Major Morphological Changes (major + morphological_change)

Distribution by Scientific Domains

Selected Abstracts

Reproduction and metabolism at , 10C of bacteria isolated from Siberian permafrost

Corien Bakermans
Summary We report the isolation and properties of several species of bacteria from Siberian permafrost. Half of the isolates were spore-forming bacteria unable to grow or metabolize at subzero temperatures. Other Gram-positive isolates metabolized, but never exhibited any growth at , 10C. One Gram-negative isolate metabolized and grew at , 10C, with a measured doubling time of 39 days. Metabolic studies of several isolates suggested that as temperature decreased below + 4C, the partitioning of energy changes with much more energy being used for cell maintenance as the temperature decreases. In addition, cells grown at , 10C exhibited major morphological changes at the ultrastructural level. [source]

Functional morphology of embryonic development in the Port Jackson shark Heterodontus portusjacksoni (Meyer)

K. R. Rodda
The oviparous Port Jackson shark Heterodontus portusjacksoni embryo has a long incubation of 10,11 months during which it undergoes major morphological changes. Initially the egg capsule is sealed from the external environment by mucous plugs in either end of the capsule. Four months into incubation, the egg capsule opens to the surrounding sea water. Fifteen stages of development are defined for this species, the first 10 occur within the sealed capsule, the remaining five after capsule opening to hatching. The functional significance of major definitive characters such as circulation within the yolk membrane and embryo, rhythmic lateral movement of the embryo, external gill filaments, heart activity, internal yolk supplies, egg jelly and the significance of the opening of the egg capsule are described. The egg jelly in the sealed capsule functions to mechanically protect the embryo during early development, however, it eventually creates a hypoxic environment to the embryo as the available oxygen is used up. This generates several physiological challenges to the developing embryo. It is able to overcome these problems by morphological changes such as increasing the effective surface area for gaseous exchange with the development of external gill filaments, fins and extensive circulation in both the embryo and attached external yolk sac. These adaptations become limiting as the embryo grows and respiratory needs outweigh the available oxygen. At this time, the mucous plugs dissolve and the capsule becomes open to the external environment. [source]

Effect of Pasteurization, High-Pressure Processing, and Retorting on the Barrier Properties of Nylon 6, Nylon 6/Ethylene Vinyl Alcohol, and Nylon 6/Nanocomposites Films

L. Halim
ABSTRACT:, This study determined the impact of pasteurization, high-pressure processing (HPP), and retorting on the barrier properties of nylon 6 (N6), nylon 6/ethylene vinyl alcohol (N6/EVOH), and nylon 6/nanocomposite (N6/nano) materials. The pasteurized and high-pressure treated films were coextruded with low-density polyethylene (PE) as the heat-sealing layer. The retorted films were coextruded with polypropylene (PP). Oxygen transmission rate (OTR) and water vapor transmission rate (WVTR) of the samples were measured after pasteurization (75 C for 30 min), HPP (800 MPa for 10 min at 70 C), and retorting (121 C for 30 min) treatments. These were compared with the thermal characteristics and morphologies of the samples using differential scanning calorimetry (DSC) and X-ray diffraction (XRD). Results showed that OTR of N6 and N6/Nano increased after HPP (16.9% and 39.7%), pasteurization (13.3% and 75.9%), and retorting (63.3% and 112.6%), respectively. For N6/EVOH, a decrease in OTR after HPP (53.9%) and pasteurization (44.5%) was observed. The HPP treatment increased the WVTR of N6 (21.0%), N6/EVOH (48.9%), and N6/Nano (21.2%). The WVTR of N6, N6/EVOH, and N6/Nano increased by 96.7%, 43.8%, and 40.7%, respectively, after pasteurization. The DSC analyses showed that the enthalpy and percent crystallinity increased (2.3% to 6.5%) in the N6/Nano when compared with the N6 material after each treatment. Retorting caused a decrease (3.5%) in the percent crystallinity of the polypropylene material. HPP did not cause major morphological changes to the samples. Results of the barrier studies were influenced by the crystallinity changes in the materials as seen in the XRD diffractograms. [source]

MADS-Box Genes Controlling Flower Development in Rice

PLANT BIOLOGY, Issue 1 2003
F. Fornara
Abstract: The separation between monocot and dicot plants occurred about 120 - 180 million years ago and since then major morphological changes have led to the striking differences that can be observed today. To understand whether, despite these differences, the processes controlling flower development are fundamentally comparable in dicot and monocot species, it is necessary to perform comparative studies. However, until recently flower development has been studied mainly in dicot plant species. Genetic and molecular analyses of two dicot model species, Arabidopsis thaliana and Antirrhinum majus, led to the formulation of the ABC model of flower development that describes how the combined activities of three classes of genes are required to drive flower organ development. This model has recently been extended by the inclusion of two other gene classes, namely D and E, which are involved in ovule development, and petal, stamen and carpel development, respectively. Most of the A, B, C, D and E genes identified so far have been shown to encode MADS-box transcription factors. In rice a number of regulatory genes belonging to the MADS-box transcription factor family have been cloned in the last few years and the functions of some of them have been investigated in detail. Here we review the current state of knowledge on rice flower development and focus on MADS-box genes that determine floral organ identity in this species. We compare results obtained in rice with the information known for Arabidopsis and the differences between these two species are discussed. [source]