Why are there “dew drops” at the tips of leaf veins?

Why are there “dew drops” at the tips of leaf veins?

❦ Have you ever seen clear orbs of water glisten along a leaf edge? You may have mistaken them for dew drops, which are caused by moisture from the air condensing on cool surfaces. But these drops are only found at the edges of leaves and if you look around- they won’t be found on dead leaves. So what are they?

❦ Plants use a plumbing system of xylem tubes to move water and nutrients. During the day, transpiration (water evaporation) from leaves creates a vacuum that pulls the column of water up from the roots to the leaves. At night, the stomata (leaf pores) close, transpiration stops and salts accumulate in the xylem of roots, drawing in water from the surrounding soil by osmosis. The excess water rises up the xylem tubes and is forced out at the leaf tips through openings called hydathodes. This exudation of plant sap is known rather inelegantly as guttation, and only happens at night. The water pressure is not strong enough to rise beyond 3 feet, so guttation is not seen on tree leaves. The thermal image (inset) taken by infrared photography shows the cooler temperature (blue) in the guttation droplets.

❦ When the drops dry, they sometimes leave behind a residue of salts and minerals. This is not a problem, unless the soil is over-fertilized resulting in fertilizer burn of leaf tips. In the same way, guttation droplets in corn seedlings were shown to have high levels of neonicotinoid compounds, used as pesticidal coatings on the seed. These concentrations could be a lethal dose for honey bees that sip on guttation drops as a water source. While shedding toxins through guttation drops protects the plant, it may have repercussions – both beneficial and harmful, on insects and other animals. 

Inset of thermal image: http://thermal-imaging-blog.com/index.php/page/13/#.Vq1LIvkrLcs

REF on neonicotinoids in guttation droplets #openaccess: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4284396/

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Desmid Dividing!

A desmid is a single-celled algae

And then there were two! Watch this mesmerizing time lapse video of a desmid dividing. Desmids are single celled, microscopic algae that are beautifully symmetrical. Each cell has two half-cells connected in the middle by the cell nucleus.

Did you know? Desmids thrive in clear, nutrient-poor and unpolluted fresh water. They are considered an “indicator species” of water quality because they disappear when water turns murky.

Credit Dr. Jeremy Pickett-Heaps

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Something smells!

Did you know that smell receptors are sniffing out cues and signals all over our body, not just in the nose? Watch Jen Pluznick, my lab neighbor at Johns Hopkins University, explain the weird facts about smells in this TEDMED talk. 

Do you have a gut feeling that this could be important? You could be right! Jen has discovered smell receptors in the kidney that appear to be responding to chemicals from gut bacteria that end up regulating blood pressure. Read more on the story here: https://goo.gl/AyBFE6

 
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Denmark: one week, two conferences

Denmark: one week, two conferences

The first was on acid-base regulation and proton transport, 49th in a series that was first organized by legendary Danish scientists Hans Ussing and Nobelist Jens Skou. The Ussing chamber is a classical apparatus used to measure electrical current across a layer of cells known as epithelium, as a proxy for the ions that are transported in and out of the cells. Skou discovered one of the most important of these transporter proteins, known as the sodium pump. The meeting was held at the historic Sandbjerg estate, near Sonderburg, which dates back to the 16th century and eventually ended up with the family of author Isak Dinesan (real name, Karen Blixen) of Out of Africa fame (http://www.sandbjerg.dk/en/). It is now owned by Aarhus University, to the enjoyment of lucky researchers! The second conference was to celebrate the achievements of a colleague, Poul Nissen, structural biologist extraordinaire, of Aarhus University. Poul received the Novo Nordisk prize for his beautiful atomic structures of ion pumps, including the sodium pump that was discovered by Jens Skou. We stayed at Norsminde Kro (Kro=inn) and the science talks were at Mosegaard museum. Back to Aarhus, where the sun barely sets, before heading back home.

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Yesterday, on Earth Day, tens of thousands of scientists and science enthusiasts across the world took to the…

Yesterday, on Earth Day, tens of thousands of scientists and science enthusiasts across the world took to the streets to march for science in an unprecedented show of solidarity. We came wearing white lab coats, pink knit brain caps and costumes. We sang, chanted and cheered. We carried signs that were prophetic, political, nerdy, funny, witty and even obscure. Here are some of my favorite signs and photographs from various marches. Thanks to Chris Robinson for marching with me in Chicago, where we were both attending our respective science conferences, and taking some great photographs. Tell us if you marched (and where) and feel free to post photos of your favorite signs in the comments!

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Earth Day: When is Green NOT Good?

Algal Art What is the mysterious 3D whorl in this latest addition to Art or Science ? Look closer and there seems to be a scratch in top center..and is that a white speck of dust marring your monitor?

You may be surprised to learn that these delicate green swirls are an aerial view of a giant algal bloom floating in the Baltic Sea, captured by the orbiting satellite Sentinel-2A. The white speck heading into the “eye of the storm” is a ship. You can see the ship’s “wake”, caused by the propeller’s cutting through the floating algae as a straight dark line.

Annie, Fannie and Mike: They seem friendly enough, but these are actually nicknames for three types of cyanobacteria that account for the vast majority of algal blooms world-wide: Anabaena, Aphanizomenon, and Microcystis. Caused by eutrophication of water from fertilizer dumping, what could be bad about these temporary blooms of harmless sounding photosynthesizing microorganisms?  “Annie” and “Fannie” produce toxins that attack your nervous system. “Mike” makes microcystin, one of the most potent toxins on the planet. Even inhaling a few droplets of contaminated water can make you nauseous and dizzy, and larger doses kill. They grow best in warm water with lots of nutrients. Thanks to warming climate and fertilizer run offs, algal blooms are on the rise, starting as early as March and April.

As algal blooms grow, others die. Bacteria divide quickly, using up the oxygen supply. Fish and aquatic life are starved of oxygen. This leads to dead zones. Scientists are combating algal blooms through innovative strategies. One way is artificial destratification by mixing up upper, warm layers with deep, cooler water using propellers. This effectively starves algae and cyanobacteria of nutrients and light. Another way is biomanipulation by introducing aquatic plants that compete with algae or predatory fish that eat other plankton eating fish. Sadly, support for this research is at an all time low. That’s why we #MarchForScience today. Show your support for #EarthDay and support science!

 

Source: http://www.esa.int/spaceinimages/Images/2015/09/Eye_of_an_algal_storm

 
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Olympic Gold..or….Green?

Olympic Gold..or….Green?

♒ We know that green is Brazil’s favorite color, and the Olympics are trying to Go Green for the environment, but even so, the overnight change in color of the Olympic swimming pool from an azure blue to murky green took scientists and sportsmen by surprise. While officials hastened to assure athletes that the green waters posed no health threat, the mystery caused much speculation. Caipirinha-flavored Soylent? Stiffed by Trump’s pool cleaning service? Who peed in the water?

♒ “Midafternoon, there was a sudden decrease in the alkalinity in the diving pool, and that’s the main reason the color changed,” said Mario Andrada, a Rio 2016 spokesman. So, the pool became more acidic. But acidic water is not green. There are two likely explanations: first, excess copper in the water can turn it green, but not murky. The latter is caused by a sudden and rapid growth of algae, triggered by the warm weather, lack of wind, insufficient chlorine and ineffective filters.

♒ Algal spores can enter the water inadvertently, carried by wind, rain and contaminated swimsuits. When the conditions are right, they can “bloom” overnight. Because these algae are visible only under the microscope, there must be millions of them in the water to change the pool color from blue to green. One way to deal with them, after normalizing the pH, is *superchlorination*—aka shocking them with high levels of chlorine. Not all the Olympians are complaining: Canadian divers said that the contrast with the sky helped them win the bronze.

♒ Pix: The Olympic diving pool on August 8 (left) and the Olympic diving pool on August 9 (right) Image: AP

#rioolympics2016   #swimming  

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Eye See You: Moving Retina in Jumping Spiders

Eye See You: Moving Retina in Jumping Spiders

⦿ Jumping spiders (Salticidae) don’t use a web to catch prey. Instead they locate, stalk and mount a jumping ambush when they are 1-2 cm away. To do this, they need to detect and then evaluate objects so they don’t confuse a potential mate as prey! Fortunately, jumping spiders have among the sharpest vision among invertebrates.

⦿ Unlike insects, spiders don’t have compound eyes. Instead their 8 “simple” eyes point forward (for high focus) and sideways (to detect motion). Strategically, this is similar to the division of labor in our eyes: we detect peripheral vision at the edges of our retina with low resolution but wide field of view, and sharp images at the fovea in the center of the retina, which is packed with a high density of vision receptors, but has a limited field of view. Since the spider’s large central eyes are set close together and have a limited field of view, they must be moved to point the fovea towards the object. How do they do this?

⦿ Involuntary leg movements are triggered by stimuli from the lateral eyes to reposition the body. However, the spider cannot swivel its whole eyeball as we do, because the lens is built into the carapace, or outer skeleton. Instead, a set of six muscles moves the retina: up and down, sideways and rotationally, while the lens stays fixed. In a transparent spider, you can see the unusual movements of the retina in the tube-like principle eyes. Just one more addition to the cuteness quotient of these tiny spiders! 

REF: M.F. Land (1969) Movements of the retinae of jumping spiders (Salticidae: Dendryphantinae) in response to visual stimuli. http://jeb.biologists.org/content/jexbio/51/2/471.full.pdf

Video Source: Yellow amycine jumping spider from Ecuador, https://www.youtube.com/watch?v=gvN_ex95IcE

GIF Source: http://gph.is/1n7n4aR

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