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- Morphological, physiological and oxidative stress markers during acclimatization and field transfer of micropropagated Tuberaria major plantsPublication . Osório, Maria Leonor; Gonçalves, Sandra; Coelho, N.; Osório, Júlio; Romano, AnabelaTuberaria major (Willk.) P. Silva and Rozeira is a critically-endangered rock rose species endemic to Portugal. Because the species needs to be preserved, this study evaluated the morphological and physiological traits of micropropagated T. major plants during acclimatization and field transfer. There were no significant differences between wild and micropropagated plants in the field, although the latter underwent significant changes during acclimatization. Leaf pubescence and leaf mass per area increased during acclimatization whereas the chlorophyll content and chlorophyll/carotenoid ratio declined to eventually match those of wild plants. Stomatal conductance (g(s)) and transpiration rates (E) also declined substantially during acclimatization, thus preventing uncontrolled wilting. Photosynthetic rate (P-N) was initially negative but increased during the later stages of acclimatization. Maximum quantum yield of PSII (F-v/F-m) remained constant at 0.78-0.85, showing that the plants were healthy and unstressed. PSII quantum efficiency (I center dot(PSII)) was initially low but increased during acclimatization along with photosynthetic performance as the energy partitioning in PSII was adjusted. This was balanced by the decline in non-regulated energy dissipation (I center dot(NO)) from an initially high value. Electrolyte leakage and malondialdehyde content remained constant at similar levels in both groups of plants, but H2O2 levels were higher in the field, perhaps indicating the early induction of antioxidant defense systems. The present study shows that T. major has enough phenotypic plasticity to adapt to changing environments and that the procedure described herein can be used for the restoration and preservation of this species.
- How to monitor the acclimatization of micropropagated plants - From in vitro to the field?Publication . Osório, Maria Leonor; Gonçalves, Sandra; Coelho, N.; Romano, Anabela; Osório, JúlioThe high mortality experienced by plants during ex vitro transplantation stage is the major bottleneck in large scale application of micropropagation. The abnormal physiological and anatomical characteristics of micropropagated plantlets require that they should be gradually acclimatized to the environment of the greenhouse or field. Environmental factors, especially relative humidity and irradiance, play a critical role in both physiological and biochemical functions, namely water relations, gas exchange, photosynthetic efficiency and water oxidation, during transition from in vitro to ex vitro conditions. Throughout this period of transition and acclimatization substantial changes in those characteristics are necessary to achieve a successful micropropagation. This adaptation should be accurately monitored using relevant physiological parameters including pigment content, chlorophyll a fluorescence imaging, net photosynthetic rate, transpiration rate, and stomatal conductance. Growth traits and oxidative stress markers, such as electrolyte leakage, lipid peroxidation and hydrogen peroxide content, should be also analyzed. These parameters must be assessed during the course of ex vitro acclimatization in several periods and compared with those of plants growing in their natural habitat. The performance plants of Tuberaria major, an endangered species endemic from the Algarve region (Portugal), during their acclimatization through indoor-to-outdoor conditions was monitored using several physiological and biochemical traits as indicators. In view of the results, we concluded that the transplantation protocol described can be used for restoration purposes, contributing to the preservation of the species. © ISHS 2013.
- Impact of chitosan on plant tissue culture: recent applicationsPublication . Coelho, N.; Romano, A.Chitosan is a very versatile biomaterial with countless applications in different fields. Due to its biodegradability, non-toxicity, and biocompatibility, the use of chitosan is associated with sustainable practices. When applied to plants, in an agricultural context, chitosan induces defense mechanisms, stress resistance, and increased productivity and it has proven to be a feasible alternative to harmful agrochemicals. For in vitro plant culture, chitosan has been also applied to crops and other economically important species, with promising results. In this review, we discuss the recent applications of chitosan on plant tissue culture. Chitosan has been mainly used for the improvement of several growth parameters, but it has been also applied to enhance in vitro seed germination and accumulation of secondary metabolites. The plant material used, the concentrations and forms of chitosan employed, and the influence of chitosan on other plant parameters during in vitro culture are revised. We anticipate that chitosan applications will increase in a near future because of its potential and the increasing demand for more eco-friendly procedures.
- Molecular cloning and expression analysis of three omega-6 desaturase genes from purslane (Portulaca oleracea L.)Publication . Teixeira, Monica; Coelho, N.; Olsson, M. E.; Brodelius, P. E.; Carvalho, Isabel Saraiva de; Brodelius, MariaTwo full-length cDNA clones of PoleFAD2 and one full-length cDNA clone of PoleFAD6, encoding omega-6 fatty acid desaturases, the key enzymes for the conversion of oleic into linoleic acid, were isolated from purslane (Portulaca oleracea L.) leaves and seeds. The deduced amino acid sequence of both isoforms of PoleFAD2 showed higher similarities to other microsomal omega-6 desaturases then to PoleFAD6 or other plastidial orthologues, and vice versa. Expression analysis by RT-PCR showed that all genes are expressed in all tissues of purslane tested, but higher levels of mRNA accumulation were detected in reproductive organs and cells that proliferate rapidly or store lipids. Wounding affected the levels of mRNA accumulation of both, FAD2 and FAD6 genes in purslane leaves, while chilling stress affected only FAD2 transcript level. The expression patterns observed reflect the discrete roles of these genes in membrane synthesis for cell division, thylakoid development, and lipid storage or in the biosynthetic pathway for the production of signaling molecules that influence plant development or defense.