Silicon modulates copper absorption and increases yield of Tanzania guinea grass under copper toxicity

Silicon (Si) is a beneficial element which was proven to enhance the tolerance of plants to excess metal in a given growth medium. However, the efficacy of Si in mitigating Cu toxicity in plants can vary between plant species and with the amount of copper (Cu) present in the soil/medium. An experiment was performed to investigate the role of Si in alleviating Cu toxicity in Tanzania guinea grass (Panicum maximum cv. Tanzania). The experimental design consisted on complete random blocks with tree replicates containing three Si rates (0, 1, and 3 mmol L-1) and four Cu rates (0.3, 250, 500, and 750 μmol L-1). The grass was grown for 62 days in a greenhouse under hydroponic conditions, with a total of 36 pots. Thirteen days after sowing, seedlings were transplanted to pots and grown for further 25 days, and then exposed to the set Cu rates for 7 days. The plants were also evaluated more for 30 days after the first harvesting. The results confirmed that the Si supply to Tanzania guinea grass can alleviate the effects of excessive Cu. Plant yield increased with Si supply and decreased with the increment of Cu rates in both growth periods. Copper concentration in diagnostic leaves (DL) and in roots, and Cu content in shoots and roots were higher in plants exposed to Cu of 750 μmol L-1 with no Si application than in other combinations. Besides reducing Cu concentration in plant tissues, the most important Si role was reducing the transport of Cu from roots to shoots, which allowed successive harvesting. Graphical abstract.

Nitrogen form regulates cadmium uptake and accumulation in Tanzania guinea grass used for phytoextraction

Plants benefit from the simultaneous uptake of nitrate (NO₃^-) and ammonium (NH₄⁺), which can influence the bioaccumulation of heavy metals. Nevertheless, there are no studies on the effect of nitrogen forms on grasses used for cadmium (Cd) phytoextraction. The objective was to evaluate the response of Panicum maximum cv. Tanzania to NO₃^-/NH₄⁺ ratios and Cd levels. A 3 × 3 factorial experiment was conducted under greenhouse conditions, in a randomized complete block design replicated three times, with three NO₃^-/NH₄⁺ ratios (100/0, 70/30 and 50/50) and three Cd levels (0.0, 0.5 and 1.0 mM). Although it increased plant total nitrogen concentration, Cd exposure reduced shoot and root growth. Moreover, it altered nitrogen metabolism and induced the accumulation of NO₃^- and NH₄⁺ mainly in shoots. The supply of 50/50 disturbed glutamine synthetase activity and changed root morphology under Cd toxicity. However, while the exclusive use of NO₃^- mitigated toxicity symptoms, by favoring Cd accumulation in roots and maintaining normal nitrogen metabolism, plants grown with 50/50 showed increased uptake, transport and accumulation of this metal. Thus, Cd uptake and accumulation are strongly related to the form of nitrogen available, and the supply of 50/50 increases the phytoextraction of this metal.

Potassium affects the phytoextraction potential of Tanzania guinea grass under cadmium stress

The supply of potassium (K) is a strategy to increase the tolerance of plants exposed to Cd toxicity. The aim of this study was to verify the influence of K on the growth and potential of Tanzania guinea grass (Panicum maximum Jacq. cv. Tanzania (syn. Megathyrsus maximus (Jacq.) B.K. Simon & S.W.L. Jacobs)) for Cd phytoextraction as well as to evaluate nutritional attributes of this grass under conditions of Cd stress. The experiment was conducted in a randomized complete block design, using a 3 × 4 factorial arrangement, with three replications. Three rates of K (0.4, 6.0, and 11.6 mmol L^-1) were combined with four rates of Cd (0.0, 0.5, 1.0, and 1.5 mmol L^-1) in nutrient solution. Two plant growth periods were evaluated. The increase in K supply to plants exposed to Cd rates of up to 1.0 mmol L^-1 caused increase in morphogenic and production attributes, as well as reduction in tiller mortality rate, in the second growth period. K concentrations (in both harvests) increased, while calcium and magnesium concentrations in the second harvest decreased with increasing Cd rates. The high availability of Cd (1.5 mmol L^-1) in the nutrient solution caused decrease in relative chlorophyll index (RCI) in both harvests. The high supply of K to plants exposed to Cd resulted in high shoot dry mass production, reducing Cd concentration in the photosynthetic tissues (which means great tolerance of the plant) and increasing the accumulation of this metal in the shoots that can be harvested. Therefore, K increases the Cd phytoextraction capacity of Tanzania guinea grass.

Ozone phytotoxicity to Panicum maximum and Cenchrus ciliaris at Indo-Gangetic plains: an assessment of antioxidative defense and growth responses

Two common tropical grassland species, Panicum maximum Jacq. (Guinea grass) and Cenchrus ciliaris (Buffel grass) of Indo-Gangetic plains were assessed for their responses under future level of O₃ (ambient +30 ppb) using open top chambers. Plants were assessed for foliar injuries, pigments, growth, biomass accumulation, histochemical localization of reactive oxygen species (ROS), antioxidant defense system and ROS scavenging activities at two stages. Foliar injuries were noticed at an early stage in P. maximum compared to C. ciliaris. Significant reductions were observed in total chlorophyll, growth and total biomass in both species. Significant increases in contents of melondialdehyde and ascorbic acid in P. maximum while total phenolics and thiols in C. ciliaris were found. Histochemical analysis showed more production of superoxide radicals and hydrogen peroxide in leaf tissues of P. maximum compared to C. ciliaris. It can be concluded that higher level of primary antioxidants (total phenolics and thiols) along with superoxide dismutase and ascorbate peroxidase scavenged O₃ effectively in C. ciliaris causing less reduction of biomass which is used as a feed for cattles. In P. maximum, more photosynthates were allocated for defense, leading to higher reduction in total biomass compared to C. ciliaris. The leaf area ratio was higher in P. maximum compared to C. ciliaris under elevated O₃. The study further suggests higher susceptibility of P. maximum compared to C. ciliaris under future level of O₃ exposure.

Partial replacement of nitrate by ammonium increases photosynthesis and reduces oxidative stress in tanzania guinea grass exposed to cadmium

In order to grow and effectively uptake and accumulate cadmium (Cd), plants used for phytoextraction have to cope with toxicity, which may be influenced by the supply of nitrate (NO₃^-) and ammonium (NH₄⁺). Thus, we evaluated the effect of these nitrogen forms on the photosynthetic and antioxidant enzyme activities of Panicum maximum cv. Tanzania (tanzania guinea grass) under Cd stress. Plants were grown in nutrient solution under greenhouse conditions and subjected to a 3 × 3 factorial experiment. They were supplied with three NO₃^-/NH₄⁺ ratios (100/0, 70/30 and 50/50) and exposed to three Cd rates (0.0, 0.5 and 1.0 mmol L^-1), being arranged in a randomized complete block design with three replications. Gas exchange parameters, oxidative stress indicators, proline concentration and antioxidant enzyme activities were studied. Exposure to Cd reduced photosynthesis by causing stomatal closure and impairing electron transport. However, the simultaneous supply of NO₃^- and NH₄⁺, particularly at a 50/50 ratio, restored gas exchange and improved the function of photosystem II, increasing the photosynthetic capacity of the grass. Plants grown with 50/50 showed reduced lipid peroxidation along with increased proline synthesis. Moreover, this NO₃^-/NH₄⁺ ratio increased the tolerance of tanzania guinea grass to Cd by inducing high superoxide dismutase and glutathione reductase activities in shoots and roots, respectively, maintaining cellular homeostasis and reducing oxidative stress. The negative effects of Cd on photosynthesis and on the balance between oxidants and antioxidants are attenuated by the partial replacement of NO₃^- by NH₄⁺ in the nutrient solution.

Effects of supplementing herbaceous forage legume pellets on growth indices and blood profile of West African dwarf sheep fed Guinea grass

Twenty West African dwarf (WAD) rams with average body weight of 12.43 ± 0.5 kg were used for the experiment that lasted 84 days to investigate the effects of supplementing herbaceous forage legume pellets on weight change and blood profile of animals fed Panicum maximum basal diet. Sole Panicum maximum served as the control diet and three other experimental diets were P. maximum supplemented with Lablab purpureus pellets, P. maximum supplemented with Calopogonium mucunoides pellets and P. maximum supplemented with Mucuna pruriens pellets constituted the four treatments which were arranged in a completely randomised design. The rams were divided into four groups of five animals each and were balanced for variation in live weight before they were assigned the experimental diets. Panicum maximum was offered to the animals ad libitum and legume pellets were supplemented. Significant differences (P < 0.05) were observed in weight gain of the rams. Those fed the control diet had the lowest value of 41.88 g/day while rams supplemented L. purpureus pellets had the highest value (83.66 g/day). Haematological parameters, leucocyte values and serum biochemical indices of WAD rams were significantly (P < 0.05) different across the dietary treatments at the final stage of the trial. The values for red blood cells, haemoglobin concentration, packed cell volume and mean corpuscular haemoglobin decreased slightly in rams supplemented with M. pruriens pellets. Reduction of serum biochemical parameters was also noticed in rams supplemented with M. pruriens pellets. It can be concluded that L. purpureus pellets ranked the best among the herbaceous legume pellets as supplemental feed for West African dwarf sheep resulting in higher weight gain and better feed conversion efficiency with no deleterious effect on blood profile.

Nitrate and ammonium proportion plays a key role in copper phytoextraction, improving the antioxidant defense in Tanzania guinea grass

Various nitrate and ammonium proportions (NO₃^-/NH₄⁺) in the growth media can increase metal phytoextraction compared to supplying solely NO₃^-. However, there are no studies showing these effects in plants under copper (Cu) contamination as well as their consequences in plant stress tolerance. The objective was to evaluate the effect of NO₃^-/NH₄⁺ proportions in Cu phytoextraction by Panicum maximum cv. Tanzania and its consequence in the oxidative stress, photosynthesis, and antioxidant system under Cu stress. The experiment was carried out in a randomized complete block design, by using a 3 × 4 factorial with six replications. Three NO₃^-/NH₄⁺ proportions (100/0, 70/30, and 50/50) were combined with four Cu rates (0.3, 250, 500, and 1000 µmol L^-1) in the nutrient solution. It was found that the largest Cu accumulation in the shoots occurred at the first harvest of the plants supplied with 70/30 NO₃^-/NH₄⁺ and Cu 1000 µmol L^-1. Such plants also displayed high concentrations of proline in the shoots as well as high superoxide dismutase activity in the roots. Malondialdehyde concentration was high in the plant parts at the Cu rate of 1000 µmol L^-1. Hence, transpiration rates, stomatal conductance, quantum efficiency of photosystem II, electron transport rate, and net photosynthesis were all low at the Cu rate of 1000 µmol L^-1. Catalase, guaiacol peroxidase, ascorbate peroxidase, and glutathione reductase activities in the roots were high when plants were exposed to Cu 1000 µmol L^-1. In conclusion, the combination of NO₃^- with NH₄⁺ increases copper phytoextraction that causes oxidative stress, but also favors the antioxidant system of Tanzania guinea grass in attempt to tolerate such stress.

Metabolite and transcript profiling of Guinea grass (Panicum maximum Jacq) response to elevated [CO2] and temperature

INTRODUCTION

By mid-century, global atmospheric carbon dioxide concentration ([CO₂]) is predicted to reach 600 μmol mol^-1 with global temperatures rising by 2 °C. Rising [CO₂] and temperature will alter the growth and productivity of major food and forage crops across the globe. Although the impact is expected to be greatest in tropical regions, the impact of climate-change has been poorly studied in those regions.

OBJECTIVES

This experiment aimed to understand the effects of elevated [CO₂] (600 μmol mol^-1) and warming (+ 2 °C), singly and in combination, on Panicum maximum Jacq. (Guinea grass) metabolite and transcript profiles.

METHODS

We created a de novo assembly of the Panicum maximum transcriptome. Leaf samples were taken at two time points in the Guinea grass growing season to analyze transcriptional and metabolite profiles in plants grown at ambient and elevated [CO₂] and temperature, and statistical analyses were used to integrate the data.

RESULTS

Elevated temperature altered the content of amino acids and secondary metabolites. The transcriptome of Guinea grass shows a clear time point separations, with the changes in the elevated temperature and [CO₂] combination plots.

CONCLUSION

Field transcriptomics and metabolomics revealed that elevated temperature and [CO₂] result in alterations in transcript and metabolite profiles associated with environmental response, secondary metabolism and stomatal function. These metabolic responses are consistent with greater growth and leaf area production under elevated temperature and [CO₂]. These results show that tropical C₄ grasslands may have unpredicted responses to global climate change, and that warming during a cool growing season enhances growth and alleviates stress.

Partitioning Apomixis Components to Understand and Utilize Gametophytic Apomixis

Apomixis is a method of reproduction to generate clonal seeds and offers tremendous potential to fix heterozygosity and hybrid vigor. The process of apomictic seed development is complex and comprises three distinct components, viz., apomeiosis (leading to formation of unreduced egg cell), parthenogenesis (development of embryo without fertilization) and functional endosperm development. Recently, in many crops, these three components are reported to be uncoupled leading to their partitioning. This review provides insight into the recent status of our understanding surrounding partitioning apomixis components in gametophytic apomictic plants and research avenues that it offers to help understand the biology of apomixis. Possible consequences leading to diversity in seed developmental pathways, resources to understand apomixis, inheritance and identification of candidate gene(s) for partitioned components, as well as contribution towards creation of variability are all discussed. The potential of Panicum maximum, an aposporous crop, is also discussed as a model crop to study partitioning principle and effects. Modifications in cytogenetic status, as well as endosperm imprinting effects arising due to partitioning effects, opens up new opportunities to understand and utilize apomixis components, especially towards synthesizing apomixis in crops.

Transcriptomic data of pre-meiotic stage of floret development in apomictic and sexual types of guinea grass (Panicum maximum Jacq.)

Guinea grass (Panicum maximum Jacq), an important fodder crop of humid and sub-humid tropical regions, reproduces through apomixis, a method of clonal propagation through seeds. Lack of knowledge of the genetic and molecular control of this phenomena has hindered the genetic improvement of this crop. The dataset provided here represents the first RNA-Seq based assembly and analysis of florets at pre-meiotic stage from the apomictic and sexual genotypes of guinea grass. The raw sequence files in FASTQ format were deposited in the NCBI SRA database with accession number SRP115883. A total of 24.8 Gb raw sequence data, corresponding to 17,96,65,827 raw reads was obtained by paired end sequencing. We used Trinity for de-novo assembly and identified 57,647 transcripts in sexual and 49,093 transcripts in apomictic type. This transcriptome data will be useful for identification and comparative analysis of genes regulating the mode of reproduction in grasses.

A glimpse into the symplastic and apoplastic Cd uptake by Massai grass modulated by sulfur nutrition: Plants well-nourished with S as a strategy for phytoextraction

To date, there have been no studies demonstrating the influence of sulfur (S) on the cadmium (Cd) uptake kinetics, which limits the understanding of mechanisms involved in the uptake of this element. Therefore, this study was carried out in order to quantify the contribution of symplastic and apoplastic uptakes of Cd (0.1 and 0.5 mmol L^-1) by Massai grass (Panicum maximum cv. Massai) grown under low and adequate S-supply (0.1 and 1.9 mmol L^-1) by measuring Cd concentration in the nutrient solution (V_max, K_m, and C_min) along the plant's exposure time (108 h) and determining Cd concentration in root symplast and apoplast. The V_max of Cd influx in Massai grass exposed to higher Cd and S concentrations was 38% higher than that plants supplied with lower S concentration. The K_m and C_min of plants exposed to the highest Cd concentration was higher than that plants subjected to the lowest Cd concentration, although values were not affected by S supply. Symplastic influx of Cd in plants subjected to the lower Cd and S concentrations was 20% higher as compared to plants supplied with the higher concentration of S, whereas the apoplastic influx of Cd was higher when there was a higher supply S, regardless of Cd concentration in the solution. This result indicates that an adequate supply of S decreases the contribution of the symplastic Cd uptake and increases the contribution of the apoplastic Cd uptake when the toxicity caused by Cd is lower.

Performance, nitrogen balance and microbial efficiency of beef cattle under concentrate supplementation strategies in intensive management of a tropical pasture

The objective of this study was to evaluate the effect of concentrate supplementation strategies on the nutritional characteristics of beef cattle in intensive management of tropical pasture. Twenty-four Nellore steer at 250 kg body weight (BW) were used, divided into two plots, with 12 animals in each plot. The experimental area consisted of 32 paddocks with 0.25 ha of Panicum maximum cv. Mombaça. The experiment consisted of 96-day experimental periods, with three periods of 32 days. The strategies studied were P = exclusively on pasture and without concentrate supplementation (control), ES = pasture and supplemented with a concentrate low in protein, PS = pasture and supplemented with high protein content, and PES = pasture and supplementation with balanced protein-energy. There was reduced intake of DM in animals of the treatment P in relation to supplemented pasture, regardless of supplementation. Animals fed on ES showed an intake of more nutrients than the animals on PS. The CP and TDN were also lower in P than in pastures where animals received the additional types of concentrate, and the PS animals showed greater digestibility of CP and TDN than the ES animals. However, the animals exhibited similar weight gains. Animals on P ingested smaller amounts of N and had lower fecal excretion compared to the supplemented animals, but there was no difference between treatments in nitrogen balance. Urea nitrogen and urea from the blood were higher in the supplemented animals than in animals fed on pasture; these levels were also higher in PS animals compared to animals receiving ES. Both the purines absorbed and microbial protein production were similar between treatments. However, the animals fed with concentrate supplementation, independent of the strategy involved, showed higher microbial efficiency compared to animals fed exclusively on pasture.

Root-knot Nematode Management in Dryland Taro with Tropical Cover Crops

Twenty-two cover crops were evaluated for their ability to reduce damage by root-knot nematode, Meloidogyne javanica, to taro, Colocastia esculenta, in a tropical cropping system. Cover crops were grown and incorporated into the soil before taro was planted. Barley, greenpanic, glycine, marigold, sesame, sunn hemp, and sorghum x sudangrass DeKalb ST6E were poor or nonhosts to the nematode as measured by low population changes of nematodes in soil between cover crop planting and taro planting. Alfalfa, buckwheat, cowpea, lablab, Lana vetch, mustard, oat, okra, rhodes grass, ryegrain, ryegrass, siratro, sweet corn, and wheat allowed nematode populations to increase dramatically. Taro yields were greatest in the marigold plots and lowest in the ryegrain plots. Taro corm weight decreased with increasing initial nematode population (Pi) (r = 0.22, P = 0.056). Siratro, ryegrass, and Blizzard wheat plots had higher taro yield than plots with similar Pi's but planted to other cover crops. These cover crops may have antagonism to other soil microorganisms or their decomposition products may be toxic or adversely affect the nematodes. Cover crops can be an effective and valuable nematode management tactic for use in minor tropical cropping systems such as taro.