ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00861.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00862.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00863.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Desiccation tolerance is a fundamental principle for resting stages of plant development which include the dormancy of seeds and the quiescent stages of resurrection plants. To prevent the deleterious effects of cellular desiccation, a complex interplay of several adaption mechanisms is required. The ability to cope with free radicals, the formation of which is well documented in desiccated tissues, is one of these basic requirements. Detoxification of free radicals by several antioxidants and scavenging enzymes include reactions of reduced glutathione (GSH) resulting in the formation of glutathione disulfide (GSSG). In free radical processing pathways GSSG is considered to be immediately reduced back to GSH by the action of glutathione reductase (EC 1.6.4.2.). However, in desiccated tissues GSSG accumulates. Protein‐glutathione mixed disulfides (PSSG) are also reported to increase in plants under drought leading to the hypothesis that glutathione protects protein thiol groups from auto‐oxidation. The irreversible formation of intramolecular disulfides resulting in denaturation of proteins would be one of the primary sites of desiccation injury. We suggest that PSSG is formed by the reaction of GSSG with high molecular weight thiols and introduce a thiol‐disulfide cycle that involves reduction/oxidation processes of glutathione and protein thiol groups during the dehydration/rehydration processes in desiccation tolerant ti

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00864.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:New details of F‐actin organisation in leaf epidermal and stomatal cells were revealed by rhodamine — and fluorescein — phalloidin staining of fixed epidermal peels ofTradescantia virginianaand visualisation by confocal microscopy. Non‐specialised epidermal cells contain highly organised arrays of fine cortical actin filaments aligned in transverse or oblique orientations. In interphase guard mother cells (GMCs), the arrangement of cortical F‐actin changes on the periclinal and anticlinal cell walls at different times during differentiation. Initially, cortical F‐actin on the periclinal surfaces is oriented transversely and F‐actin is evenly distributed around the anticlinal walls. Following polarisation of the adjacent subsidiary mother cells (SMCs), actin in GMCs concentrates on the lateral anticlinal walls, but not on the transverse walls. Subsequently, F‐actin on the periclinal walls reorients to radial and then longitudinal. Organisation of F‐actin in SMCs appears to be influenced by the adjacent GMCs and co‐ordination in F‐actin arrangements in cells of the stomatal complex continues through to the formation of the guard cell pair. Our studies indicate that actin bands marking the division site in prophase cells, and detected in microinjected living material, are a particularly labile subset of F‐actin. Actin bands were difficult to preserve, even when aldehyde fixation was avoided, in contrast to all interph

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00865.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:The control of maize root growth by root cap mucilage and extracellular calcium (Ca) was examined. Special attention was paid to the influence of these factors on cellular aspects of root growth, such as cell shape and organization of the microtubular (MT) cytoskeleton. Externally supplied Ca impaired the transition of early post‐mitotic cells from a more‐or‐less apolar mode of expansion to a strictly anisotropic mode of elongation accompanied by their more rapid growth. However, this inhibitory effect of Ca was not associated with any re‐arrangement of the cortical MTs, their transverse arrays, with respect to the root axis, being maintained under these conditions. Root mucilage, collected from donor root caps and placed around root tips, exerted a similar effect on cell shapes as did externally supplied Ca. In contrast, roots grown in a medium of low Ca content, or from which the root cap mucilage was continually removed, had more elongated cell shapes in their post‐mitotic growth regions when compared to the control roots. These findings are consistent with a notion that Ca is present in the root cap mucilage in physiologically relevant amounts and can mediate growth responses in both the PIG region and the apical part of the elongation zone.Integrating several known effects of Ca ions on growth at the root apex, a hypothesis is proposed that a Ca‐mediated and MT‐independent control of cell growth in the PIG region might be involved in morphogenetic root movements (e.g. gravitropism), and that root growth responses could be initiated by an asymmetric distribution of extracellular calcium, or root cap slime, around the gro

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00866.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:The impact of UV‐B irradiation on unialgal cultures of the temperate marine diatomOdontella sinensisand of the AntarcticOdontella weissflogiiwas tested under controlled laboratory conditions. Uptake rates of inorganic nitrogen byOdontella sinensiswere more affected by UV‐B radiation than those ofOdontella weissflogii. Utilization of15N‐ammonium was reduced after 3 h of UV‐B exposure. Values of Kmfrom several marine phytoplankton species were estimated from algae not exposed to UV‐B and from those after 3 h of UV‐B radiation. Calculation of Lineweaver‐Burk plot showed, under UV‐B stress, a noncompetitive inhibition for15NH+4uptake and a competitive inhibitory effect for15NO−3byOdontella weissflogii. The damage to15NH+4uptake by UV‐B was more pronounced under red than blue light; a contradictory result was obtained for15NO−3utilization byOdontella weissflogii. Reduction of the pigments by UV‐B under white light was dependent on the exposure time; a strong depression of the contents of chlorophyllide a, chlorophyll c, diatoxanthin and the fucoxanthins was found. Contents of the chlorophylls are markedly affected by UV‐B under red light whereas the chlorophyll a concentration is enhanced in blue and green light. UV‐B exposure in conjunction with blue and green light led to a reduction of the protein content and an increase in the amino acid contents. The pattern of pool sizes of free amino acids varied after UV‐B exposure. UV‐A irradiance had no effect. The possible targets of UV‐B irradiation on the uptake system of inorganic nitrogen are discussed in detail. Adaptation to the environmental conditions, e.g. via synthesis of UV stress proteins or mycosporine‐lik

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00867.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Lichens, being poikilohydric, have varying thallus water contents (WC) and show a complex interaction between net photosynthesis (NP) and WC. NP can be depressed at low WC (desiccation effects) and, in some species, also at high WC. In the latter case the depression is normally ascribed to increased CO2diffusion resistances through water blockage. Recently, an earlier explanation, that the depression at high WC is due to recycling of CO2from increased dark respiration processes (DR), has been given renewed prominence.The two explanations were distinguished by the concurrent use of gas exchange and chlorophyll fluorescence techniques to investigate NP: WC relationships in the lichensPeltigera leucophlebia(green algal) andP. neckeri(cyanobacterial). Both species had a distinct optimal WC for NP with depressed values at low and high WC. The maximal quantum yield for both CO2fixation (initial slope of light response curves of NP) and photosystem II (fluorescence signals of dark‐adapted thalli) was depressed only at low WC and remained high at optimal and greater WC. In contrast, the relative electron transport rate (ETR, derived from fluorescence signals of thalli in the light) tracked NP and was depressed at low and high WC. The depression of both NP and ETR at high WC (not that at low WC) could be prevented by using elevated external CO2concentrations. A single, linear relationship was found between all values of gross photosynthesis (NP + DR) and ETR regardless of external CO2concentration or WC.Our results show that, for these lichens, the depression in NP at high WC is a real fall in photosynthetic rate of the photobionts and is not due to recycling of CO2. The removal of the depression in NP and ETR at high WC by using elevated external CO2levels allows us to conclude that an additional CO2diffusion resistance is presen

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00868.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:A new combined turgor/membrane potential probe (T‐EP probe) monitored cell turgor and membrane potential simultaneously in single giant cells. The new probe consisted of a silicone oil‐filled micropipette (oil‐microelectrode), which conducted electric current. Measurements of turgor and hydraulic conductivity were performed as with the conventional cell pressure probe besides the membrane potential. In internodal cells ofChara corallina, steady state turgor (0.5‐0.7 MPa) and resting potentials (‐200 to −220 mV) in APW, and hydraulic conductivity (0.07 to 0.21 × 10∼5m s−1MPa−1) were measured with the new probe, and cells exhibited healthy cytoplasmic streaming for at least 24 h during measurements. When internodal cells ofChara corallinawere treated with 30, 20, 10, and 5 mM KCI, turgor responded immediately to all concentrations, and the osmotic changes in the medium were measured. Action potentials, which brought the membrane potential to a steady depolarization that measured the concentration difference of K+in the medium, were induced in a concentration — dependent delay and occurred only 30, 20, and 10 mM of KCl. When the solution was changed back to APW, the repolarization of membrane potential consisted of a quick and a following slow phase. During the quick phase, which took place immediately and lasted 1 to 3 min, the plasma membrane remained activated. The membrane was gradually deactivated in the slow phase, and entirely deactivated when the membrane potential recovered to the resting potential in APW. Although the activated plasma membrane was permeable to K+, no major ion channels were activated on the tonoplast, and therefore, internodal cells ofChara corallinadid not regulate turgor when osmotic potential changed in th

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00869.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Abstract:Incorporation of radiolabelled amino acids into proteins ofEuglena gracilisrevealed that the amount of labelled protein depends on the conditions of illumination and temperature of cultivation. Protein synthesis was generally lower under dark conditions except at 37 °C. The largest amounts of labelled protein were measured at 21 °C and decreased at higher and lower temperatures. By separating the labelled proteins of the membraneous cell fraction from subcultures under a range of culture conditions, the synthesis of some specific proteins was found to be light‐ and/or temperature‐dependent. On incubating cells taken at different times during a light/dark cycle and under constant conditions, a circadian rhythm of35S‐methionine‐ as well as35S‐cysteine‐incorporation was detected. Thereby the cells incorporated ten‐times less cysteine than methionine. Protein synthesis always peaked during the last quarter of the daily light phase, confirming the rhythmic rise in total protein. The length of the rhythm period, approximately 24 h, was nearly independent of the applied temperature in the range

ISSN:0932-8629    

DOI:10.1111/j.1438-8677.1996.tb00870.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY