Correlations between Growth and Flowering in Chenopodium amaranticolor: II. Leaf and Stem Growth

Plants of Chenopodium amaranticolor grown in long photoperiodsfor 26 days were exposed to 0, 2, 6, or continuous short days(SD) and the resultant changes in leaf and stem growth on returnto long days recorded. Growth of the leaves, the main stem,and the axillary branches was initially strongly stimulatedby short days. Continued growth of leaves was inhibited by thedevelopment of flowers to anthesis; strong inhibition was observedafter 6 and continuous SDs, but not in the 2-SD or control groups,neither of which reached anthesis during the investigation. In the groups which flowered strongly, the intensity of inhibitionwas sufficient to mask completely the effect of the initialstimulation on final leaf and stem size. In the 2-SD group,however, lack of inhibition allowed full expression of the effectsof stimulation on the final leaf and stem dimensions. The system of stimulators and inhibitors controlling leaf growthprobably also brings about the changes in leaf shape associatedwith the onset of flowering. The results are discussed in relation to previous findings andit is suggested that similar stimulations of growth correlatedwith the induction of flowering might occur widely in both short-and long-day plants.     

Studies of Growth and Development in the Genus Fragaria: V. Spring Growth

From observations of leaf emergence dates and periodical dissectionsof stem apices it appears that leaf initiation does not keeppace with leaf emergence during the spring. This leads to asubnormal number of enclosed leaf initials at each stem apexat some time in April or May. Forced plants behave similarly,and it is concluded from these results and from direct experimentsthat part of the lag of leaf initiation on leaf emergence isconnected in some way with the flowering of the first inflorescenceto emerge from the crown. Conditions in the bud at the end ofthe winter also lead to an excess of leaf emergence over leafinitiation in the early spring.     

Studies of Growth and Development in the Genus Fragaria: IV. Winter Growth

The initiation and growth of leaf primordia has been followedduring four winters, and similar rates were obtained in eachseason. When allowance is made for temperature differences,these rates are at a much lower level than during the activegrowing season. In this respect winter dormancy involves a physiologicalchange resulting in a lower level of activity rather than acomplete cessation of activity. Leaf emergence and expansion,on the other hand, is completely stopped during the winter;this appears to be the result of photoperiodic induction bythe shortening days of August and September and is not primarilydependent on the fall in temperature.     

Cell Growth and Division: III. Conditions for Balanced Exponential Growth in a Mathematical Model

In a previous paper, we proposed a model in which the volume growth rate and probability of division of a cell were assumed to be determined by the cell's age and volume. Some further mathematical implications of the model are here explored. In particular we seek properties of the growth and division functions which are required for the balanced exponential growth of a cell population. Integral equations are derived which relate the distribution of birth volumes in successive generations and in which the existence of balanced exponential growth can be treated as an eigenvalue problem. The special case in which all cells divide at the same age is treated in some detail and conditions are derived for the existence of a balanced exponential solution and for its stability or instability. The special case of growth rate proportional to cell volume is seen to have neutral stability. More generally when the division probability depends on age only and growth rate is proportional to cell volume, there is no possibility of balanced exponential growth. Some comparisons are made with experimental results. It is noted that the model permits the appearance of differentiated cells. A generalization of the model is formulated in which cells may be described by many state variables instead of just age and volume.     

Cell Growth and Division: IV. Determination of Volume Growth Rate and Division Probability

Volume growth rate and division probability functions for mammalian cells have been determined as functions of cell volume with good reproducibility and statistical precision using Coulter volume spectrometry and the equations of the Bell model. Results are compared with independent measurements on synchronous cultures. The slow rate of volume dispersion requires that the growth rate F(tau, V) be closely proportional to volume for cells of a given age. However, when F(tau, V) is averaged over the age distribution of a population in balanced exponential growth to give the growth rate function f(V), the latter may rise more steeply than V.     

Studies of Growth and Development in the Genus Fragaria: III. The Growth of Leaves and Shoot

Changes in leaf size and in the number and size of the leafcells have been followed throughout the growing season and duringdrought and defoliation. The duration of the meristematic phaseof primordium growth is the major factor affecting leaf sizein all cases, and a hypothesis is developed to account for thechanges. A new index of shoot growth reflecting the rate ofcell production is used, together with the leaf initiation rate,to distinguish changes in growth rate at the time of runnerproduction and inflorescence initiation.     

Growth and timing of puberty: reciprocal effects.

Based on the analysis of the pubertal growth spurt and final height in different pathological conditions, this paper provides evidence that variations in age at onset of puberty have a major influence on the subsequent acceleration of the growth rate but a minor impact on final height. A reciprocal effect of the growth rate on the timing of onset of puberty is also suggested by a number of clinical observations.     

Studies in the Growth of Young of Pinus sylvestris L.: I. The Annual Cycle of Assimilation and Growth

The annual cycle of growth in plants of P. sylvestris L. varyingin age from 2 to 5 years was studied mainly by following theirweight changes through periodic sampling. Immediately followingbud-break there was a period of about 1 month in which, althoughmeristematic and extension growth were rapid in both shoot androot, there was no gain in weight by the plant. There was evidencethat the needles remaining from previous years contained a considerableamount of storage material which was utilized at this time.During May and June the main increase in weight was in the newshoots, but in August and September assimilates were more evenlydivided between the new shoots on the one hand, and the oldstem and the root on the other. The average relative growth-ratesfor the months May to September were between 1·0 and0·4 per cent, per day in plants growing in favourableconditions, the lower rates being found in older plants. Duringthe months October to March slow increase in weight occurredin needles, stem, and root, and the R.G.R.s in two experimentswere 0·21 and 0·15 per cent, per day. The netassimilation rate fell with increasing age and in the summerof the fifth year was 0·06g./g./week or 0·10g./dm.²/week.This low value of N.A.R. is discussed in relation to the knownhigh rate of production of P. sylvestris stands and their evergreenhabit.     

Petiole Growth in Ranunculus sceleratus L.: Ethylene Synthesis and Submergence

Petioles of the celery-leaved buttercup (Ranunculus sceleratusL.) elongate in response to treatment with ethylene in air whenthe leaf blades are attached. An enhanced rate of elongationgrowth also occurs when the leaves are submerged. Submergencecauses an increase in extractable ethylene gas within the tissues,and these levels appear to approach those required to saturatethe ethylene-promoted elongation growth response. Coincidentwith a rise in ethylene in the tissues is a dramatic increasein the level of I-aminocyclopropane-1-carboxylic acid (ACC),the precursor of ethylene. Both the petiole and leaf blade tissueshave a similar capacity to evolve ethylene in the presence ofadded ACC. However, in air the leaf blade evolves more ethylenefrom endogenous resources than the petiole. The simultaneousincreases in ethylene and ACC levels in submerged tissues areconsidered in terms of the low diffusivity of ethylene in water,the ‘autocatalytic’ effect of ethylene on ethylenebiosynthesis and the rôle of both carbon dioxide and oxygenfluxes in ethylene metabolism of submerged tissues. Ranunculus sceleratus, celery-leaved buttercup, petiole growth, submergence, ethylene metabolism     

Growth factors and receptors in cancer.

There have been a number of recent developments in mechanisms of action of growth factors and their receptors with particular relevance to cancer. The tyrosine kinase receptor family, in particular, has been shown to be important in tumour growth. These receptors are the products of oncogenes, or can interact with other oncogene pathways. Thus, antibodies to either the receptor or its ligand can be used as therapeutic agents. Peptide analogues of ligands that can block receptor activation are also potential therapeutic agents.     

Growth and Reproductive Strategy in VeronicaSpp.

Seed production, germination and plant growth form were studiedin several species of Veronica. The objectives were to comparethe reproductive strategies of annual and perennial speciesof Veronica which varied in their habitats and aggressivenessas weeds. ‘Reproductive effort’ was fairly similar for bothannuals and perennials, falling within the commonly observedrange for annual species. Seed number per capsule and the 100-seedweight were unaffected by the growth conditions but plant growthform was substantially modified in V. agrestis. The small-seeded Veronica species required light for germinationand the winter annual V. hederifolia germinated much more vigorouslyafter a low temperature treatment. The growth form, vigour andextent of adventitious root production and rapid seed germinationof V. persica must be significant factors in the spread andestablishment of this species. Veronica spp., germination, growth form, reproductive strategy     

Investigations on the Growth and Metabolism of Plant Cells: V. Tumorous Growth in Relation to Growth Factors of the Type found in Coconut

1. It has been shown that aqueous extracts of plant tumours,induced by Agro-bacterium tumefaciens (Smith and Townsend) onBryophyllum and Kalanchoe, will act in place of coconut milkusing the tissue-culture procedures previously described inthis series of papers. 2. In a large number of experiments it has been shown that tumoursof this kind yield extracts which have a growth-promoting effectsimilar to that of coconut milk. This effect may be enhancedby, though it is distinguishable from the effects of, addedcasein- hydrolysate in the basal medium. The activity of thetumour extracts was consistently greater than the activity ofextracts of stems and leaves of the same plants and of normal,non-tumorous plants. 3. Partial fractionation of the tumour extracts has shown thatactivity was concentrated in the alcohol extracts, and to alesser extent in the water extracts. Activity was completelylacking in the ether extracts. 4. The effect of coconut milk, which is replaceable wholly orin part by tumour extracts, is primarily an effect on cell divisionin the carrot tissue. 5. The bearing of these results on tumorization in plants isdiscussed.