Comparison of Horizontal Spread of White Clover (Trifolium repensL.) Grown Under Two Artificial Light Sources Differing in their Content of Blue Light

The effects of blue light on the growth and development of differentbranches were studied to determine if variations in the bluelight supply modified the horizontal spread of white clover.Cuttings of white clover (‘Huia’) were grown for56 d in two controlled chambers under conditions similar exceptfor level of blue light (BL). The horizontal spread of whiteclover was characterised by the phyllochron, internode lengthand branching or flowering of different axes. The responsesto a reduction in BL were different according to axis degree:(1) on the main axis, lowering BL slightly decreased the phyllochronand had no effect on internode length or stolon length; (2)on older primary branches, it decreased their phyllochron, butreduced stolon length due to a reduction in internode length;(3) on secondary branches, it increased the phyllochron anddecreased internode length, triggering a strong reduction instolon length (up to 54%). Moreover, an increase in BL reversedthese effects. The switch to lower BL or higher BL had no effecton internode length of primary branches, but triggered changesin internode length of the main axis. These differential effectsof variations in BL on the morphogenesis of different branchesare discussed in relation to the clonal integration of variationsin light composition. Changes in the horizontal spread of whiteclover induced by BL could play a role, combined with responsesto low red:far-red ratio and low photosynthetic photon flux(PPF) in the strategy of horizontal colonisation and shade-avoidanceof white clover.Copyright 1998 Annals of Botany Company Blue light, branching, horizontal spread, morphogenesis, phyllochron, plant development, plant morphology, stolon growth,Trifolium repensL., white clover.     

On the races of Arenaria tetraquetra L. (Caryophyllaceae)

FAVARGER, C. & NIETO FELINER, G., 1988 On the races of Arenoria tetraquetra L. (Caryophyllaceae). The caryological study of some Betic populations of Arenaria tetraquetra northwards from Sierra Nevada has proved that they are polyploids ( 3x, 4x, 5x ). Even though their Rowers are pentamerous, they differ from the Nevadean Arenaria tetraguetra subsp. amabilis (2x ) not only by the chromosome number but also by the micromorphology of the seed coat and the hairiness of the stem internodes. They also differ from Arenaria tetraquetra subsp. tetraquetra , the Rowers of which are tetramerous and the degree of polyploidy higher (6x in the Pyrenees, 7x in the Sierra de Pela eastwards from Sierra de Guadarrama). The authors proposed to give a subspecific status to such Betic polyploid populations with a new combination. They suggest a hypothesis to explain the evolution of the A. tetraguetra polyploid complex.     

<Emphasis Type="Italic">De novo</Emphasis> Synthesis of Transfer and 55 RNA<Superscript>1f</Superscript> in Cleaving Sea Urchin Embryos

SIGNIFICANT changes in RNA metabolism have been described during early sea urchin development. Until recently the only detectable class of RNA synthesized during cleavage stages was that with a low G + C base composition and heterogeneous sedimentation properties (DNA-Jike RNA)¹. The genes for nucleolar ribosomal RNA (26S and 18S) were believed to become active only following gastrulation^2–4 and the products of nuclear transfer RNA (4S) genes were first detected at the mesenchyme blastula stage⁵. Any label in the 4S region of sucrose gradients of RNA from the cleavage stages of embryogenesis was interpreted as reflecting the turnover of the pCpCpA region of pre-existing transfer RNA (tRNA) molecules.