Volume 1 Number 2 2007

CONTENTS AND ABSTRACTS

Martin M. Sachs (USA), Boris B. Vartapetian (Russia) Plant Anaerobic Stress I. Metabolic Adaptation to Oxygen Deficiency (pp 123-135)

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Invited Review: The establishment and further development of a novel branch of science in the field of ecological physiology, biochemistry and molecular biology, dedicated to plant life under hypoxic and anoxic stresses, is considered in the present review focusing upon strategies of adaptation and injury exhibited by plants under hypoxia and anoxia. Taking into account that the results of investigations over the last few decades confirmed the conclusions about the existence of two general strategies for plant adaptation to hypoxic and anoxic stresses: (a) true tolerance realized at the molecular level due to cardinal rearrangement of cellular metabolism under conditions of oxygen deficiency or complete absence of oxygen, and (b) apparent tolerance that is brought about by avoidance of anaerobiosis thanks to long-distance oxygen translocation, the accumulated experimental information is considered and discussed mainly with respect to basic strategies. The physiological role of anaerobic proteins synthesized under conditions of hypoxia and anoxia as well as advances in molecular biology and molecular genetics in the study of regulation of synthesis of these proteins at the level of transcription, translation and post-translation are discussed. The key significance of energy (glycolysis and fermentation) and related processes of carbohydrate (mobilization and utilization of reserved carbohydrate) metabolism in plant metabolic adaptation to oxygen deficiency is stressed. Special attention is given to an earlier period of active investigations in this field that played a substantial role in the establishment and international recognition of this new biological discipline. The strategy of avoidance of anaerobiosis by long-distance oxygen translocation and some other aspects of plant life under hypoxia and anoxia will be considered in the following publication (Vartapetian, Sachs, Fagerstedt 2008).

Simona Antonacci, Tommaso Maggiore, Antonio Ferrante (Italy) Nitrate Metabolism in Plants under Hypoxic and Anoxic Conditions (pp 136-141)

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Invited Mini-Review: Plants are frequently exposed to a variety of external conditions able to affect their growth, development and productivity. Their ability to adapt and live in a changing environment relies on tolerance or resistance to adverse growing seasons. Oxygen limitation is the major abiotic stress in flooded soils. In the open field, during winter or the raining season in poorly drained soils, plants can experience waterlogging, an event causing scarce root oxygenation and leading to a hypoxic stress. The metabolism of plants undergoes deep modifications in order to minimize energy losses, the most important changes concerning of course glycolysis. With the reduction of oxygen availability specific anaerobic enzymes become activated and their transcripts are over-expressed. Fermentation is induced and potentially toxic metabolites like ethanol are accumulated into anoxic tissues. Among the metabolic pathways strongly affected by oxygen deficiency stands also nitrate metabolism. The enzymes involved in nitrate assimilation and reduction are up-regulated during oxygen deficiency and some authors showed several correlations between nitrate availability and plant survival to flooding. Moreover nitrites and nitric oxide seem to be directly involved in plant survival at least during the first hours after the onset of hypoxia/anoxia. Intracellular nitrates and nitrites concentrations may play an effective role in maintaining cellular pH homeostasis, limiting cytoplasmic acidosis deriving from fermentation and thus contributing to survival. This mini-review is intended to summarize and discuss nitrate metabolism under limited oxygen conditions with a brief introduction on the metabolic pathways that interact with nitrate assimilation.

Fabio F. Nocito, Clarissa Lancilli, Barbara Giacomini, Gian Attilio Sacchi (Italy) Sulfur Metabolism and Cadmium Stress in Higher Plants (pp 142-156)

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Invited Review: Plant sulfur metabolism is deeply affected by cadmium (Cd) stress, mainly as a consequence of the activation of a wide range of adaptive responses involving glutathione (GSH) consuming activities. In fact, GSH not only acts as a direct or indirect antioxidant in mitigating Cd-induced oxidative stress, but also represents a key intermediate for the synthesis of phytochelatins (PCs), a class of cysteine-rich heavy metal-binding peptides involved in buffering cytosolic metal concentration. As a consequence, Cd exposure may result in a depletion of the cell GSH pools which in turn increases the plant demand for reduced sulfur compounds. In this condition the need for maintaining GSH homeostasis and an adequate PC biosynthesis rate is met by a general induction of enzyme activities directly or indirectly involved in sulfur metabolism. Transgenic plants overexpressing these enzymes exhibit a greater production of GSH and an increased Cd tolerance, confirming this pathway to be crucial for plant survival in metal polluted environments. In the present paper we analyze and discuss the biochemical and molecular mechanisms involved in the regulation of sulfate (the main sulfur source for plants) uptake and assimilation, and GSH synthesis during Cd detoxification.

Ajay Arora, V.P. Singh, S.S. Sindhu, D.N. Rao, S.R. Voleti (India) Oxidative Stress Mechanisms during Flower Senescence (pp 157-172)

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Invited Review: Free radicals and other active derivatives of oxygen are inevitable by-products of biological redox reactions and universal under stress situations. Reactive oxygen species inactivate enzymes and damage important cellular processes and subsequently cell components also. Plants and other organisms have evolved a wide range of mechanisms to contend with this problem by promoting the synthesis of antioxidant molecules and enzymes. The effects of the action of free radicals on membranes include the induction of lipid peroxidation and fatty acid de-esterification. Both ethylene biosynthesis and membrane breakdown, which appear to be closely linked, seem to involve free radicals, although the sequence of events generating these free radicals is still poorly understood. The death of petal cells is preceded by a loss in membrane permeability, partly due to increases in reactive oxygen species that are in turn related to the up-regulation of oxidative enzymes and to a decrease in activity of protective enzymes. It also consists of losses in soluble proteins, nucleic acids caused by the activation of proteinases and nucleases and enzyme-mediated alterations of carbohydrate polymers. Many of the genes for these senescence-associated enzymes have been cloned. In some flowers, the degradative changes of petal cells are initiated by ethylene; in others, abscisic acid may play a role.

Xiao-Ming Pang, Zhi-Yi Zhang, Xiao-Peng Wen (China), Yusuke Ban, Takaya Moriguchi (Japan) Polyamines, All-Purpose Players in Response to Environment Stresses in Plants (pp 173-188)

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Invited Review: The polyamines (PAs), putrescine (Put), spermidine (Spd) and spermine (Spm), are small aliphatic amines that are ubiquitous in all living organisms. PA metabolism in higher plants is involved in both biotic and abiotic stresses including nutrient deficiency, salitniy, hyperosmosis, temperature stress, drought, pH, hypoxia, paraquat, environmental pollutants, and wouuding. PA biosynthetic pathway has now been revealed at molecular level in plants and more and more molecular evidences support the roles of PA in plant stress responses, to which transgenic approaches to modulate PA biosynthetic genes have provided further evidence. Transcriptomic and proteomic approaches will help to elucidate the roles of PA in signaling network under environment stresses.

Federico D. Ariel, Pablo A. Manavella, Jorge I. Giacomelli, Raquel L. Chan (Argentina) HD-Zip I and II, Transcription Factors Involved in the Adaptive Response to Environmental Stress (pp 189-196)

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Mini-Review: The response to abiotic stress results in a dramatic change of the whole plant transcriptome. This regulation takes place mostly at the transcriptional level for which the role of transcription factors turns out to be essential. Here we compile the knowledge acquired about the participation of HD-Zip I and II transcription factors in the response to abiotic stress, such as water deficit, low temperature, osmotic stress and different illumination conditions. We finally analyze the effect of transgenic model plants that over express some of the HD-Zip members and infer their potential use as biotechnological tools for the obtaining of tolerant transgenic crops.

Chantal Teulières (France), Gerd Bossinger, Gavin Moran (Australia), Christiane Marque (France) Stress Studies in Eucalyptus (pp 197-215)

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Invited Review: Eucalypts are endemic to Australia where they are the dominant species in more than 40 million ha of natural forest and grow across a large range of climatic environments and soil types. Due to its adaptability, extremely fast growth rate and excellent wood and fiber properties, the genus became the most widely planted forest tree (18 million ha) at a world scale mainly for pulpwood and timber. Eucalyptus globulus is the most planted species for temperate zone plantations (e.g. Portugal, Spain, Chile and Australia) while E. grandis and E. urophylla are extensively grown in tropical and subtropical regions (e.g. Brazil, South-Africa, Congo). Adaptation to aridity is considered a major factor in the evolution of the genus and resulting geographic distribution of the species. Apart from drought other environmental stresses such as extreme temperatures, salt or excess light limit productivity which is often less than its very high potential. Moreover frost, drought and competition are the major causes of mortality in juvenile plantations. Among biotic stresses the genus Eucalyptus has to deal with a diverse range of invertebrate and mammalian herbivores that consume foliage and fungal diseases also cause great losses very detrimental to economically important Eucalyptus species. This review describes the main studies conducted in Eucalyptus on these different stresses and specific problems occurring in natural forests or in the plantations spread out around the world. For each type of stress we describe the impact on the trees; the corresponding tolerance mechanisms developed by the plant and the methods designed for protection or genetic improvement.

Etan Pressman, Rachel Shaked, Nurit Firon (Israel) Tomato (Lycopersicon esculentum) Response to Heat Stress: Focus on Pollen Grains (pp 216-227)

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Invited Review: Exposure to higher than optimal temperatures, heat-stress (HS), reduces yield and decreases the quality of many crops, including tomato. Pollen development is one of the most heat-sensitive developmental stages in a large variety of plant species. Impaired fruit set in response to HS conditions may thus be largely due to HS-induced changes in pollen characteristics. This review emphasizes the effect of HS on the developing pollen grains, though the available data are still very limited. Recently accumulated data on the molecular control of pollen development are included, which indicate the processes important for the production of functional pollen grains. These recent studies are put in the context of data on HS effects on the other parts of the tomato plant (whole plant, leaves, anther cells) likely to affect the development and functioning of the gametes. Among other effects, HS was found to affect membrane integrity, Ca²⁺ flux, protein conformation and production of reactive oxygen species (ROS) which, in turn, elicit defense mechanisms that include the production of heat shock factors, heat shock proteins and ROS-scavenging enzymes. In the developing pollen grain HS directly affects sugar and starch metabolism ? effects that are associated with reduced pollen quality. In parallel, defense mechanisms are elicited, including the induction of heat shock proteins. The full understanding of the heat sensitivity of pollen, on the one hand, and of the mechanisms that may enable the pollen to cope with HS, on the other hand, requires additional data, including data on other components of the chaperone network, as well as data on other protective mechanisms (such as ROS scavengers and compatible solute accumulation).

Suriyan Cha-um, Sittiruk Roytrakul, Chalermpol Kirdmanee (Thailand), Issei Akutagawa, Michiko Takagaki (Japan) A Rapid Method for Identifying Salt Tolerant Water Convolvulus (Ipomoea aquatica Forsk) under In Vitro Photoautotrophic Conditions (pp 228-234)

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Original Research Paper: Water convolvulus is an aquatic plant capable of growing in a low nutrient solution and poor water quality. There are many reports on utilization of this plant for the efficient remediation of salt contaminated wastewater. The aim of this investigation was to identify the criteria that could be used to classify the salt tolerance and salt sensitivity of water convolvulus using multivariate characters. Six lines of water convolvulus plantlets were photoautotrophically grown in a controlled environmental system and then treated with 0 (control) or 342 mM NaCl (salt stress) for a week. Pigment levels, chlorophyll a fluorescence and growth reduction were measured as potential multivariate parameters to group plants into two classes: salt tolerant (WC083, SR739 and SR716) and salt sensitive (MK98, WC001 and WC092). Total chlorophyll and carotenoid pigments in salt-stressed plantlets were reduced by 80.0% and 68.6% in salt tolerant lines. In salt-sensitive lines these pigments were degraded by 88.0% and 79.8%, respectively. This suggests that the major pigments, total chlorophyll and carotenoids in salt-tolerant lines were more stable than those in salt-sensitive lines. The function of both major pigments in salt-tolerant lines was strongly related to light harvesting (F_PSII) (r = 0.81) and photooxidative damage (NPQ) defenses (r = 0.81), respectively. Further, several growth parameters (plant height, number of leaves, root length, number of roots, fresh weight) progressively decreased when exposed to salt stress, especially in salt-sensitive lines. The salt-tolerant lines of water convolvulus can be further utilized for NaCl-contaminated wastewater phytoremediation, while the salt-sensitive lines may be applied as effective indicators of salt contamination in the water.