Acclimation of the photosynthesis of C3 plants to elevated atmospheric CO2 concentrations is ffequently observed. Some hypotheses ffequently proposed to explain this phenomenon are: (7) stomatal closure; (2) inhibition of photosynthesis by starch accumulation, and (5) reduced activity or concentration of ribulose-1,5- bisphosphate carboxylase/oxygenase. These hypotheses are compared with experimental evidence ffom the literature.
Článek se zabývá přechylováním španělských životných substantiv. Na základě jazykového materiálu z korpusu CREA nejprve mapuje současný úzus a z něj pak vyvozuje některé tendence. Ukazuje se, že se v rodovém systému posilují flexivní rysy na úkor izolačních a že ubývá substantiv, která vyjadřují rod jinak než sufixálně, U některých substantiv během 25 let existence korpusu původně neexistující sufixálně přechýlená forma postupně zcela vytlačila ncpřechýlenou variantu. Tendence k sufixálnímu přechylování je posilována faktory vnějšími (vědomý tlak společnosti, kodifikovaná norma) i vnitřními: vyjadřování rodu determinanty je v systému považováno za nedostatečné, navíc v mnoha kontextech se determinant nevyskytuje nebo je příliš vzdálen od svého substantiva.
In most amoeboid cells, the main protein involved in motility is actin. Nematode sperm are an exception, and their amoeboid motility is based on major sperm protein (MSP). We have studied the localization of actin and MSP in spermatids and spermatozoa of Graphidium strigosum (Dujardin, 1845), a species which has elongate male germ cells in which organelles are easily identified. Electrophoreses of G. slrigosum sperm proteins indicate that the main protein band, about 15 kDa in molecular weight, is specifically recognized by an anti-MSP polyclonal antibody developed against MSP of Caenorhabditis elegans (Burke and Ward 1983). Actin is present in small quantities. Immunocytochemical observations reveal that actin and MSP have an identical localization in precise areas of the male germ cells. Spermatids are labelled as dots around a central unlabelled zone, and spermatozoa are labelled only at the level of the anterior cap. Observations in G. strigosum are similar to that previously obtained in Heligmosomoides polygyrus (Mansir and Justine 1996). Co-localization of actin and MSP in the anterior cap of the spermatozoon, the region associated with pseudopod production, does not demonstrate directly that actin is involved in amoeboid movements, but shows that the role of actin in the cytoskeleton of nematode sperm should be re-investigated.
From mature needles of white spruce, Picea glauca (Moench) Voss we isolated thylakoids capable of high rates of oxygen evolution. Oxygen-evolving activity of spruce thylakoids was labile in the absence of osmoticum and declined by 40 % during 1 h on ice, compared to a 9 % dechne observed in spinách thylakoids. We compared the relative activity in spruce and spinách of the oxygen evolving complex (OEC) and the reaction centre in Triton X-100 fractionated membranes prepared and stored for 20 or 240 h at 0 or -80 °C in media with different combinations of sucrose (0.3, 0.5 and 1.0 M) and two pH values (6.0 and 7.6). In membranes detergent- fractionated and stored at pH 7.6, photosystem 2 (PS2) activity (H2O -> DCIP) was sensitive to sucrose concentration of the medium. Spruce and spinách membranes prepared and stored in 0.3 M sucrose and pH 7.6, showed 22 and 48 % activity of their respective control membranes, freshly prepared in 1 M sucrose at pH 6.0. In contrast, in membranes prepared and stored at pH 6.0, PS2 activity was less sensitive to sucrose concentration: spruce and spinách membranes in 0.3 M sucrose showed 73 and 88 % (respectively) of the activity of membranes freshly prepared in 1 M sucrose. In both species, the degree of stimulation of DCIP photoreduction by diphenylcarbazide suggested minimal damage to the reaction centre (RC) except during preparation in 0.3 M sucrose, pH 7.6. Since the spruce RCs were not more labile than those of spinách, the extra sensitivity of spruce thylakoids in media of low sucrose concentration was likely due to extra lability of the OEC.