[Potential of Intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for Phytoremediation of Heavy-metal Contaminated Soil around Mining Areas].

In order to study the potential of intercropping Pennisetum purpureum Schum with Melia azedarach L. and Broussonetia papyrifera for phytoremediation of heavy-metal contaminated soil around mining areas, a pot experiment was conducted to investigate the effects of intercropping on plant biomass, heavy metal accumulation, dynamic changes in heavy metal content in soil solution, and response characteristics of the rhizosphere microbial community. The results indicated that the shoot biomass of P. purpureum and M. azedarach from their intercropping system (KX) was increased by 26.5% and 13.2%, respectively, and the shoot biomass of B. papyrifera from the intercropping system of P. purpureum and B. papyrifera (GX) was increased by 13.5% compared with their corresponding monoculture systems. The shoot Cd content of M. azedarach in the KX treatment was significantly increased by 24.9% (P<0.05), and their Cd and Pb accumulation in shoots were also significantly increased. The shoot contents and accumulations of Cd and Pb from P. purpureum in the GX treatment were significantly increased; however, those in B. papyrifera shoots were decreased. The total accumulations of Cd and Pb in each pot from intercropping systems were higher than that from the monoculture treatment, with that from the KX treatment being the highest at 1065 µg·pot-1. During the 150-day cultivation process, the pH value and dissolved organic carbon (DOC) content in the soil solution under the intercropping systems of KX and GX were higher than those of original soil (CK). After 150 d cultivation, the DOC contents of the soil solution under the KX and GX treatments were significantly increased by 40.5% and 33.1% in comparison with that under CK (P<0.05), respectively. Compared with those from CK and P. purpureum and B. papyrifera monoculture treatments, the Cd content in soil solution from the KX treatment was significantly decreased by 56.1%, 35.5%, and 46.5%, and that in the GX treatment was decreased by 54.5%, 33.2%, and 44.6% (P<0.05), respectively. The Shannon and Chao1 indices of rhizosphere microorganisms under the intercropping systems were significantly higher than those under CK. The number of unique OTUs in intercropping systems was significantly higher than that in CK and the M. azedarach and B. papyrifera monocultures. Intercropping improved the abundance of dominant bacteria such as Actinobacteriota and Acidobacteriota, and the abundance of Actinobacteriota increased by 31.6%, 20.9%, and 25.3% in the KX treatment and by 32.3%, 21.5%, and 25.9% in the GX treatment, respectively, in comparison with those in CK and the P. purpureum and M. azedarach monocultures. It was concluded that intercropping P. purpureum with wood plants could increase their shoot biomass and the accumulations of Cd and Pb, as well as soil environmental quality, whereas the availability and migration risk of heavy metals in soil were reduced. Moreover, the intercropping of P. purpureum and M. azedarach was more beneficial to the remediation of polymetallic-contaminated soil around mining areas.

A comparative study on the circadian rhythm of the electrical signals of Broussonetia papyrifera and Morus alba.

The circadian clock regulates a wide range of physiological processes in plants. Here we showed the circadian variations of the electrical signals in Broussonetia papyrifera L. and Morus alba L. in a natural state, which were analyzed using the day-night cycle method. The circadian characteristics of different plant electrical signals were compared by constructing a coupling model for the circadian rhythm of plant electrical signals. The electrical signal sensor had two electrode plates, which were fixed on the two ends of the splint, leaves could then be clamped and measured. The clamping force between the two electrode plates was uniform, which enabled continuous and nondestructive measurements. The results showed that an electric cyclic behavior was observed (circadian cycle) with the circadian variation in the plants within 24 h. Both the resistance (R) and the impedance (Z) increased firstly in the early morning and then decreased subsequently, while the capacitance (C) showed an opposite variation. Under different weather conditions, plant electrical signals showed periodic changes when the temperature and light intensity in the environment slightly changed within the physiological tolerance of plant. This indicated that the circadian clock of plant electrical signals could be maintained endogenously. The variation curves of plant electrical signals as time increased were fitted using the sine equation. The characteristic parameters of circadian rhythm of plant electrical signals were obtained. We found that although all plant electrical signals exhibited electric cyclic behavior, but the characteristics of circadian rhythms of electrical signals were different. This study provided a scientific basic for precisely monitoring plant electrical signals, and a reference for revealing circadian rhythms of plant electrical signals and their occurrence rules.

Identification of the PP2C gene family in paper mulberry (Broussonetia papyrifera) and its roles in the regulation mechanism of the response to cold stress.

OBJECTIVES: To study the possible roles of type-2C protein phosphatases (PP2Cs) which have been confirmed to play roles in the response to diverse abiotic stresses in paper mulberry, we launched a series of genomic and functional studies of BpPP2Cs. RESULTS: Sixty-three PP2C proteins in paper mulberry (Broussonetia papyrifera) were classified into 13 clades. Four BpPP2Cs with kinase domains were verified to be highly conserved in organisms ranging from algae to dicots. Seven pairs of BpPP2C genes were found to be expanding, and 18 BpPP2C genes had orthologues in Arabidopsis. BpPP2Cs showed broad expression in different tissues; the expression levels of 18 BpPP2Cs were changed and the phosphorylation levels of seven BpPP2C proteins increased at low temperature. Cold-response elements were found in the promoter region of 31 BpPP2Cs. Finally, Bp01g0320 was found to act as a hub protein and Bp01g0512 and Bp09g1278 played key roles in the ABA-signaling pathway and MAPK cascades, respectively. CONCLUSION: These results suggest that the PP2C gene family of paper mulberry is evolutionarily conserved and participates the regulation of the response to cold stress, which will play a vital role in further research on phosphatases in paper mulberry.

Improvement of manganese phytoremediation by Broussonetia papyrifera with two plant growth promoting (PGP) Bacillus species.

Combining phytoremediation plants and microorganisms is a promising method of remediating heavy metal contaminated soil. In this study, two manganese-tolerant strains were isolated from Mn slag and identified as Bacillus cereus HM5 and Bacillus thuringiensis HM7. These two Bacillus spp. have the ability to dissolve phosphorus, produce IAA and iron carrier. A pot experiment of Broussonetia papyrifera was conducted to explore potential of B. cereus HM5 and B. thuringiensis HM7 to improve effect of remedying Mn pollution by B. papyrifera. The strains were inoculated under different Mn treated (5 mmol/L, 50 mmol/L, Mn slag) respectively and the growth, root structure, root activity, physiological and biochemical characteristics of the leaves and accumulation of Mn for B. papyrifera were determinated. The effects of the soil environment to remediation were observed, the results showed that the biomass, total root length, surface area, crossings, tips, forks and root activity of B. papyrifera with inoculated strain were higher than those of the control group. The inoculation of these two Bacillus spp. increased the absorption of Mn by B. papyrifera and the concentration of Mn in the aerial parts of plants, indicating that the two strains could promote the growth of B. papyrifera and the accumulation of Mn. In addition, microbes reduced malonaldehyde content and the activities of antioxidant enzymes in leaves, suggesting that the two Bacillus spp. reduced Mn-induced oxidative stress. The principal component analysis showed that the added Bacillus strain prefer to promote plant root function maintenance and improve soil environment, rather than direct adsorption of heavy metals. These observations indicated that B. cereus HM5 and B. thuringiensis HM7 were valuable microorganisms, which could improve the remediating efficiency of B. papyrifera under Mn-contaminated soil.

Human mediated translocation of Pacific paper mulberry [Broussonetia papyrifera (L.) L'Hér. ex Vent. (Moraceae)]: Genetic evidence of dispersal routes in Remote Oceania.

Paper mulberry, Broussonetia papyrifera (L.) L'Hér. ex Vent. (Moraceae), a dioecious species, was transported by humans from Taiwan to the islands of Remote Oceania. Its introduction and cultivation in Remote Oceania was intentional due to its cultural importance as a fiber source for barkcloth textiles. The aim of this study was to explore the genetic diversity and structure of paper mulberry populations within Remote Oceania in order to infer dispersal patterns that may reflect past human interaction among island groups. We present the integrated analysis of 380 samples (313 contemporary and 67 herbarium specimens) collected in Near and Remote Oceania. Genetic characterization was based on a set of ten microsatellites developed for B. papyrifera and complemented with the analysis of the ribosomal internal transcribed spacer ITS-1 sequence, a sex marker and the chloroplast ndhF-rpl32 intergenic spacer. Microsatellite data identify a total of 64 genotypes, despite this being a clonally propagated crop, and show three major dispersal hubs within Remote Oceania, centered on the islands of Fiji, Tonga, and Pitcairn. Of 64 genotypes identified, 55 correspond to genotypes associated to female-sexed plants that probably descend from plants introduced by the prehistoric Austronesian-speaking voyagers. The ratio of accessions to genotypes between herbarium and contemporary samples, suggests recent loss of genetic diversity. In addition to the chloroplast haplotypes described previously, we detected two new haplotypes within Remote Oceania both originating in Taiwan. This is the first study of a commensal species to show genetic structuring within Remote Oceania. In spite of the genetic bottleneck, the presence of only one sex, a timespan of less than 5000 years, and asexual propagation of this crop in Remote Oceania, we detect genetic diversity and regional structuring. These observations suggest specific migration routes between island groups within Remote Oceania.

Physiological responses of Broussonetia papyrifera to manganese stress, a candidate plant for phytoremediation.

Effective phytoremediation of Mn contaminated soil requires the selection of a species with good manganese tolerance. Broussonetia papyrifera is an important economic plant and pioneer species, it could be well adapted to drought and saline-alkali environment. In order to understand the effect of Mn stress on B. papyrifera, the effects of different concentrations of Mn (0-50 mmol/L) stress on the growth, morphology, Mn tolerance and physiological indexes of the plant were explored. The results showed that the biomass, surface area, length, root volume, tips, forks, and crossings of B. papyrifera reached the maximum at the Mn concentration of 1 mmol/L. Mn content in the tissue and TF in plants increased with the increase of concentration, while the BCF increased first and then decreased, and the maximum BCF was 0.154 at 10 mmol/L. The accumulation of Mn lead to cell membrane lipid peroxidation, which increased toxic substances in plants, resulting in the increase of MDA and PRO, and affected the synthesis of chlorophyll. However, B. papyrifera could effectively alleviate oxidative stress by increasing the activities of antioxidant enzymes (SOD, POD, CAT), protein and soluble sugar. The results suggested that B. papyrifera had a good oxidative stress mechanism to Mn stress and could be used as candidates for remediation of pollution in mining areas.

Phytoextraction potential of Pteris vittata L. co-planted with woody species for As, Cd, Pb and Zn in contaminated soil.

The objective of this study was to determine the phytoextraction potential of a hyperaccumulator co-planted with a large biomass of woody plant in metal(loid)-contaminated soil. A pot experiment was conducted for 270 days (d) to study the growth, physiological responses, and metal(loid)s accumulation characteristics of plants, which included a shade-requiring, As-hyperaccumulator perennial herb, Pteris vittata L., co-planted with a woody tree, namely Morus alba L. or Broussonetia papyrifera L., for soil contaminated with arsenic (As), cadmium (Cd), lead (Pb), and zinc (Zn). The results showed that the biomass, photosynthetic pigment contents, antioxidant enzyme activity, and uptake of As in P. vittata L. were significantly enhanced by co-planting with M. alba L. or B. papyrifera L. Especially, the uptake of As by P. vittata L. was significantly (p < 0.05) increased by 80.0% and 64.2% when it was co-planted with M. alba L. or B. papyrifera L., respectively, while the As, Cd, Pb, and Zn contents of both M. alba L. and B. papyrifera L. were not significantly promoted by the co-planting. The comprehensive phytoextraction of metal(loid)s could be optimized by the co-planting of P. vittata L. with M. alba L. or B. papyrifera L. The total amount of As in the shoots from co-planting species was significantly (p < 0.05) higher than that of the monoculture with M. alba L. or B. papyrifera L., and that of Cd and Zn in the shoots was significantly (p < 0.05) higher than that of the monoculture with P. vittata L. The results showed that the co-planting of P. vittata L. with M. alba L. or B. papyrifera L. can alleviate the toxic effects of metal(loid)s on plant growth and improve the comprehensive phytoextraction amounts of metal(loid)s, and is a promising strategy for remediation of metal(loid)-contaminated soil.

Improvement of paper mulberry tolerance to abiotic stresses by ectopic expression of tall fescue FaDREB1.

Dehydration-responsive element binding/C-repeat-binding factors (DREB/CBF) control the activity of multiple stress response genes and therefore represent attractive targets for genetic improvement of abiotic stress tolerance. Paper mulberry (Broussonetia papyrifera L. Vent) is well known for its bark fibers and high levels of chalcone and flavonoid derivatives. Transgenic paper mulberry plants expressing a tall fescue (Festuca arundinacea Schreb.) FaDREB1 gene under the control of CaMV 35S were produced to examine the potential utility of FaDREB1 to increase the tolerance of paper mulberry plants to abiotic stress. The overexpressing FaDREB1 plants showed higher salt and drought tolerance than the wild-type plants (WT). After 13 days of withholding water, or 15 days in the presence of 250 mM NaCl, all the WT plants died, while the over-expressing FaDREB1 plants survived. The FaDREB1 plants had higher leaf water and leaf chlorophyll contents, accumulated more proline and soluble sugars, and had less ion leakage (which reflects membrane damage) than the WT plants had under high salt- and water-deficient conditions. The 35S promoter-driven expression of FaDREB1 did not cause growth retardation under normal growth conditions. Therefore, improved tolerance to multiple environmental stresses in paper mulberry might be achieved via genetic engineering through the ectopic expression of an FaDREB1 gene.

Ectopic expression of FaDREB2 enhances osmotic tolerance in paper mulberry.

Dehydration-responsive element binding (DREB) proteins are a subfamily of AP2/ERF transcription factors that have been shown to improve tolerance to osmotic stresses in plants. To improve the osmotic stress tolerance of paper mulberry (Broussonetia papyrifera L. Vent), an economically important tree, we transformed it with a plasmid carrying tall fescue (Festuca arundinacea Schreb) FaDREB2 under the control of CaMV 35S. The ectopic expression of FaDREB2 did not cause growth retardation, and the paper mulberry seedlings expressing FaDREB2 showed higher salt and drought tolerance than wild-type plants (WT). After 13 d of withholding water, or 15 d in the presence of 250 mM NaCl, all the WT plants died, while the plants expressing FaDREB2 survived. The FaDREB2 transgenic plants had higher leaf water and chlorophyll contents, accumulated more proline and soluble sugars, and had less membrane damage than the WT plants under high salt and water-deficient conditions. Taken together, the results indicate the feasibility of improving tolerance to multiple environmental stresses in paper mulberry seedlings via genetic engineering, by introducing FaDREB2, which promotes the increased accumulation of osmolytes (soluble sugars and proline), to counter osmotic stresses caused by abiotic factors.

Overexpression of AtNHX5 improves tolerance to both salt and drought stress in Broussonetia papyrifera (L.) Vent.

Paper mulberry (Broussonetia papyrifera L. Vent) is well known for its bark fibers, which are used for making paper, cloth, rope, etc. It was found that, in addition to its well-documented role in the enhancement of plant salt tolerance, overexpression of the Na+/H+ antiporter (AtNHX5) gene in paper mulberry plants showed high drought tolerance. After exposure to water deficiency and salt stress, the wild-type (WT) plants all died, while the AtNHX5-overexpressing plants remained alive under high salt stress, and had a higher survival rate (>66%) under drought stress. Measurements of ion levels indicated that Na+ and K+ contents were all higher in AtNHX5-overexpressing leaves than in WT leaves in high saline conditions. The AtNHX5 plants had higher leaf water content and leaf chlorophyll contents, accumulated more proline and soluble sugars, and had less membrane damage than the WT plants under water deficiency and high saline conditions. Taken together, the results indicate that the AtNHX5 gene could enhance the tolerance of paper mulberry plants to multiple environmental stresses by promoting the accumulation of more effective osmolytes (ions, soluble sugars, proline) to counter the osmotic stress caused by abiotic factors.

Influence of drought intensity on the response of six woody karst species subjected to successive cycles of drought and rewatering.

Tolerance to the effects of drought and subsequent recovery after a rainfall appear to be critical for plants in the karst regions of southwestern China, which are characterized by frequent but temporary drought events. This study investigated the effects of drought intensity and repetition on photosynthesis and photoprotection mechanisms of karst plants during successive cycles of drought and subsequent recovery. Leaf water potential, gas exchange, chlorophyll fluorescence and several associated metabolic processes were studied in six plant species, including Pyracantha fortuneana (PF), Rosa cymosa (RC), Broussonetia papyrifera (BP), Cinnamomum bodinieri (CB), Platycarya longipes (PL) and Pteroceltis tatarinowii (PT) during three cycles of drought treatments at four different intensities. The four treatments were: well-watered, mild drought, moderate drought and severe drought, each followed by rewatering events. We found that limitations to CO(2) diffusion accounted for photosynthetic declines under mild and moderate drought treatments, while metabolic limitations dominated the response to severe drought. Repetition of drought did not intensify the impairment of photosynthetic metabolism regardless of drought intensity in the six species studied. Repetition of severe drought delayed the photosynthetic recoveries in PF, RC and CB after rewatering. Repetition of drought increased thermal dissipation in PF, CB and BP, as well as superoxide dismutase (EC 1.15.1.1) activity in RC and CB. Enhanced photosynthetic performance, measured as increased intrinsic water use efficiency, photosynthetic performance per unit of photosynthetic pigment, maintenance of high thermal dissipation and high ratios of carotenoids to chlorophylls, was observed during the rewatering periods. This enhanced photosynthetic performance allowed for the complete recovery of the six karst species from successive intermittent drought events.

[Absorption and allocation characteristics of K+, Ca2+, Na+ and Cl- in different organs of Broussonetia papyrifera seedlings under NaCl stress].

One-year-old Broussonetia papyrifera seedlings were subjected to 0.4, 1, 2, 3, and 4 g x kg(-1) of soil NaCl stress, and their biomass accumulation, leaf plasma membrane permeability, and the absorption, allocation and translocation of K+, Ca2+, Na+, and Cl-, as well as the symptoms of salt injury, were studied and investigated. The leaf plasma membrane permeability increased with the increase of soil NaCl concentration and of the duration of soil NaCl stress, and the seedling's root/shoot ratio also increased with increasing soil NaCl concentration. When the soil NaCl concentration exceeded 3 g x kg(-1), leaf plasma membrane permeability and seedling' s biomass accumulation were affected significantly. The Na+ and Cl- concentrations in different organs of seedlings increased with increasing soil NaCl concentration while the K+ and Ca2+ concentrations were in adverse, and the ion contents in leaves were always much higher than those in other organs, illustrating that soil NaCl stress affected the K+ and Ca2+ absorbing capability of roots, and inhibited the selective translocation of K+ and Ca2+ to aboveground parts. As a result, the K+ and Ca2+ concentrations in leaves and stems decreased. The study showed that B. papyrifera could effectively resist the injury of osmotic stress from soil salt via absorbing and accumulating Na+ and Cl-, but excessive accumulation of Na+ and Cl- could induce salt toxicity. As a non-halophyte species with relatively strong salt resistance, the aboveground parts of B. papyrifera did not have significant salt-exclusion effect.

[Photosynthetic characteristics of Cuscuta japonica and its hosts during parasitization and after detachment].

The study on the photosynthetic characteristics of Cuscuta japonica and its hosts showed that there was a negative correlation between the photosynthetic pigment content (PPC) of C. japonica and its hosts. The PPC increased in the C. japonica-preferred hosts' parasitized and neighboring leaves, but decreased in its less preferred hosts' parasitized and neighboring leaves. The leaves parasitized by C. japonica and their neighboring far from the parasitized ones had a lowered net photosynthesis rate P(n), and the decreasing order accorded with that of parasitization. The decrease of P(n) for C. japonica-less preferred hosts was mainly due to the stomatal factors, but that for the preferred hosts was regulated by multi-factors. Under light, the PPC of C. japonica detached from preferred hosts increased faster than that of C. japonica detached from less preferred hosts, but the dry matter decrease was in adverse. In dark, however, the changes in PPC and dry matter content of C. japonica were not significant, whatever hosts it was detached from.