两种不同生境苦苣苔科植物的复苏特性及其对水分的光合和生理响应

复苏植物可以耐受极度干旱的环境,脱水至10％相对水分含量后仍然可以复苏.苦苣苔科植物包含有较多复苏植物,不同类群的复苏机理可能存在差异.该文选择分布在亚热带和温带石灰岩地区的锈色蛛毛苣苔(Paraboea rufescens)和心叶马铃苣苔(Oreocharis cordatula)两种苦苣苔科植物,并对这两个物种的叶...     

Photosynthetic activity of homoiochlorophyllous desiccation tolerant plant <Emphasis Type="Italic">Haberlea rhodopensis</Emphasis> during dehydration and rehydration

The functional state of the photosynthetic apparatus of flowering homoiochlorophyllous desiccation tolerant plant Haberlea rhodopensis during dehydration and subsequent rehydration was investigated in order to characterize some of the mechanisms by which resurrection plants survive drought stress. The changes in the CO₂ assimilation rate, chlorophyll fluorescence parameters, thermoluminescence, fluorescence imaging and electrophoretic characteristics of the chloroplast proteins were measured in control, moderately dehydrated (50% water content), desiccated (5% water content) and rehydrated plants. During the first phase of desiccation the net CO₂ assimilation decline was influenced by stomatal closure. Further lowering of net CO₂ assimilation was caused by both the decrease in stomatal conductance and in the photochemical activity of photosystem II. Severe dehydration caused inhibition of quantum yield of PSII electron transport, disappearance of thermoluminescence B band and mainly charge recombination related to S₂Q_A⁻ takes place. The blue and green fluorescence emission in desiccated leaves strongly increased. It could be suggested that unchanged chlorophyll content and amounts of chlorophyll–proteins, reversible modifications in PSII electron transport and enhanced probability for non-radiative energy dissipation as well as increased polyphenolic synthesis during desiccation of Haberlea contribute to drought resistance and fast recovery after rehydration.     

Effect of drought stress on net CO2 uptake by Zea leaves

The net CO₂ assimilation by leaves of maize (Zea mays L. cv. Adonis) plants subjected to slow or rapid dehydration decreased without changes in the total extractable activities of phosphoenolpyruvate carboxylase (PEPC), malate dehydrogenase (MDH) and malic enzyme (ME). The phosphorylation state of PEPC extracted from leaves after 2–3 h of exposure to light was not affected by water deficit, either. Moreover, when plants which had been slowly dehydrated to a leaf relative water content of about 60% were rehydrated, the net CO₂ assimilation by leaves increased very rapidly without any changes in the activities of MDH, ME and PEPC or phosphorylation state of PEPC. The net CO₂-dependent O₂ evolution of a non-wilted leaf measured with an oxygen electrode decreased as CO₂ concentration increased and was totally inhibited when the CO₂ concentration was about 10%. Nevertheless, high CO₂ concentrations (5–10%) counteracted most of the inhibitory effect of water deficit that developed during a slow dehydration but only counteracted a little of the inhibitory effect that developed during a rapid dehydration. In contrast to what could be observed during a rapidly developing water deficit, inhibition of leaf photosynthesis by cis-abscisic acid could be alleviated by high CO₂ concentrations. These results indicate that the inhibition of leaf net CO₂ uptake brought about by water deficit is mainly due to stomatal closure when a maize plant is dehydrated slowly while it is mainly due to inhibition of non-stomatal processes when a plant is rapidly dehydrated. The photosynthetic apparatus of maize leaves appears to be as resistant to drought as that of C₃ plants. The non-stomatal inhibition observed in rapidly dehydrated leaves might be the result of either a down-regulation of the photosynthetic enzymes by changes in metabolite pool sizes or restricted plasmodesmatal transport between mesophyll and bundle-sheath cells.     

Proteome analysis of leaves of the desiccation-tolerant grass, Sporobolus stapfianus, in response to dehydration

Drought and its affects on agricultural production is a serious issue facing global efforts to increase food supplies and ensure food security for the growing world population. Understanding how plants respond to dehydration is an important prerequisite for developing strategies for crop improvement in drought tolerance. This has proved to be a difficult task as all of the current research plant models do not tolerate cellular dehydration well and, like all crops, they succumb to the effects of a relatively small water deficit of −4 MPa or less. For these reasons many researchers have started to investigate the usefulness of resurrection plants, plants that can survive extremes of dehydration to the point of desiccation, to provide answers as to how plants tolerate water loss. We have chosen to investigate the leaf proteome response of the desiccation-tolerant grass Sporobolus stapfianus Gandoger to dehydration to a water content that encompasses the initiation of the cellular protection response evident in these plants. We used a combination of two-dimensional Difference Gel Electrophoresis (2D-DIGE) and liquid chromatography-tandem-mass spectrometry to compare the proteomes of young leaves from hydrated plants to those dehydrated to approximately 30% relative water content. High-resolution 2D-DIGE revealed 96 significantly different proteins and 82 of these spots yielded high-quality protein assignments by tandem-mass spectrometry. Inferences from the bioinformatic annotations of these proteins revealed the possible involvement of protein kinase-based signaling cascades and brassinosteroid involvement in the regulation of the cellular protection response. Enzymes of glycolysis, both cytoplasmic and plastidic, as well as five enzymes of the Calvin cycle increased in abundance. However, the RuBisCO large subunit and associated proteins were reduced, indicating a loss of carbon fixation but a continued need to supply the necessary carbon skeletons for the constituents involved in cell protection. Changes in abundance of several proteins that appear to have a function in chromatin structure and function indicate that these structures undergo significant changes as a result of dehydration. These observations give a unique “snap-shot” of the proteome of S. stapfianus at a critical point in the passage towards desiccation.     

Plant recovery from maize somatic embryos subjected to controlled relative humidity dehydration

Summary Maize (Zea mays L.) embryogenic type-II calli were grown on medium containing 0,0.1 μM ABA or 60 g/liter sucrose or both before dehydration of solitary somatic embryos under three relative humidity regimes for up to 6 wk. Viability of dehydrated embryos after 2 wk rehydration was assessed by their ability to produce chlorophyll (greening), roots, coleoptiles, and/or leaves. Only embryos sequentially pretreated with ABA and high sucrose remained viable after 2 wk of dehydration at 70% RH. Up to 34% of the somatic embryos survived 2 wk dehydration at 70% RH, whereas embryos dehydrated at 50 or 90% RH exhibited reduced viability (8.7 and 0.8%, respectively). Approximately 15% of the embryos dehydrated at 70% RH developed into plants, whereas 0.9 and 0% of embryos dehydrated at 50 and 90% RH produced plants. Three percent of maize somatic embryos remained viable after 6 wk of dehydration at 70% RH, and 1.7% developed into plants. Embryo size influenced the ability of maize somatic embryos to survive dehydration. Only embryos greater than 5 mm survived 2 wk dehydration at 70% RH.     

Effects of Dehydration and Rehydration on Photosynthesis of Detached Leaves of the Resurrective Plant Boea hygrometrica

Fluorescence induction kinetics was used to investigate the effects of dehydration and rehydration on photosynthesis of detached leaves of the desiccation-tolerant, resurrective plant Boea hygrometrica (Bunge) R. Br. In comparison with the desiccation-intolerant plant Chirita heterotricha Merr., the PSⅡphotochemical activity of Boea hygrometrica was characterized by a faster decline during dehydration and a much higher capacity of recovery during rehydration. By means of native PAGE, it was further shown that the thylakoid pigment-protein complexes of Boea hygrometrica were highly stable during dehydration and rehydration. These features may contribute to the extreme desiccation resistance of photosynthesis apparatus of resurrective plant Boea hygrometrica.     

The effect of dehydration with or without abscisic acid pretreatment on buds regeneration from <Emphasis Type="Italic">Polypodium vulgare</Emphasis> L. rhizomes

Polypodium vulgare L., a widely distributed fern, is water-stress tolerant. Under controlled dehydration conditions (20% mannitol, 9 h) without and with abscisic acid (ABA) pretreatment (2 mg l⁻¹, 24 h), dehydration tolerance and regenerative, potential of common polypody rhizomes was investigated. We demonstrated the positive effect of ABA on changes in dehydrated rhizome metabolism. ABA pretreatment reduced electrolyte leakage from cells: it has also a role in regulating sucrose accumulation and thus, osmotic adjustment. Our findings confirm that P. vulgare rhizomes are well adapted to stress conditions through maintaining of ability to bud formation by dehydrated and rehydrated rhizomes.     

Responses of the resurrection plant <Emphasis Type="Italic">Haberlea rhodopensis</Emphasis> to high irradiance

The effect of high irradiance (HI) during desiccation and subsequent rehydration of the homoiochlorophyllous desiccation-tolerant shade plant Haberlea rhodopensis was investigated. Plants were irradiated with a high quantum fluence rate (HI; 350 μmol m⁻² s⁻¹ compared to ca. 30 μmol m⁻² s⁻¹ at the natural rock habitat below trees) and subjected either to fast desiccation (tufts dehydrated with naturally occurring thin soil layers) or slow desiccation (tufts planted in pots in peat-soil dehydrated by withholding irrigation). Leaf water content was 5 % of the control after 4 d of fast and 19 d of slow desiccation. Haberlea was very sensitive to HI under all conditions. After 19 d at HI, even in well-watered plants there was a strong reduction of rates of net photosynthesis and transpiration, contents of chlorophyll (Chl) and carotenoids, as well as photosystem 2 activity (detected by the Chl fluorescence ratio R_Fd). Simultaneously, the blue/red and green/red fluorescence ratios increased considerably suggesting increased synthesis of polyphenolic compounds. Desiccation of plants in HI induced irreversible changes in the photosynthetic apparatus and leaves did not recover after rehydration regardless of fast or slow desiccation. Only young leaves survived desiccation.     

Photosynthetic parameters of sexually different parts of <Emphasis Type="Italic">Porphyra katadai</Emphasis> var. <Emphasis Type="Italic">hemiphylla</Emphasis> (Bangiales,Rhodophyta) during dehydration and re-hydration

Physiological data from extreme habitat organisms during stresses are vital information for comprehending their survival. The intertidal seaweeds are exposed to a combination of environmental stresses, the most influential one being regular dehydration and re-hydration. Porphyra katadai var. hemiphylla is a unique intertidal macroalga species with two longitudinally separated, color distinct, sexually different parts. In this study, the photosynthetic performance of both PSI and PSII of the two sexually different parts of P. katadai thalli during dehydration and re-hydration was investigated. Under low-grade dehydration the variation of photosystems of male and female parts of P. katadai were similar. However, after the absolute water content reached 42%, the PSI of the female parts was nearly shut down while that of the male parts still coordinated well and worked properly with PSII. Furthermore, after re-hydration with a better conditioned PSI, the dehydrated male parts were able to restore photosynthesis within 1 h, while the female parts did not. It is concluded that in P. katadai the susceptibility of photosynthesis to dehydration depends on the accommodative ability of PSI. The relatively lower content of phycobiliprotein in male parts may be the cause for a stronger PSI after severe dehydration.     

Protein dynamics in thylakoids of the desiccation-tolerant plant Boea hygroscopica during dehydration and rehydration

Plants of Boea hygroscopica F. Muell were dehydrated to 9% relative water content (RWC) by withholding water for 26 d, and afterward the plants were rehydrated. Leaves were taken from control plants after 7, 12, and 26 d from the beginning of dehydration, and after 6 and 48 h from rehydration. The RWC decreased by 80% during dehydration, but the leaves regained RWC with rehydration. Dehydrated plants showed lesser amounts of proteins, lipids, and chlorophyll, all of which increased following rewatering. The lipid-to-protein ratio, which decreased during dehydration, returned to control level after 48 h of rehydration. Thylakoid lipids were more unsaturated when RWC reached the value of 9%. EPR measurements of spin-labeled proteins showed the presence of three different groups of proteins with different mobility in thylakoid membranes. The rotational correlation time of groups 1 and 2 increased with dehydration and decreased upon rehydration, whereas group 3 showed little changes. Desiccation did not cause thylakoid swelling or breakage, but the membrane system assemblage showed changes in thylakoid stacking. After 48 h of rehydration the membrane system recovered completely the organization of the fully hydrated state, showing several well-defined and regularly distributed grana.     

Effects of dehydration rate on physiological responses and survival after rehydration in larvae of the anhydrobiotic chironomid

Strategies to combat desiccation are critical for organisms living in arid and semi-arid areas. Larvae of the Australian chironomid Paraborniella tonnoiri resist desiccation by reducing water loss. In contrast, larvae of the African species Polypedilum vanderplanki can withstand almost complete dehydration, referred to as anhydrobiosis. For successful anhydrobiosis, the dehydration rate of P. vanderplanki larvae has to be controlled. Here, we desiccated larvae by exposing them to different drying regimes, each progressing from high to low relative humidity, and examined survival after rehydration. In larvae of P. vanderplanki, reactions following desiccation can be categorized as follows: (I) no recovery at all (direct death), (II) dying by unrepairable damages after rehydration (delayed death), and (III) full recovery (successful anhydrobiosis). Initial conditions of desiccation severely affected survival following rehydration, i.e. P. vanderplanki preferred 100% relative humidity where body water content decreased slightly. In subsequent conditions, unfavorable dehydration rate, such as more than 0.7 mg water lost per day, resulted in markedly decreased survival rate of rehydrated larvae. Slow dehydration may be required for the synthesis and distribution of essential molecules for anhydrobiosis. Larvae desiccated at or above maximum tolerable rates sometimes showed temporary recovery but died soon after.     

Metabolic processes sustaining the reviviscence of lichen <Emphasis Type="Italic">Xanthoria elegans</Emphasis> (Link) in high mountain environments

To survive in high mountain environments lichens must adapt themselves to alternating periods of desiccation and hydration. Respiration and photosynthesis of the foliaceous lichen, Xanthoria elegans, in the dehydrated state were below the threshold of CO₂-detection by infrared gas analysis. Following hydration, respiration totally recovered within seconds and photosynthesis within minutes. In order to identify metabolic processes that may contribute to the quick and efficient reactivation of lichen physiological processes, we analysed the metabolite profile of lichen thalli step by step during hydration/dehydration cycles, using ³¹P- and ¹³C-NMR. It appeared that the recovery of respiration was prepared during dehydration by the accumulation of a reserve of gluconate 6-P (glcn-6-P) and by the preservation of nucleotide pools, whereas glycolytic and photosynthetic intermediates like glucose 6-P and ribulose 1,5-diphosphate were absent. The large pools of polyols present in both X. elegans photo- and mycobiont are likely to contribute to the protection of cell constituents like nucleotides, proteins, and membrane lipids, and to preserve the integrity of intracellular structures during desiccation. Our data indicate that glcn-6-P accumulated due to activation of the oxidative pentose phosphate pathway, in response to a need for reducing power (NADPH) during the dehydration-triggered down-regulation of cell metabolism. On the contrary, glcn-6-P was metabolised immediately after hydration, supplying respiration with substrates during the replenishment of pools of glycolytic and photosynthetic intermediates. Finally, the high net photosynthetic activity of wet X. elegans thalli at low temperature may help this alpine lichen to take advantage of brief hydration opportunities such as ice melting, thus favouring its growth in harsh high mountain climates.     

The novel gene<Emphasis Type="Italic"> CpEdi-9</Emphasis> from the resurrection plant<Emphasis Type="Italic"> C. plantagineum</Emphasis> encodes a hydrophilic protein and is expressed in mature seeds as well as in response to dehydration in leaf phloem tissues

The resurrection plant Craterostigma plantagineum Hochst. is used as an experimental system to investigate desiccation tolerance in higher plants. A search for genes activated during early stages of dehydration identified the gene CpEdi-9, which is expressed in mature seeds and in response to dehydration in the phloem cells of vascular tissues of leaves. Elements for the tissue-specific expression pattern reside in the isolated promoter of the CpEdi-9 gene, as shown through the analysis of transgenic plants. The CpEdi-9 promoter could be a suitable tool for expressing genes in the vascular system of dehydrated plants. CpEdi-9 encodes a small (10 kDa) hydrophilic protein, which does not have significant sequence homologies to known genes. The predicted protein CpEDI-9 shares some physicochemical features with LEA proteins from plants and a nematode. Based on the unique expression pattern and on the nucleotide sequence we propose that CpEdi-9 defines a new class of hydrophilic proteins that are supposed to contribute to cellular protection during dehydration. This group of proteins may have evolved because desiccation tolerance requires the abundant expression of protective proteins during early stages of dehydration in all tissues.Abbreviations ABA Abscisic acid - ABRE ABA-responsive element - Edi Early dehydration induced - GUS Glucuronidase - LEA Late embryogenesis abundant - MU Methylumbelliferone This article is dedicated to Prof. Dr. Francesco Salamini on the occasion of his 65th birthday and his departure from the Max Planck Institute in Köln     

Distinct contractile and cytoskeletal protein patterns in the Antarctic midge are elicited by desiccation and rehydration

Desiccation presents a major challenge for the Antarctic midge, Belgica antarctica. In this study, we use proteomic profiling to evaluate protein changes in the larvae elicited by dehydration and rehydration. Larvae were desiccated at 75% relative humidity (RH) for 12 h to achieve a body water loss of 35%, approximately half of the water that can be lost before the larvae succumb to dehydration. To evaluate the rehydration response, larvae were first desiccated, then rehydrated for 6 h at 100% RH and then in water for 6 h. Controls were held continuously at 100% RH. Protein analysis was performed using 2‐DE and nanoscale capillary LC/MS/MS. Twenty‐four identified proteins changed in abundance in response to desiccation: 16 were more abundant and 8 were less abundant; 84% of these proteins were contractile or cytoskeletal proteins. Thirteen rehydration‐regulated proteins were identified: 8 were more abundant and 5 were less abundant, and 69% of these proteins were also contractile or cytoskeletal proteins. Additional proteins responsive to desiccation and rehydration were involved in functions including stress responses, energy metabolism, protein synthesis, glucogenesis and membrane transport. We conclude that the major protein responses elicited by both desiccation and rehydration are linked to body contraction and cytoskeleton rearrangements.     

Unusual composition of thylakoid membranes of the resurrection plant Boea hygroscopica: Changes in lipids upon dehydration and rehydration

Boea hygroscopica is a resurrection plant that is able to pass from biosis to anabiosis and vice versa following slow dehydration, but loses this ability following a rapid water loss. Fresh leaves were detached from plants grown in well-watered conditions and subjected to either rapid or slow dehydration and rehydration. Upon rehydration only slowly dried leaves revived. Analysis of thylakoid membranes revealed a rather small amount of total lipids (1,4–2 μmol g^?1 dry weight) in comparison with other flowering plants. The main glycolipid was digalactosyldiacylglycerol (DGDG) rather than monogalactosyldiacylglycerol (MGDG) as is common in higher plants. Linoleic acid was the main fatty acid (30–40 mol% of total fatty acids), while linolenic acid was present from 14 to 26 mol%. In both the fresh and rehydrated leaves nearly all lipid components were present in similar amounts. Following dehydration the DGDG/MGDG molar ratio, which was 1.1 in control and rehydrated leaves, doubled by the end of the rapid drying period and was three times as high in slowly dried leaves. The total polar lipid/free sterol molar ratio as well as the free fatty acid level assumed the highest values in the rapidly dehydrated leaves. A shift towards the more unsaturated fatty acids was observed in all lipid classes upon dehydration irrespective of whether it was slow or rapid. Our data show only small differences between rapidly and slowly dehydrated leaves which can be correlated to the capacity of slowly dehydrated leaves to revive.     

复苏植物旋蒴苣苔棉子糖合酶基因的克隆和表达

复苏植物是研究植物耐脱水机制的特殊模式植物和宝贵的耐旱基因资源植物。以复苏植物旋蒴苣苔(Boea hygrometrica) 为材料研究其在脱水和复水过程中棉子糖系列寡糖含量的变化, 并克隆了旋蒴苣苔棉子糖合酶基因BhRFS。荧光定量PCR检测表明, BhRFS受干旱、低温(4°C)、高盐(200 mmol·L^–1NaCl)和ABA(100 μmol·L^–1)诱导表达上调, 而高温(37°C)抑制其表达, H₂O₂(200 μmol·L^–1)处理对其没有影响。研究结果表明, BhRFS可能参与了多种非生物逆境胁迫抗性反应, 并受到ABA依赖的信号通路调控。