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Biotechnological approach of improving plant salt tolerance using antioxidants as markers. Biotechnology advances, 84— Bartels D.
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Productivity and irrigation requirements of halophytes grown with seawater in the Sonoran Desert. After his Ph. He has published more than 20 research papers in peer reviewed journals and 4 book chapters. He has also edited a volume which is in press with Studium Press Pvt. India Ltd. Parvaiz is actively engaged in studying the molecular and physio-biochemical responses of different plants mulberry, pea, Indian mustard under environmental stress.
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Read this book on SpringerLink. Recommended for you. PAGE 1. For all that was stated above, trehalose is one of the most studied osmoprotectants and in recent years there has been a growing interest in trehalose metabolism as a means of engineering stress tolerance in crop plants [ ]. Several experiments have been conducted to obtain transgenic plants over-expressing genes codifying enzymes of the trehalose biosynthetic pathway of E.
Additional, attempts have been made using an alternative approach: the inhibition of the expression of trehalase gene. Those experiments and their main results are summarized in Table 1. The previously mentioned genetic engineering obtained a variable degree of success. Generally speaking, transgenic plants were found to have higher tolerance than controls to some form of water stress imposed, following in most cases, confirmed trehalose accumulation.
Albeit such fact, trehalose engineered plants frequently had altered phenotypes, particularly dwarfism and leaf abnormalities.
Abiotic Stress Responses In Plants Metabolism Productivity and Sustainability
Such fact was particularly true for the first transformation events in which genes of microbial origin were used. Later events, in which endogenous or plant origin genes were used seem to counter that tendency [ , ]. Genetic engineering of plants with trehalose biosynthesis genes seems therefore to be of extreme pertinence to the increase of abiotic stress tolerance in plants, particularly plants of agricultural importance such as cereals and legumes. Polyamines PAs are small low-molecular-weight , positively charged, aliphatic amines that are found in all living organisms.
The major forms of PAs are putrescine Put , spermidine Spd and spermine Spm , although plants also synthesized a variety of other related compounds. Arginine Arg and ornithine Orn are the precursors of plant PAs. In animals and fungi Put is synthesized primarily through the activity of ODC while in plants and bacteria the main pathway involves ADC. Polyamines levels in plants increase under a number of environmental stress conditions, including drought and salinity [ - ].
Several biological roles were proposed for polyamines action in stress situations; PAs could act as osmoprotectants, as scavengers of active oxygen species AOS or by stabilizing cellular structures, such as thylakoid membranes [ , , ]. The first reports of transgenic approaches using genes responsible for PA biosynthesis were conducted in two species, tobacco and rice [ - ].
Recently, new insights into the role and regulatory function of polyamines in plant abiotic stress tolerance have been achieved, with several abiotic salt, drought, freezing, heat stress tolerant transgenic plants overproducing polyamines being described in the following reviews [ , - ].
Plants respond to changes in water status by accumulating low molecular-weight osmolytes including PAs.
Polyamines may have a primary role of turgor maintenance but they may also be involved in stabilizing proteins and cell structures. The polycationic nature of PAs at physiological pH is believed to mediate their biological activity, since they are able to bind to several negatively charged molecules, such as DNA, membrane phospholipids, pectic polysaccharides and proteins [ ].
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In respect to the antioxidant activity of PAs, the research data is contradictory; on the one hand, PAs have been suggested to protect cells against AOS and on the other hand, their catabolism generates AOS [ ]. PA catabolism produces H 2 O 2 , a signaling molecule that can act promoting activation of antioxidative defense response upon stress, but can also act as a peroxidation agent. In a recent study, the effect of increased putrescine Put accumulation was found to negatively impact the oxidative state of poplar cells in culture due to the enhanced turnover of Put [ ]. Gill and Tuteja [ ] stated that, while increase Put accumulation may have a protective role against AOS in plants, enhanced Put turnover can actually make them more vulnerable to increased oxidative damage.
The higher polyamines, Spd and Spm are believed to be most efficient antioxidants and are considered scavengers of oxyradicals [ ]. As plants with elevated putrescine contents are able to tolerate drought stress because Put has a direct protective role in preventing the symptoms of dehydration, higher PAs Spd and Spm appear to play an important in role in stress recovery [ ].
Recently, transgenic rice plants overexpressing samdc S-Adenosyl methionine decaboxylase gene , with increased Spd and Spm levels, were considered to be non drought tolerant, but showed a more robust recovery from drought compared to wild type [ ]. The de novo synthesis of Spd and Spm in transgenic plants under drought stress, at the expenses of Put, was responsible for the stress tolerance observed in these plants.
The covalent linkage of PAs to proteins appeared to be of extreme importance in plant light-induced stabilization of the photosynthetic complexes and Rubisco therefore exerting a positive effect on photosynthesis and photo-protection. In a recent study, the characterization at the proteomic level of the TGase interaction with thylakoid proteins, demonstrated its association with photosystem II PSII protein complexes using maize thylakoid protein extracts [ ].
Binding of Put to thylakoid membranes has been proposed to be a photoadaptation response under controlled stress conditions. Campos and collaborators [ ] results reinforce the importance of the TGase in photo-protection by polyamine conjugation to light-harvesting complex II LHCII proteins. Recently, PAs were proposed to be components of signaling pathways and fulfill the role of second messengers [ , ].
Studies with ABA-deficient and ABA-insensitive Arabidopsis mutants with differential abiotic stress adaptations [ ] support the conclusion that the up-regulation of PA biosynthetic genes and Put accumulation under water stress are mainly ABA-dependent responses.
Liu et al. In our experiments, we transformed the model legume Medicago truncatula cv. Jemalong with the arginine decarboxylase gene adc from Avena sativa to overexpress the heterologous ADC enzyme aiming to increase the levels of polyamines in transgenic plants [ , ]. Several transgenic lines overexpressing This oat adc construct were obtained.