Ana M. Pelacho

Critical evaluation of strategies for mineral fortification of staple food crops.

Staple food crops, in particular cereal grains, are poor sources of key mineral nutrients. As a result, the world’s poorest people, generally those subsisting on a monotonous cereal diet, are also those most vulnerable to mineral deficiency diseases. Various strategies have been proposed to deal with micronutrient deficiencies including the provision of mineral supplements, the fortification of processed food, the biofortification of crop plants at source with mineral-rich fertilizers and the implementation of breeding programs and genetic engineering approaches to generate mineral-rich varieties of staple crops. This review provides a critical comparison of the strategies that have been developed to address deficiencies in five key mineral nutrients—iodine, iron, zinc, calcium and selenium—and discusses the most recent advances in genetic engineering to increase mineral levels and bioavailability in our most important staple food crops.

The genetic manipulation of medicinal and aromatic plants

Medicinal and aromatic plants have always been intimately linked with human health and culture. Plant-derived medicines constitute a substantial component of present day human healthcare systems in industrialized as well as developing countries. They are products of plant secondary metabolism and are involved in many other aspects of a plant’s interaction with its immediate environment. The genetic manipulation of plants together with the establishment of in vitro plant regeneration systems facilitates efforts to engineer secondary product metabolic pathways. Advances in the cloning of genes involved in relevant pathways, the development of high throughput screening systems for chemical and biological activity, genomics tools and resources, and the recognition of a higher order of regulation of secondary plant metabolism operating at the whole plant level facilitate strategies for the effective manipulation of secondary products in plants. Here, we discuss advances in engineering metabolic pathways for specific classes of compounds in medicinal and aromatic plants and we identify remaining constraints and future prospects in the field. In particular we focus on indole, tropane, nicotine, isoquinoline alcaloids, monoterpenoids such as menthol and related compounds, diterpenoids such as taxol, sequiterpenoids such as artemisinin and aromatic amino acids.

Constitutive expression of a barley Fe phytosiderophore transporter increases alkaline soil tolerance and results in iron partitioning between vegetative and storage tissues under stress.

Cereals have evolved chelation systems to mobilize insoluble iron in the soil, but in rice this process is rather inefficient, making the crop highly susceptible to alkaline soils. We therefore engineered rice to express the barley iron-phytosiderophore transporter (HvYS1), which enables barley plants to take up iron from alkaline soils. A representative transgenic rice line was grown in standard (pH 5.5) or alkaline soil (pH 8.5) to evaluate alkaline tolerance and iron mobilization. Transgenic plants developed secondary tillers and set seeds when grown in standard soil although iron concentration remained similar in leaves and seeds compared to wild type. However, when grown in alkaline soil transgenic plants exhibited enhanced growth, yield and iron concentration in leaves compared to the wild type plants which were severely stunted. Transgenic plants took up iron more efficiently from alkaline soil compared to wild type, indicating an enhanced capacity to increase iron mobility ex situ. Interestingly, all the additional iron accumulated in vegetative tissues, i.e. there was no difference in iron concentration in the seeds of wild type and transgenic plants. Our data suggest that iron uptake from the rhizosphere can be enhanced through expression of HvYS1 and confirm the operation of a partitioning mechanism that diverts iron to leaves rather than seeds, under stress.

Amyloplast division in kinetin induced potato tubers

Abstract Amyloplast division was studied in an in vitro potato (Solanum tuberosum L. cv. Kennebec) stolon tuberizing system which was triggered by the presence of added kinetin. Amyloplast division proceeded by binayr fission of dumbbell shaped amyloplasts. A visible tubular coiled structure from the amylobody appeared to be associated with amyloplast division. Possible ways of daughter amyloplast separation are discussed.

Jasmonates promote cabbage (Brassica oleracea L. var Capitata L.) root and shoot development

Jasmonates are a new group of plant hormones; their roles on plant development are still little known. The aim of this work is to determine the action of jasmonates on cabbage, Brassica oleracea L. var Capitata,development both in in vitro cultured explants and in whole plants. Jasmonic acid (JA) enhanced nodal explant development when applied at 2–50 nM and inhibited it when supplied at 1250 and 6000 nM JA. Overall plant development was enhanced most under the 10 nM JA treatment; which significantly increased the explant shoot, leaf, and root dry weight. The root system of the explants cultured under the lower JA concentrations appeared more vigorous. Jasmonic acid also promoted the development of isolated in vitro cultured roots when applied at 2 and 10 nM. Root length and weight significantly increased, while concentrations 250 nM JA and over were detrimental. Isolated roots were progressively thicker as the JA concentration increased. Methyl jasmonate promoted both the below-and above-ground cabbage plant development when applied in a confined atmosphere at a concentration of only 1.225 nl.l−1 MJ: plants were higher and heavier, and showed an improved root system development. On the other hand, the 2.43 n1.1−1 MJ treatment decreased plant growth. The present work reveals a role for jasmonates as enhancers of in vitro and in vivo cabbage plant development. To our knowledge, no corresponding studies on the effects of jasmonates on whole plants have been previously published.

Transcriptional regulation of the rice arginine decarboxylase (Adc1) and S-adenosylmethionine decarboxylase (Samdc) genes by methyl jasmonate.

We investigated the effect of methyl jasmonate (MeJa) treatment on the expression of two genes in the rice polyamine biosynthesis pathway and on the polyamine content in wild type plants and transgenic rice plants expressing a Datura stramonium (Ds) Adc cDNA, the latter accumulating up to three-fold the normal level of putrescine. Exogenous MeJa transiently inhibited the expression of OsAdc1, OsSamdc and Spermidine synthase (OsSpds) genes in the polyamine biosynthesis pathway, probably through transcriptional repression. There was also a similar negative impact on the DsAdc transgene in transgenic plants, even though a constitutive promoter was used to drive transgene expression. The free putrescine content was reduced significantly in the leaves of both wild type and transgenic plants in response to MeJa, although the magnitude of the effect was greater in wild type plants. We discuss our findings with respect to the previously proposed threshold model of polyamine metabolism in plants subjected to abiotic stress.

In vitro Tuberization of Potato: Effect of Several Morphogenic Regulators in Light and Darkness

Summary A significant increase in the number of tubers was obtained in the presence of either kinetin (11.6·10 -3 mM), paclobutrazol (8.5·10 -3 mM) or acetate (5.4 mM) for in vitro stolons in darkness, and both single-node sections and intact 3-cm long sprouts were produced after long photoperiod (16 h) subculture. Longitudinal growth decreased whenever tuberization was promoted, especially in the presence of paclobutrazol. Calcium chloride (6 mM) slightly induced tuberization in the dark. Putrescine (0.15 mM) favoured vegetative development in all explants.

In vitro induction of potato tuberization by organic acids

SummaryPotato microtubers are usually induced in media containing growth regulatory, typically cytokinins and growth retardants. However, since these substances may imbalance the physiology of the cultured explants and cause adverse carry-over effects on the subsequent performance of the microtubers, the potential acid-induction of in vitro-mass tuberization was investigated as an alternative. For this purpose, a range of explant types (stolons, single-node or apex-containing multinodal sections), organic acids (acetic, propionic, ascorbic, acetylsalicylic or salicylic acid), and photoperiods (continuous dark, 8 or 16 h photoperiod) were established. Gellified medium or raft membranes on liquid medium were also tested.Although variations due to explant type, photoperiod, organic acid supplemented, and medium type were found, all organic acids tested under the different experiments caused tuberization. Multiple tuber formation or bigger tubers did not develop on multinodal explants. In terms of tuberization rate and mean tuber weight, gellified medium performed better than liquid medium with rafts. The recently established role of the salicylic and acetylsalicylic acids on tuberization is corroborated by our system. The results with the acetic, propionic and ascorbic acids show that in vitro hormone-free tuberization can be easily and rapidly achieved.

Above-soil and in-soil degradation of oxo- and bio-degradable mulches: a qualitative approach

Degradable materials have been suggested to overcome accumulation in the field of persistent plastic residues associated with the increasing use of polyethylene mulches. New degradable materials have been proven successful for increasing crop productivity; however, their degradation in the field has been hardly addressed. A qualitative scale was used in the present study to assess the above-soil and in-soil degradation of degradable mulches during the cropping season. Degradation was determined in three biodegradable plastic mulches (Biofilm, BF; Mater-Bi, MB; Bioflex, BFx), two paper sheet mulches (Saikraft, PSA; MimGreen, PMG) and one oxo-degradable plastic mulch (Enviroplast, EvP). Polyethylene (PE) mulch was used as control. Mulches were tested in five Spanish locations (Castilla-La Mancha, La Rioja, Navarra, Aragon and Catalunya), with three crop seasons of processing tomato. Biodegradable plastic mulches BF and MB degraded more and faster above-soil than paper mulches; among biodegradable mulches BF degraded more than MB, and MB more than BFx. The above-soil degradation of the oxo-degradable mulch EvP was highly dependent on location and crop season, and it degraded more than PE. Main environmental factors triggering above-soil degradation were radiation, rainfall and crop cover. In-soil, paper mulches and BF degraded more and faster than MB, whereas BFx and EvP barely degraded. Environmental factors triggering in-soil degradation during the crop season were rainfall and irrigation water. The effect of soil parameters (organic matter, nutrient availability) on degradation during the cropping season was not evidenced. The qualitative scale used proved convenient for determining mulch field degradation. A visual scale for supporting the qualitative evaluation is provided. In order to standardise parameters and criteria for future studies on field mulching degradation evaluation, a unified degradation qualitative scale is suggested.

Agronomic Effects of Biodegradable Films on Crop and Field Environment

This chapter describes the state of the art of the agronomic effects of degradable bioplastics used as agricultural films. Current use of bioplastics and certified commercial biodegradable materials, both as granulates and as final products, are introduced. Following, agronomic effects on crops are reported and compared to the routinely used oil-based nondegradable plastics, basically the polyethylene films. Biodegradable films for agriculture were initially developed mostly for mulching application, which still remains the most significant one. Since last reviews published in 2011, new progress and perspectives have mainly arisen regarding the agronomic effects of biodegradable mulching on vegetable crops, not only as films but also as nonwoven biobased mulches. The film mechanical laying and the effects on yield, earliness, product quality, weed control efficacy, microclimatic improvement and film soil coverage and degradation are presented in detail for tomato crops and for other crops where mulching is a common technique (pepper, melon and other cucurbits, strawberry, lettuce,…). Some information is provided for crops not so frequently mulched (broccoli, sweet potato, sweet corn). New findings published on the use of biodegradable films for solarisation are also reviewed, while no significant progress on the use of films for low tunnel covers has been made. Recent proposals for vineyards and future potential application of bioplastics for orchard crops are also addressed. Finally, pros and cons for the adoption of biodegradable films for cultivating crops are discussed.