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1.
Summary. In leaf mesophyll cells of transgenic Arabidopsis thaliana plants expressing GFP in the chloroplast, stromules (stroma-filled tubules) with a length of up to 20 μm and a diameter of about 400–600 nm are observed in cells with spaces between the chloroplasts. They appear extremely dynamic, occasionally branched or polymorphic. In order to investigate the effect of temperature on chloroplasts, we have constructed a special temperature-controlled chamber for usage with a light microscope (LM-TCC). This LM-TCC enables presetting of the temperature for investigation directly at the microscope stage with an accuracy of ±0.1 °C in a temperature range of 0 °C to +60 °C. With the LM-TCC a temperature-dependent appearance of chloroplast protrusions has been found. These structures have a considerably smaller length-to-diameter ratio than typical stromules and reach a length of 3–5 μm. At 5–15 °C (low temperatures), almost no chloroplast protrusions are observed, but they appear with increasing temperatures. At 35–45 °C (high temperatures), numerous chloroplast protrusions with a beaklike appearance extend from a single chloroplast. Interaction of stromules with other organelles has also been investigated by transmission electron microscopy. At 20 °C, transverse sections of stromules are frequently observed with a diameter of about 450 nm. A close membrane-to-membrane contact of stromules with the nucleus and mitochondria has been visualised. Golgi stacks and microbodies are found in the spatial vicinity of stromules. At 5 °C, virtually no chloroplast protrusions or stromules are observed. At 35 °C, chloroplast protrusions are present as broader thylakoid-free stroma-filled areas, resulting in an irregular chloroplast appearance. Correspondence and reprints: Department of Physiology and Cell Physiology of Alpine Plants, Institute of Botany, University of Innsbruck, Sternwartestrasse 15, 6020 Innsbruck, Austria.  相似文献   

2.

Background  

Plastid stromules are stroma-filled tubules that extend from the surface of plastids in higher plants and allow the exchange of protein molecules between plastids. These structures are highly dynamic; stromules change both their shape and position in the cytoplasm very rapidly. Previous studies with microfilament inhibitors indicated that stromule shape and movement are dependent on the actin cytoskeleton. To learn more about the nature of the interactions of stromules and the cytoskeleton, we imaged fluorescently-labeled microfilaments and plastids.  相似文献   

3.
Stromules: Mobile Protrusions and Interconnections Between Plastids   总被引:7,自引:0,他引:7  
Abstract: Stroma-filled tubules, recently named stromules, extend from the surface of plastids in most cell types and plant species examined. Stromules are highly dynamic structures, continuously and rapidly changing shape. They have been shown to interconnect plastids and permit the exchange of green fluorescent protein (GFP) between plastids. Stromules are enclosed by the inner and outer plastid envelope membranes and are 0.4 - 0.8 μm in diameter and up to 65 μm long. Movement of stromules is dependent on the actin cytoskeleton and the ATPase activity of myosin. Stromules are more abundant in cells containing a relatively small plastid volume and provide a means of enormously increasing the plastid surface area. Many important questions on the structure, function and mobility of stromules remain unanswered.  相似文献   

4.

Background  

The leaf is an important plant organ, and how it will respond to future global warming is a question that remains unanswered. The effects of experimental warming on leaf photosynthesis and respiration acclimation has been well studied so far, but relatively little information exists on the structural and biochemical responses to warming. However, such information is very important to better understand the plant responses to global warming. Therefore, we grew Arabidopsis thaliana at the three day/night temperatures of 23/18°C (ambient temperature), 25.5/20.5°C (elevated by 2.5°C) and 28/23°C (elevated by 5°C) to simulate the middle and the upper projected warming expected within the 21st century for this purpose.  相似文献   

5.
6.
In each of the species examined — 4 Chlorophyceae, 7 Phaeophyceae and 4 Rhodophyceae — the optimum temperature for photosynthesis was apparently higher in summer material than in winter material. In the brown algae the optimum temperature for the apparent photosynthesis lies between 20°C and 23°C, in the green algae and in most of the red algae between 25° and 30°C. In most of the red algae the activity decreased markedly at 35°GC, while a considerable part of the green algae survived at this temperature. In 50% of the species of brown algae examined the photosynthetic activity decreased at 30°C and was completely lost at 35°C, while in the remaining species a strong resistance to high temperatures was observed.  相似文献   

7.
Net photosynthetic carbon uptake of Panamanian lowland tropical forest species is typically optimal at 30–32 °C. The processes responsible for the decrease in photosynthesis at higher temperatures are not fully understood for tropical trees. We determined temperature responses of maximum rates of RuBP‐carboxylation (VCMax) and RuBP‐regeneration (JMax), stomatal conductance (Gs), and respiration in the light (RLight) in situ for 4 lowland tropical tree species in Panama. Gs had the lowest temperature optimum (TOpt), similar to that of net photosynthesis, and photosynthesis became increasingly limited by stomatal conductance as temperature increased. JMax peaked at 34–37 °C and VCMax ~2 °C above that, except in the late‐successional species Calophyllum longifolium, in which both peaked at ~33 °C. RLight significantly increased with increasing temperature, but simulations with a photosynthesis model indicated that this had only a small effect on net photosynthesis. We found no evidence for Rubisco‐activase limitation of photosynthesis. TOpt of VCMax and JMax fell within the observed in situ leaf temperature range, but our study nonetheless suggests that net photosynthesis of tropical trees is more strongly influenced by the indirect effects of high temperature—for example, through elevated vapour pressure deficit and resulting decreases in stomatal conductance—than by direct temperature effects on photosynthetic biochemistry and respiration.  相似文献   

8.
Rhodamine-phalloidin staining of winter oilseed rape suspension cells revealed that the structure of actin cytoskeleton changes with the phase of cell growth. In small, 4-day-old cells, entering the exponential phase of growth, a dense and uniformly distributed cortical microfilament networks was seen. In six-day-old vacuolated cells, which reached the stationary phase of growth, the actin cytoskeleton was composed of thicker microfilament cables in irregular arrangements. In cells acclimated in cold for 7 days a dense, uniformly distributed and cortical microfilament network was still seen. The fine microfilament network was sensitive to extracellular freezing since the structures underwent depolymerization at −3 °C (in the presence of extracellular ice), both in non-acclimated and cold-acclimated cells. The thicker transvacuolar cables in cells of the stationary growth phase resisted freezing to −7 °C. Acclimation of suspensions at 2 °C resulted in slowing down growth of cells and in the increased freezing tolerance of cells as indicated by a decrease of LT50 from −11 °C to −17.5o or to −25 °C when determined 7 or 20 days after the beginning of the cold treatment, respectively. Freezing tolerance of non-acclimated cells decreased from −11 °C to −8 °C during subculture, showing a transient increase to −17 °C on the day 6. Results indicate that the arrangement of actin microfilaments and their sensitivity to freezing-induced depolymerization depends on the phase of cell growth rather than on cell acclimation status. Possible mechanisms involved in the freezing-induced depolymerization of actin microfilaments are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

9.
The chloroplast is one of the most dynamic organelles of a plant cell. It carries out photosynthesis, synthesizes major phytohormones, plays an active part in the defence response and is crucial for interorganelle signalling. Viruses, on the other hand, are extremely strategic in manipulating the internal environment of the host cell. The chloroplast, a prime target for viruses, undergoes enormous structural and functional damage during viral infection. Indeed, large proportions of affected gene products in a virus‐infected plant are closely associated with the chloroplast and the process of photosynthesis. Although the chloroplast is deficient in gene silencing machinery, it elicits the effector‐triggered immune response against viral pathogens. Virus infection induces the organelle to produce an extensive network of stromules which are involved in both viral propagation and antiviral defence. From studies over the last few decades, the involvement of the chloroplast in the regulation of plant–virus interaction has become increasingly evident. This review presents an exhaustive account of these facts, with their implications for pathogenicity. We have attempted to highlight the intricacies of chloroplast–virus interactions and to explain the existing gaps in our current knowledge, which will enable virologists to utilize chloroplast genome‐based antiviral resistance in economically important crops.  相似文献   

10.
Entry of HeLa and CHO-10 cells into mitosis can be inhibited by incorporation of p-fluorophenylalanine at certain temperatures, 37 °C for the former cell type and 39.5 °C for the latter. At lower temperatures, 32 °C in the former and 37 °C in the latter, the analogue does not inhibit entry of cells into mitosis. The possibility that the analogue is not incorporated at the permissive temperatures has been ruled out; indeed incorporation is relatively greater at the permissive temperatures. The results suggest that the physiological properties of analogue protein molecules differ depending on the temperature at which they are synthesized; the higher the temperature the more likely they are to malfunction.  相似文献   

11.
To test the hypothesis that the up‐regulation of sucrose biosynthesis during cold acclimation is essential for the development of freezing tolerance, the acclimation responses of wild‐type (WT) Arabidopsis thaliana (Heynh.) were compared with transgenic plants over‐expressing sucrose phosphate synthase (over‐sps) or with antisense repression of either cytosolic fructose‐1,6‐bisphosphatase (antifbp) or sucrose phosphate synthase (antisps). Plants were grown at 23 °C and then shifted to 5 °C. The leaves shifted to 5 °C for 10 d and the new leaves that developed at 5 °C were compared with control leaves on plants at 23 °C. Plants over‐expressing sucrose phosphate synthase showed improved photosynthesis and increased flux of fixed carbon into sucrose when shifted to 5 °C, whereas both antisense lines showed reduced flux into soluble sugars relative to WT. The improved photosynthetic performance by the over‐sps plants shifted to 5 °C was associated with an increase in freezing tolerance relative to WT (?9.1 and ?7.2 °C, respectively). In contrast, both antisense lines showed impaired development of freezing tolerance (? 5.2 and ?5.8 °C for antifbp and antisps, respectively) when shifted to 5 °C. In the new leaves developed at 5 °C the recovery of photosynthesis as typically seen in WT was strongly inhibited in both antisense lines and this inhibition was associated with a further failure of both antisense lines to cold acclimate. Thus, functional sucrose biosynthesis at low temperature in the over‐sps plants reduced the inhibition of photosynthesis, maintained the mobilization of carbohydrates from source leaves to sinks and increased the rate at which freezing tolerance developed. Modification of sucrose metabolism therefore represents an additional approach that will have benefits both for the development of freezing tolerance and over‐wintering, and for the supply of exportable carbohydrate to support growth at low temperatures.  相似文献   

12.

Background and Aims

Photosynthesis is one of the processes most susceptible to low-temperature inhibition in maize, a tropical C4 crop not yet fully adapted to a temperate climate. C4 photosynthesis relies on symplasmic exchange of large amounts of photosynthetic intermediates between Kranz mesophyll (KMS) and bundle sheath (BS) cells. The aim of this study was to test the hypothesis that the slowing of maize photosynthesis at low temperature is related to ultrastructural changes in the plasmodesmata between KM and BS as well as BS and vascular parenchyma (VP) cells.

Methods

Chilling-tolerant (CT) KW 1074 and chilling-sensitive (CS) CM 109 maize (Zea mays) lines were studied. The effect of moderate chilling (14 °C) on the rate of photosynthesis, photosynthate transport kinetics, and the ultrastructure of plasmodesmata linking the KMS, BS and VP cells were analysed. Additionally, the accumulation of callose and calreticulin was studied by the immunogold method.

Key Results

Chilling inhibited photosynthesis, photosynthate transfer to the phloem and photosynthate export from leaves in both lines. This inhibition was reversible upon cessation of chilling in the CT line but irreversible in the CS line. Simultaneously to physiological changes, chilling induced swelling of the sphincters of plasmodesmata linking KMS and BS cells and a decreased lumen of the cytoplasmic sleeve of plasmodesmata at the BS/VP interface in the CS line but not in the CT line. Accumulation of calreticulin, which occurred near the neck region of the closed plasmodesmata was observed after just 4 h of chilling and over-accumulation of callose at the KMS/BS and BS/VP interfaces occurred after 28 h of chilling.

Conclusions

Stronger chilling sensitivity of the CM 109 maize line compared with the KW 1074 line, shown by decreased photosynthesis and assimilate export from a leaf, is related to changes in the ultrastructure of leaf plasmodesmata at low temperature. The chain of reactions to chilling is likely to include calreticulin action resulting in rapid and efficient closure of the plasmodesmata at both KMS/BS and BS/VP interfaces. Callose deposition in a leaf was a secondary effect of chilling.  相似文献   

13.
The responses of respiration and photosynthesis to temperature fluctuations in marine macroalgae have the potential to significantly affect coastal carbon fluxes and sequestration. In this study, the marine red macroalga Gracilaria lemaneiformis was cultured at three different temperatures (12, 19, and 26°C) and at high‐ and low‐nitrogen (N) availability, to investigate the acclimation potential of respiration and photosynthesis to temperature change. Measurements of respiratory and photosynthetic rates were made at five temperatures (7°C–33°C). An instantaneous change in temperature resulted in a change in the rates of respiration and photosynthesis, and the temperature sensitivities (i.e., the Q10 value) for both the metabolic processes were lower in 26°C‐grown algae than 12°C‐ or 19°C‐grown algae. Both respiration and photosynthesis acclimated to long‐term changes in temperature, irrespective of the N availability under which the algae were grown; respiration displayed strong acclimation, whereas photosynthesis only exhibited a partial acclimation response to changing growth temperatures. The ratio of respiration to gross photosynthesis was higher in 12°C‐grown algae, but displayed little difference between the algae grown at 19°C and 26°C. We propose that it is unlikely that respiration in G. lemaneiformis would increase significantly with global warming, although photosynthesis would increase at moderately elevated temperatures.  相似文献   

14.
The photosynthetic and respiratory responses to irradiance, salinity and temperature of the red alga, Gracilaria vermiculophylla, collected from Kumamoto, Shizuoka and Iwate in Japan were studied using an electronic Dissolved Oxygen sensor. The parameters derived from the photosynthesis versus irradiance relationship indicated the potential to acclimate to broad irradiance variations in all of the populations of G. vermiculophylla collected from these three sites. In addition, the light-saturated photosynthesis rate (P max) and the dark respiration rate of all populations increased with increasing temperature up to 20–30°C, while the P max decreased at 35°C. All populations also showed a broad variation of photosynthetic responses to salinity changes in the range from 10 to 30 psu. On the other hand, the population from Iwate showed high photosynthetic efficiency, especially in the temperature range of 5–10°C, and showed low values of saturation irradiance compared to the populations from Shizuoka and Kumamoto. These results suggest that there is greater potential to acclimate to low irradiance and low temperature in the population from Iwate compared to those from the Shizuoka and Kumamoto populations. However, the P max of the populations from Iwate and Shizuoka was reached at 20°C and 25°C, respectively, while the Kumamoto population reached P max at 30°C. This implies that the latter population has greater potential to tolerate higher temperatures than the former. Such characteristics in photosynthesis and respiration of G. vermiculophylla collected from the three locations probably indicate an acclimation to prevailing environmental conditions in their respective habitats.  相似文献   

15.
Morphological and functional preservation of urinary bladder epithelium–urothelium after extirpation from an organism enables physiological studies of that tissue and provides the basis for successful organ transplantations. The aim of this study was to determine the optimal temperature for maintaining urothelium in ex vivo conditions. Mouse urinary bladders were kept at the three temperatures usually used for maintaining tissue during transportation: at the temperature of melting ice (1°C), at room temperature (22–24°C), and at the body temperature of most mammals (37°C). Autolytic structural changes were followed with electron microscopy, while destruction of cytoskeleton and intercellular junctions was observed by immunolabeling. The first ultrastructural changes, swelling of mitochondria and necrosis of individual cells, became evident 30 min after extirpation if the tissue was kept at 1°C. After 60 and 120 min in ex vivo conditions, the most severe changes with increasing plasma membrane ruptures were detected at 1°C, while at room temperature only mild changes were detected. At 37°C, the extent of ultrastructural changes was between those of the other two experimental temperatures. Autolytic destruction of cytoskeleton and intercellular junctions was not observed before 2 h after extirpation. After 4 h, severe degradation of cytokeratin 20 and microtubules were found at 1°C and 37°C, while being almost undisturbed at room temperature. On the other hand, the reduction of desmoplakin and ZO-1 labeling was more evident at 37°C than at 1°C and room temperature. These findings provide evidence that room temperature is most appropriate for short ex vivo preservation of urothelial tissue.  相似文献   

16.
Two clones ofAlexandrium cohorticula were isolated at Aburatsubo, Sagami Bay, Japan. Cultured cells of both contained high amounts of paralytic shellfish toxins. The toxicity of these isolates was comparable with that of highly toxic Thai clones. No significant difference in toxin components or their proportions was observed between Japanese and Thai strains. The optimum growth temperature of both strains was around 25 °C. Japanese strains survived at 15 °C, whereas Thai strains did not; the latter grew faster than the former at 30 °C.  相似文献   

17.
Functional studies on molecular transport through plasmodesmata in leaf mesophyll and trichome cells revealed significant differences in their basal size-exclusion limits and their response to microinjected tobacco mosaic virus movement protein (E. Waigmann et al., 1994, Proc. Natl. Acad. Sci. USA 91: 1433–1437; E. Waigmann and P. Zambryski, 1995, Plant Cell 7: 2069–2079). To address the basis for these functional differences, Nicotiana clevelandii trichome and mesophyll plasmodesmata were compared ultrastructurally. Trichome plasmodesmata increase in ultrastructural complexity from the tip to the base cell. Their neck regions, thought to control molecular traffic through plasmodesmata, are clearly distinct from necks of mesophyll plasmodesmata. In contrast to the electron-dense desmotubular area in mesophyll plasmodesmata, trichome plasmodesmata contain an electron-translucent circle in their center, surrounded by an electron-dense ring. This latter ring is connected to the inner leaflet of the plasma membrane by multiple spokes or filaments. Two monoclonal antibodies raised against a maize plasmodesmal protein preparation (A. Turner et al., 1994, J Cell Sci. 107: 3351–3361) interact with both trichome and mesophyll N. clevelandii plasmodesmata. Based on the localization pattern and the high degree of cross-reactivity, both antibodies likely recognize a conserved structural component of plasmodesmata, and may be useful to mark plasmodesma in a variety of plants and tissues. Received: 24 January 1997 / Accepted: 3 March 1997  相似文献   

18.
Upon immune activation, chloroplasts switch off photosynthesis, produce antimicrobial compounds and associate with the nucleus through tubular extensions called stromules. Although it is well established that chloroplasts alter their position in response to light, little is known about the dynamics of chloroplast movement in response to pathogen attack. Here, we report that during infection with the Irish potato famine pathogen Phytophthora infestans, chloroplasts accumulate at the pathogen interface, associating with the specialized membrane that engulfs the pathogen haustorium. The chemical inhibition of actin polymerization reduces the accumulation of chloroplasts at pathogen haustoria, suggesting that this process is partially dependent on the actin cytoskeleton. However, chloroplast accumulation at haustoria does not necessarily rely on movement of the nucleus to this interface and is not affected by light conditions. Stromules are typically induced during infection, embracing haustoria and facilitating chloroplast interactions, to form dynamic organelle clusters. We found that infection-triggered stromule formation relies on BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED KINASE 1 (BAK1)-mediated surface immune signaling, whereas chloroplast repositioning towards haustoria does not. Consistent with the defense-related induction of stromules, effector-mediated suppression of BAK1-mediated immune signaling reduced stromule formation during infection. On the other hand, immune recognition of the same effector stimulated stromules, presumably via a different pathway. These findings implicate chloroplasts in a polarized response upon pathogen attack and point to more complex functions of these organelles in plant–pathogen interactions.  相似文献   

19.
By using green fluorescent protein targeted to the plastid organelle in tomato (Lycopersicon esculentum Mill.), the morphology of plastids and their associated stromules in epidermal cells and trichomes from stems and petioles and in the chromoplasts of pericarp cells in the tomato fruit has been revealed. A novel characteristic of tomato stromules is the presence of extensive bead-like structures along the stromules that are often observed as free vesicles, distinct from and apparently unconnected to the plastid body. Interconnections between the red pigmented chromoplast bodies are common in fruit pericarp cells suggesting that chromoplasts could form a complex network in this cell type. The potential implications for carotenoid biosynthesis in tomato fruit and for vesicles originating from beaded stromules as a secretory mechanism for plastids in glandular trichomes of tomato is discussed.  相似文献   

20.
Plasmodesmata and plant cytoskeleton.   总被引:4,自引:0,他引:4  
Plant cell-to-cell communication is achieved by membranous conduits called plasmodesmata, which bridge the cytoplasm of neighboring cells. A growing body of immunolocalization data shows an association of the cytoskeleton machinery with plasmodesmata. The role of the cytoskeleton in the plasmodesmata-mediated transport has been well documented for virus movement. Because viruses are known to exploit existing host pathways and because the cytoskeleton is involved in intracellular trafficking, the cytoskeleton is thought to drive and target macromolecules to plasmodesmata. It is this link between plasmodesmata and the cytoskeleton that will be described here.  相似文献   

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