Uptake in Plants: Endocytosis or Anion Transport; A Critical Opinion

Because of its membrane-impermeant-properties Lucifer Yellow-CH (LY) is regarded by animal cell biologists as an ideal tracer for fluid-phase endocytosis. When presented to plant cells or protoplasts this fluoroprobe accumulates in the vacuole. On the other hand there are many cases where LY does not enter the vacuole when loaded into the plant cytosol. These, superficially divergent, results have previously been explained in terms of endocytosis whereby access to the vacuole is considered to occur through vesicle transport. This interpretation has now been challenged in three recent papers where the benzoic acid derivative, probenecid, has been shown to prevent vacuolar LY accumulation in plants. Since probenecid is a well-known inhibitor of organic anion transport in animal cells it has been argued that anion carriers capable of transporting LY might also exist at the plasma membrane and tonoplast of plant cells. Unfortunately probenecid has rarely, if ever, been used in plant transport studies. The fact that it is a weak acid, whose inhibitory effects are observed at concentrations of around 1 mM suggests that caution should prevail when interpreting results obtained with probenecid. The purpose of this article is therefore to highlight the current controversy surrounding LY uptake by plants and to critically evaluate the recent probenecid data.     

A Comparative Study of Scores for Correspondence Analysis with Ordered Categories

Ordered categorical data can be analysed using correspondence analysis with the ordered categories taken into consideration. Such an analysis was proposed by Beh (1997) and uses orthogonal polynomials which require the input of a scoring scheme to reflect the ordered structure of the categories. This method of correspondence analysis visualises the relationship between the categories, in terms of the location, dispersion and higher order components. The impact of the scoring method on the orthogonal polynomials, and hence upon the correspondence plot and other output of the analysis should therefore be considered. This paper aims at identifying this impact by considering four scoring schemes: integer valued (natural) scores, midrank scores, Nishisato scores and singular vectors from the classical correspondence analysis of the data. It is shown that while the latter two maximise the location component, generally there is little difference when comparing them with the output of the former two scoring schemes. A simple comparative study of profile co-ordinates using different scoring schemes is also discussed.     

Current-Voltage Curves for Plant Membrane Studies: A Critical Analysis of the Method

The evolution of the steady-state current-voltage (I/V) methodis followed to its present sophistication of bipolar staircase.When applied to Chara plasmalemma the resultant I/V characteristicsvary enormously depending on the physiological state of themembrane (which is, in turn, dictated by the outside conditions).This variety of response makes formulation of ‘correct’,that is artefact-free, I/V technique quite a challenge. Thetime-dependence of the clamp current in each electrophysiologicalstate is different and this must be taken into considerationwhen steady-state I/V is investigated. Clamping of the plasmalemmaalone is also necessary, as under some conditions the conductanceof the two membranes becomes similar and the effects of thetonoplast can no longer be neglected when both membranes areclamped in series. The data obtained by point clamping and spaceclamping are compared. The use of bipolar staircase introducesmore subtle artifacts: the I/V profiles can be severely misinterpreteddue to transient conductance changes arising from the excitationor the outward and inward rectifier currents. The excitationcan be blocked by temporary exposure to lanthanum ion, but theconcentration must be carefully chosen. It is necessary to optimizethe staircase parameters to allow the rectifier currents toreturn to resting level before the next staircase pulse. Finally,brief comparison of the Chara I/Vprofile to that of other cellsis included and the relevance to patch clamp studies discussed. Key words: Current-voltage characteristics, Chara, space clamp, lanthanum blockade     

Multi-Scale Modeling in Morphogenesis: A Critical Analysis of the Cellular Potts Model

Cellular Potts models (CPMs) are used as a modeling framework to elucidate mechanisms of biological development. They allow a spatial resolution below the cellular scale and are applied particularly when problems are studied where multiple spatial and temporal scales are involved. Despite the increasing usage of CPMs in theoretical biology, this model class has received little attention from mathematical theory. To narrow this gap, the CPMs are subjected to a theoretical study here. It is asked to which extent the updating rules establish an appropriate dynamical model of intercellular interactions and what the principal behavior at different time scales characterizes. It is shown that the longtime behavior of a CPM is degenerate in the sense that the cells consecutively die out, independent of the specific interdependence structure that characterizes the model. While CPMs are naturally defined on finite, spatially bounded lattices, possible extensions to spatially unbounded systems are explored to assess to which extent spatio-temporal limit procedures can be applied to describe the emergent behavior at the tissue scale. To elucidate the mechanistic structure of CPMs, the model class is integrated into a general multiscale framework. It is shown that the central role of the surface fluctuations, which subsume several cellular and intercellular factors, entails substantial limitations for a CPM''s exploitation both as a mechanistic and as a phenomenological model.     

我国热带药用植物开发现状(综述)

热带药用植物是一类重要的森林资源。中国热带药用植物以四大南药--砂仁、益智、槟榔、巴戟天为主。我国在部分热带药用植物的标准化、规范化开发已取得进展,但是相对于我国丰富的热带药用植物资源而言,力度还不够。用现代科学手段和方法研究热带植物药,从热带植物天然产物中寻找新的活性成分,是发展创新天然药物的有效途径。与此同时,必须加强GAP规范的推广应用和质量控制。     

谈谈植物中的几丁质酶

几丁质酶及其底物几丁质均广泛存在于自然界.由于几丁质酶及其降解产物在生物学、医学、化学、农业及环境科学等方面的潜在价值而越来越受到重视.着重介绍了几丁质酶的作用原理,植物的几丁质酶基因,植物中几丁质酶的特性以及几丁质酶在植物中的作用和在转基因植物中的应用.