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PubMed2005

Genetic manipulation of proline accumulation influences the concentrations of other amino acids in soybean subjected to simultaneous drought and heat stress.

The effect of simultaneous drought and heat stress on free amino acid levels was compared in wild type and transgenic soybean (Glycine max (L.) Merr cv Ibis) plants transformed with the cDNA coding for the last enzyme of Pro biosynthesis, l-Delta(1)-pyrroline-5-carboxylate reductase (EC 1.5.1.2), in sense and antisense directions. The most rapid increase in Pro content was found in the sense transformants that exhibited the least water loss, while the slowest elevation of Pro levels was detected in the antisense transformants that exhibited the greatest water loss during stress. Correspondingly, the level of the Pro precursors Glu and Arg was higher in sense transformants and lower in antisense ones compared to the wild type plants during the initial part of the stress. Interestingly, genetic manipulation of Pro levels also affected the stress-induced changes in the concentration of several other amino acids, which indicates the coordinated regulation of their metabolic pathways.

Amino Acids↗
PubMed1997

A drought-stress-inducible histone gene in Arabidopsis thaliana is a member of a distinct class of plant linker histone variants.

We have isolated and characterized a gene, His1-3, encoding a structurally divergent linker histone in Arabidopsis thaliana. Southern and northern hybridization data indicate that A. thaliana expresses three single-copy linker histone genes, each encoding a structurally distinct variant. H1-3 is a considerably smaller protein (167 amino acids with a mass of 19.0 kDa) than any other described linker histone from higher eukaryotes. We examined the expression of His1-3 at the RNA and protein levels and found that it is induced specifically by water stress. In contrast, expression of His1-1, His1-2 and His4 appear unaffected by water stress. Furthermore, the primary structure of the protein possesses distinct characteristics that are shared with another drought-inducible linker histone, H1-D, isolated from Lycopersicon pennellii. Based on structural characteristics of the deduced protein and its inducible expression, we hypothesize that H1-3 and H1-D are linker histone variants that have specialized roles in the structure and function of plant chromatin and therefore they can be considered to be members of a unique subclass of plant histones. Immunoblotting with an antibody produced against a short polypeptide in the conserved domain of this subtype indicates that similar proteins may exist in other plants.

Amino Acid Sequence↗
PubMed2000

Isolation and characterization of a dehydrin gene from white spruce induced upon wounding, drought and cold stresses.

A cDNA clone encoding a dehydrin gene was isolated from a cDNA library prepared from white spruce (Picea glauca) needle mRNAs. The cDNA, designated PgDhn1, is 1159 nucleotides long and has an open reading frame of 735 bp with a deduced amino acid sequence of 245 residues. The PgDhn1 amino acid sequence is highly hydrophilic and possesses four conserved repeats of the characterized lysine-rich K-segment (EKKGIMD-KIKEKLPG), and an 8-serine residue stretch prior to the first lysine-rich repeat that is common to many dehydrins. The DEYGNP conserved motif is, however, absent in the PgDhn1 sequence. In unstressed plants, the highest level of transcripts was detected in stem tissue and not fully expanded vegetative buds. PgDhn1 expression was also clearly detected in reproductive buds, at various stages of development. The mRNAs corresponding to PgDhn1 cDNA were induced upon wounding and by jasmonic acid (JA) and methyl jasmonate (MeJa) treatments. Upon drought stress, increased transcript accumulation was observed in needle tissue reaching a maximum level 48 h after treatment. Treatments of seedlings with abscisic acid or ethephon also resulted in high levels of transcript accumulation in needle tissue. Finally, cold induction of PgDhn1 transcripts was also detected as early as 8 h after treatment.

Abscisic Acid↗
PubMed2000

Phytophagous mite populations on Tahiti lime, Citrus latifolia, under induced drought conditions.

In the north-western region of Venezuela, Phyllocoptruta oleivora, Tetranychus mexicanus and Brevipalpus phoenicis are common plant-feeding mites on leaves, fruits and branches of Tahiti lime, Citrus latifolia. The population dynamics of these herbivores are affected by many factors, such as weekly treatments with wettable sulphur, particularly during the wet season, maintenance pruning of plants, irrigation with microsprinklers, induction of water stress by withholding irrigation and biotic and abiotic environmental factors. During October 1994-January 1995, 31 trees in a commercial orchard were sampled weekly in order to describe population fluctuations of plant-feeding mites (mean number of mites per leaf or fruit), before (4 weeks) and after (4 weeks) a period of 6 weeks of drought stress (no irrigation). The population density of P. oleivora increased progressively during the last 3 weeks of the irrigation period and reached a maximum of 24 mites per fruit. In contrast, the populations of the other two species, T. mexicanus and B. phoenicis, remained at the same low density as before the withholding-irrigation period. After 6 weeks without irrigation, only T. mexicanus increased, to a high mean value of 11 mites per leaf. The withholding-irrigation practice appears to affect the population size of P. oleivora towards the end of this period and that of T. mexicanus at the beginning of the re-establishment of the water supply. The highest proportion of trees (32%) was infested by T. mexicanus after the withholding-irrigation period, when irrigation was resumed, whereas the highest levels of infestation of trees by P. oleivora and B. phoenicis were 16 and 10%, respectively, during the last week of the water-stress period. Although factors affecting the dynamics of the mites in the orchard are likely to be complex, irrigation management apparently plays an important role.

Animals↗
PubMed2002

Impact of four years exposure to different levels of ozone, phosphorus and drought on chlorophyll, mineral nutrients, and stem volume of Norway spruce, Picea abies.

Saplings of one clone of Norway spruce, Picea abies (L.) Karst, were planted in 120 l pots in 1991 and exposed to three levels of ozone, two levels of phosphorus and two levels of water supply in 42 open-top chambers (OTCs), during 1992-1996. The effects of pots and OTCs were also tested. Nutrient concentrations of the needles were not affected by ozone, while the low phosphorus supply (LP) and drought stress (D) treatments had significant effects on several mineral nutrients, e.g. phosphorus, calcium, magnesium, manganese, sulphur and boron. Ozone reduced the chlorophyll concentration in the 2- and 3-year-old needles in 1994 and 1995. The highest ozone concentration reduced the stem volumes (- 8%), as well as the stem lengths (- 5%), of the saplings in 1993 and 1994, after two and three years of exposure. After the fourth growing season this ozone-induced reduction in stem volume disappeared which might be caused by pot limitation. LP supply and D both caused large decreases in the stem volume and length. The needles from LP treatment had as high P concentration as 1.2-1.5 mg g-1, implying a need for increasing the critical value for phosphorus. The OTC enclosure stimulated the stem volume growth significantly compared to saplings growing in ambient plots. This was suggested to be attributed to the slightly higher temperature in the OTCs. The overall result is that ozone in southern Sweden is likely to have negative effects on Norway spruce trees, although much less than other environmental factors, e.g. water and phosphorus.

Journal Article↗
PubMed2002

A gene encoding stellacyanin is induced in Capsicum annuum by pathogens, methyl jasmonate, abscisic acid, wounding, drought and salt stress.

A stellacyanin cDNA clone (CASLP1) was isolated from a pepper cDNA library from hypersensitive response (HR) lesions of leaves infected with an avirulent strain of Xanthomonas campestris pv. vesicatoria. The deduced amino acid sequences of CASLP1 are homologous to those of stellacyanins from cucumber, maize, pea and Arabidopsis. The CASLP1 mRNA was not constitutively expressed in all organs of pepper, but strongly induced and accumulated in pepper tissues infected with X. campestris pv. vesicatoria, Colletotrichum coccodes, Phytophthora capsici or C. gloeosporioides. In situ hybridization results revealed that CASLP1 transcripts were strongly localized in the phloem areas of vascular bundles in infected tissues of pepper stems and fruits. CASLP1 mRNA accumulation was found in lower pepper leaves infected by either virulent or avirulent strains of X. campestris pv. vesicatoria and non-pathogenic Pseudomonas fluorescens, but not in uninoculated upper leaves. Induction of this CASLP1 gene occurred in pepper leaves applied with methyl jasmonate (MeJA), but not with ethylene, salicylic acid, dl-beta-amino-n-butyric acid and benzothiadiazole. Accumulation of CASLP1 transcripts was locally or systemically induced in pepper leaves upon mechanical wounding and was activated in a MeJA-dependent manner. The CASLP1 transcript was also strongly induced in leaf and stem tissues after exposure of pepper plants to abscisic acid, salt and drought.

Journal Article↗
PubMed2000

Rainfall and drought in equatorial east Africa during the past 1,100 years.

Knowledge of natural long-term rainfall variability is essential for water-resource and land-use management in sub-humid regions of the world. In tropical Africa, data relevant to determining this variability are scarce because of the lack of long instrumental climate records and the limited potential of standard high-resolution proxy records such as tree rings and ice cores. Here we present a decade-scale reconstruction of rainfall and drought in equatorial east Africa over the past 1,100 years, based on lake-level and salinity fluctuations of Lake Naivasha (Kenya) inferred from three different palaeolimnological proxies: sediment stratigraphy and the species compositions of fossil diatom and midge assemblages. Our data indicate that, over the past millennium, equatorial east Africa has alternated between contrasting climate conditions, with significantly drier climate than today during the 'Medieval Warm Period' (approximately AD 1000-1270) and a relatively wet climate during the 'Little Ice Age' (approximately AD 1270-1850) which was interrupted by three prolonged dry episodes. We also find strong chronological links between the reconstructed history of natural long-term rainfall variation and the pre-colonial cultural history of east Africa, highlighting the importance of a detailed knowledge of natural long-term rainfall fluctuations for sustainable socio-economic development.

Africa, Eastern↗
PubMed2001

Guard cell abscisic acid signalling and engineering drought hardiness in plants.

Guard cells are located in the epidermis of plant leaves, and in pairs surround stomatal pores. These control both the influx of CO2 as a raw material for photosynthesis and water loss from plants through transpiration to the atmosphere. Guard cells have become a highly developed system for dissecting early signal transduction mechanisms in plants. In response to drought, plants synthesize the hormone abscisic acid, which triggers closing of stomata, thus reducing water loss. Recently, central regulators of guard cell abscisic acid signalling have been discovered. The molecular understanding of the guard cell signal transduction network opens possibilities for engineering stomatal responses to control CO2 intake and plant water loss.

Abscisic Acid↗
PubMed2001

Drought-induced guard cell signal transduction involves sphingosine-1-phosphate.

Stomata form pores on leaf surfaces that regulate the uptake of CO2 for photosynthesis and the loss of water vapour during transpiration. An increase in the cytosolic concentration of free calcium ions ([Ca2+]cyt) is a common intermediate in many of the pathways leading to either opening or closure of the stomatal pore. This observation has prompted investigations into how specificity is controlled in calcium-based signalling systems in plants. One possible explanation is that each stimulus generates a unique increase in [Ca2+]cyt, or 'calcium signature', that dictates the outcome of the final response. It has been suggested that the key to generating a calcium signature, and hence to understanding how specificity is controlled, is the ability to access differentially the cellular machinery controlling calcium influx and release from internal stores. Here we report that sphingosine-1-phosphate is a new calcium-mobilizing molecule in plants. We show that after drought treatment sphingosine-1-phosphate levels increase, and we present evidence that this molecule is involved in the signal-transduction pathway linking the perception of abscisic acid to reductions in guard cell turgor.

Abscisic Acid↗
PubMed2001

Increased damage from fires in logged forests during droughts caused by El Niño.

In 1997-98, fires associated with an exceptional drought caused by the El Niño/Southern Oscillation (ENSO) devastated large areas of tropical rain forests worldwide. Evidence suggests that in tropical rainforest environments selective logging may lead to an increased susceptibility of forests to fire. We investigated whether this was true in the Indonesian fires, the largest fire disaster ever observed. We performed a multiscale analysis using coarse- and high-resolution optical and radar satellite imagery assisted by ground and aerial surveys to assess the extent of the fire-damaged area and the effect on vegetation in East Kalimantan on the island of Borneo. A total of 5.2 +/- 0.3 million hectares including 2.6 million hectares of forest was burned with varying degrees of damage. Forest fires primarily affected recently logged forests; primary forests or those logged long ago were less affected. These results support the hypothesis of positive feedback between logging and fire occurrence. The fires severely damaged the remaining forests and significantly increased the risk of recurrent fire disasters by leaving huge amounts of dead flammable wood.

Borneo↗
PubMed2005

Europe-wide reduction in primary productivity caused by the heat and drought in 2003.

Future climate warming is expected to enhance plant growth in temperate ecosystems and to increase carbon sequestration. But although severe regional heatwaves may become more frequent in a changing climate, their impact on terrestrial carbon cycling is unclear. Here we report measurements of ecosystem carbon dioxide fluxes, remotely sensed radiation absorbed by plants, and country-level crop yields taken during the European heatwave in 2003. We use a terrestrial biosphere simulation model to assess continental-scale changes in primary productivity during 2003, and their consequences for the net carbon balance. We estimate a 30 per cent reduction in gross primary productivity over Europe, which resulted in a strong anomalous net source of carbon dioxide (0.5 Pg C yr(-1)) to the atmosphere and reversed the effect of four years of net ecosystem carbon sequestration. Our results suggest that productivity reduction in eastern and western Europe can be explained by rainfall deficit and extreme summer heat, respectively. We also find that ecosystem respiration decreased together with gross primary productivity, rather than accelerating with the temperature rise. Model results, corroborated by historical records of crop yields, suggest that such a reduction in Europe's primary productivity is unprecedented during the last century. An increase in future drought events could turn temperate ecosystems into carbon sources, contributing to positive carbon-climate feedbacks already anticipated in the tropics and at high latitudes.

Atmosphere↗
PubMed2003

Supply control and harm reduction: lessons from the Australian heroin 'drought'.

AIMS: To examine the effects of supply-side drug law enforcement on the dynamics of the Australian heroin market and the harms associated with heroin. SETTING: Around Christmas 2000, heroin users in Sydney and other large capital cities in Australia began reporting sudden and significant reductions in the availability of heroin. The changes, which appear to have been caused at least in part by drug law enforcement, provided a rare opportunity to examine the potential impact of such enforcement on the harm associated with heroin. DESIGN: Data were drawn from a survey of 165 heroin users in South-Western Sydney, Australia; from the Drug Use Monitoring in Australia (DUMA) project; from NSW Health records of heroin overdoses; and from the Computerized Operational Policing System (COPS) database. FINDINGS: Heroin price increased, while purity, consumption and expenditure on the drug decreased as a result of the shortage. The fall in overall heroin use was accompanied by a significant reduction in the rate of overdose in NSW. However, the health benefits associated with the fall in overdose may have been offset by an increase in the use of other drugs (mainly cocaine) since the onset of the heroin shortage. There does not appear to have been any enduring impact on crime rates as a result of the heroin 'drought'. CONCLUSION: Supply control has an important part to play in harm reduction; however, proponents of supply-side drug law enforcement need to be mindful of the unintended adverse consequences that might flow from successfully disrupting the market for a particular illegal drug.

Adult↗
PubMed2002

Signalling drought in guard cells.

A number of environmental conditions including drought, low humidity, cold and salinity subject plants to osmotic stress. A rapid plant response to such stress conditions is stomatal closure to reduce water loss from plants. From an external stress signal to stomatal closure, many molecular components constitute a signal transduction network that couples the stimulus to the response. Numerous studies have been directed to resolving the framework and molecular details of stress signalling pathways in plants. In guard cells, studies focus on the regulation of ion channels by abscisic acid (ABA), a chemical messenger for osmotic stress. Calcium, protein kinases and phosphatases, and membrane trafficking components have been shown to play a role in ABA signalling process in guard cells. Studies also implicate ABA-independent regulation of ion channels by osmotic stress. In particular, a direct osmosensing pathway for ion channel regulation in guard cells has been identified. These pathways form a complex signalling web that monitors water status in the environment and initiates responses in stomatal movements.

Journal Article↗
PubMed1996

A transcriptional activation domain of ATMYB2, a drought-inducible Arabidopsis Myb-related protein.

Trans-activation activity of ATMYB2, a drought-inducible Myb-related protein in Arabidopsis thaliana, was analyzed using a transient assay of Arabidopsis leaf protoplasts. ATMYB2 activated the transcription of a reporter gene from the MYB-binding site in a sequence-specific manner. Deletion of the C-terminal region of ATMYB2 reduced the trans-activation of the reporter gene, indicating that the acidic region at the C-terminus of ATMYB2 is required for transcriptional activation. The domain exchange analysis with the yeast GAL4 revealed that the C-terminal acidic region of ATMYB2 contains a sufficient domain for trans-activation. These results indicate that ATMYB2 acts as a transcriptional activator and that the C-terminal acidic region of ATMYB2 can function as a transcriptional activation domain.

Arabidopsis↗
PubMed1998

A history of stress alters drought calcium signalling pathways in Arabidopsis.

Environmental stresses commonly encountered by plants lead to rapid transient elevations in cytosolic free calcium concentration ([Ca2+]cyt) (Bush, 1995; Knight et al., 1991). These cellular calcium (Ca2+) signals lead ultimately to the increased expression of stress-responsive genes, including those encoding proteins of protective function (Knight et al., 1996; Knight et al., 1997). The kinetics and magnitude of the Ca2+ signal, or 'calcium signature', differ between different stimuli and are thought to contribute to the specificity of the end response (Dolmetsch et al., 1997; McAinsh and Hetherington, 1998). We measured [Ca2+]cyt changes during treatment with mannitol (to mimic drought stress) in whole intact seedlings of Arabidopsis thaliana. The responses of plants which were previously exposed to osmotic and oxidative stresses were compared to those of control plants. We show here that osmotic stress-induced Ca2+ responses can be markedly altered by previous encounters with either osmotic or oxidative stress. The nature of the alterations in Ca2+ response depends on the identity and severity of the previous stress: oxidative stress pre-treatment reduced the mannitol-induced [Ca2+]cyt response whereas osmotic stress pretreatment increased the [Ca2+]cyt response. Therefore, our data show that different combinations of environmental stress can produce novel Ca2+ signal outputs. These alterations are accompanied by corresponding changes in the patterns of osmotic stress-induced gene expression and, in the case of osmotic stress pre-treatment, the acquisition of stress-tolerance. This suggests that altered Ca2+ responses encode a 'memory' of previous stress encounters and thus may perhaps be involved in acclimation to environmental stresses.

Aequorin↗
PubMed2000

Cell-type-specific calcium responses to drought, salt and cold in the Arabidopsis root.

Little is known about the signalling processes involved in the response of roots to abiotic stresses. The Arabidopsis root is a model system of root anatomy with a simple architecture and is amenable to genetic manipulation. Although it is known that the root responds to cold, drought and salt stress with increases in cytoplasmic free calcium, there is currently no information about the role(s) of the functionally diverse cell types that comprise the root. Transgenic Arabidopsis with enhancer-trapped GAL4 expression in specific cell types was used to target the calcium reporting protein, aequorin, fused to a modified yellow fluorescent protein (YFP). The luminescence output of targeted aequorin enabled in vivo measurement of changes in cytosolic free calcium concentrations ([Ca2+]cyt) in specific cell types during acute cold, osmotic and salt stresses. In response to an acute cold stress, all cell types tested as well as plants constitutively expressing aequorin displayed rapid [Ca2+]cyt peaks. However, there were significant quantitative differences between different cell types in terms of their response to cold stress, osmotic stress (440 mM mannitol) and salt stress (220 mM NaCl), implying specific roles for certain cell types in the detection and/or response to these stimuli. In response to osmotic and salt stress, the endodermis and pericycle displayed prolonged oscillations in cytosolic calcium that were distinct from the responses of the other cell types tested. Targeted expression of aequorin circumvented the technical difficulties involved in fluorescent dye injection as well as the lack of cell specificity of constitutively expressed aequorin, and revealed a new level of complexity in root calcium signalling.

Aequorin↗
PubMed2002

Maize DRE-binding proteins DBF1 and DBF2 are involved in rab17 regulation through the drought-responsive element in an ABA-dependent pathway.

The abscisic acid-responsive gene rab17 of maize is expressed during late embryogenesis, and is induced by ABA and desiccation in embryo and vegetative tissues. ABRE and DRE cis-elements are involved in regulation of the gene by ABA and drought. Using yeast one-hybrid screening, we isolated two cDNAs encoding two new DRE-binding proteins, designated DBF1 and DBF2, that are members of the AP2/EREBP transcription factor family. Analysis of mRNA accumulation profiles showed that DBF1 is induced during maize embryogenesis and after desiccation, NaCl and ABA treatments in plant seedlings, whereas the DBF2 mRNA is not induced. DNA-binding preferences of DBFs were analysed by electrophoretic mobility shift assays, and showed that both DBF1 and DBF2 bound to the wild-type DRE2 element, but not to the DRE2 mutant or to the DRE1 element which differs only in a single nucleotide. Transactivation activity using particle bombardment showed that DBF1 functioned as activator of DRE2-dependent transcription of rab17 promoter by ABA, whereas DBF2 overexpression had a repression action downregulating not only the basal promoter activity, but also the ABA effect. These results show that ABA plays a role in the regulation of DBF activity, and suggests the existence of an ABA-dependent pathway for the regulation of genes through the C-repeat/DRE element.

Abscisic Acid↗
PubMed2000

Arabidopsis basic leucine zipper transcription factors involved in an abscisic acid-dependent signal transduction pathway under drought and high-salinity conditions.

The induction of the dehydration-responsive Arabidopsis gene, rd29B, is mediated mainly by abscisic acid (ABA). Promoter analysis of rd29B indicated that two ABA-responsive elements (ABREs) are required for the dehydration-responsive expression of rd29B as cis-acting elements. Three cDNAs encoding basic leucine zipper (bZIP)-type ABRE-binding proteins were isolated by using the yeast one-hybrid system and were designated AREB1, AREB2, and AREB3 (ABA-responsive element binding protein). Transcription of the AREB1 and AREB2 genes is up-regulated by drought, NaCl, and ABA treatment in vegetative tissues. In a transient transactivation experiment using Arabidopsis leaf protoplasts, both the AREB1 and AREB2 proteins activated transcription of a reporter gene driven by ABRE. AREB1 and AREB2 required ABA for their activation, because their transactivation activities were repressed in aba2 and abi1 mutants and enhanced in an era1 mutant. Activation of AREBs by ABA was suppressed by protein kinase inhibitors. These results suggest that both AREB1 and AREB2 function as transcriptional activators in the ABA-inducible expression of rd29B, and further that ABA-dependent posttranscriptional activation of AREB1 and AREB2, probably by phosphorylation, is necessary for their maximum activation by ABA. Using cultured Arabidopsis cells, we demonstrated that a specific ABA-activated protein kinase of 42-kDa phosphorylated conserved N-terminal regions in the AREB proteins.

Abscisic Acid↗