I read this book the same weekend that the Packers took on the Rams, and the experience of the latter event, obviously, colored my judgment. Although I abhor anything that smacks of being a handbook (like, \"How to Earn a Merit Badge in Neurosurgery\") because too many volumes in biomedical science already evince a boyscout-like approach, I must confess that parts of this volume are fast, scholarly, and significant, with certain reservations. I like parts of this well-illustrated book because Dr. Sj6strand, without so stating, develops certain subjects on technique in relation to the acquisition of judgment and sophistication. And this is important! So, given that the author (like all of us) is somewhat deficient in some areas, and biased in others, the book is still valuable if the uninitiated reader swallows it in a general fashion, realizing full well that what will be required from the reader is a modulation to fit his vision, propreception, adaptation and response, and the kind of problem he is undertaking. A major deficiency of this book is revealed by comparison of its use of physics and of chemistry to provide understanding and background for the application of high resolution electron microscopy to problems in biology. Since the volume is keyed to high resolution electron microscopy, which is a sophisticated form of structural analysis, but really morphology in a modern guise, the physical and mechanical background of The instrument and its ancillary tools are simply and well presented. The potential use of chemical or cytochemical information as it relates to biological fine structure , however, is quite deficient. I wonder when even sophisticated morphol-ogists will consider fixation a reaction and not a technique; only then will the fundamentals become self-evident and predictable and this sine qua flon will become less mystical. Staining reactions (the most inadequate chapter) ought to be something more than a technique to selectively enhance contrast of morphological elements; it ought to give the structural addresses of some of the chemical residents of cell components. Is it pertinent that auto-radiography gets singled out for more complete coverage than other significant aspects of cytochemistry by a high resolution microscopist, when it has a built-in minimal error of 1,000 A in standard practice? I don't mean to blind-side (in strict football terminology) Dr. Sj6strand's efforts for what is \"routinely used in our laboratory\"; what is done is usually well done. It's just that …

Methods in Enzymology.

Plant responses to different stresses are highly complex and involve changes at the transcriptome, cellular, and physiological levels. Recent evidence shows that plants respond to multiple stresses differently from how they do to individual stresses, activating a specific programme of gene expression relating to the exact environmental conditions encountered. Rather than being additive, the presence of an abiotic stress can have the effect of reducing or enhancing susceptibility to a biotic pest or pathogen, and vice versa. This interaction between biotic and abiotic stresses is orchestrated by hormone signalling pathways that may induce or antagonize one another, in particular that of abscisic acid. Specificity in multiple stress responses is further controlled by a range of molecular mechanisms that act together in a complex regulatory network. Transcription factors, kinase cascades, and reactive oxygen species are key components of this cross-talk, as are heat shock factors and small RNAs. This review aims to characterize the interaction between biotic and abiotic stress responses at a molecular level, focusing on regulatory mechanisms important to both pathways. Identifying master regulators that connect both biotic and abiotic stress response pathways is fundamental in providing opportunities for developing broad-spectrum stress-tolerant crop plants.

The interaction of plant biotic and abiotic stresses: from genes to the field

High temperature (HT) stress is a major environmental stress that limits plant growth, metabolism, and productivity worldwide Plant growth and development involve numerous biochemical reactions that are sensitive to temperature Plant responses to HT vary with the degree and duration of HT and the plant type HT is now a major concern for crop production and approaches for sustaining high yields of crop plants under HT stress are important agricultural goals Plants possess a number of adaptive, avoidance, or acclimation mechanisms to cope with HT situations In addition, major tolerance mechanisms that employ ion transporters, proteins, osmoprotectants, antioxidants, and other factors involved in signaling cascades and transcriptional control are activated to offset stress-induced biochemical and physiological alterations Plant survival under HT stress depends on the ability to perceive the HT stimulus, generate and transmit the signal, and initiate appropriate physiological and biochemical changes HT-induced gene expression and metabolite synthesis also substantially improve tolerance The physiological and biochemical responses to heat stress are active research areas, and the molecular approaches are being adopted for developing HT tolerance in plants This article reviews the recent findings on responses, adaptation, and tolerance to HT at the cellular, organellar, and whole plant levels and describes various approaches being taken to enhance thermotolerance in plants

Physiological, biochemical, and molecular mechanisms of heat stress tolerance in plants

MicroRNAs (miRNAs) are small regulatory RNAs found in diverse eukaryotic lineages. In plants, a minority of annotated MIRNA gene families are conserved between plant families, while the majority are family- or species-specific, suggesting that most known MIRNA genes arose relatively recently in evolutionary time. Given the high proportion of young MIRNA genes in plant species, new MIRNA families are likely spawned and then lost frequently. Unlike highly conserved, ancient miRNAs, young miRNAs are often weakly expressed, processed imprecisely, lack targets, and display patterns of neutral variation, suggesting that young MIRNA loci tend to evolve neutrally. Genome-wide analyses from several plant species have revealed that variation in miRNA foldback expression, structure, processing efficiency, and miRNA size have resulted in the unique functionality of MIRNA loci and resulting miRNAs. Additionally, some miRNAs have evolved specific properties and functions that regulate other transcriptional or posttranscriptional silencing pathways. The evolution of miRNA processing and functional diversity underscores the dynamic nature of miRNA-based regulation in complex regulatory networks.

Evolution and Functional Diversification of MIRNA Genes

Trehalose metabolism and signaling is an area of emerging significance. In less than a decade our views on the importance of trehalose metabolism and its role in plants have gone through something of a revolution. An obscure curiosity has become an indispensable regulatory system. Mutant and transgenic plants of trehalose synthesis display wide-ranging and unprecedented phenotypes for the perturbation of a metabolic pathway. Molecular physiology and genomics have provided a glimpse of trehalose biology that had not been possible with conventional techniques, largely because the products of the synthetic pathway, trehalose 6-phosphate (T6P) and trehalose, are in trace abundance and difficult to measure in most plants. A consensus is emerging that T6P plays a central role in the coordination of metabolism with development. The discovery of trehalose metabolism has been one of the most exciting developments in plant metabolism and plant science in recent years. The field is fast moving and this review highlights the most recent insights.

Trehalose metabolism and signaling.

High-throughput sequencing technology is capable to identify novel short RNAs in plant species. We used Solexa sequencing to find new microRNAs in one of the model legume species, barrel medic (Medicago truncatula). 3,948,871 reads were obtained from two separate short RNA libraries generated from total RNA extracted from M. truncatula leaves, representing 1,563,959 distinct sequences. 2,168,937 reads were mapped to the available M. truncatula genome corresponding to 619,175 distinct sequences. 174,504 reads representing 25 conserved miRNA families showed perfect matches to known miRNAs. We also identified 26 novel miRNA candidates that were potentially generated from 32 loci. Nine of these loci produced eight distinct sequences, for which the miRNA* sequences were also sequenced. These sequences were not described in other plant species and accumulation of these eight novel miRNAs was confirmed by Northern blot analysis. Potential target genes were predicted for most conserved and novel miRNAs. Deep sequencing of short RNAs from M. truncatula leaves identified eight new miRNAs indicating that specific miRNAs exist in legume species.

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High-throughput sequencing of Medicago truncatula short RNAs identifies eight new miRNA families

Plants are often subjected to unfavorable environmental conditions – abiotic factors, causing abiotic stresses that play a major role in determining productivity of crop yields [1] but also the differential distribution of the plants species across different types of environment [2]. Some examples of abiotic stresses that a plant may face include decreased water availability, extreme temperatures (heating or freezing), decreased availability of soil nutrients and/or excess of toxic ions, excess of light and increased hardness of drying soil that hamper roots growth [3]. The ability of plants to adapt and/or acclimate to different environments is directly or indirectly related with the plasticity and resilience of photosynthesis, in combination with other processes, determining plant growth and development, namely reproduction [4]. A remarkable feature of plant adaptation to abiotic stresses is the activation of multiple responses involving complex gene interactions and crosstalk with many molecular pathways [5, 6].

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Abiotic Stress Responses in Plants: Unraveling the Complexity of Genes and Networks to Survive

A simple and efficient regeneration–transformation method was established to obtain transgenic plants of the model legume Medicago truncatula cv. Jemalong. This method takes advantage of a new highly embryogenic line (M9-10a) isolated in our laboratory. Leaflets of in vitro grown M9-10a plants were co-cultured with Agrobacterium tumefaciens EHA105. Plasmid constructs containing the oat arginine decarboxylase gene, Adc and the GUS reporter gene (p35SAdc–Gus) or ELIP-like drought stress protein 22 (DSP22) encoding gene from Craterostigma plantagineum (p35SDsp22) were used. Both constructs include the nptII gene as selection marker. Embryogenic calli (100–97%) were obtained on embryo induction medium containing 100 mg l −1 kanamycin and 500 mg l−1 carbenicillin. Using a two-fold increase in kanamycin concentration, instead of 50 mg l−1 usually used, we reduced the number of emerging false kanamycin-resistant (KanR) embryos, which is an important improvement to the method, making it less laborious and very efficient. Isolation of late torpedo/cotyledonary-stage embryos to lower carbenicillin/agar media reduced secondary embryogenesis and prevents hyperhydricity, improving embryo conversion. Primary transformants (T0) were regenerated within 3–4 months and those that were able to root in a 50 mg l−1 kanamycin medium were transferred to the greenhouse to produce seeds. Southern blot hybridisation analysis confirmed the integration of either the Adc or Dsp22 transgenes in the genome of the T0 transformants. Detection of β-glucuronidase (GUS) activity in Adc–Gus T0 plants demonstrated the expression of the inserted transgene. In average, 1–2 independent transgenic lines are obtained per KanR embryogenic callus, independently of the plasmid construct used for transformation. Inheritance of the transgenes is shown to be stable in the T1 generation.

An Efficient Transformation Method to Regenerate a High Number of Transgenic Plants Using a New Embryogenic Line of Medicago truncatula cv. Jemalong

Trehalose (a non-reducing disaccharide) plays an important role in abiotic stress protection. It has been shown that using trehalose synthesis genes of bacterial origin, drought and salt tolerance could be achieved in several plants. A cassette harboring the AtTPS1 gene under the control of the CaMV35S promoter and the Bialaphos resistance gene was inserted in the binary plasmid vector pGreen0229 and used for Agrobacterium-mediated transformation of tobacco (Nicotiana tabacum). T0 plants obtained were analyzed by PCR for the presence of AtTPS1 gene. Thirty lines were positive and seeds were germinated on media with 6 mg/l PPT to obtain T1 plants that were grown in the greenhouse to obtain T2 seeds that were germinated on selective media. Lines which seeds showed a 100 % survival rate were considered homozygous transgenic T1 lines. Three lines were selected and gene expression confirmed by northern and western blots. Transgenic seeds were germinated on media with different concentrations of mannitol (0, 0.25, 0.5 and 0.75 M) and sodium chloride (0, 0.07, 0.14, 0.2, 0.27 and 0.34 M) to score their tolerance to osmotic stress. Assays were conducted to test the tolerance of transgenic plants to drought (measurement of water percentage as a consequence of water withdrawal), desiccation (measurement of water loss as a consequence leaf detaching) and temperature stresses (germination at 15 ∘C and 35∘C). Transgenic tobacco plant lines registered higher germination rates under osmotic and temperature stress situations than did wild-type plants. Responses to drought and desiccation stresses were similar for all plant lines. It can hence be suggested that the heterologous expression of TPS1 gene from Arabidopsis can be used successfully to increase abiotic stress tolerance in model plants and probably in other crops.

Transformation of tobacco with an Arabidopsis thaliana gene involved in trehalose biosynthesis increases tolerance to several abiotic stresses

Trehalose, a nonreducing disaccharide of glucose, is one of the most effective osmoprotectants. Several strategies leading to its accumulation have been envisaged in both model and crop plants using genes of bacterial, yeast and, more recently, plant origin. Significant levels of trehalose accumulation have been shown to cause abiotic stress tolerance in transgenic plants. In this review, we describe the most biologically relevant features of trehalose: chemical and biological properties; occurrence and metabolism in organisms with special reference to plants; protective role in stabilizing molecules; physiological role in plants with special reference to carbohydrate metabolism. The emphasis of this review, however, will be on manipulation of trehalose metabolism to improve abiotic stress tolerance in plants.

Dulce M. Santos

Papers

High-throughput sequencing of Medicago truncatula short RNAs identifies eight new miRNA families

Abiotic Stress Responses in Plants: Unraveling the Complexity of Genes and Networks to Survive

An Efficient Transformation Method to Regenerate a High Number of Transgenic Plants Using a New Embryogenic Line of Medicago truncatula cv. Jemalong

Transformation of tobacco with an Arabidopsis thaliana gene involved in trehalose biosynthesis increases tolerance to several abiotic stresses

Trehalose and its applications in plant biotechnology