A differential mechanical technique for tissue separation, based on the different physical resistance to grinding between mesophyll (M) and bundle sheath (BS) cells, was tested on dicotyledonous C4 plants A triplex canscens, A triplex halimus, Gomphrena globosa, Amaranthus retroflexus, Amaranthus caudatus and Portulaca oleracea. A metal sieve (35 mesh) was placed inside a mortar and pieces of leaves (0.5 cm2) were ground in an aqueous medium on the sieve to obtain a homogenate. The homogenate was at first collected below the sieve and was then filtered through six layers of muslin. Microscopic examination showed that the filtrate was enriched by the M cells and the residue was enriched by BS cells, few of which were broken. The BS cell fraction was then vigorously ground and filtered; this second filtrate was named the BS cell fraction and the first filtrate was named the M cell fraction. Ribulose 1,5-bisphosphate carboxylase (EC 4.1.1.39) (RuBPC) and phosphoenolpyruvate carboxylase (EC 4.1.1.31) (PEPC) were assayed, and chlorophyll determinations and protein estimations were made on both fractions. As expected, PEPC showed higher activities in the M fractions; contrary to expectation RuBPC was present in M cell fractions in the six dicotyledonous C4 plants tested. The relative high RuBPC activities found in the M fraction could not be explained in terms of bundle sheath contamination.
An indoor sun simulator was used to provide elevated UV-B radiation (280-315 nm) in combination with realistic ratios to PAR (400-700 nm) and UV-A radiation (315-400 nm) in order to test the physiological response of a soil- and snow microalga during a three-day stress scenario, which may occasionally occur in their respective arctic and alpine habitats.
Chlamydomonas nivalis and Tetracystis sp. are initial colonizers of harsh habitats like summer snow fields and bare arctic soils. The two species were chosen because of their role as primary successors in places where life is generally limited by extreme climatic and nutritional conditions.
The influence of the increased UV-B irradiation (1.43 W m-2; control: 0.52 W m-2) on photosynthesis and pigment composition was measured. Both species survived this incubation without any morphological signs of damage, but oxygen production was reduced by 20-56%. Under control conditions, the amount of chlorophylls (Chls) and carotenoids (Cars) per dry mass increased after three days due to optimal light conditions. After the same period, the treated samples of the soil alga Tetracystis sp. showed a smaller increase in Chls and primary Cars than the control. However, the production of extraplastidal, secondary Cars was induced. On the contrary, the snow alga C. nivalis already had high amounts of secondary Cars before the experiment, and after exposure, all pigment classes increased more compared to control conditions. The results show that these microalgae can tolerate short episodes of enhanced UV-B radiation. Photosynthesis may be temporally impaired, but the cells respond by the production of secondary Cars, which can shield their chloroplasts against excessive irradiation or quench reactive oxygen species. and D. Remias, A. Albert, C. Lütz.
Plants of Nicotiana benthamiana (Gray) (60 d old) were mechanically inoculated by a spreading of the fourth and fifth leaves with inoculum with or without plum pox potyvirus (PPV). Changes in growth parameters and selected photosynthetic characteristics were followed in control and inoculated plants in the locally affected leaves (LA) during 11 d after inoculation (DAI), in systemically affected leaves immature at time of inoculation (SAI) during 14-25 DAI, and in systemically affected leaves developed after the inoculation (SAD) during 28-39 DAI. The pure mechanical damage caused by inoculation induced a decrease in the net photosynthetic rate (PN) in LA and SAD leaves, and an increase in the steady-state value of the non-photochemical chlorophyll (Chl) fluorescence quenching qN. The qN increase appeared in certain time intervals in all measured leaves on plants, so it could be regarded as indication of a systemic reaction of plant to the local mechanical injury. The viral infection developed in LA leaves and spread to SAI and SAD leaves was documented by the ELISA-DASI method. The plant height and area of SAI and SAD leaves were lower in infected plants. The combined effect of mechanical damage and viral infection caused a decrease in PN only in LA and SAD leaves. In SAD leaves, an increased relative height of the J step (VJ) in the O-J-I-P Chl fluorescence transient together with a lower B/A band ratio of thermoluminescence glow curves reflected a damage to the acceptor side of photosystem 2 (PS2) caused by the viral infection, and a faster kinetics of the induction of the photochemical quenching coefficient qP of Chl fluorescence indicated a faster QA- re-oxidation in the remaining undamaged centres of PS2. and V. Hlaváčková ... [et al.].
Time of concentration (TC) of surface flow in watersheds depends on the coupled response of hillslopes and stream networks. The important point in this background is to study the effects of the geometry and the shape of complex hillslopes on the time of concentration considering the degree of flow convergence (convergent, parallel or divergent) as well as the profile curvature (concave, straight or convex). In this research, the shape factor of complex hillslopes as introduced by Agnese et al. (2007) is generalized and linked to the TC. A new model for calculating TC of complex hillslopes is presented, which depends on the plan shape, the type and degree of profile curvature, the Manning roughness coefficient, the flow regime, the length, the average slope, and the excess rainfall intensity. The presented model was compared to that proposed by Singh and Agiralioglu (1981a,b) and Agiralioglu (1985). Moreover, the results of laboratory experiments on the travel time of surface flow of complex hillslopes were used to calibrate the model. The results showed that TC for convergent hillslopes is nearly double those of parallel and divergent ones. TC in convex hillslopes was very close to that in straight and concave hillslopes. While the effect of convergence on TC is considerable, the curvature effect confirmed insignificant. Finally, in convergent hillslopes, TC increases with the degree of convergence, but in divergent hillslopes, it decreases as degree of divergence increases.
The induced unsteady flow due to a stretching porous surface in a rotating fluid, where the unsteadiness is caused by the suddenly stretched surface is studied in this paper. After a similarity tranformation, the unsteady Navier-Stokes equations have been solved numerically using the Adams Predictor Corrector Method. It is found that there is a smooth transition from the small time solution to the large time or steady state solution. and Obsahuje seznam literatury a názvosloví