Heavy metals are toxic substances released into the environment, contributing to a variety of toxic effects on living organisms in food chain by accumulation and biomagnifications. Certain pollutants such as arsenic (As) remain in the environment for an extensive period. They eventually accumulate to levels that could harm physiochemical properties of soils and lead to loss of soil fertility and crop yield. Arsenic, when not detoxified, may trigger a sequence of reactions leading to growth inhibition, disruption of photosynthetic and respiratory systems, and stimulation of secondary metabolism. Plants respond to As toxicity by a variety of mechanisms including hyperaccumulation, antioxidant defense system, and phytochelation. Arbuscular mycorrhizae symbiosis occurs in almost all habitats and climates, including disturbed soils. There is growing evidence that arbuscular mycorrhizae fungi may alleviate metal/metalloid toxicity to host plant. Here, we review (1) arsenic speciation in the environment and how As is taken up by the roots and metabolised within plants, and (2) the role of arbuscular mycorrhizae in alleviating arsenic toxicity in crop plants.

Arsenic toxicity in crop plants: physiological effects and tolerance mechanisms

Chenopodium quinoa (quinoa) is a highly nutritious grain identified as an important crop to improve world food security. Unfortunately, few resources are available to facilitate its genetic improvement. Here we report the assembly of a high-quality, chromosome-scale reference genome sequence for quinoa, which was produced using single-molecule real-time sequencing in combination with optical, chromosome-contact and genetic maps. We also report the sequencing of two diploids from the ancestral gene pools of quinoa, which enables the identification of sub-genomes in quinoa, and reduced-coverage genome sequences for 22 other samples of the allotetraploid goosefoot complex. The genome sequence facilitated the identification of the transcription factor likely to control the production of anti-nutritional triterpenoid saponins found in quinoa seeds, including a mutation that appears to cause alternative splicing and a premature stop codon in sweet quinoa strains. These genomic resources are an important first step towards the genetic improvement of quinoa.

The Genome of Chenopodium quinoa

A pot study was conducted to determine the effects of arbuscular mycorrhizal (AM) fungi (Glomus mosseae and Paraglomus occultum) and salt (NaCl) stress on growth, photosynthesis, root morphology and ionic balance of citrus (Citrus tangerine Hort. ex Tanaka) seedlings. Eighty-five-day-old seedlings were exposed to 100 mM NaCl for 60 days to induce salt stress. Mycorrhizal colonization of citrus seedlings was not affected by salinity when associated with P. occultum, but significantly decreased when with G. mosseae. Compared with the non-mycorrhizal controls, mycorrhizal seedlings generally had greater plant height, stem diameter, shoot, root and total plant biomass, photosynthetic rate, transpiration rate and stomatal conductance under the 0 and 100 mM NaCl stresses. Root length, root projected area and root surface area were also higher in the mycorrhizal than in the non-mycorrhizal seedlings, but higher root volume in seedlings with G. mosseae. Leaf Na+ concentrations were significantly decreased, but leaf K+ and Mg2+ concentrations and the K+/Na+ ratio were increased when seedlings with both G. mosseae and P. occultum. Under the salt stress, Na+ concentrations were increased but K+ concentrations decreased in the mycorrhizal seedlings. Under the salt stress, Ca2+ concentrations were increased in the seedlings with P. occultum or without AM fungi (AMF), but decreased with G. mosseae. Ratios of both Ca2+/Na+ and Mg2+/Na+ were also increased in seedlings with G. mosseae under the non-salinity stress, while only the Mg2+/Na+ ratio was increased in seedlings with P. occultum under the salt stress. Our results suggested that salt tolerance of citrus seedlings could be enhanced by associated AMF with better plant growth, root morphology, photosynthesis and ionic balance.

Contributions of arbuscular mycorrhizal fungi to growth, photosynthesis, root morphology and ionic balance of citrus seedlings under salt stress

Arbuscular mycorrhizae in micropropagation systems and their potential applications

F ecological restorationists, it is axiomatic that biodiversity is a key foundation upon which ecosystem functioning depends. We accept that loss of diversity can have catastrophic effects on ecosystem processes and the services they provide (Duffy 2009). Indeed, conservation of biodiversity is virtually always either a stated or implied goal of ecological restoration projects. This is especially important given that recent rates of extinction may now far exceed those occurring throughout the period when humans have affected the Earth’s ecosystems. One estimate is that nearly 20% of all plant species worldwide may now be threatened with extinction (Pennisi 2010). Recognizing this reality, many restoration projects in the 1990s began to formally include active reintroduction of plant propagules into sites where the native population was absent. Such reintroduction has now become the primary tool for the recovery of endangered plant populations to viable levels in many areas of the world. The nascent state of the science and practice of plant reintroduction was reviewed previously in Restoring Diversity: strategies for reintroduction of endangered plants (Falk et al. 1996). The current volume represents a thoroughly updated and expanded version of this review some 15 years on. In addition to examining the experience, knowledge, and data that have accumulated since, this work more directly addresses the controversial topic of managed relocation (MR) where endangered organisms are purposefully introduced outside their native ranges. As the current title suggests, the omnipresent effects of changing climate also now play a more prominent role in all plant conservation activities and this is addressed in this work as well. This volume, which is based on presentations and discussion at a symposium held in 2009, is divided into four parts. The first part includes two complementary reviews of available information derived from the majority of specific plant reintroductions conducted primarily since the mid-1980s. These summaries of success, failure, and accumulated knowledge provides valuable context for what follows. The existence of the Center for Plant Conservation (CPC) International Reintroduction Registry (2013) greatly facilitated these reviews and serves as a dynamic and valuable resource for plant reintroduction practitioners and scientists. The second part addresses advances in the science and practice of plant reintroduction. The sorts of topics restoration ecologists might expect are certainly here (e.g. the importance of genetics, associated microorganisms, identifying suitable habitats, propagule type and number, longterm monitoring, and dealing with extremely small population size and native ranges). Importantly, the role of volunteer and community outreach groups in facilitating reintroduction is also considered. The two chapters in part III directly consider the contentious and still emerging topic of MR, where introductions occur in novel locations, often to counteract the negative effects of climate change. Included here are discussions of the history and development of this practice and the possibility that plants involved in MR could become invasive. Part IV presents a summary of the volume, including the many areas where additional research is needed, along with what may be its most valuable component, the CPC Best Reintroduction Practice Guidelines. This appendix provides a step-by-step process for practitioners to follow when planning and executing a reintroduction project. While many chapters were focused on conservation science, each one had some portion dealing directly with the linkage of science with reintroduction practice and its connection with MR. Despite its prominence in the title, the effects of changing climate on reintroduction practice received relatively little direct treatment, although many authors recognized the urgency of reintroduction given what we understand about climate change and biodiversity loss. One theme does emerge from the volume as whole: as the rate of habitat repositioning exceeds that of plant migration, reintroduction that includes MR will necessarily become a much more prominent tool for those tasked with endangered plant management. This book, especially the CPC Best Reintroduction Practice Guidelines, will serve as a very useful resource for anyone interested or involved in the management of rare plants. While the vast majority of plant reintroduction examples considered have occurred in relatively few countries (primarily in Europe, United States, and Australia). I believe the content and conclusions of this book would be valuable to those working in reintroduction worldwide. As would be expected from a volume based on symposium presentations, the most recent contributions to the field are absent although I see this as a minor limitation. Much of this book necessarily focuses on the conservation of individual species and not systems or processes. As a researcher not directly involved in plant reintroduction, outside of the Practice Guidelines I might have liked to see more explicit recognition that plant

Plant reintroduction in a changing climate: promises and perils.

Changes in root morphology accompanying mycorrhizal alleviation of phosphorus deficiency in micropropagated Annona cherimola Mill. plants

In vitro germination of cherimoya (Annona cherimola Mill.) seeds

Petunia, a commercially important ornamental plant worldwide, has been subjected to breeding programs that have yielded a high number of varieties. One of the key factors in the commercial value of these varieties is plant compactness. Currently, compact petunias are obtained through the application of expensive, harmful and short-lasting chemicals. To avoid the use of these chemicals, transgenic plants that over-express dwarf-inducing genes have been recently proposed as an alternative, but the current legislation regarding transgenic plants restricts their commercialization. In this work, we studied the effect of polyploidization in the plant architecture of Petunia axillaris, an Argentine native petunia. We developed a new polyploidization protocol that consisted in culturing petunia leaves in RL medium (MS medium supplemented with 30 g l−1 sucrose, 1 mg l−1 BA and 0.2 mg l−1 IAA) supplemented with 0.2 g l−1 colchicine for 15 days. This protocol allowed the regeneration of stable autotetraploid petunias (polyploidization rate: 29.0 ± 8,2%), which were 54% more compact than the diploid ones. Furthermore, they exhibited no variations in agronomical traits compared to the initial genotypes, except for a short delay in blooming. These autotetraploid plants can be used in different breeding programs and the polyploidization method developed can be tested in others cultivars of the genus Petunia for the same purpose.

Production of compact petunias through polyploidization

Polyploid plants have been induced in different Asparagus officinalis L. breeding programs in order to obtain plants with improved agronomical traits, such as large spear diameter or segregation ratios with a higher number of males. The polyploidization methods can produce somaclonal variation in the polyploid plants obtained and, therefore, unwanted changes in the agronomical traits of the initial elite plants. We used two different polyploidization methods to induce polyploid plants from diploid genotypes of commercial varieties and tetraploid genotypes of the Spanish landrace “Morado de Huetor”. The first method was the culture of rhizome buds in the medium ARBM-3 (Asparagus Rhizome Bud Medium), supplemented with different concentrations of colchicine (0.1–0.75 g l−1) for 10 and 20 days. The best polyploidization rate obtained was 25 % (0.5 g l−1 colchicine for 10 days). The second method was the regeneration of polyploid plants from callus culture, resulting in a polyploidization rate of 40 and 12.5 % for the diploid genotype CM077 and the tetraploid genotype HT156, respectively. Additionally, we have developed a new protocol to separate the mixoploids generated into their different genetic components, obtaining plants with a unique ploidy level. EST-SSRs markers were employed to analyze the genetic stability of polyploidy plants. Somaclonal variation was not detected for polyploidy plants obtained through the culture of rhizome bud explants. Therefore, these polyploid plants should maintain the agronomical traits of the initial elite plants. However, somaclonal variation was detected in the polyploid plants regenerated from callus culture.

Study of the somaclonal variation produced by different methods of polyploidization in Asparagus officinalis L.

An efficient micropropagation method for asparagus species was developed in this study. The method allows the fast cloning of the elite genotypes from different asparagus species and the interspecific hybrids obtained from these species. Rhizome bud explants were disinfected using 3 g l−1 of benomyl and 20 g l−1 of sodium hypochlorite. Then, they were cultured on Asparagus Rhizome Bud Medium 3 (ARBM-3) consisting in modified Murashige and Skoog medium with salts with EDDHA-Fe (85.7 mg l−1) instead of EDTA-Fe and vitamins, supplemented with 0.3 mg l−1 NAA, 0.1 mg l−1 KIN, 2 mg l−1 ancymidol and 6 % sucrose. Results showed that the method developed produced high disinfection rates (70–95 %). More than 70 % of the explants developed shoots and the rooting rate on ARBM-3 medium was 30–45 %. The rooting rate increased to 60–85 % when the unrooted shoots were subjected to an additional cycle of rooting, reaching 100 % after two cycles of rooting. The multiplication was achieved through mechanical division of rooted shoot clusters growing in ARBM-3. The acclimatization rate of the micropropagated plantlets was higher than 90 %. The micropopagated plantlets were screened for somaclonal variation using 12 expressed sequence tag derived simple sequence repeat markers. The results confirmed the character “true to type” of the plantlets, indicating that the method developed in this study can be used to successfully micropropagate asparagus species.

Micropropagation of wild species of the genus Asparagus L. and their interspecific hybrids with cultivated A. officinalis L., and verification of genetic stability using EST-SSRs

C. L. Encina

Papers

Changes in root morphology accompanying mycorrhizal alleviation of phosphorus deficiency in micropropagated Annona cherimola Mill. plants

In vitro germination of cherimoya (Annona cherimola Mill.) seeds

Production of compact petunias through polyploidization

Study of the somaclonal variation produced by different methods of polyploidization in Asparagus officinalis L.

Micropropagation of wild species of the genus Asparagus L. and their interspecific hybrids with cultivated A. officinalis L., and verification of genetic stability using EST-SSRs