Ultradian Growth in Prochlorococcus spp.

Species of the widespread marine prokaryote Prochlorococcus exhibited ultradian growth (faster than 1 division per day) both in situ and in culture, even though cell division is strictly phased to the light-dark cycle. Under optimal conditions a second DNA replication and cell division closely followed, but did not overlap with, the first division. The timing of cell cycle events was not affected by light intensity or duration, suggesting control by a light-triggered timer or circadian clock rather than by completion of a light-dependent assimilation phase. This mode of ultradian growth has not been observed previously and poses new questions about the regulation of cellular rhythms in prokaryotes. In addition, it implies that conclusions regarding the lack of nutrient limitation of Prochlorococcus in the open ocean, which were based on the appearance that cells were growing at their maximal rate, need to be reconsidered.     

Plant Growth Regulators in Cucumis melo L. var. flexuosus Naud Fruit during Rapid Growth

The fruit growth of the snake melon (Cucumis melo L. var. flexuosusNaud) and the plant hormones contained in its immature fruitwere investigated. The fruit growth started 5 days after pollinationand its rapid growth continued for about 10 days. During thisperiod the growth rate (length) was 9 cm per day. The finalsize of the fruit was about 120 cm in length and 6 cm in width25 days after pollination. The cell number of the fruit increasedto more than twice that of the fruitlet before pollination.The increase started immediately after pollination and stoppedat 10 days after pollination. On the other hand, no change incell size was observed during the first 7 days after pollination.After this period, rapid growth started and continued to theend of the fruit growth. The cell size increased to more than7 times that of the fruitlet before pollination. In rapidly developing immature fruit including placenta andimmature seeds, trans-zeatin riboside (ZR) and ABA were identifiedwith gas-liquid chromatography-selected ion monitoring or gas-liquidchromatography-mass spectrometry analysis. In addition, thepresence of trans-zeatin (Z) and another very polar cytokinin,and a novel gibberellin-like substance which is probably anisomer of GA₃ was suggested. The possible significance of theseplant hormones in fruit growth is discussed. (Received June 27, 1985; Accepted April 8, 1986)     

Growth cone motility.

Neurons obtain their stereotyped morphologies and connections as a result of growth cone migration. In the past year, studies on growth cone migration and pathfinding have helped to define certain properties of cytoskeletal filaments and cell membranes that may be important in growth cone function. Antisense mRNAs have proved to be particularly useful for examining the roles of specific neurite proteins.     

Growth cone motility.

The exact nature of growth cone motility is far from understood but progress has been made in several areas. It now appears that growth cones pull and not push; we will review the biophysical basis of growth cone movement. Current ideas on the regulation of growth cone motility and the relationship between motility and axon pathfinding are also discussed.     

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     

Growth Regulators in Populus tremula I. Distribution of Auxin and Growth Inhibitors

The content of acid ether-soluble auxins and inhibitors in vegetative tissues of aspen (Populus tremula L.) was determined with the Avena coleoptile straightgrowth assay. A growth promotor, tentativety identified as indol-3-yl-acetic acid, occurred in highest concentration in the growing stem parts. It was also detected in various parts of the roots. Large amounts of inhibitors (inhihitor β) were found in growing stem tissue and in upper mature stem parts. Considerably lower content of inhibitors was found in leaves, in the basal stem part and in the roots. Nonwoody growing roots and the wood of older root segments, especially, contained very smalt quantities of inhibitors. The elution volume of a part of the inhibitory activity on a Sephadex column was similar to that of abscisic acid.     

Growth of Lettuce, Onion and Red Beet. 2. Growth Modelling

Data from a field experiment carried out on growth of lettuce,onion, and red beet were used: (a) to fit logistic, Gompertz,expolinear and ‘Scaife and Jones’ (Journal of AgriculturalScience, Cambridge86 : 83–91, 1976) functions using time,day-degrees and effective day-degrees; and (b) to test a mechanistically-basedmodel that combines the effects of potentially limiting variables,such as temperature and light, and allows for plant zone areain light interception (Aikman and Benjamin,Annals of Botany73 : 185–194, 1994). The use of day-degrees and effective day-degrees instead oftime, in general, improved the fit and gave a better estimateof growth parameters. The best fit was obtained by the Gompertzfunction for lettuce, and by the expolinear function for redbeet and for onion. The expolinear function seemed the mostreliable function in estimating the early relative growth ratewhich is the crucial value in all the mechanistic models. Thezone area model showed very good simulations for lettuce andred beet, but it requires a modification for canopy senescencein onion. Lettuce; Lactuca sativa L. var.crispa ; onion; Allium cepa L.; red beet; Beta vulgaris L. var.conditiva ; growth modelling; logistic; expolinear; Gompertz; zone area; time; day-degrees; effective day-degrees     

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.