Exogenous ABA accentuates the differences in root hydraulic properties between mycorrhizal and non mycorrhizal maize plants through regulation of PIP aquaporins

The arbuscular mycorrhizal (AM) symbiosis has been shown to modulate the same physiological processes as the phytohormone abscisic acid (ABA) and to improve plant tolerance to water deficit. The aim of the present research was to evaluate the combined influence of AM symbiosis and exogenous ABA application on plant root hydraulic properties and on plasma-membrane intrinsic proteins (PIP) aquaporin gene expression and protein accumulation after both a drought and a recovery period. Results obtained showed that the application of exogenous ABA enhanced osmotic root hydraulic conductivity (L) in all plants, regardless of water conditions, and that AM plants showed lower L values than nonAM plants, a difference that was especially accentuated when plants were supplied with exogenous ABA. This effect was clearly correlated with the accumulation pattern of the different PIPs analyzed, since most showed reduced expression and protein levels in AM plants fed with ABA as compared to their nonAM counterparts. The possible involvement of plant PIP aquaporins in the differential regulation of L by ABA in AM and nonAM plants is further discussed.     

Plant potassium content modifies the effects of arbuscular mycorrhizal symbiosis on root hydraulic properties in maize plants

It is well known that the arbuscular mycorrhizal (AM) symbiosis helps the host plant to overcome several abiotic stresses including drought. One of the mechanisms for this drought tolerance enhancement is the higher water uptake capacity of the mycorrhizal plants. However, the effects of the AM symbiosis on processes regulating root hydraulic properties of the host plant, such as root hydraulic conductivity and plasma membrane aquaporin gene expression, and protein abundance, are not well defined. Since it is known that K(+) status is modified by AM and that it regulates root hydraulic properties, it has been tested how plant K(+) status could modify the effects of the symbiosis on root hydraulic conductivity and plasma membrane aquaporin gene expression and protein abundance, using maize (Zea mays L.) plants and Glomus intraradices as a model. It was observed that the supply of extra K(+) increased root hydraulic conductivity only in AM plants. Also, the different pattern of plasma membrane aquaporin gene expression and protein abundance between AM and non-AM plants changed with the application of extra K(+). Thus, plant K(+) status could be one of the causes of the different observed effects of the AM symbiosis on root hydraulic properties. The present study also highlights the critical importance of AM fungal aquaporins in regulating root hydraulic properties of the host plant.     

Plant Responses to Drought Stress and Exogenous ABA Application are Modulated Differently by Mycorrhization in Tomato and an ABA-deficient Mutant (<Emphasis Type="Italic">Sitiens</Emphasis>)

The aims of the present study are to find out whether the effects of arbuscular mycorrhizal (AM) symbiosis on plant resistance to water deficit are mediated by the endogenous abscisic acid (ABA) content of the host plant and whether the exogenous ABA application modifies such effects. The ABA-deficient tomato mutant sitiens and its near-isogenic wild-type parental line were used. Plant development, physiology, and expression of plant genes expected to be modulated by AM symbiosis, drought, and ABA were studied. Results showed that only wild-type tomato plants responded positively to mycorrhizal inoculation, while AM symbiosis was not observed to have any effect on plant development in sitiens plants grown under well-watered conditions. The application of ABA to sitiens plants enhanced plant growth both under well-watered and drought stress conditions. In respect to sitiens plants subjected to drought stress, the addition of ABA had a cumulative effect in relation to that of inoculation with G. intraradices. Most of the genes analyzed in this study showed different regulation patterns in wild-type and sitiens plants, suggesting that their gene expression is modulated by the plant ABA phenotype. In the same way, the colonization of roots with the AM fungus G. intraradices differently regulated the expression of these genes in wild-type and in sitiens plants, which could explain the distinctive effect of the symbiosis on each plant ABA phenotype. This also suggests that the effects of the AM symbiosis on plant responses and resistance to water deficit are mediated by the plant ABA phenotype.     

Arbuscular mycorrhizal symbiosis induces strigolactone biosynthesis under drought and improves drought tolerance in lettuce and tomato

Arbuscular mycorrhizal (AM) symbiosis alleviates drought stress in plants. However, the intimate mechanisms involved, as well as its effect on the production of signalling molecules associated with the host plant–AM fungus interaction remains largely unknown. In the present work, the effects of drought on lettuce and tomato plant performance and hormone levels were investigated in non‐AM and AM plants. Three different water regimes were applied, and their effects were analysed over time. AM plants showed an improved growth rate and efficiency of photosystem II than non‐AM plants under drought from very early stages of plant colonization. The levels of the phytohormone abscisic acid, as well as the expression of the corresponding marker genes, were influenced by drought stress in non‐AM and AM plants. The levels of strigolactones and the expression of corresponding marker genes were affected by both AM symbiosis and drought. The results suggest that AM symbiosis alleviates drought stress by altering the hormonal profiles and affecting plant physiology in the host plant. In addition, a correlation between AM root colonization, strigolactone levels and drought severity is shown, suggesting that under these unfavourable conditions, plants might increase strigolactone production in order to promote symbiosis establishment to cope with the stress.     

Arbuscular mycorrhizal symbiosis modifies the effects of a nitric oxide donor (sodium nitroprusside;SNP) and a nitric oxide synthesis inhibitor (Nω-nitro-L-arginine methyl ester;L-NAME) on lettuce plants under well watered and drought conditions

Arbuscular mycorrhizal (AM) symbiosis is known to help the host plant to overcome environmental stresses as drought by a combination of multiple mechanisms including enhancing of root water uptake capacity. On the other hand, Nitric oxide (NO) is involved in regulating the response of plants to environmental stresses and colonization process of AM fungi. The objective of this research was to study how AM and non-AM lettuce plants responded to a NO donor (sodium nitroprusside; SNP) or to a NO synthesis inhibitor (Nω-nitro-L-arginine methyl ester hydrochloride; L-NAME) under well watered and drought conditions. Most remarkable results were that L-NAME increased the percentage of AM colonized roots under both water regimes and AM plants modified the shoot:root ratio by both chemicals under well watered conditions. Also, the deleterious effects of SNP treatment were partially prevented by AM symbiosis. Moreover, NO could be involved in the diminution of leaf water content under drought conditions, and SNP treatment seems to favor apoplastic water path inside roots. Therefore, different outcomes of relative water content, stomatal conductance and root hydraulic conductivity observed between AM and non-AM plants could be mediated by NO.     

Arbuscular mycorrhizal influence on leaf water potential, solute accumulation, and oxidative stress in soybean plants subjected to drought stress

This study investigated several aspects related to drought tolerance in arbuscular mycorrhizal (AM) soybean plants. The investigation included both shoot and root tissues in order to reveal the preferred target tissue for AM effects against drought stress. Non-AM and AM soybean plants were grown under well-watered or drought-stressed conditions, and leaf water status, solute accumulation, oxidative damage to lipids, and other parameters were determined. Results showed that AM plants were protected against drought, as shown by their significantly higher shoot-biomass production. The leaf water potential was also higher in stressed AM plants (-1.9 MPa) than in non-AM plants (-2.5 MPa). The AM roots had accumulated more proline than non-AM roots, while the opposite was observed in shoots. Lipid peroxides were 55% lower in shoots of droughted AM plants than in droughted non-AM plants. Since there was no correlation between the lower oxidative damage to lipids in AM plants and the activity of antioxidant enzymes, it seems that first the AM symbiosis enhanced osmotic adjustment in roots, which could contribute to maintaining a water potential gradient favourable to the water entrance from soil into the roots. This enabled higher leaf water potential in AM plants during drought and kept the plants protected against oxidative stress, and these cumulative effects increased the plant tolerance to drought.     

Arbuscular mycorrhizal symbiosis regulates physiology and performance of <Emphasis Type="Italic">Digitaria eriantha</Emphasis> plants subjected to abiotic stresses by modulating antioxidant and jasmonate levels

This study evaluates antioxidant responses and jasmonate regulation in Digitaria eriantha cv. Sudafricana plants inoculated (AM) and non-inoculated (non-AM) with Rhizophagus irregularis and subjected to drought, cold, or salinity. Stomatal conductance, photosynthetic efficiency, biomass production, hydrogen peroxide accumulation, lipid peroxidation, antioxidants enzymes activities, and jasmonate levels were determined. Stomatal conductance and photosynthetic efficiency decreased in AM and non-AM plants under all stress conditions. However, AM plants subjected to drought, salinity, or non-stress conditions showed significantly higher stomatal conductance values. AM plants subjected to drought or non-stress conditions increased their shoot/root biomass ratios, whereas salinity and cold caused a decrease in these ratios. Hydrogen peroxide accumulation, which was high in non-AM plant roots under all treatments, increased significantly in non-AM plant shoots under cold stress and in AM plants under non-stress and drought conditions. Lipid peroxidation increased in the roots of all plants under drought conditions. In shoots, although lipid peroxidation decreased in AM plants under non-stress and cold conditions, it increased under drought and salinity. AM plants consistently showed high catalase (CAT) and ascorbate peroxidase (APX) activity under all treatments. By contrast, the glutathione reductase (GR) and superoxide dismutase (SOD) activity of AM roots was lower than that of non-AM plants and increased in shoots. The endogenous levels of cis-12-oxophytodienoc acid (OPDA), jasmonic acid (JA), and 12-OH-JA showed a significant increase in AM plants as compared to non-AM plants. 11-OH-JA content only increased in AM plants subjected to drought. Results show that D. eriantha is sensitive to drought, salinity, and cold stresses and that inoculation with AM fungi regulates its physiology and performance under such conditions, with antioxidants and jasmonates being involved in this process.     

Tolerance of Mycorrhiza infected pistachio (Pistacia vera L.) seedling to drought stress under glasshouse conditions

The influence of Glomus etunicatum colonization on plant growth and drought tolerance of 3-month-old Pistacia vera seedlings in potted culture was studied in two different water treatments. The arbuscular mycorrhiza (AM) inoculation and plant growth (including plant shoot and root weight, leaf area, and total chlorophyll) were higher for well-watered than for water-stressed plants. The growth of AM-treated seedlings was higher than non-AM-treatment regardless of water status. P, K, Zn and Cu contents in AM-treated shoots were greater than those in non-AM shoots under well-watered conditions and drought stress. N and Ca content were higher under drought stress, while AM symbiosis did not affect the Mg content. The contents of soluble sugars, proteins, flavonoid and proline were higher in mycorrhizal than non-mycorrhizal-treated plants under the whole water regime. AM colonization increased the activities of peroxidase enzyme in treatments, but did not affect the catalase activity in shoots and roots under well-watered conditions and drought stress. We conclude that AM colonization improved the drought tolerance of P. vera seedlings by increasing the accumulation of osmotic adjustment compounds, nutritional and antioxidant enzyme activity. It appears that AM formation enhanced the drought tolerance of pistachio plants, which increased host biomass and plant growth.     

Involvement of root ABA and hydraulic conductivity in the control of water relations in wheat plants exposed to increased evaporative demand

We studied the possible involvement of ABA in the control of water relations under conditions of increased evaporative demand. Warming the air by 3°C increased stomatal conductance and raised transpiration rates of hydroponically grown Triticum durum plants while bringing about a temporary loss of relative water content (RWC) and immediate cessation of leaf extension. However, both RWC and extension growth recovered within 30 min although transpiration remained high. The restoration of leaf hydration and growth were enabled by increased root hydraulic conductivity after increasing the air temperature. The use of mercuric chloride (an inhibitor of water channels) to interfere with the rise on root hydraulic conductivity hindered the restoration of extension growth. Air warming increased ABA content in roots and decreased it in shoots. We propose this redistribution of ABA in favour of the roots which increased the root hydraulic conductivity sufficiently to permit rapid recovery of shoot hydration and leaf elongation rates without the involvement of stomatal closure. This proposal is based on known ability of ABA to increase hydraulic conductivity confirmed in these experiments by measuring the effect of exogenous ABA on osmotically driven flow of xylem sap from the roots. Accumulation of root ABA was mainly the outcome of increased export from the shoots. When phloem transport in air-warmed plants was inhibited by cooling the shoot base this prevented ABA enrichment of the roots and favoured an accumulation of ABA in the shoot. As a consequence, stomata closed.     

Arbuscular mycorrhizae and nitrogen assimilation in maize after drought and recovery

In a greenhouse experiment, the effect of arbuscular mycorrhizal (AM) fungus (Glomus intraradices Schenck & Smith) colonization on N assimilation in maize (Zea mays L.) was examined after well-watered, drought and recovery periods. Seeds of selection cycles C0 (drought-sensitive) and C8 (drought-resistant) of the tropical maize cultivar Tuxpeño sequía were used for this study. Maize plants were exposed or not to drought stress for 3 weeks (45-65 days after sowing, DAS) followed by 3 weeks of recovery (66-86 DAS) at the preflowering stage. Root and shoot samples harvested at the end of the drought or well-watered and recovery periods were determined for key enzymes involved in N assimilation (NR, nitrate reductase; NiR, nitrite reductase; GS, glutamine synthetase; GOGAT, glutamate synthase), protein and amino acid concentrations, and total N contents. Drought stress significantly (P ≤ 0.01 or P ≤ 0.001) decreased all the enzyme activities except NiR in the roots and shoots of both cultivars. After 3 weeks of drought, the AM roots of both cultivars had higher activities of NR (C0, 45%; C8, 26%), GS (C0, 76%; C8, 33%) and GOGAT (C0, 41%; C8, 53%) than non-AM roots and were comparable to well-watered plants. These enzyme activities were also enhanced in drought-stressed AM shoots of C0 and C8. Total amino acid concentrations in AM plants of C0 were 4.6 and 1.6 times higher in roots and shoots, respectively, compared to non-AM plants. The predominant amino acids detected were Ala, Arg, Asn, Asp, Gln and Glu which constituted approximately 56 and 75% of the total pool in roots and shoots, respectively. Soluble proteins and total N contents were also higher in AM plants than non-AM plants under drought conditions. The enhancement of N-assimilating enzymes and nitrogenous compounds in maize may indicate a transfer of NO₃^? through the extraradical mycelium or increased N assimilation due to the AM symbiosis. Our overall results suggest that AM association plays an important role in enhancing N assimilation or N nutritional status which enables the host plant to withstand drought conditions and recover after stress is relieved.     

Arbuscular mycorrhizal symbiosis increases relative apoplastic water flow in roots of the host plant under both well-watered and drought stress conditions

Background and Aims

The movement of water through mycorrhizal fungal tissues and between the fungus and roots is little understood. It has been demonstrated that arbuscular mycorrhizal (AM) symbiosis regulates root hydraulic properties, including root hydraulic conductivity. However, it is not clear whether this effect is due to a regulation of root aquaporins (cell-to-cell pathway) or to enhanced apoplastic water flow. Here we measured the relative contributions of the apoplastic versus the cell-to-cell pathway for water movement in roots of AM and non-AM plants.

Methods

We used a combination of two experiments using the apoplastic tracer dye light green SF yellowish and sodium azide as an inhibitor of aquaporin activity. Plant water and physiological status, root hydraulic conductivity and apoplastic water flow were measured.

Key Results

Roots of AM plants enhanced significantly relative apoplastic water flow as compared with non-AM plants and this increase was evident under both well-watered and drought stress conditions. The presence of the AM fungus in the roots of the host plants was able to modulate the switching between apoplastic and cell-to-cell water transport pathways.

Conclusions

The ability of AM plants to switch between water transport pathways could allow a higher flexibility in the response of these plants to water shortage according to the demand from the shoot.     

Arbuscular mycorrhizal symbiosis and methyl jasmonate avoid the inhibition of root hydraulic conductivity caused by drought

Hormonal regulation and symbiotic relationships provide benefits for plants to overcome stress conditions. The aim of this study was to elucidate the effects of exogenous methyl jasmonate (MeJA) application on root hydraulic conductivity (L) of Phaseolus vulgaris plants which established arbuscular mycorrhizal (AM) symbiosis under two water regimes (well-watered and drought conditions). The variation in endogenous contents of several hormones (MeJA, JA, abscisic acid (ABA), indol-3-acetic acid (IAA), salicylic acid (SA)) and the changes in aquaporin gene expression, protein abundance and phosphorylation state were analyzed. AM symbiosis decreased L under well-watered conditions, which was partially reverted by the MeJA treatment, apparently by a drop in root IAA contents. Also, AM symbiosis and MeJA prevented inhibition of L under drought conditions, most probably by a reduction in root SA contents. Additionally, the gene expression of two fungal aquaporins was upregulated under drought conditions, independently of the MeJA treatment. Plant aquaporin gene expression could not explain the behaviour of L. Conversely, evidence was found for the control of L by phosphorylation of aquaporins. Hence, MeJA addition modified the response of L to both AM symbiosis and drought, presumably by regulating the root contents of IAA and SA and the phosphorylation state of aquaporins.     

Localized and non‐localized effects of arbuscular mycorrhizal symbiosis on accumulation of osmolytes and aquaporins and on antioxidant systems in maize plants subjected to total or partial root drying

The arbuscular mycorrhizal (AM) symbiosis alters host plant physiology under drought stress, but no information is available on whether or not the AM affects respond to drought locally or systemically. A split‐root system was used to obtain AM plants with total or only half root system colonized as well as to induce physiological drought affecting the whole plant or non‐physiological drought affecting only the half root system. We analysed the local and/or systemic nature of the AM effects on accumulation of osmoregulatory compounds and aquaporins and on antioxidant systems. Maize plants accumulated proline both, locally in roots affected by drought and systemically when the drought affected the whole root system, being the last effect ampler in AM plants. PIPs (plasma membrane intrinsic proteins) aquaporins were also differently regulated by drought in AM and non‐AM root compartments. When the drought affected only the AM root compartment, the rise of lipid peroxidation was restricted to such compartment. On the contrary, when the drought affected the non‐AM root fraction, the rise of lipid peroxidation was similar in both root compartments. Thus, the benefits of the AM symbiosis not only rely in a lower oxidative stress in the host plant, but it also restricts locally such oxidative stress.     

Influence of salinity on biomass production by Australian Pisolithus spp. isolates

Four Glomus species/isolates from arid, semi-arid and mesic areas were evaluated for their effects on growth and water use characteristics of young Citrus volkameriana (′Volkamer′ lemon) under well-watered conditions, followed by three soil-drying episodes of increasing severity (soil moisture tensions of –0.02, –0.06, and –0.08 MPa) and recovery conditions. Arbuscular mycorrhizal (AM) plants were also compared to non-AM plants given extra phosphorus (P) fertilizer. AM plants and non-AM plants had similar shoot size (dry weight and canopy area), but all AM fungus treatments stimulated root growth (dry weight and length). Leaf P concentrations were 12–56% higher in AM plants than non-AM plants. Enhanced root growth was positively correlated with leaf P concentration. In general, AM plants had greater whole-plant transpiration than non-AM plants under well-watered conditions, under mild water stress and during recovery from moderate and severe soil drying. This suggests a faster recovery from moisture stress by AM plants. AM plants had lower leaf conductance than non-AM plants when exposed to severe soil drying. Although the greatest differences were between AM and non-AM plants, plants treated with Glomus isolates differed in colonization level, leaf P concentration, root length, transpiration flux and leaf conductance.     

How does arbuscular mycorrhizal symbiosis regulate root hydraulic properties and plasma membrane aquaporins in Phaseolus vulgaris under drought, cold or salinity stresses?

Here, we evaluated how the arbuscular mycorrhizal (AM) symbiosis regulates root hydraulic properties and root plasma membrane aquaporins (PIP) under different stresses sharing a common osmotic component. Phaseolus vulgaris plants were inoculated or not with the AM fungus Glomus intraradices, and subjected to drought, cold or salinity. Stress effects on root hydraulic conductance (L), PIP gene expression and protein abundance were evaluated. Under control conditions, L in AM plants was about half that in nonAM plants. However, L was decreased as a result of the three stresses in nonAM plants, while it was almost unchanged in AM plants. At the same time, PIP2 protein abundance and phosphorylation state presented the same trend as L. Finally, the expression of each PIP gene responded differently to each stress and was dependent on the AM fungal presence. Differential expression of the PIP genes studied under each stress depending on the AM fungal presence may indicate a specific function and regulation by the AM symbiosis of each gene under the specific conditions of each stress tested.     

丛枝菌根真菌对百喜草的生理特性的影响

采用盆栽法研究了丛枝菌根（AM）真菌摩西球囊霉（Glomus mosseae）对水分胁迫条件下百喜草（Paspalum notatum）生长、渗透调节及抗氧化酶的影响。结果表明：接种AM真菌显著提高了百喜草的株高、地上部与根部鲜重、地上部P、K、Mn及根部P、Ca、Mn含量,明显降低了地上部Zn及根部Fe、B、Cu水平;随着干旱程度的加深,接种株的地上部相对含水量及叶绿素含量相对稳定且均显著高于未接种株,接种株地上部相对电导率、MDA含量均显著低于未接种株,接种株的地上部POD活性与脯氨酸含量均显著增加且均显著高于未接种株,AM侵染对SOD活性的影响较小。可见,接种AM真菌Glomus mosseae提高了植株体内保护酶活性（如POD）及渗透调节能力（如脯氨酸、P、K、Ca等渗透调节物含量的增加）,从而显著增强了百喜草的抗旱性。     

丛枝菌根真菌对百喜草的生理特性的影响

采用盆栽法研究了丛枝菌根（AM）真菌摩西球囊霉（Glomus mosseae）对水分胁迫条件下百喜草（Paspalum notatum）生长、渗透调节及抗氧化酶的影响。结果表明：接种AM真菌显著提高了百喜草的株高、地上部与根部鲜重、地上部P、K、Mn及根部P、Ca、Mn含量,明显降低了地上部Zn及根部Fe、B、Cu水平;随着干旱程度的加深,接种株的地上部相对含水量及叶绿素含量相对稳定且均显著高于未接种株,接种株地上部相对电导率、MDA含量均显著低于未接种株,接种株的地上部POD活性与脯氨酸含量均显著增加且均显著高于未接种株,AM侵染对SOD活性的影响较小。可见,接种AM真菌Glomusmossecte提高了植株体内保护酶活性（如POD）及渗透调节能力（如脯氨酸、P、K、Ca等渗透调节物含量的增加）,从而显著增强了百喜草的抗旱性。     

Effects of Arbuscular Mycorrhizal Fungi on Physiological Characterof Bahia Grass (Paspalum notatum,Poaceae)

The effects of arbuscular mycorrhizal (AM) fungus, Glomus mosseae, on growth, osmotic adjustment and antioxidant enzymes of bahia grass (Paspalum notatum) were studied in potted plants under water stress conditions. AM colonization significantly enhanced the plant height, root and shoot fresh weight, Phosphorus (P), potasium (K), manganese (Mn) contents in shoots, P, calcium (Ca), Mn contents in roots, whereas obviously decreased zinc (Zn) content in shoots, iron (Fe), boron (B), copper (Cu) contents in roots. During water stress, the relative water and chlorophyll contents were relatively stable and signifciantly higher in AM than in non-AM plants, AM inoculation notabley decreased the shoot relative conductivity and malondialdehyde (MDA) content, markedly increased shoot peroxidase (POD) activity and proline content, while AM infection did not affect the dismutase (SOD) activity of shoots. Our results suggested that AM colonization improved the protective enzyme activity (such as POD) and osmotic adjustment originating from proline P, K, Ca, resulting in the enhancement of drought tolerance.     

Azospirillum and arbuscular mycorrhizal colonization enhance rice growth and physiological traits under well-watered and drought conditions

The response of rice plants to inoculation with an arbuscular mycorrhizal (AM) fungus, Azospirillum brasilense, or combination of both microorganisms, was assayed under well-watered or drought stress conditions. Water deficit treatment was imposed by reducing the amount of water added, but AM plants, with a significantly higher biomass, received the same amount of water as non-AM plants, with a poor biomass. Thus, the water stress treatment was more severe for AM plants than for non-AM plants. The results showed that AM colonization significantly enhanced rice growth under both water conditions, although the greatest rice development was reached in plants dually inoculated under well-watered conditions. Water level did not affect the efficiency of photosystem II, but both AM and A. brasilense inoculations increased this value. AM colonization increased stomatal conductance, particularly when associated with A. brasilense, which enhanced this parameter by 80% under drought conditions and by 35% under well-watered conditions as compared to single AM plants. Exposure of AM rice to drought stress decreased the high levels of glutathione that AM plants exhibited under well-watered conditions, while drought had no effect on the ascorbate content. The decrease of glutathione content in AM plants under drought stress conditions led to enhance lipid peroxidation. On the other hand, inoculation with the AM fungus itself increased ascorbate and proline as protective compounds to cope with the harmful effects of water limitation. Inoculation with A. brasilense also enhanced ascorbate accumulation, reaching a similar level as in AM plants. These results showed that, in spite of the fact that drought stress imposed by AM treatments was considerably more severe than non-AM treatments, rice plants benefited not only from the AM symbiosis but also from A. brasilense root colonization, regardless of the watering level. However, the beneficial effects of A. brasilense on most of the physiological and biochemical traits of rice plants were only clearly visible when the plants were mycorrhized. This microbial consortium was effective for rice plants as an acceptable and ecofriendly technology to improve plant performance and development.     

摩西球囊霉对三叶鬼针草保护酶活性的影响

旱地农田入侵杂草三叶鬼针草(Bidens pilosa L.)与摩西球囊霉(Glomus mosseae)(AM真菌)经常形成长效的共生体,该霉菌对三叶鬼针草的入侵能力起到促进作用,但机理并不清楚。盆栽试验对正常浇水、中度干旱和重度干旱条件下接种AM真菌的三叶鬼针草植株与未接种植株之间叶片丙二醛(MDA)含量及超氧化物歧化酶(SOD)、过氧化氢酶(CAT)、抗坏血酸氧化酶(ASP)和过氧化物酶(POD)等保护酶活性进行了比较研究。结果表明,干旱胁迫导致三叶鬼针草叶片内MDA含量升高,SOD、CAT、ASP和POD的活性升高;正常浇水条件下,接种G. mosseae 对MDA含量,SOD、ASP和CAT活性影响不显著;中度干旱条件下,接种没有显著影响ASP活性,但对SOD和CAT活性影响显著;在处理前期(7,14,21d)POD活性影响不显著,在处理后期(28,35d)接种植株显著低于未接种植株;重度干旱条件下,未接种植株MDA含量、CAT活性显著高于接种植株,POD活性差异不显著。ASP活性在21d前差异不显著,之后,未接种植株显著高于接种植株。因此,AM真菌G. mosseae 有效地降低了干旱胁迫对三叶鬼针草的伤害程度,随着土壤含水量的严重亏缺和胁迫时间的延长,摩西球囊霉对三叶鬼针草的保护作用逐渐减弱。由于三叶鬼针草和AM真菌之间普遍存在着共生关系,该共生关系可能是三叶鬼针草入侵能力强的关键生物因子之一。