Chloroplast Differentiation in Tomato Root Galls Induced by the Root Knot Nematode Meloidogyne incognita

Primary roots of tomato, Lycopersicon esculentum cv. Marglobe, were cultured aseptically on agar containing a standard nutrient formulation with or without kinetin. When secondary roots developed, cultures were inoculated with the root-knot nematode, Meloidogyne incognita. Following inoculation, the cultures were divided into two groups which were incubated either in total darkness or in 16-h light-8-h dark cycles. At 24 h, 1, 2, 3, and 4 wk after incubation, roots from all cultures were processed for transmission electron microscopy. Fine structural observation of the parenchyma tissue in galls from the inoculated cultures indicated that starch containing plastids or amyloplasts, which are usually present and remain undifferentiated in these root cells, developed into chloroplasts. These chloroplasts contained a membrane system indistinguishable from those found in leaves of intact plants. Although plastid development was not affected when uninoculated cultures were incubated in the light, differentiation of the amyloplast was induced when roots were cultured on the medium containing kinetin. These results suggest that plastid differentiation in the inoculated tissue may be influenced by an accumulation of kinetin in the gall, which is induced by the nematode and serves as the nutrient sink for its feeding.     

Inhibition of Syncytia Formation and Root-knot Nematode Development on Cultures of Excised Tomato Roots

Two different defined growth media were used to culture aseptically the root-knot nematode, Meloidogyne incognita, on excised roots of tomato, Lycopersicon esculentum cv ''Marglobe.'' One of these media, STW, was a formulation by Skoog, Tsui, and White and the other, MS, a formulation by Murashige and Skoog. From 1 through 4 weeks, inoculated tissues were fractured to observe root infection, giant-cell formation, and nematode development with the scanning electron microscope (SEM). Four weeks after inoculation, the fresh weights of roots and developmental stages of nematodes were recorded. SEM observations indicated that roots cultured on the STW medium had normal growth and infection sites with galls that supported the development of mature females by 4 weeks. Roots cultured on the MS medium were less vigorous and had infection sites with galls containing only one to four syncytialike cells that did not support the development of mature females. Eighty percent of the larvae infecting roots cultured on the MS medium failed to develop into mature females. To determine which factor(s) affected root growth and nematode development, inoculated and uninoculated roots were grown on media consisting of different combinations of the organic and inorganic fractions of the STW and MS formulations. These experiments indicated that the organic fraction of STW was essential for normal root growth; however, the inorganic fraction of MS inhibited normal gall formation and nematode development. Further testing of the inorganic fractions revealed that the high concentration of ammonium nitrate in the MS medium was a factor that inhibited giant-cell formation and nematode development.     

Nucleic acid fragmentation on the millisecond timescale using a conventional X-ray rotating anode source: application to protein–DNA footprinting

Nucleic acid fragmentation (footprinting) by ·OH radicals is used often as a tool to probe nucleic acid structure and nucleic acid–protein interactions. This method has proven valuable because it provides structural information with single base pair resolution. Recent developments in the field introduced the ‘synchrotron X-ray footprinting’ method, which uses a high-flux X-ray source to produce single base pair fragmentation of nucleic acid in tens of milliseconds. We developed a complementary method that utilizes X-rays generated from a conventional rotating anode machine in which nucleic acid footprints can be generated by X-ray exposures as short as 100–300 ms. Our theoretical and experimental studies indicate that efficient cleavage of nucleic acids by X-rays depends upon sample preparation, energy of the X-ray source and the beam intensity. In addition, using this experimental set up, we demonstrated the feasibility of conducting X-ray footprinting to produce protein–DNA protection portraits at sub-second timescales.     

Lipid products of PI(3)Ks maintain persistent cell polarity and directed motility in neutrophils

In gradients of external chemo-attractant, mammalian neutrophilic leukocytes (neutrophils) and Dictyostelium discoideum amoebae adopt a polarized morphology and selectively accumulate lipid products of phosphatidylinositol-3-OH kinases (PI(3)Ks), including PtdIns(3,4,5)P(3), at their up-gradient edges; the internal PtdIns(3,4,5)P(3) gradient substantially exceeds that of the external attractant. An accompanying report presents evidence for a positive feedback loop that amplifies the gradient of internal signal: PtdIns(3,4,5)P(3) at the leading edge stimulates its own accumulation by inducing activation of one or more Rho GTPases (Rac, Cdc42, and/or Rho), which in turn increase PtdIns(3,4,5)P(3) accumulation. Here we show that interruption of this feedback by treatment with PI(3)K inhibitors reduces the size and stability of pseudopods and causes cells to migrate in jerky trajectories that deviate more from the up-gradient direction than do those of controls. Moreover, amplification of the internal PtdIns(3,4,5)P(3) gradient is markedly impaired by latrunculin or jasplakinolide, toxins that inhibit polymerization or depolymerization of actin, respectively. Thus reciprocal interplay between PtdIns(3,4,5)P(3) and polymerized actin initiates and maintains the asymmetry of intracellular signals responsible for cell polarity and directed motility.     

Some ways to improve QTL mapping accuracy

In this paper, we review some approaches for QTL mapping developed by our research group in collaboration with, following the recommendation of, or under inspiration of Moshe Soller. Specifically, we explain at a simple intuitive level the main principles and ideas of: (a) QTL mapping by fractioned DNA pooling, (b) increasing the detection power of QTL mapping (in the case of individual genotyping) by multiple-trait analysis, and (c) the role of variance-covariance effects in QTL mapping. On each of these themes we had long and deep discussions with Soller on the statistical aspects of the proposed procedures. We hope that together we made important contributions towards making QTL mapping procedures easier and more effective.     

A Role of the Gelatinous Matrix in the Resistance of Root-Knot Nematode (Meloidogyne spp.) Eggs to Microorganisms

The survival of eggs of the root-knot nematode Meloidogyne javanica was studied in a series of experiments comparing the infectivity of egg masses (EM) to that of separated eggs (SE). The EM or SE were placed in the centers of pots containing citrus orchard soil and incubated for 24 hours, 10 days, or 20 days. Following each incubation time, 10-day-old tomato plants were planted in each pot, and 3 to 4 weeks later the plants were harvested and the galling indices determined. In the EM treatments, galling indices of ca. 4.0 to 5.0 were recorded after all three incubation periods; in the SE treatments, the infectivity gradually declined to trace amounts by 20 days. Incubating EM and SE for 2 weeks in four different soil types showed the same pattern in all the soil types: EM caused heavy infection of the test plants while the infection rate from the SE was extremely low. Incubating EM and SE in soil disinfested with formaldehyde resulted in comparable galling indices in most treatments. In petri dish experiments, 100 mg of natural soil was spread at the perimeter of a Phytagel surface and EM or SE of M. incognita were placed in the center. Light microscopy revealed that within 5 to 10 days the SE were attacked by a broad spectrum of microorganisms and were obliterated while the eggs within the EM remained intact. Separated eggs placed within sections of gelatinous matrix (GM) were not attacked by the soil microorganisms. When selected microbes were placed on Phytagel surfaces with EM of M. incognita, electron microscopy demonstrated that at least some microbes colonized the GM. As the major difference between the EM and the SE was the presence of the GM, the GM may serve as a barrier to the invasion of some microorganisms.     

Re-drawing the Maps for Endemic Mycoses

Mycopathologia - Endemic mycoses such as histoplasmosis, coccidioidomycosis, blastomycosis, paracoccidioidomycosis, and talaromycosis are well-known causes of focal and systemic disease within...