Plants of cassava (Manihot esculenta Crantz) were raised in a sand root medium watered with nutrient solutions, under greenhouse conditions. As the N-supply increased, shoot dry mass was enhanced to a greater extent than root dry mass, thus leading to an increased shoot to root ratio. In leaves, contents of total soluble saccharides, non-reducing saccharides, and inorganic phosphate increased linearly with increasing N-supply. An opposite response was found for reducing saccharides and starch. In general, content of non-reducing saccharides was considerably greater than starch content. Activity of sucrose synthase was not detected, regardless of the N-treatments; by contrast, activity of neutral and acid invertases increased with increasing N-availability. Roots accumulated more total soluble saccharides, but less reducing saccharides and starch, as the N-supply increased. Photosynthetic rates decreased with increasing N-deficiency. Such a decrease was circumstantially associated to reducing saccharide, but not starch, accumulation. Results suggest a limited capacity for carbon export from source leaves under N-limitation. and J. L. Cruz ... [et al.].
The effects of iso-osmotic salinity and drought stresses on leaf net photosynthetic rate (PN) in two wheat (Triticum aestivum L.) cultivars BR 8 and Norin 61, differing in drought tolerance, were compared. In drought-sensitive Norin 61, the decline of PN was larger than that in drought-tolerant BR 8. Under NaCl treatment, PN decreased in two phases similarly in both cultivars. In the first phase, photosynthetic depression was gradual without any photochemical changes. In the second phase, photosynthetic depression was rapid and accompanied with a decline of the energy conversion efficiency in photosystem 2 (ΦPS2). Our observations suggest that the osmotic factor may induce a gradual depression of photosynthesis due to stomatal closure under both stress treatments. However, under NaCl treatment, a ionic factor (uptake and accumulation of excess Na+) may have direct effects on electron transport and cause more severe photosynthetic depression. The drought tolerance mechanism of BR 8 was insufficient to maintain single-leaf photosynthesis under salinity. and S. Muranaka, K. Shimizu, M. Kato.
The earlier developed double-modulation chlorphyll (Chl) fluorometer was modified for measurements with intact leaves of higher plants. The Chl fluorometer is based on a non-periodic modulation of both actinic and measuring flashes. In addition, continuous orange actinic and far-red radiation were produced by separate arrays of light-emitting diodes (LEDs). Programmable timing of the flashes allows to cover a wide dynamic range from microseconds to minutes. We have demonstrated that the LEDs can produce single-turnover flashes that saturate QA reduction of intact leaves of Glyceria maxima and shoots of Picea abies. and O. Urban ... [et al.].
The correct determination of material properties of construction materials from experiments is important not only during their development, but also during final verification. Specimens for testing mechanical properties of fiber-reinforced composites with a quasi-brittle matrix are usuall prepared by casting into a sutable mold. But they can be also prepared by cutting to desired shape from large body of material. The method of preparation may affect the measured values of material characteristics. In the case of sawed specimens, the fibers in surface layer are damaged, while in the case of casted specimens, fibers in surface layer tended to align with mold surface. The purpose of this article is to clarify the influence of these phenomena using numerical simulations. and Obsahuje seznam literatury
The structure of the local interstellar medium is reviewed with emphasis on the new observations of the cold neutral component. The properties of the high latitude molecular clouds are discussed as well as their relationship to the “infrared cirrus” and atomic gas. The molecular clouds are shown to the preferentially along the loops and filaments of local HI gas, but a detailed examination shows the CO and HI peaks are offset from one another. An expansion velocity of 7 km is derived for one of the shells suggesting an expansion energy of - 8 X 10^47 ergs. which is somewhat smaller than that expected for a supernova explosion. If the pressure in the clumps of the high latitude clouds is in equilibrium with the surrounding gas, the pressure in the shells is
10^4-10^5 cm^-3 K, an order of magnitude higher than what is generally argued to exist in the interstellar medium.