Photosynthetic pigments and photosynthetic products of endophyte-infected and endophyte-free Lolium perenne L.under drought strees conditions

Endophyte-infected fED seeds of Lolium perenne L.were used to attain endophyte-free fED population by heating the seeds at 43℃ for 15 min and then 57℃ for 25 min.Relative water content(RWC),chlorophyll,soluble sugar and starch content of EI and EF populations under normal and drought stress conditions were compared to investigate the effect of endophyte infection on the host plant.Under severe stress.RWC of EI leaf was significantly higher than that Of EF leaf,i.e.EI plants took more advantages over EF plants in water-holding ability.Under mild stress,endophytc could enhance soluble sugars in host plants to improve their osmotic ability.With stress intensification,the improvement of endophyte no longer existed,and more photosynthetic products(such as starch)accumulated in EI plants to survive through the undesirable condidons.In the next spring,EI populations will recover more rapidly than EF populations.The biomass of a population is closely related to its photosynthesis.Under severe stress,EI population significantly accumulated more biomass than EF population.As far as photosynthetic pigments were concerned,contents of Chla,Chlb and Car of EI plants were close to those of EF plants,which suggested that endophyte infection didn't alleviate photosynthetic pigments from being destroyed by drought stress,and endophyte might improve photosynthesis ability of its host plant in other ways.     

Photosynthetic pigments and photosynthetic products of endophyte-infected and endophyte-free Lolium perenne L. under drought stress conditions

Endophyte-infected (EI) seeds of Lolium perenne L. were used to attain endophyte-free (EF) population by heating the seeds at 43°C for 15 min and then 57°C for 25 min. Relative water content (RWC), chlorophyll, soluble sugar and starch content of EI and EF populations under normal and drought stress conditions were compared to investigate the effect of endophyte infection on the host plant. Under severe stress, RWC of EI leaf was significantly higher than that of EF leaf, i.e. EI plants took more advantages over EF plants in water-holding ability. Under mild stress, endophyte could enhance soluble sugars in host plants to improve their osmotic ability. With stress intensification, the improvement of endophyte no longer existed, and more photosynthetic products (such as starch) accumulated in EI plants to survive through the undesirable conditions. In the next spring, EI populations will recover more rapidly than EF populations. The biomass of a population is closely related to its photosynthesis. Under severe stress, EI population significantly accumulated more biomass than EF population. As far as photosynthetic pigments were concerned, contents of Chla, Chlb and Car of EI plants were close to those of EF plants, which suggested that endophyte infection didn’t alleviate photosynthetic pigments from being destroyed by drought stress, and endophyte might improve photosynthesis ability of its host plant in other ways. __________ Translated from Acta Ecologica Sinica, 2005, 25 (2) [译自: 生态学报, 2005, 25(2)]     

内生真菌感染对干旱胁迫下黑麦草生长的影响

 内生真菌是生活在健康植物的茎叶内,形成不明显感染的一类真菌。以黑麦草（Lolium perenne L.）为实验材料,研究在不同强度的干旱胁迫下内生真菌（Neotyphodium lolii）侵染对其叶片延伸生长、分蘖数和生物量的影响。结果表明,与非感染种群相比,内生真菌感染对黑麦草叶片延伸速率无明显促进作用;内生真菌感染种群具有明显较多的分蘖数;在重度胁迫并经过恢复期后,内生真菌感染种群具有较高的根冠比。因而内生真菌可能通过提高植物的分蘖能力和促进有机物向根系的分配来促进宿主植物的营养生长并提高其抗旱性     

Endophyte-Mediated Effects on the Growth and Physiology of Achnatherum sibiricum Are Conditional on Both N and P Availability

The interaction of endophyte–grass associations are conditional on nitrogen (N) availability, but the reported responses of these associations to N are inconsistent. We hypothesized that this inconsistency is caused, at least in part, by phosphorus (P) availability. In this experiment, we compared the performance of endophyte-infected (EI) and endophyte-free (EF) Achnatherum sibiricum subjected to four treatments comprising a factorial combination of two levels of N (N+ vs. N−, i.e. N supply vs. N deficiency) and two levels of P (P+ vs. P−, i.e. P supply vs. P deficiency) availability. The results showed that A. sibiricum–Neotyphodium associations were conditional on both N and P availability, but more conditional on N than P. Under N+P− conditions, endophyte infection significantly improved acid phosphatase activity of EI plants, such that the biomass of EI plants was not affected by P deficiency (i.e. similar growth to N+P+ conditions), and resulted in more biomass in EI than EF plants. Under N−P+ conditions, biomass of both EI and EF decreased compared with N+P+; however, EI biomass decreased slowly by decreasing leaf N concentration more rapidly but allocating higher fractions of N to photosynthetic machinery compared with EF plants. This change of N allocation not only improved photosynthetic ability of EI plants but also significantly increased their biomass. Under N−P− conditions, EI plants allocated higher fractions of N to photosynthesis and had greater P concentrations in roots, but there was no significant difference in biomass between EI and EF plants. Our results support the hypothesis that endophyte–grass interactions are dependent on both N and P availability. However, we did not find a clear cost of endophyte infection in A. sibiricum.     

Endophytic benefit for a competitive host is neutralized by increasing ratios of infected plants

Leaf endophytes such as Epichloë can affect the competitive ability of host grasses, but the reported responses are inconsistent. We hypothesized that this inconsistency is caused, at least in part, by the following two aspects. One is that a competitive advantage might occur as a result of an increase in storage compounds for both growth and defense. Another is that the effect of the endophyte might be related to both water availability and host density. In a greenhouse experiment, we compared the competitive abilities of endophyte-infected (EI) and endophyte-free (EF) Leymus chinensis, a dominant grass native to the Inner Mongolia Steppe of China, subjected to ten treatments comprised of a factorial combination of two levels of water availability (well-watered and drought) and five proportions of EI to EF plants (12:0, 4:8, 6:6, 8:4, 0:12). The results showed that the competitive ability of EI plants was higher than that of EF under drought. Here, greater belowground biomass and water use efficiency might contribute to better competitiveness of EI plants. When competing under well-watered conditions, endophyte infection did not provide a benefit to the host plant in biomass accumulation, but more carbon was allocated to defense (total phenolics) in EI plants. This scenario could help EI plants suffer less damage than EF when exposed to herbivores in natural habitats. The competitive ability of EI plants was regulated by EI:EF ratios. Competitive ability of EI plants was higher than that of EF plants in mixtures with lower numbers of EI plants, but the beneficial effect of endophyte infection was neutralized in mixtures with higher numbers of EI plants. Overall, endophyte infection improved the competitive ability of the host under either drought or well-watered conditions but in the presence of herbivore, only this benefit was neutralized by increasing ratios of EI plants. We suspect that both the conditional beneficial effects and stabilizing effects of density differences are likely to keep the endophyte infection rate of L. chinensis at an intermediate level.     

Effects of endophytic fungi on some drought tolerance mechanisms of tall fescue in a hydroponics culture

Neotyphodium, a seed-transmissible nonpathogenic fungal endophyte (symbiont) is considered beneficial because endophyte-infected grasses are more drought-tolerant, produce more dry matter, utilize soil nitrogen more efficiently, and deter insects. In this study, the effects of endophytes on physiological mechanisms of drought tolerance in tall fescue (Festuca arundinacea Schreb.) were studied in a greenhouse. Two clonally propagated genotypes of tall fescue (F. arundinacea Schreb.), naturally containing endophyte (EI), and their endophyte-free ramets (EF) were tested at three water stress treatments exerted by PEG 6000 in a hydroponics system. Relative water content (RWC), cell membrane stability (CMS), proline and chlorophyll contents in plant leaves were measured during water stress treatments. After harvest, K⁺, Ca²⁺, and Mg²⁺ contents were measured in plant roots and shoots. After 20 days under stress conditions, plants were transferred to basal hydroponics medium, and their survival after stress relief was evaluated. The results showed that endophyte considerably contributes to host grass water stress tolerance. Both genotypes of EI and EF plants did not differ in RWC, but, regardless of the infection status, genotype 75 had the higher RWC than genotype 83. EI clones of both genotypes maintained slightly higher chlorophyll content and membrane stability than EF clones, although these differences were not significant. The EI plants of genotype 83 concentrated significantly more proline than EF plants, but in the genotype 75, differences between EI and EF clones were not significant. Plant mineral absorption was also influenced by the endophyte presence. EI clones had the higher concentrations of K⁺ in the shoots of both genotypes. The Mg²⁺ and Ca²⁺ contents in EF plants of both genotypes were higher than EI plants in the roots, but in the shoots there were no differences between EI and EF clones. EI clones survived longer after stress removal. These results strongly suggest that Neotyphodium endophytes exert their effects on tall fescue drought tolerance through alteration of various physiological mechanisms involved. Published in Russian in Fiziologiya Rastenii, 2009, Vol. 56, No. 4, pp. 563–570. This test was submitted by the authors in English.     

不同氮素营养条件下内生真菌感染对黑麦草光合和蒸腾速率及生物量的影响

以黑麦草(Lolium perenne L.)为实验材料,研究在不同氮素营养条件下内生真菌(Neotyphodium lolii)感染对其光合特性及生物量的影响。结果表明：1)整个实验中,内生真菌感染对黑麦草净光合速率、蒸腾速率以及水分利用效率均无显著影响,但在中氮和高氮水平时,感染种群的净同化累积值有超过非感染种群的趋势;2)在本实验的第一处理期和第二处理期,内生真菌感染对黑麦草绿色部分的干物质产量无显著影响,但在第三处理期感染种群的绿色部分的干物质产量显著高于非感染种群。     

干旱胁迫下内生真菌感染对黑麦草实验种群光合、蒸腾和水分利用的影响

 以黑麦草(Lolium perenne L．)为实验材料,研究在不同强度的干旱胁迫下内生真菌(Neotyphodium lolii (原 Acremonium lolii))感染对其净同化速率、蒸腾速率和水分利用效率的影响。结果显示：1)在干旱胁迫前期,内生真菌感染(EI)种群和非感染(EF)种群之间的群体净同化速率无显著差异;到胁迫后期,在重度胁迫下EI种群的净同化速率高于EF种群;复水后,各个胁迫强度EI和EF种群的净同化速率均迅速恢复,差异消失;2)在群体蒸腾速率上,干旱胁迫对其影响大于内生真菌的影响;3)在群体水分利用效率上,只是在重度胁迫后期,EI种群才高于EF种群。     

Neotyphodium Coenophialum-Infected Tall Fescue and Its Potential Application in the Phytoremediation of Saline Soils

The growth response of endophyte-infected (EI) and endophyte-free (EF) tall fescue to salt stress was investigated under two growing systems (hydroponic and soil in pots). The hydroponic experiment showed that endophyte infection significantly increased tiller and leaf number, which led to an increase in the total biomass of the host grass. Endophyte infection enhanced Na accumulation in the host grass and improved Na transport from the roots to the shoots. With a 15 g l^?1 NaCl treatment, the phytoextraction efficiency of EI tall fescue was 2.34-fold higher than EF plants. When the plants were grown in saline soils, endophyte infection also significantly increased tiller number, shoot height and the total biomass of the host grass. Although EI tall fescue cannot accumulate Na to a level high enough for it to be termed a halophyte, the increased biomass production and stress tolerance suggested that endophyte / plant associations had the potential to be a model for endophyte-assisted phytoextraction in saline soils.     

Arbuscular Mycorrhizal Fungi Alter Fractal Dimension Characteristics of Robinia pseudoacacia L. Seedlings Through Regulating Plant Growth,Leaf Water Status,Photosynthesis, and Nutrient Concentration Under Drought Stress

The influence of arbuscular mycorrhizal fungi (AMF), Funneliformis mosseae and Rhizophagus intraradices, on plant growth, leaf water status, chlorophyll concentration, photosynthesis, nutrient concentration, and fractal dimension (FD) characteristics of black locust (Robinia pseudoacacia L.) seedlings was studied in pot culture under well-watered, moderate drought stress, and severe drought stress treatments. Mycorrhizal seedlings had higher dry biomass, leaf relative water content (RWC), and water use efficiency (WUE) compared with non-mycorrhizal seedlings. Under all treatments, AMF colonization notably enhanced net photosynthetic rate, stomatal conductance, and transpiration rate, but decreased intercellular CO₂ concentration. Leaf chlorophyll a and total chlorophyll concentrations were higher in AM seedlings than those in non-AM seedlings although there was no significant difference between AMF species. AMF colonization improved leaf C, N, and P concentrations, but decreased C:N, C:P, and N:P ratios. Mycorrhizal seedlings had a larger FD value than non-mycorrhizal seedlings. The FD value was positively and significantly correlated to the plant growth parameters, photosynthesis, RWC, WUE, and nutrient concentration but negatively correlated to leaf/stem ratio, C:N and C:P ratios, and intercellular CO₂ concentration. We conclude that AMF lead to an improvement of growth performance of black locust seedlings under all growth conditions, including drought stress via improving leaf water status, chlorophyll concentration, photosynthesis, and nutrient uptake. Moreover, FD technology proved to be a powerful non-destructive method to characterize the effect of AMF on the physiology of host plants during drought stress.     

不同浓度和形态磷处理下内生真菌感染对高羊茅的影响

以感染内生真菌(endophyte-infected,EI)和不感染内生真菌(endophyte-free,EF)的高羊茅(Festuca arundinacea Schreb.)为材料,在温室沙培条件下研究内生真菌对高羊茅适应缺磷及利用不同形态磷肥的影响。结果表明,1)缺磷条件下,高羊茅EI和EF植株生长差异不显著;正常供磷条件下,高羊茅EI植株拥有更多分蘖数和绿叶数。说明正常供磷条件下内生真菌改善了宿主高羊茅的生长。2)与水溶性磷相比,高羊茅根有机酸和酸性磷酸酶(acid phosphatase,APase)活性在难溶性磷条件下显著增加,而根总酚含量无显著变化。在水溶性磷条件下,高羊茅EI植株根总酚含量显著高于EF植株,此时EI植株比EF植株拥有更多分蘖数和绿叶数,说明在水溶性磷条件下内生真菌对宿主地上部生长具有一定贡献。在难溶性磷条件下,虽然高羊茅EI植株根总酚含量仍然高于EF植株,但同时EI植株根有机酸含量显著低于EF植株,因此内生真菌感染只是增大了宿主植物的根冠比,而对分蘖数和绿叶数等无显著影响,说明内生真菌对宿主利用难溶性磷贡献不大。可见,内生真菌对宿主植物的生长在水溶性磷条件下更有利。     

Plant population and genotype effects override the effects of Epichloë endophyte species on growth and drought stress response of Achnatherum robustum plants in two natural grass populations

Aims In cool-season grasses, systemic and vertically transmitted Epichlo? infections often provide a suite of benefits including increased growth, reproduction and competitive abilities. However, these effects of Epichlo? endophytes on their hosts often depend upon host and endophyte genotype and environmental factors.Methods Achnatherum robustum (sleepygrass) harbors at least two Epichlo? species within natural populations in the Southwest USA. We tested the effects of endophyte infection and species, host population and plant genotype (by experimentally removing the endophyte), and soil moisture (a key limiting factor) on growth and drought stress response of infected A. robustum plants from two populations (Weed and Cloudcroft) in the Sacremento Mountains of New Mexico, USA).Important findings Although the two populations harbor distinct Epichlo? species each with very different chemoprofiles, neither endophyte status (infected vs. uninfected) nor endophyte species affected most growth parameters at 8 or 25 weeks of the experiment, except for leaf length. In high water treatment, infected plants from the Weed population had longer leaf length compared with uninfected plants. In contrast, the population of origin affected all growth parameters, including plant height, leaf number, length and width, tiller number and shoot and root biomass, as well as wilting time. Grasses from the Cloudcroft population generally showed greater growth than grasses from the Weed population. Endophyte infection did affect wilting time, with infection in the Weed population generally reducing time to wilting under low and high water, whereas infection in the Cloudcroft population reduced time to wilting only under high water conditions. Our results suggest that plant population and their associated plant genotypes may play a much larger role in endophyte–host grass interactions in varying environments than previously thought. Asexual Epichlo? species may be compatible with only specific host genotypes within populations such that the phenotypic effects due to population may be greater than phenotypic changes influenced by variation in the endophyte.     

Benefits of a fungal endophyte in Elymus virginicus decline under drought stress

In most natural systems, it remains unclear whether microbial symbionts can help plants adapt to rapidly changing environments. Here, we tested the hypothesis that fungal endophyte symbiosis in a widespread, native grass species, Elymus virginicus, would promote host tolerance of drought. In a growth chamber experiment, we manipulated water availability to plants naturally infected with the endophyte Epichloë elymi and to plants that were experimentally disinfected. The drought treatment imposed a ～67% reduction in water, corresponding to the very high end of drought predictions for the Midwestern US, where E. virginicus is common. In contrast to expectations, E. virginicus benefited more from the endophyte under daily watering than under drought. Disinfected plants had 45% less aboveground biomass than naturally infected plants under daily watering and only 23% less under drought. Both the number of tillers produced and root biomass were reduced by disinfection, with a greater difference between endophyte treatments under daily watering than under drought. There were no effects of either the endophyte or drought on aphid colonization of the plants. To put these results into a broader geographic context, we surveyed endophyte infection frequencies across 43 populations, including wild populations, commercial stock and germplasm resources. Endophyte frequencies varied from 0% to 100%, and frequencies were much higher for wild populations than germplasm resources. Natural variation in endophyte frequencies combined with the heritable transmission of endophytes from plants to seeds provides opportunities for climate change to affect selection on the maintenance of endophyte symbiosis in E. virginicus.     

Growth,photosynthesis and water relations as affected by different drought regimes and subsequent recovery in <Emphasis Type="Italic">Medicago laciniata</Emphasis> (L.) populations

The aims of this study were to investigate the effects of water deficit and recovery on growth, photosynthesis and water relations in four Medicago laciniata populations from saharian (Ml-90), inferior arid (Ml-204), superior arid (Ml-306) and semi-arid (Ml-376) Tunisian regions. After 28 d of sowing with ample irrigation, the plants were subjected to 4 water regimes: optimal irrigation (100% of field capacity, FC), moderate drought (75% FC), severe drought (35% FC) and rewatering (plants submitted to 35% FC during 7 d, afterwards the plants were rewatered to 100% FC). Harvest was carried out after 28 d of treatments. The drought tolerance in M. laciniata populations was found to be increased particularly with increasing temperatures of collection site of the population. The Ml-204 and Ml-90 populations used mainly physiological strategies for survival under moderate water shortage. Higher severe drought tolerance in both signaled populations would be related to their lower photosynthesis metabolic impairment, relatively higher leaf RWC and greater osmotic potential decrease. The results suggest that plants with low values of leaf features are likely to maintain higher leaf RWC under sever drought. The largest decrease of osmotic potential was found associated with the solute accumulations such as proline and K⁺.     

不同氮素营养条件下内生真菌感染对黑麦草光合和蒸腾速率及生物量的影响

以黑麦草(Lolium perenne L)为实验材料,研究在不同氮素营养条件下内生真菌(Neotyphodium lolii)感染对其光合特性及生物量的影响.结果表明:1)整个实验中,内生真菌感染对黑麦草净光合速率、蒸腾速率以及水分利用效率均无显著影响,但在中氮和高氮水平时,感染种群的净同化累积值有超过非感染种群的趋势;2)在本实验的第一处理期和第二处理期,内生真菌感染对黑麦草绿色部分的干物质产量无显著影响,但在第三处理期感染种群的绿色部分的干物质产量显著高于非感染种群.     

内生真菌和丛枝菌根真菌对羊草生长的影响

该研究比较了摩西球囊霉(Glmous mosseae)和幼套球囊霉(Glmous etunicatum)两种丛枝菌根真菌和内生真菌单独及混合接种对羊草(Leymus chinensis)生长的影响。结果表明, 内生真菌对2种菌根真菌的侵染均无显著影响, 内生真菌可极显著增加羊草的分蘖数、地上生物量、总生物量。内生真菌与菌根真菌之间的相互作用因菌根真菌种类而不同, 幼套球囊霉对宿主植物生长无明显影响且和内生真菌之间也无明显的相互作用; 单独接种摩西球囊霉显著增加羊草的地上、地下和总生物量, 当其与内生真菌共同存在时, 二者之间存在一定的拮抗作用。冗余分析结果表明, 在内生真菌-AM真菌-羊草共生体中, 内生真菌对宿主植物生长的影响最大, 摩西球囊霉对宿主植物生长也有一定的贡献, 幼套球囊霉对宿主植物生长无明显影响。     

Differences in the responses of stem diameter and pod thickness to drought stress during the grain filling stage in soybean plants

This study investigated the factor of the physiological characteristics causing the reduction of yield of soybean plants (Glycine max (L.) Merr.) by drought stress, by monitoring changes in stem diameter and pod thickness, and photosynthetic activity, partitioning of ¹³C-labeled photosynthate. Drought stress reduced the whole plant dry weight due to the decrease in leaf and pod dry matter accumulation; however, this stress did not have a significant effect on stem growth. Leaf photosynthesis was also severely decreased by drought stress in the early stage of stress treatment as leaf water potential decreased. Imposition of stress decreased pod thickness, but stem diameter increased. The adverse effect of drought stress on pod thickness was more evident at night than during the day. The stem diameter also shrank during the day and expanded at night, but the nocturnal increase in stem diameter during drought stress treatment was greater for stressed plants compared with well-watered controls. Drought stress significantly promoted ¹³C partitioning from the fed leaf to other parts of the plant; the stem was the largest beneficiary. Soluble carbohydrates accumulated in various plant parts under the influence of the stress, but starch concentration declined in all organs except the stem. These results indicated that stem growth was promoted by drought stress compared to pod growth at the early grain-filling stage.     

干旱-复水处理对杠柳幼苗光合作用及活性氧代谢的影响

采用人工控制土壤水分试验,以80%田间持水量处理为对照,研究了3次干旱-复水处理对2年生杠柳幼苗叶片光合作用,根、茎、叶膜脂过氧化和抗氧化系统的影响.结果表明: 在干旱条件下, 杠柳叶片相对含水量和光合速率(P_n)显著降低,光合色素含量升高. 干旱复水后,叶片相对含水量完全恢复,反映了杠柳较强的旱后修复能力;叶绿素含量和P_n均明显高于对照,表现出补偿效应,适度干旱诱导了杠柳的抗旱适应性.干旱胁迫使P_n下降,以气孔限制为主,但在中午发生了非气孔限制;幼叶、新茎和细根中的超氧阴离子产生速率升高,丙二醛含量则降低,说明这些幼嫩组织未受到氧化伤害.不同器官中SOD、CAT和POD活性及变化趋势不同,以细根的3种保护酶的反应最为灵敏,说明细根是杠柳适应干旱环境的重要器官.器官间的相互合作与协调使杠柳能有效地适应干湿交替的干旱环境.     

Adaptive photosynthetic and physiological responses to drought and rewatering in triploid <Emphasis Type="Italic">Populus</Emphasis> populations

Cuttings of Populus cathayana Rehd, originating from three triploid and one diploid populations with the same parents but different gamete origins, were used to examine physiological responses to drought stress and rewatering by exposure to three progressive water regimes. Progressive drought stress significantly decreased the leaf relative water content (RWC), photosynthesis, and chlorophyll fluorescence parameters, and increased the relative electrolyte leakage, malondialdehyde (MDA), free proline (Pro), and antioxidant enzymes, such as superoxide dismutase, peroxidase, and catalase, in the four populations evaluated. However, compared to the diploid population, triploid populations showed lower relative electrolyte leakage and MDA, higher RWC and Pro content, and more efficient photosynthesis and antioxidant systems under the same water regime. Our data indicated that triploid populations possessed more efficient protective mechanisms than that of diploid population with gradually increasing drought stress. Moreover, some triploid genotypes were less tolerant to water stress than that of diploids due to large intrapopulation overlap.     

缺磷对黑麦草-内生真菌共生体生长和根中酚含量的影响

培养液中缺磷或内生真菌感染对黑麦草地上部生长的影响不显著,但二者的交互作用却有着显著影响。随着磷浓度的下降,感染内生真菌的黑麦草显示出较强的生长优势,其根长和根中酚类物质的含量显著增加。