A passion for plant life

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Polar relaxation by dynein-mediated removal of cortical myosin II

Nearly 6 decades ago, Lewis Wolpert proposed the relaxation of the polar cell cortex by the radial arrays of astral microtubules as a mechanism for cleavage furrow induction (White and Borisy, 1983; Wolpert, 1960). While this mechanism has remained controversial (Rappaport, 1996), recent work has provided evidence for polar relaxation by astral microtubules (Chen et al., 2008; Dechant and Glotzer, 2003; Foe and Dassow, 2008; Murthy and Wadsworth, 2008; Werner et al., 2007), although its molecular mechanisms remain elusive. Here, using C. elegans embryos, we show that polar relaxation is achieved through dynein-mediated removal of myosin II from the polar cortexes. Mutants that position centrosomes closer to the polar cortex accelerated furrow induction whereas suppression of dynein activity delayed furrowing. We provide evidence that dynein-mediated removal of myosin II from the polar cortexes triggers cortical flow towards the cell equator, which induces the assembly of the actomyosin contractile ring. These studies for the first time provide a molecular basis for the aster-dependent polar relaxation, which works in parallel with equatorial stimulation to promote robust cytokinesis

Shortening the juvenile phase for flowering in Kalanchoe pinnata Pers

Plants of Kalanchoe pinnata flower normally at the end of 2 years. Flowering in the juvenile phase (3- and 9-month-old plants) has been induced by application of gibberellin (GA) either to the shoot tip and the youngest pair of leaves, or to the third leaf. Three-month-old plants required more exogenous GA (50 μg/plant) than 9-month-old plants (5 μg/plant). The simultaneous application of the growth retardant (2-chloroethyl)trimethylammonium chloride=CCC via the roots did not interfere with GA-induced flowering but overcame the inhibitory effects produced by a high concentration of GA (150 μg/plant) when applied alone

Retardation of inflorescence development in Calendula officinalis by a morphactin and its application

The morphactin - chlorflurenol at 1, 5, 25, 125 and 625 μg/plant either caused total damage of the shoot apices or allowed a few inflorescences to develop with few or no flowers. The inflorescences arising in the lateral branches showed suppressed bracts and modified flowers. With time the treated plants recovered and showed a significant increase in the growth of laterals and the number of inflorescences. Thus morphactin can be used for prolonging the growth period and for obtaining more wholesome plants

In-vitro induction of aerial leaves and of precocious flowering in submerged shoots of Limnophila indica by abscisic acid

Nodal explants of submerged shoots of Limnophila indica (L.) Druce were cultured in Nitsch's liquid medium containing abscisic acid (ABA, 10-9-10-6 M). At 10-7 and 10-6 M, ABA induced typical aerial leaves (entire, ovate, opposite-decussately arranged) even under submerged conditions and completely suppressed the development of water leaves (pinnately dissected and whorled). Flowers that invariably arise from aerial shoots were induced precociously by ABA even on submerged nodes

Morphogenic potentialities of flower buds of Kalanchoe pinnata Pers. grown in vitro

Excised flower buds of Kalanchoe pinnata Pers. representing two early stages of development (designated sets I and II), were cultured on modified White's medium (WB). They failed to attain full development on WB or on WB containing any of the following supplements: indole-3yl-acetic acid (IAA), 2,4-dichlorophenoxyacetic acid (2,4-D), naphthaleneacetic acid (NAA), kinetin, or coconut milk (CM). A slight stimulation of the growth of corolla was caused by kinetin (10 ppm). IAA (I ppm) and NAA (I ppm) induced rooting from the cut end of the pedicel and from the proliferated torus tissue situated between the sepals and petals. 2,4-D (I ppm) either singly or in concert with CM (10 per cent) stimulated the formation of shoot buds and root growth. Addition of kinetin (I and 10 ppm) to WB favoured shoot formation, but suppressed rooting. Flower buds of set II developed shoot buds more readily than those of set I. Thus, the primordia floral organs present in the immature buds lose their ability for normal morphogenesis under culture conditions. Buds destined to form flowers can be made to revert to vegetative growth

Logical Topology Design Using Efficient Heuristics in Wavelength Routed Networks

Wavelength Division Multiplexed (WDM) point to point networks play a vital role in the backbone transport networks. The set of light paths at optical layer forms a Logical Topology. This paper deals with the design of Logical Topology for wavelength routed WDM networks. This paper proposes new heuristics on fiber optic networks to develop efficient logical topology design and to examine the critical aspects of performance constraints like single hop traffic maximization, Average weighted hop count and number of wavelengths/Transceivers. Further two new heuristics LUMHSN and ILUMHSN are proposed, tested and compared the performances with the existing HLDA on 14-node NSFNET Model. Keywords: wavelength routed WDM, Logical Topology, single hop traffic, Average weighted hop Count, LUMHSN, ILUMHSN

Parsec-scale jet properties of the gamma-ray quasar 3C 286

The quasar 3C~286 is one of two compact steep spectrum sources detected by the {\it Fermi}/LAT. Here, we investigate the radio properties of the parsec(pc)-scale jet and its (possible) association with the $\gamma$-ray emission in 3C~286. The Very Long Baseline Interferometry (VLBI) images at various frequencies reveal a one-sided core--jet structure extending to the southwest at a projected distance of $\sim$1 kpc. The component at the jet base showing an inverted spectrum is identified as the core, with a mean brightness temperature of $2.8\times 10^{9}$~K. The jet bends at about 600 pc (in projection) away from the core, from a position angle of $-135^\circ$ to $-115^\circ$. Based on the available VLBI data, we inferred the proper motion speed of the inner jet as $0.013 \pm 0.011$ mas yr$^{-1}$ ($\beta_{\rm app} = 0.6 \pm 0.5$), corresponding to a jet speed of about $0.5\,c$ at an inclination angle of $48^\circ$ between the jet and the line of sight of the observer. The brightness temperature, jet speed and Lorentz factor are much lower than those of $\gamma$-ray-emitting blazars, implying that the pc-scale jet in 3C~286 is mildly relativistic. Unlike blazars in which $\gamma$-ray emission is in general thought to originate from the beamed innermost jet, the location and mechanism of $\gamma$-ray emission in 3C~286 may be different as indicated by the current radio data. Multi-band spectrum fitting may offer a complementary diagnostic clue of the $\gamma$-ray production mechanism in this source.Comment: 9 pages, 4 figures, accept for publication in MNRA