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News Article | April 8, 2016

Some cells are meant to live, and some are meant to die. The linker cell of Caenorhabditis elegans, a tiny worm that is a favored model organism for biologists, is among those destined for termination. This cell helps determine the shape of the gonad in male worms--and then it dies, after two days, just as the worms are transitioning from larvae into adults. This programmed cell death is a normal part of the animal's development, yet the genetic and molecular mechanisms underpinning it have not been worked out. Scientists in Rockefeller University's Laboratory of Developmental Genetics, headed by Shai Shaham, had previously shown that the linker cell does not expire by apoptosis, a more commonly studied form of programmed cell death. "Everything about this death process is different from apoptosis," he says. "It looks different under the microscope, it requires different genes, and it has different kinetics." Many ways for cells to die have been observed and described in the artificial milieu of a tissue culture dish, but not in a living organism. Now, the Shaham lab has been able to study the molecular mechanism that causes linker cell death in worms. Their findings, reported in eLife, suggest that the linker cell's newly discovered dying process resembles that which leads to the loss of neurons, or neuronal parts, in people with some neurodegenerative disorders. A new role for an old protein To figure out the molecular processes that cause linker cell death, Shaham's team introduced mutations at random in worms and then searched for animals in which the linker cell survives for longer than normal. They identified a number of mutations that prolong the survival of linker cells, including one that affects the function of HSF-1, a protein known to shield cells from physiological stresses like heat. "It was a big surprise that HSF-1, which typically plays a protective role in the cell, was found to be such a key regulator of this cell death," notes Shaham. His lab found that the protein performs two separate tasks in the cell that are independent from one another. So much so that when worms with a normal, functional HSF-1 were raised at high temperatures, their linker cells survived for longer than they normally do--presumably because the protein was kept busy protecting the cells from the heat, and hence failed to promote linker cell death. HSF-1 kills the linker cell by activating specific components of a protein destruction machinery apparatus in the cell, called the ubiquitin proteasome system. Mutations in components of this machinery have been shown previously to influence the degradation of neuron extensions in Drosophila and mice, suggesting that the new worm pathway may be used broadly. Apoptosis, one form of programmed cell suicide, is well described--scientists know which molecules induce it, which molecules suppress it, and the processes that take place in the cell as it occurs. However, blocking apoptosis in mice appears to have little effect on overall mouse development. "This is a surprising observation, given how prevalent cell death is during growth," Shaham notes. "It suggests that other means of killing cells likely exist that we know little about." Non-apoptotic cell death is also seen in some disease states. In the current study, the researchers found that the process in which linker cells are culled during a worm's development resembles the way brain neurons die during normal development in mice, and in people with Huntington's disease and other neurodegenerative disorders. It is also reminiscent of the neuronal cell death seen when nerve cells get severed, as they do during spinal injuries. Based on their recent findings in worms, Shaham and his coworkers hope to find out whether the human counterparts of the proteins promoting linker cell death in worms might be involved in neurodegeneration. If this turns out to be the case, these proteins might serve as targets for future drugs to slow the progression of Huntington's disease, or to help people regain mobility after a spinal injury. "For example, if we stress the nerve cells while they are dying, so that the HSF-1 protein is forced to go into protective mode rather than cell killing mode, perhaps we can slow their death," speculates Shaham.

Teitel M.,Israel Agricultural Research Organization | Garcia-Teruel M.,Israel Agricultural Research Organization | Alon H.,Besor Experimental Station | Gantz S.,Shaham | And 6 more authors.
Acta Horticulturae | Year: 2014

The use of screenhouses in protected cultivation is nowadays a common practice in many countries. When fine mesh screens are used in the screenhouse construction, the resistance of the screens to airflow is high and ventilation rate is strongly reduced in comparison to the open field. Thus, growers tend to move to higher screenhouses since they assume that in such structures accumulation of warm and humid air near the plants is diminished. The goal of this research was to investigate, in insect-proof screenhouses, the effect of screenhouse height on air temperature. Experiments were conducted in two flat top screenhouses each of an area of 745 m2; one with a roof height of 4 m (LSH) and the other with a roof height of 6 m (HSH) with 16 m of separation between them. The houses were covered with a '50-mesh' screen which is commonly used with tomato cultivation in Israel. The daily courses of air temperature were very similar in the two houses. The average air temperature in the HSH was nearly at all times higher than in the LSH. The largest differences in temperature between the houses, of about 1°C, were observed during day; slightly lower differences were observed during night. The most significant difference between the two houses was related to the vertical gradients of temperature. The results show that the microclimate in the vertical direction appears to be more homogenous in the HSH than in the LSH.

Teitel M.,Institute of Agricultural Engineering | Gahali Y.,Institute of Agricultural Engineering | Barak M.,Institute of Agricultural Engineering | Lemcoff H.,Institute of Soil, Water and Environmental Sciences | And 5 more authors.
Acta Horticulturae | Year: 2012

A major problem confronting Mediterranean greenhouse horticulture is the excess of heat during summer. One of the methods to alleviate the heat load is shading with nets. Shading nets can either be fixed or mobile. They can be external (above the greenhouse) or internal (inside the greenhouse above the crop). Experiments were carried out in a greenhouse in which a tomato crop was grown. The greenhouse was divided into two separated compartments of three spans each. In one compartment a 30% shading net was applied above the greenhouse, on top of the polyethylene cover, while in the other compartment it was stretched horizontally inside the compartment, at gutter height. Solar radiation outside and inside each compartment and light intensity above the crop and at ground level, and air temperature and humidity, in each compartment, were continuously measured over the growing period. The results show that in well ventilated houses net position does not significantly affect the values of the measured parameters and hence has no significant effect on greenhouse microclimate when the shading percentage is 30% or lower.

Silber A.,Institute of Soil, Water and Environmental Sciences | Israeli Y.,Northern R and D | Levi M.,Northern R and D | Keinan A.,Northern R and D | And 8 more authors.
Agricultural Water Management | Year: 2013

The effects of drip irrigation frequency on 'Hass' avocado trees grown in lysimeters were examined. The experimental design comprised three irrigation frequencies: (a) pulsed irrigation (10-20min every 30min) throughout the day (Irg1); (b) one daily irrigation event beginning at night and terminated in the morning every day (Irg2); and (c) one irrigation event every two days (Irg3). Irrigation treatments induced significant differences in water availability in the root zone and in plant water uptake. The effects of the fruit sink on gas-exchange properties and water uptake were assessed by comparing the performance of fruiting and defruited avocado trees. Despite the higher vegetative growth of defruited trees, their daily water uptake was 40% lower than that of fruiting trees and therefore, crop load should play an important role on irrigation scheduling. Measurements of stomatal conductance (gs) and photosynthesis per unit leaf area (A) during two vegetative years were not in accordance with irrigation treatments or with diurnal changes in atmospheric conditions. Similar pattern was observed for the defruited trees. Leaf-carbohydrate concentrations in trees with and without fruits were lowest before sunrise, and increased during the day in different patterns. In defruited trees the carbohydrate concentrations increased steeply to a maximum around 09:00, while in fruiting trees, it increased monotonically until midday. Our findings may indicate that leaf-carbohydrate plausibly play a role in the complex framework of stomata aperture. © 2012 Elsevier B.V.

Silber A.,Israel Agricultural Research Organization | Israeli Y.,Northern RandD | Levi M.,Northern RandD | Keinan A.,Northern RandD | And 6 more authors.
Agricultural Water Management | Year: 2012

The performance of 'Hass' avocado trees grown in lysimeters under different irrigation regimes obtained by manipulating drip irrigation frequency and root volume was examined. The experimental design comprised six treatments (3×2) with three irrigation frequencies and two container volumes (100- and 200-L). The three irrigation frequencies were: pulsed irrigation (10-20min every 30min) throughout the day (Irg1), one daily irrigation event beginning at night and terminated in the morning every day (Irg2) and one irrigation event every two days (Irg3). Irrigation management induced significant differences in water availability in the root zone and subsequently, the diurnal and periodic water uptake. Water uptake of trees in the Irg1 treatment closely followed changes in the meteorological conditions (air temperature, pan evaporation and vapour pressure deficit) while that of trees in the Irg2 and Irg3 treatments was depressed by intermediate and severe water stress, respectively. The experimental treatments had little effect on the vegetative growth, flowering or fruit-set processes. However there were significant treatment differences on fruitlet abscission and accordingly, on fruit yield. Black spots initiated from the seed became apparent on some of the fruits at the beginning of June, and about two weeks later an intensive abscission of fruitlet begun that ended at the beginning of July. The abscission was more intense in the 100-L than the 200-L containers, in the following order: Irg3>Irg2≥Irg1 regardless of the container volume. Net CO 2 assimilation during periods of fruit growth decreased in trees exposed to moderate or severe water stress (Irg2 and Irg3, respectively) and therefore, it is plausible that fruitlet abscission resulted from carbohydrate stress. Improvement of water and nutrient availability, especially in periods where the activity of the root system was weak as a result of low carbohydrate supply presumably played a dominant role in seeds or fruit function. © 2011 Elsevier B.V.

Harari A.R.,Israel Agricultural Research Organization | Zahavi T.,Shaham | Steinitz H.,Israel Agricultural Research Organization
Pest Management Science | Year: 2015

Background: Studies of the mechanisms by which mating-disruption techniques control insect pest populations have traditionally focused on the effects of the species-specific sex pheromone on the male moths, while neglecting possible direct effects of the pheromone on females. Here, the effects of exposure to synthetic species-specific sex-pheromone on Lobesia botrana (European grapevine moth) females were tested. Results: Females in vineyards that were treated with mating-disruption pheromone burst into short bouts of flying more frequently, but called significantly less frequently than females in untreated plots. Reduced calling caused by exposure to the species-specific sex-pheromone may increase the age at which females mate and thereby reduce female fecundity. Females that called in a pheromone-saturated environment experienced a decrease in number of oviposited eggs. A further decrease in reproductive success may occur if females delay oviposition when exposed to access of the synthetic pheromone. Conclusions: In addition to reducing the ability of males to locate females, the mating-disruption technique can suppress pest numbers as a consequence of its direct effects on females. The two mechanisms probably act synergistically. © 2014 Society of Chemical Industry.

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