The traditional terms „race“ and „racial group (type)“, referring to a division of humankind possessing a combination of physical traits that characterize it as a distinet human type, are no longer usable. Even in the past, the concept of race was far from unambiguous: Darwin gave examples of' classifications of' humans that ranged from two to sixty-three different varieties. The modern view of the concept of race recognizes that mass migrations as well as mixed marriages have occurred so frequently during the last several centuries that the so-called races are for the most part no longer definably distinet. Two approaches are now used to discuss human physical variety. One is clinal: a cline is a gradient of morphological or physiological change in a group of related organisms, usually along a line of geographical or environmental transition. For example, if one maps the distribution (presence or absence) of epicanthus or of the degree of skin pigmentation in the world's populations, one realizes that physical traits are not covariant. The second approach is to recognize that a breeding population has a noticeable frequency of' certain genes in comparison or contrast with other populations.
Ca2+ has been considered as a necessary ion for alleviation of stress-induced damages in plants. We investigated effects of exogenous Ca2+ on waterlogging-induced damage to pepper and its underlying mechanisms. Pepper seedlings under stress were treated by spraying of 10 mM CaCl2. Applying exogenous Ca2+ increased the biomass of pepper leaves and roots, improved photosynthetic characteristics, membrane permeability, root activity, osmotic substance contents, antioxidant enzyme and alcohol dehydrogenase activities, while it reduced lactate dehydrogenase activity. It maintained hydroxide radical contents and activities of malate dehydrogenase and succinate dehydrogenase relatively high. Our results suggested that applying exogenous Ca2+ could regulate osmotic substance contents, antioxidant system activity, root respiration, and metabolism, and subsequently alleviate waterlogging-induced damages to pepper plants., B. Z. Yang, Z. B. Liu, S. D. Zhou, L. J. Ou, X. Z. Dai, Y. Q. Ma, Z. Q. Zhang, W. C. Chen, X. F. Li, C. L. Liang, S. Yang, X. X. Zou., and Obsahuje bibliografii
Melatonin mediates many physiological processes in animals and plants. To examine the potential roles of melatonin in salinity tolerance, we investigated the effects of exogenous melatonin on growth and antioxidant system in cucumber under 200 mM NaCl stress conditions. The results showed that the melatonin-treated plants significantly increased growth mass and antioxidant protection. Under salinity stress, the addition of melatonin effectively alleviated the decrease in the net photosynthetic rate, the maximum quantum efficiency of PSII, and the total chlorophyll content. Our data also suggested that melatonin and the resistance of plants exhibited a concentration effect. The application of 50-150 μM melatonin significantly improved the photosynthetic capacity. Additionally, the pretreatment with melatonin reduced the oxidative damage under salinity stress by scavenging directly H2O2 or enhancing activity of antioxidant enzymes (including superoxide dismutase, peroxidase, catalase, ascorbate peroxidase) and concentrations of antioxidants (ascorbic acid and glutathione). Therefore, the melatonin-treated plants could effectively enhance their salinity tolerance., L. Y. Wang, J. L. Liu, W. X. Wang, Y. Sun., and Obsahuje seznam literatury
This year‘s Nobel Prize in Physics was awarded to three astrophysicists, Jim Peebles, Michel Mayor and Didier Queloz. Peebles was awarded half of the prize for cosmology and Mayor and Queloz were awarded a quarter each for the discovery of the first exoplanet orbiting a Sun-like star 51 Pegasi. Their discovery was reported almost 25 years ago and started a new era of exoplanetary research. This article presents the steps leading to the discovery of planet 51 Pegasi b and the following efforts to detect and characterise exoplanets. The future of the exoplanetary research field is also discussed in this article. and Petr Kabáth.
Polární záře jsou konečným důsledkem řetězce událostí souvisících se sluneční aktivitou. Nabité částice se od Slunce šíří jako součást slunečního větru meziplanetárním prostorem. Malá část z nich je zachycena magnetosférami planet a některé z nich magnetosférou naší Země. Zejména elektrony pak interagují s horními vrstvami atmosféry a excitované atomy či molekuly kyslíku a dusíku způsobují při deexcitaci překrásné nebeské divadlo - polární záři. V článku jsou vysvětleny makroskopické a mikroskopické mechanismy vzniku polárních září včetně historie jejich výzkumu. Stručně jsou shrnuty výsledky expedice Aurora 2002 pořádané katedrou fyziky FEL ČVUT a sdružením Aldebaran Group for Astrophysics. Diskutovány jsou naše zkušenosti s fotografováním a pozorováním polárních září., Jakub Rozehnal, Petr Kulhánek., and Obsahuje bibliografii