When a beam of light hits your eye, a chain of events is set off that is really quite amazing. Kendall J. Blumer (Washington University School of Medicine) describes a little of it in the Jan. 1 issue of Nature.1 You don’t have to understand the following description; just be glad you don’t have to operate your retina in manual mode:Light streaming into the eye is detected by specialized neurons (photoreceptors) in the retina. In response to light, a coordinated series of molecular events � the so-called phototransduction cascade � is triggered in these cells (Fig. 1). Photons excite pigment-containing proteins called rhodopsins, which then switch on the protein transducin by loading it with the small molecule guanosine triphosphate (GTP). When bound to GTP, transducin turns on a phosphodiesterase, an enzyme that breaks down cyclic guanosine monophosphate (cGMP � another small molecule). High concentrations of cGMP open specialized ion channels in the outer cell membrane. Thus, by reducing the concentration of cGMP, light changes the flow of ions across the membrane of photoreceptive neurons, producing an electrical signal that is necessary for communicating with the brain. (Emphasis added in quotes.)Now that’s just to turn the signal on. When the light stops, it needs to be turned off quickly. Normally, it would take too long for this process to reverse, but the retina has a standard procedure that takes care of it:But this presents a problem. Photoreceptor cells can turn off in less than a second in response to a brief flash of light. In contrast, the hydrolysis of GTP by transducin requires tens of seconds to complete, making it difficult to understand how such a mechanism could account for the rapid turn-off of photoreceptor cells. To get around this problem, photoreceptor cells possess a protein called regulator of G-protein signalling 9 (RGS9) that accelerates transducin’s ability to hydrolyse GTP.Blumer describes what happens when a person has a defect in this accelerator protein. It can take tens of seconds to adjust to a bright room when walking out of a theater. It can take tens of seconds to see when driving into a dark tunnel. And perhaps the worst of all (for Rose Bowl fans): “Moreover, people with this problem also suffer from difficulties in seeing certain moving objects (such as balls thrown during a sporting event).” Having one such accelerator protein would be amazing enough, but now – the rest of the story: “RGS9 is one of nearly 30 such RGS proteins, which regulate signalling by hundreds of receptors coupled to transducin-like G proteins in cell networks of the nervous, cardiovascular, sensory and immune systems.”Kendall J. Blumer, “Vision: the need for speed,” Nature 427, 20 – 21 (01 January 2004); doi:10.1038/427020a.We need to know things like this to avoid taking our bodies for granted. This one deserves a little pondering. Do some simple experiments; see how quickly your eye adjusts to different light levels, and think about all those little protein machines knowing just what to do on cue. Poor Charlie. The eye as he knew it was enough to give him cold shudders. In 1859, biochemistry was not even a science yet. Charlie must be approaching absolute zero by now. A book preceding The Origin of Species by about 2900 years, by a wiser man (Solomon), makes a lot more sense after reading the above description: “The hearing ear and the seeing eye, The LORD has made them both” (Proverbs 20:12).(Visited 13 times, 1 visits today)FacebookTwitterPinterestSave分享0
They follow the sun, but how? Scientists are just finding out the mechanisms behind light tracking in sunflowers.According to New Scientist, the mystery of why some sunflowers track the sun across the sky has been solved. But what a solution! Notice the observations needing to be explained:Growing sunflower plants face the sun at sunrise and point the opposite direction at sunset.During the night, they turn around, ready for the next sunrise.When mature, the flowers stop tracking the sun and just face the sunrise.You can’t trick them to follow a 30-hour cycle with artificial lights. They refuse to move.When artificial lights keep a 24-hour cycle, the sunflowers again move with them.“I’m continually astonished at how sophisticated plants are,” says Stacey Harmer of UC Davis, lead author of experiments. “They’re really masters of coping with the environment.” Sun tracking is called heliotropism. But how do plants know direction without eyes? How do they keep time without clocks?Actually, sunflowers have clocks. All organisms do. In plants, they consist of proteins that interact on a 24-hour cycle in a feedback loop with genes that express them. That’s why a different light cycle doesn’t work. Somehow, they can tell if the artificial day is too long, and they’ll stop moving. You can turn potted plants around, but you can’t fool them. The research is published in Science.How is the light linked to growth? Using markers on the stems, Harmer’s team observed the shaded side of stems growing faster than the sunlit side. Sunlight apparently breaks down growth hormones, causing the stem to bend toward the light. That doesn’t explain, though, how the plant turns back to the east during the night. Gene expression tied to the circadian clock takes care of this in the absence of light cues. PhysOrg says,“The plant anticipates the timing and the direction of dawn, and to me that looks like a reason to have a connection between the clock and the growth pathway,” Harmer said. This behavior of sunflowers had been described by scientists as far back as 1898, but no one had previously thought to associate it with circadian rhythms.It’s astonishing that something everyone has noticed for centuries is just getting explained in 2016. Millions of students have played with plants and light in school for a long time. Observing something, though, is not the same as explaining it. Even so, it doesn’t appear Harmer’s team has it all figured out. They mainly established two things:Here we show that heliotropism in the common sunflower, Helianthus annuus, is generated by the coordinate action of light-signaling pathways and the circadian clock and enhances plant performance in the natural environment.But why does the mature sunflower face east at sunrise and stop tracking the sun all day? The researchers found that east-facing flowers got about five times more pollinators than flowers they turned to face west. Insects seem to like the warm flowers, too, even when they were heated artificially. So it makes sense for the flowers to catch the morning swarm, but why not all day? Two possible reasons were found: one is that the plant reaches its maximum height, so that stems stop growing. Another is that the plant shifts its sensitivity to certain wavelengths of light when mature.The authors summarize their findings:Circadian oscillators enhance fitness by coordinating physiological processes with predictable changes in the environment. Our findings demonstrate that such effects accrue in part through the coordinate regulation of directional growth by environmental response pathways and the circadian oscillator. Such coordination generates the heliotropic movement of young sunflowers, enhancing plant growth, and also leads to the eastward orientation of blooming sunflower disks, promoting a key component of reproductive performance.They credit Charles Darwin with being the first to recognize phototropism. He published a book on The Power of Movement in Plants in 1880. Certainly many a farmer or observant person had noticed the phenomenon long before Darwin did. “Heliotropism, or solar tracking, is a more dynamic form of phototropism, with aerial portions of the plant following the Sun’s movement throughout the day.”Genes, clocks, enzymes — that’s a lot of complexity to regulate this wonder of nature. Sunflowers could do just as well by pointing to the sunrise and staying put. That would be simpler. “Ah,” the Darwinian will say, “but those that follow the sun would be warmer and attract more pollinators.” Look; observing a benefit does not explain how the benefit arrived. How did a blind plant without a brain originate proteins and enzymes that can keep time? How is the circadian rhythm calibrated? How do the enzymes respond to certain wavelengths of light, and not others? Why does the plant follow the sun before the flowers open to be pollinated? Why doesn’t the mature flower track the sun all day to stay warm for pollinators? Heliotropism is costly to the plant. Things don’t just happen; they need to be explained at a detailed level.The simplistic Dar-wine story dulls the senses. It gives a warm feeling of having explained something when it explains nothing. In fact, none of the 3 articles cited here referred to evolution or natural selection at all. Harmer’s team just did good old-fashioned experimentation on the plants. They figured out a few things, but not everything. A simple sunflower is enough to astonish a PhD with its sophistication. That’s the real finding in this story.(Visited 189 times, 1 visits today)FacebookTwitterPinterestSave分享0
Musa Mkalipi Seventy free call lines have been installed by the City of Cape Town in disadvantaged areas.(Image: City of Cape Town) The free call lines are located in municipal buildings such as housing offices, cash offices, libraries and community facilities.(Image:790tv)MEDIA CONTACTS• Emma PowellCity of Cape TownExecutive support to mayoral committee+27 21 400 4331Some 70 free call lines have been installed by the city of Cape Town in outlying areas and disadvantaged communities in an effort to bring services closer to residents. The lines can be used by residents to contact the city with queries or requests about services such as accounts, refuse collection, illegal dumping, water leaks, sewer blockages, street lights, pot holes and damaged roads.“The purpose of the free call lines is to improve service delivery by increasing access to the city’s call centre,” explains Demetri Qually, the mayoral committee member for corporate services. “We are extending the network of free call telephones to areas where low volumes of service complaints and requests are currently being registered.”This, he says, is due to a lack of cellphone airtime or available telephone lines in these areas. Located in Cape Town’s customer relations department within its corporate services directorate, the call centre helps residents as well as businesses.The free call lines are located in municipal buildings such as housing offices, cash offices, libraries and community facilities. But after criticism from residents that these offices were not open 24 hours a day, the city changed tack. “The customer relations department then created the free call lines that give access to service delivery without having to dedicate a full-time resource to the Strand Offices,” explains Emma Powell, executive support to mayoral committee.When a call is made using a free call line – simply by lifting the receiver – the caller is automatically connected straight to the call centre, where an agent responds to the customer’s query or complaint. Complaints are logged by means of the city’s service request system. The customer receives a reference number to follow up his or her query. There is no cost to the caller.“The lines connect directly with the city’s call centre number, and residents are encouraged to report faults, register complaints and make enquiries at no cost to them. They will also now receive an acknowledgement SMS with a reference number for follow up,” Qually says.Complaints are tracked by a specialised monitoring team. They are uploaded on to an integrated virtual dashboard which is monitored by the management teams in the respective departments.Lines have been installed in suburbs such as Athlone, Atlantis, Belhar, Lwandle, Mitchells Plain, Gugulethu and Phillipi, among others. Qually says that in a city as large as Cape Town, residents are encouraged to help in identifying municipal problems for response and maintaining a high standard of service delivery.The first free call lines were installed in July 2009, the first four of which were in the Strand municipal offices in Lwandle and Khayelitsha. Cape Town receives an average of 50 000 calls annually, mostly coming from disadvantaged areas.Call centre hours for corporate issues are from 7am until 9pm, while water and electricity centres are open 24 hours.Service delivery and educationCape Town has also worked to bring emergency services closer to the people, especially those in disadvantaged areas. Its 107 single emergency telephone number is a toll free number that visitors and residents can call to ask for help when their lives or property are in danger.Emergency calls such as for police, medical, traffic, and mountain and sea rescue go through 107. All calls to this number are answered within 10 to 20 seconds, the city says, and services are available seven days a week throughout the day. Callers can choose to be helped in English, Xhosa or Afrikaans.The 107 communication centre has been running since 2000, staffed by professional call agents to help callers with emergencies. According to The Guardian, a monthly community publication, the city’s mission is to enhance residents’ quality of life by handling all calls for service in a prompt, courteous, professional and correct manner.When a call is made on the 107 number, the emergency communication centre is able to see where the call is coming from and the telephone number that is used. The call is then directed to the relevant police, fire or ambulance service.The city holds annual public awareness and education programmes to teach people about the number, to eliminate abuse of emergency numbers. These programmes are presented at schools, libraries as well as community events. The line’s mascot, Wally 107, travels around the city educating children about the emergency toll free number. In 2010, for example, Wally visited over 120 school pupils in Western Cape.
30 April 2014The sixth edition of the Bridge Cape Pioneer Trek international mountain bike stage race is set to be the best yet in the history of the event, which has been accorded UCI status by world cycling’s governing body.The event’s elevated status means it will attract more big-name professionals when it takes place from 12 to 18 October. As a UCI-graded race, standards relating to the racing end of the field, including the amount of prize money amount and depth, as well the awarding of UCI rankings points to top finishers, is assured.DistanceCovering 550 kilometres in seven days and taking in three different eco-regions of South Africa’s Western Cape province – the Great Karoo, the Klein Karoo and the Garden Route – the event includes the richest single stage in all of mountain bike racing.Although the route for the 2014 edition of the race is set to be announced by the end of next month only, it will still include the event’s trademark mountaintop finish of stage two, the Queen Stage, which will see the riders ascend the formidable, majestic Swartberg Pass.Equal prize moneyThis will be the first year that the first women’s team to the summit finish will receive the same prize money as the men.Bridge, the event’s title sponsor, has committed a total of R250 000 (about $25 000) to the stage, with the first men’s and women’s teams each receiving R125 000 (about $12 500).‘Absolutely delighted’“I’m absolutely delighted about the news of the equal prize money on the big mountain-top finish stage,” said Swiss marathon champion, Ariane Kleinhans, who, with RECM teammate Anika Langvad, won the event’s Queen Stage and the women’s race overall in 2013, said in a statement.“It is a demonstration of the organisers’ respect towards us ladies’ performances and their motivation to increase female participation in our great sport. Equal prize money will attract more top riders to the race and push us to a higher level. Us ladies will definitely do our best to make it an exciting race,” she added.‘Even more rider-focusedCarel Herholdt of Dryland Event Management, the company that founded and manages the event, commented: “Each year we fine-tune the Bridge Cape Pioneer Trek to be even more rider-focused,” said Carel Herholdt of Dryland Event Management, the company that founded and manages the event.“At the Bridge Cape Pioneer Trek, our focus is on quality, not quantity. Our stages aren’t long just for the sake it. They’re designed to offer as much reward as they offer challenges. They’re real mountain-biking routes that include some of the Karoo and Klein Karoo’s greatest natural spectacles.”SAinfo reporter
Unseeded pair Sam Stosur and Zhang Shuai defeated second seeds Timea Babos and Kristina Mladenovic 6-3 6-4 to claim the women’s doubles title at the Australian Open on Friday.Australian Stosur, who has a history of suffering attacks of nerves in front of home fans, struggled to serve out the match at Rod Laver Arena and double-faulted on match point.But she and China’s Zhang held on and claimed the win when Hungary’s Babos struck long in a baseline duel with Stosur.Stosur claimed her third Grand Slam doubles title after winning the 2005 U.S. Open and 2006 French Open, while Zhang celebrated her first.”We have a great friendship and I think that really shows when we play.”@bambamsam30 credits partner @zhangshuai121 for their #AusOpen title. pic.twitter.com/Wl57GNIGJI#AusOpen (@AustralianOpen) January 25, [email protected] considered retirement in 2015. @bambamsam30 urged her to keep playing.Four years later, they are Grand Slam champions together #AusOpen pic.twitter.com/IP1vtMCgdo#AusOpen (@AustralianOpen) January 25, 2019Also Read | Outdoor matches suspended at Australian Open due to heat wave and blackoutsAlso Read | Naomi Osaka sets up final vs Petra Kvitova after beating Karolina PliskovaAlso Read | Rafael Nadal outclasses Stefanos Tsitsipas to storm into final