PZ Myers is bored in San Diego so he came up with another meme for bloggers. This time we're supposed to Goggle for the first image that comes up when you enter your name [What's your image?]. 
Isovaleric acid [3-Methylbutanoic acid] smells like sweat. It is responsible for some of the odor in a locker room, for example. Although we can all detect that odor, some of us are much more sensitive to it than others. In fact, the concentrations of isovaleric acid that can be detected differs by as much as 10,000-fold from one individual to the next. 
Mice have about 1000 genes for olfactory receptors and this single gene family accounts for about 4% of all the genes in the mouse genome. Since each receptor is presumably capable of binding a specific odorant, it seems very likely that mice can detect a large number of different smells.
Menashe, I., Abaffy, T., Hasin, Y., Goshen, S., Yahalom, V., Luetje, C.W. and Lancet, D. (2007) Genetic Elucidation of Human Hyperosmia to Isovaleric Acid. PLoS Biology 5:e284 doi:10.1371/journal.pbio.0050284. [PLoS Biology]
The detection of odor is a complex signal transduction pathway that begins with the binding of an odor molecule (ligand) to an olfactory receptor located in sensory neurons in the nasal cavity. The pathway is interesting for a number of reasons including the mechanism of signal transduction and the structure of the olfactory receptors. One of the important problems in the field is the identification of the specific odor molecules that bind to specific receptors—or even whether each receptor actually binds a specific molecule.
Jan. 8, 2007
"for their discovery of the mechanisms in the biological synthesis of ribonucleic acid and deoxyribonucleic acid"
Arthur Kornberg (1918-2007) received the Nobel Prize in Physiology or Medicine for discovering an enzyme that replicates DNA. The enzyme, now known as DNA polymerase I, plays a key role in joining Okazaki fragments on the lagging strand and in DNA repair [DNA Polymerase I and the Synthesis of Okazaki Fragments] [Biochemist Arthur Kornberg (1918 - 2007)]. Kornberg shared the prize with Severo Ochoa.Your Majesties, Your Royal Highnesses, Ladies and Gentlemen.
To maa man vaere hvis livet skal lykkes, «There must be two if life shall succeed», is the theme of a sentimental old Danish song. The author had in mind man and woman, but she probably did not know how right she was from a more elementary biological viewpoint. Two principles are necessary so that «life» shall «succeed». One consists of proteins, the other of nucleic acids. The analogy is more than just a play upon words. Just as man and woman are responsible for the regeneration of mankind, likewise is the interplay between proteins and nucleic acids the only, and universally repeated basic mechanism of life. In the long series of substances which build up viruses, bacteria, plants, and animals, everything else might vary, but the proteins and nucleic acids are always present as the life-supporting elements. These both show certain principal characteristics. Their molecules are very large, and are built up from thousands of smaller units linked together in chains - just like a string of pearls - which have a tendency to form helices. Single helices join together in complicated threads which can contain proteins or nucleic acids or both. In the mixed «super molecules», the reactions of life proceed in the subtle pattern of the intimately associated strands.
The proteins contain amino acids as their elementary part. In the whole of Nature on this earth, there are found only some twenty amino acids in proteins. The elementary parts of the nucleic acids, the nucleotides, consist of nitrogenous bases, sugar, and phosphoric acid. There are found in Nature practically no more than eight of these most important nucleotides, all of which contain phosphoric acid, but in which the nitrogenous base may be one of five different kinds. The sugar can be of two different kinds, one of which, «ribose», contains one more oxygen atom than the other, «deoxyribose». This seemingly insignificant difference in a single atom produces a remarkably great effect. Nucleic acids are divided into two different series because of this characteristic. These series have widely different functions, so widely different in fact, that this is the reason why we have two Prize Winners on the stage today.«Deoxyribonucleic acids», which Arthur Kornberg has now synthesized, are mainly present as the hereditary substance in chromosomes. The «ribonucleic acids», which Severo Ochoa has synthesized, have other functions, such as to assist in the synthesis of proteins. The Swedish scientist Torbjörn Caspersson has played an important role in demonstrating this last fact. From his and other research-workers' discoveries, it has been possible to conclude that nucleic acids assist in the synthesis of protein. The exact chemical mechanism, however, is as yet unknown. Inasmuch as nucleic acids and proteins are the two main principles of life, it seemed highly probable that, vice versa, the proteins should take part in the rebuilding of nucleic acids. This seems so much the more probable when we realize that proteins, in the form of enzymes, take part in practically every chemical reaction in the biological world. It is to the everlasting credit of Ochoa and Kornberg to have clarified this fundamental mechanism by preparing proteins that build up nucleic acids in test tubes.
For proteins it has been proved, and for the nucleic acids it is highly probable, that the order of the different building blocks in the chains is by no means left to chance, but on the contrary is planned in detail for each kind of molecule and for each kind of living organism.
It is this regulated order between the building blocks that always makes human children grow up to be human beings, and the serpent's offspring grow up to be serpents. It is disturbances in this regulated order which change the hereditary factors and allows the variations of species over thousands of years. The almost infinite possibilities to combine the building blocks in different ways makes it possible to vary the form in which life appears on our earth. Let me give a comparable example. By different combinations of the 28 letters in our alphabet, we can write everything that can be expressed in our own language, as well as in all other languages. The building blocks of the proteins, the amino acids, are approximately equal in number to the letters of the alphabet. The protein molecules can be compared with words with 100, 1,000, or even 10,000 letters. It is clear that Nature here has been generous with the possibility to make different combinations amounting to astronomical figures. But here, another factor might be brought up. The differences between the amino acids are necessary not only to produce the possibilities for variation, but also to enable the proteins, by their enzymatic activity, to regulate the different aspects of metabolism. Even the two types of nucleic acids with 4 different nucleotides in each, when made up from 100 to 10,000 nucleotide units in each molecule, give a fantastic number of possible combinations. Thus it would seem as if it were too heroic an enterprise to try to find out the procedure whereby Nature forms such complicated substances as nucleic acids with such an unerring accuracy in placing each building block.
A few years ago, Ochoa and Kornberg, each in his own laboratory, started to investigate the problem. The development turned for Ochoa's part in a direction that made him work with systems that produced ribonucleic acids, while for Kornberg it led him to investigate the formation of deoxyribonucleic acids. They have both, in a series of outstanding investigations, without direct cooperation, but nevertheless, as personal friends probably profiting from each other's results, reached the goal at the same time. As everyone else, they were able to make use of results obtained by preceding research workers, among whom I can only mention a few. It might be of interest to mention that uric acid, the first representative of the purines (a class of nitrogenous bases that form part of the nucleic acids) was discovered in Sweden in 1776 simultaneously by both Carl Wilhelm Scheele and Torbern Bergman. It is a curious parallel to the shared Nobel Award of today, and a reminder of Sweden's great era in the science of chemistry. The German scientist Albrecht Kossel received the Nobel Prize in 1910 for his elucidation of the chemistry of the nitrogenous bases of the nucleic acids, whereas the English scientist Alexander Todd clarified in detail the chemical properties of the nucleic acids, and received the Nobel Prize for Chemistry in 1957. But what really enabled Ochoa and Kornberg to succeed was their own excellent previous work in related fields. Both have worked with bacteria from which they have made preparations of a high degree of purity, Ochoa from an acetic acid bacterium, and Kornberg from the coli bacterium. Ochoa's enzyme produces ribonucleic acids from ribonucleotides having twice the ratio of phosphoric acid residues as that contained in ribonucleic acid. The ribonucleic acid is formed by splitting out half of the phosphoric acid residues, and linking the nucleotides together to form large molecules, which, as far as we can prove today, do not differ in any way from natural nucleic acids. Kornberg's enzyme produces deoxyribonucleic acids in a similar, but not identical fashion. Both have arrived at the same, principally important result that in order to make the reaction start, it is necessary to add in the beginning a small amount of nucleic acid to act as a template. Otherwise the enzymes do not «know» which kind of nucleic acid they are to produce. As soon as they get a template to act as a guide, they start, just like a skilled type-setter, to copy the «manuscript» they have received. Here one recognizes life's own principle that like creates like. Even though several research workers had earlier suspected that such a mechanism was involved, the actual experimental proof is of greatest importance. Furthermore, Ochoa's enzyme has given us the possibility of enzymatically synthesizing simplified nucleic acids of great interest.
To give an idea of where the discoveries that are being honored today may lead to in the near future, I want to mention one example. Other scientists, especially S. S. Cohen in the U.S.A., have shown that the nucleic acid of a certain bacteriophage, T2, which is a kind of bacterial virus, contains a somewhat chemically different nitrogenous base. If bacteria are infected with T2 phage, this different nucleic acid is soon produced in the bacteria. Kornberg succeeded in explaining the mechanism in detail. T2 phage behaves like the worst kind of usurper. Within four minutes it produces a number of enzymes which destroy a nucleotide necessary for the bacterium's normal production of nucleic acids, and rebuilds it to the different nucleotide of the T2 phage, and thereby destroys the bacteria.
We are sure to witness in the near future several important discoveries in biochemistry, virus research, genetics, and cancer research as a consequence of the work of Ochoa and Kornberg. They have helped us to advance quite some distance on the road to understanding the mechanism of life.
Professor Severo Ochoa, Professor Arthur Kornberg, dear friends and colleagues. Some 130 years ago, Friedrich Wöhler, in the laboratory of Berzelius, synthesized urea from inorganic matter. This event occurred in the heart of this city of Stockholm, less than half a mile from where we are now standing. He thus overbridged the first gap between living and dead material. You have now made the second fundamental discovery on this pathway, the synthesis in test tubes of one of the two basic principles of life.
On behalf of the Caroline Institute, I extend to you our warm congratulations, and ask you to receive this year's Nobel Prize for Physiology or Medicine from the hands of His Majesty the King.
Slightly modified from Horton et al. (2006) ...
The use of short RNA primers gets around the limitation imposed by the mechanism of DNA polymerase, namely, that it cannot initiate DNA synthesis de novo. The primers are synthesized by a DNA dependent RNA polymerase enzyme called primase—the product of the dnaG gene in E. coli. The three-dimensional crystal structure of the DnaG catalytic domain revealed its folding and active site are distinct from the well studied polymerases, suggesting that it may employ a novel enzyme mechanism. Primase is part of a larger complex called the primosome that contains many other polypeptides in addition to primase. The primosome, along with DNA polymerase III, is part of the replisome.
DNA polymerase I of E. coli was discovered by Arthur Kornberg about 45 years ago. It was the first enzyme to be found that could catalyze DNA synthesis using a template strand. In a single polypeptide, DNA polymerase I contains the activities found in the DNA polymerase III holoenzyme: 5′ → 3′ polymerase activity and 3′ → 5′ proofreading exonuclease activity. In addition, DNA polymerase I has 5′ → 3′ exonuclease activity, an activity not found in DNA polymerase III.
The Figure (right) shows the structure of the Klenow fragment complexed with a fragment of DNA containing a mismatched terminal base pair. The 3′ end of the nascent strand is positioned at the 3′ → 5′ exonuclease site of the enzyme. During polymerization, the template strand occupies the groove at the top of the structure and at least 10 bp of double-stranded DNA are bound by the enzyme, as shown in the figure. Many of the amino acid residues involved in binding DNA are similar in all DNA polymerases, although the enzymes may be otherwise quite different in three-dimensional structure and amino acid sequence.
[©Laurence A. Moran and Pearson/Prentice Hall]
Horton, H.R., Moran, L.A., Scrimgeour, K.G., Perry, M.D. and Rawn, J.D. (2006) Principles of Biochemistry. Pearson/Prentice Hall, Upper Saddle River, NJ (USA)
Monday's Molecule was polyphosphate [Monday's Molecule #49]. Polyphosphate is a string of phosphate groups joined together by phosphoanhydride linkages. The polymer serves as a convenient storehouse for phosphorus but it also has significantt roles in regulating metabolic activity. It is present in all cells, although the specifics of its synthesis and degradation have been more intensely studied in bacteria than in eukaryotes. Inorganic polyphosphate (poly P) is a chain of tens or many hundreds of phosphate (Pi) residues linked by high-energy phosphoanhydride bonds. Despite inorganic polyphosphate's ubiquity--found in every cell in nature and likely conserved from prebiotic times--this polymer has been given scant attention. Among the reasons for this neglect of poly P have been the lack of sensitive, definitive, and facile analytical methods to assess its concentration in biological sources and the consequent lack of demonstrably important physiological functions. This review focuses on recent advances made possible by the introduction of novel, enzymatically based assays. The isolation and ready availability of Escherichia coli polyphosphate kinase (PPK) that can convert poly P and ADP to ATP and of a yeast exopolyphosphatase that can hydrolyze poly P to Pi, provide highly specific, sensitive, and facile assays adaptable to a high-throughput format. Beyond the reagents afforded by the use of these enzymes, their genes, when identified, mutated, and overexpressed, have offered insights into the physiological functions of poly P. Most notably, studies in E. coli reveal large accumulations of poly P in cellular responses to deficiencies in an amino acid, Pi, or nitrogen or to the stresses of a nutrient downshift or high salt. The ppk mutant, lacking PPK and thus severely deficient in poly P, also fails to express RpoS (a sigma factor for RNA polymerase), the regulatory protein that governs > or = 50 genes responsible for stationary-phase adaptations to resist starvation, heat and oxidant stresses, UV irradiation, etc. Most dramatically, ppk mutants die after only a few days in stationary phase. The high degree of homology of the PPK sequence in many bacteria, including some of the major pathogenic species (e.g. Mycobacterium tuberculosis, Neisseria meningitidis, Helicobacter pylori, Vibrio cholerae, Salmonella typhimurium, Shigella flexneri, Pseudomonas aeruginosa, Bordetella pertussis, and Yersinia pestis), has prompted the knockout of their ppk gene to determine the dependence of virulence on poly P and the potential of PPK as a target for antimicrobial drugs. In yeast and mammalian cells, exo- and endopolyphosphatases have been identified and isolated, but little is known about the synthesis of poly P or its physiologic functions. Whether microbe or human, all species depend on adaptations in the stationary phase, which is truly a dynamic phase of life. Most research is focused on the early and reproductive phases of organisms, which are rather brief intervals of rapid growth. More attention needs to be given to the extensive period of maturity. Survival of microbial species depends on being able to manage in the stationary phase. In view of the universality and complexity of basic biochemical mechanisms, it would be surprising if some of the variety of poly P functions observed in microorganisms did not apply to aspects of human growth and development, to aging, and to the aberrations of disease. Of theoretical interest regarding poly P is its antiquity in prebiotic evolution, which along with its high energy and phosphate content, make it a plausible precursor to RNA, DNA, and proteins. Practical interest in poly P includes many industrial applications, among which is the microbial removal of Pi in aquatic environments.Much work has been done since this review was published in 1999 but the basic concepts haven't changed. Arthur Kornberg [Biochemist Arthur Kornberg (1918 - 2007)] was very interested in polyphosphates and he is responsible bringing it to the attention of the biochemistry community. His lab worked on polyphosphates for the past 25 years. As you know, Kornberg died last Friday but one of his papers on polyphosphate was just published two weeks ago (Zhang et al. 2007). That paper describes the enzyme polyphosphate kinase 1 in slime mold Dictyostelium discoideum, one of the few eukaryotes to have the enzyme that makes and degrades polyphosphate. The paper shows that polyphosphate regulates cell division in Dictyostelium.
Kornberg, A., Rao, N.N. and Ault-Riché, D. (1999) Inorganic polyphosphate: a molecule of many functions. Annu. Rev. Biochem. 68:89-125. [PubMed]
Li, L., Rao, N.N. and Kornberg, A. (2007) Inorganic polyphosphate essential for lytic growth of phages P1 and fd. Proc. Natl. Acad. Sci. (USA) 104(6):1794-1799. [PubMed]
Zhang, H., Gómez-García, M.R., Shi, X., Rao, N.N. and Kornberg, A. (2007) Polyphosphate kinase 1, a conserved bacterial enzyme, in a eukaryote, Dictyostelium discoideum, with a role in cytokinesis. Proc. Natl. Acad. Sci. (USA) 104:16486-16491. [PNAS] [PubMed]
From the [PEW Global Attitudes Survey]. Is Faith Necessary for Morality?What's interesting about these surveys is the difference between opinions in American and in Western Europe. Canada almost always falls somewhere between these two extremes.
Throughout most of Africa, Asia, and the Middle East, there is widespread agreement that faith in God is a prerequisite for morality. For example, in all 10 African countries included in the study, at least seven-in-ten respondents agree with the statement “It is necessary to believe in God in order to be moral and have good values.” In Egypt, no one in the sample of 1,000 people disagrees. Out of the 1,000 Jordanians interviewed, only one person suggests it is possible to not believe in God and still be a moral person.
In the four predominantly Muslim Asian countries – Indonesia, Bangladesh, Pakistan and Malaysia – huge majorities also believe morality requires faith in God. Elsewhere in Asia, however, opinions are a bit more mixed. Majorities in Japan and China, as well as substantial minorities of Indians and South Koreans, reject the notion that believing in God is required for morality.
In Arab countries there is a strong consensus that faith is necessary, although in Lebanon there are substantial differences among the country’s three major religious communities – Shia Muslims (81% agree), Christians (65%), and Sunni Muslims (54%). In neighboring Israel, a slim majority (55%) think faith in God is not necessary for moral values.
In Europe, the consensus view is just the opposite: throughout Western and Eastern Europe, majorities say faith in God is not a precondition for morality. This is true across Europe, regardless of whether a country’s primary religious tradition is Protestant, Catholic or Eastern Orthodox. And it is true regardless of which side of the Iron Curtain a country was on.
Still, even within Europe there is some variability – Swedes, Czechs, and the French emerge as the most likely to reject the necessity of religion, while Ukrainians, Germans, and Slovaks are the least likely.
Meanwhile, in the Americas there are considerable differences among countries. While Brazilians, Venezuelans, Bolivians, and Peruvians tend to believe faith is a necessary foundation for moral values, Mexicans, Chileans, and Argentines are more divided on this issue. Only 30% of Canadians suggest morality is impossible without faith, compared to nearly six-in-ten Americans (57%).
Eva, one of our own graduate students, asks this question on her blog easternblot [Quality of Life]. It's a multiple choice question. How hard can it be?
The title of this article is a rip-off of Canadian Cynic [ I mean, what could possibly go wrong?]. That article, in turn, is a response to a provocative article on Halls of Macadamia titled "In Canada, you have to run and hide...". Instead of embracing a citizen's "duty to retreat" in the face of a physical attack, states may be taking cues from the days of lawless frontier towns, where non-deputized Americans were within their rights to hold the bad guys at bay with the threat of deadly force.Yes, folks. This is not a joke. There really are people out there who think that Dodge City was crime free because everyone was armed to the teeth before restrictions on carrying guns were imposed [Only in America] [Should Christians Be Armed?]. After all, what could possible go wrong when you give everyone a hand gun and expect them to serve up vigilante justice?
First enacted in Florida last year, "Stand Your Ground" bills are now being considered in 21 states including Georgia, according to the National Rifle Association and the Brady Campaign to Prevent Gun Violence. The South Dakota senate approved one just last week.
These new measures would push the boundaries beyond the self-defense measures already on the books. Twelve states already allow citizens to shoot intruders in their homes, and 38 states permit concealed weapons in public places. The "Stand Your Ground" laws would allow people to defend themselves with deadly force even in public places when they perceive a life-threatening situation for themselves or others, and they would not be held accountable in criminal or civil court even if bystanders are injured.
Laws putting more judgment in an individual's hands stem from people's increased concern about crime in their communities. Proponents say it helps shift the debate from gun control to crime control, and that these laws are part of the rugged individualism of Americans.
"These laws send a more general message to society that public spaces belong to the public - and the public will protect [public places] rather than trying to run into the bathroom of the nearest Starbucks and hope the police show up," says David Kopel, director of the Independence Institute in Golden, Colo.Well, one thing that could go wrong is that innocent people could possibly get hurt. Canadian Cynic points us to this example from the New York Times in 1994 [Judge Awards Damages In Japanese Youth's Death].
Some critics say such "Wild West" laws are vigilante justice, and commonplace confrontations and more likely turn to violence.
A judge today awarded more than $650,000 in damages and funeral costs to the parents of a Japanese exchange student, saying there was "no justification whatsoever" for the killing of the 16-year-old boy who approached a suburban homeowner's door in a Halloween costume almost two years ago....This isn't the only case of this type. The problem with encouraging people to take the law into their own hands is that they tend to act aggressively instead of just running away (or slamming the door). We shouldn't encourage people to use guns to act out their paranoia.
Mr. Peairs was at home with his family in October of 1992 when the student, Yoshihiro Hattori, and an American companion mistakenly rang his doorbell in search of a Halloween party. Mr. Peairs's wife, Bonnie, answered and, frightened, yelled to her husband to get his gun. Mr. Peairs shot Mr. Hattori dead after warning him to "freeze," a phrase the young man apparently did not understand.
There's been a lot of talk recently about junk DNA and the possibility that large parts of it may, after all, have a function. Some of this speculation revolves around reports that most of the junk DNA is transcribed [Junk RNA] [Transcription of the 7SL Gene].An argument that has been persuasive in both the United States and Canada is the claim that having students decide between ID and evolution, or to have students “critically analyze” evolution, is pedagogically sound critical thinking instruction from which students would benefit. Of course, all teachers want students to be critical thinkers! It might be a useful critical thinking exercise for students to debate actual scientific disputes about patterns and processes of evolution, as long as they have a solid grounding in the basic science required. (For further discussion, see Alters & Alters, 2001; Scott & Branch, 2003; Dawkins & Coyne, 2005.) It would, however, not be a good critical thinking exercise to teach students that scientists are debating whether evolution takes place: on the contrary, it would be gross mis-education to instruct students that the validity of one of the strongest scientific theories is being questioned. It would, therefore, be gross mis-education to teach students the inaccurate science presented in Icons of Evolution, and other Intelligent Design literature.I think she's making an incorrect assumption here. We can "teach the controversy" by dealing directly with the conflict between religion and science and by explaining that scientists do not question evolution. The whole idea behind teaching, as far as I'm concerned, is to teach the truth and not some made-up stories that the Intelligent Design Creationists are pushing. Scott is assuming that in order to teach the controversy we have to present the IDC side as if it were true. That's nonsense. It makes about as much sense as assuming that you have to pretend that astrology is true in order to demonstrate that it isn't. (Everyone agrees that there's a controversy over the validity of horoscopes, right? Should we teach about it in school?)
We can't educate our students about the conflicts between science and religion because that would require teachers to bring up religion in school. It is forbidden to discuss religion in public schools in America and that's why we can't allow teaching the controversy. This is too bad because otherwise it might be a good vehicle for teaching critical thinking. It's better to allow the local churches to undermine everything we teach in school because the alternative violates the constitution. (Of course, this argument might become moot with one more appointment to the supreme court.)
Furthermore, even if we could mention religion in school, it wouldn't be a good idea to debate evolution vs. creationism because there are too many "science" teachers who reject evolution in favor of Biblical creationism. We prefer the status quo where neither evolution nor creationism is being taught. Teaching the controversy under these circumstances just opens the door to teaching creationism instead of evolution.
From UNC PHYSICS AND ASTRONOMY WEEKLY CALENDAR:Monday, October 29My daughter just called. She's now Dr. Moran!
12:20 p.,m. Room 258, Phillips Hall (UNC-CH)
Ph.D. Defense
Jane Moran (Physics and Astronomy, UNC-CH)
Investigating the Circumstellar Environments of Young Stars with the PROMPT Polarimeter
Abstract: We have designed and built a prototype imaging polarimeter for use on the PROMPT robotic telescopes located at Cerro Tololo International Observatory. The polarimeter uses a Fresnel rhomb and wollaston prism to image two orthogonal polarization states onto a single CCD chip, with an image field of view of 10 x 4.5 arcmin. Using the polarimeter, we have investigated the circumstellar regions of 11 Herbig Ae/Be stars, and done extensive follow-up observations on 3 stars of interest: KK Oph, a well-studied star with previously limited polarimetric data; NX Pup, a star known to vary photometrically but with previously unknown polarimetric variability; and SS73 44, a star with very limited previous photometric data and no prior polarimetric data. We have found polarimetric and photometric variations in KK Oph and NX Pup that are consistent with models of dust obscuration. Both KK Oph and NX Pup show an increase in polarization accompanied by a decrease in visual magnitude and a reddening. However, neither star shows the "blueing" at deep photometric minima and maximum polarization characteristic of the UXor classification of stars. We have demonstrated that SS73 44 has an intrinsic polarization component, but does not display the photometric and polarimetric variations expected from a young star with an evolving circumstellar environment, indicating that this object either has a disk seen in an orientation that has little inclination, or one with no appreciable puffed-up inner rim.
[Photo Credit: (top) PROMPT telescopes in Chile today. (bottom) Jane at the beginning of construction.]
In the Northern Hemisphere this is the time of year when the leaves of deciduous plants turn color and fall off. Why do they change color and why are some leaves so red?
The intensity of the color is influenced by the composition of the soil. When the soil is deficient in nitrogen the tree needs to recover more nitrogen from the leaves before they fall off. This leads to increased production of anthocyanins in order to prolong the period when the leaf cells can remain metabolically active to export nitrogen and carbohydrates [Why do autumn leaves bother to turn red?].Feild, T.S., Lee, D.W. and Holbrook, N.M. (2002) Why leaves turn red in autumn. The role of anthocyanins in senescing leaves of red-osier dogwood. Plant Physiol. 127:566-574. [PubMed]
Keskitalo, J., Bergquist, G., Gardeström, P. and Jansson, S. (2005) A cellular timetable of autumn senescence. Plant Physiol. 139:1635-48. [PubMed]
