New Worlds: The almond tree’s secret weapon

Also in this issue: When the hand is missing.

By
February 13, 2010 18:12
for judy's column

new worlds 88. (photo credit: )

If almond trees want to attract insects to pollinate their flowers, why are they the only known plant to have a powerful poison in their nectar? A University of Haifa study has revealed that bees are nevertheless drawn to the toxic substance, thus the almond tree seems to have developed a unique way of drawing potential pollinators. The researchers, from the departments of environmental and evolutionary biology and science education, speculate that a toxin called amygdalin found in almond-tree nectar is in fact an evolutionary development intended to give that tree an advantage over others in its surroundings.

Previous studies have already shown that amygdalin can be found in almond nectar at a concentration of four to 10 milligrams per liter. In fact, the tree’s subgenus classification is Amygdalus, named after the toxin it produces. For small mammals, it is a deadly substance, and as it is highly concentrated in the seeds of unripe wild bitter almonds, such almonds are also dangerous for human consumption.

Be the first to know - Join our Facebook page.


A group of researchers, headed by Prof. Ido Izhaki and including Prof. Gidi Ne’eman, Prof. Moshe Inbar and Dr. Natarajan Singaravelan, investigated why this plant produces such a potent toxin – a by-product of which is cyanide – in its nectar. They explain that the presence of amygdalin is seemingly incompatible with the nectar’s purpose of attracting insects and thereby contribute to the plant’s reproduction.

The researchers exposed honeybees to plates full of nectar containing varying concentrations of the toxin; they also put out plates of nectar without it. The team first monitored four different amygdalin concentrations, resembling the natural levels of the toxin in almond-tree nectar – 2.5 to 10 mgs/liter. A second experiment monitored much higher levels – 5 to 50 mgs/liter. In both cases, the bees preferred nectar containing amygdalin.

“It is difficult – and sometimes impossible – to determine the workings of evolution, but it is likely that amygdalin is produced in the almond nectar so as to give the almond tree an advantage in reproduction. Based on our observations, we can make a guess at which mechanisms come into play,” Izhaki explains. For example, even though amygdalin is poisonous for mammals, it is not poisonous for insects such as the honeybee, and even produces a stimulant that attracts such insects. Therefore it is possible that the plant produces it to attract potential pollinators. Another possibility is that the almond tree has developed this substance as a form of filter; it repulses “non-expert” pollinators, but gives access to the “experts” that have built up resistance to the toxin.

“Pollinating insects have always been lacking, so plants have had to develop ways to attract those available, in competition with other plants. Otherwise, they will not be able to reproduce. This is more than a hypothesis; it is a very practical theory. For reasons that are not fully clear, there is a significant shortage of bees in the world. The worldwide scarcity of pollinators severely harms agriculture. In California, there are enormous almond groves that will not produce fruit without bees. Due to the scarcity of bees, California almond farmers are forced to import – from as far away as Australia – truckloads of beehives during the almond flowering season,”  Izhaki stated.

WHEN THE HAND IS MISSING

One knows exactly where an object is when saying it is “within the reach of our hand.” But if a person doesn’t have a hand, can he still see the object just where it is? Apparently not, according to neuroscience researchers at the Hebrew University and Hadassah University Medical Center on Mount Scopus in Jerusalem. The space within reach of our hands – where actions such as grasping and touching occur — is known as the “action space.” Research has shown that visual information in this area is organized in hand-centered coordinates – in other words, the representation of objects in the human brain depends on their spatial position with respect to the hand.

According to research just published in Psychological Science, amputation of the hand results in distorted visuospatial perception of the action space. Dr. Tamar Makin, Meytal Wilf and Dr. Ehud Zohary of HU’s Alexander Silberman Institute of Life Sciences and Dr. Isabella Schwartz of the hospital sought to investigate how hand amputations affect visuospatial perception in near space. Volunteers whose left or right hands had been amputated were instructed to look at a central cross on a screen while two white squares were briefly shown to the left and right side of the cross. The volunteers had to indicate which of the squares was farther from the cross.

The results reveal that hand amputations affect visuospatial perception. When the right square was slightly farther from the center, participants with right-hand amputations tended to perceive it as being at the same distance  as the left square; this suggests that these volunteers underestimated the distance of the right square relative to the left. Conversely, when the left square was farther away, left-hand amputees perceived both squares as being equally far away from the center; these participants underestimated the left side of near space. Interestingly, when the volunteers were seated farther from the screen, they were more accurate in judging the distances, indicating that hand amputation may only affect perception of the space close to the body.

The findings suggest that losing a hand may shrink the action space on the amputated side, leading to permanent distortions in spatial perception. According to the researchers, “this shows that the possibility for action in near space shapes our perception – the space near our hands is really special, and our ability to move in that space affects how we perceive it.”

The neuroscientists note that these results have implications for spatial hemineglect – a condition (often following brain injury) in which a patient cannot perceive objects on one side of space. This condition is often associated with paralysis of the hand in the neglected side, which, based on the current study, might exasperate the perceptual neglect.

The authors suggest that “current rehabilitation approaches that emphasize action on the affected side may reverse this process.” For example, encouraging the use of the affected hand or providing visual feedback (through prism adaptation or mirrors) may help overcome hemi-neglect by increasing the size of the action space on the affected side.


Related Content

[illustrative photo]
September 24, 2011
Diabetes may significantly increase risk of dementia

By UNIVERSITY OF MICHIGAN HEALTH SYSTEM

Israel Weather
  • 15 - 27
    Beer Sheva
    18 - 23
    Tel Aviv - Yafo
  • 15 - 23
    Jerusalem
    16 - 22
    Haifa
  • 20 - 36
    Elat
    18 - 28
    Tiberias