The special conditions during in vitro culture result in the formation of plantlets of abnormal morphology, anatomy and physiology. After ex vitro transfer, these plantlets might easily be impaired by sudden changes in environmental conditions, and so need a period of acclimatization to correct the abnormalities. This review is focused upon contemporary information on the changes in leaf structure, water relations and photosynthesis during acclimatization of plantlets to ex vitro conditions. It also describes some ways of improving plant survival and for the speeding up of acclimatization.

Acclimatization of Micropropagated Plants to Ex Vitro Conditions

Agave plants utilize crassulacean acid metabolism (CAM) for CO2 fixation. Fructans are the principal photosynthetic products generated by agave plants. These carbohydrates are fructose-bound polymers frequently with a single glucose moiety. Agave tequilana Weber var. azul is an economically important CAM species not only because it is the sole plant allowed for tequila production but because it is a potential source of prebiotics. Because of the large amounts of carbohydrates in A. tequilana, in this study the molecular structures of its fructans were determined by fructan derivatization for linkage analysis coupled with gas chromatography−mass spectrometry (GC−MS), nuclear magnetic resonance (NMR), and matrix-assisted laser desorption time-of-flight mass spectrometry (MALDI-TOF-MS). Fructans were extracted from 8-year-old A. tequilana plants. The linkage types present in fructans from A. tequilana were determined by permethylation followed by reductive cleavage, acetylation, and finally GC-MS analysis. A...

http://agave.co.kr/info/thesis/FRUCTANS.pdf

Molecular structures of fructans from Agave tequilana Weber var. azul.

In vitro plant cell and tissue culture techniques are the basis of many micropropagation and breeding programs for scientific research. Plant tissue culture (PTC) involves organogenesis and embryogenesis, and the outcome depends on the different conditions to which the tissue is exposed. PTC is a stressful environment—high relative humidity, low ventilation rate, high concentrations of plant growth regulators, and low light availability—for plants that need to rapidly change their molecular regulation in order to respond fast and efficiently during cell division and growth. For instance, somatic embryogenesis (SE), which plays an important role in plant multiplication, requires complex cellular, biochemical and molecular processes for embryo formation and development. New data has come out about a connection between plant morphogenesis and epigenetics. Epigenetics is a very sensitive regulatory mechanism, which in most of cases is affected by the environment. Although it is known that, under plant morphogenesis, the genome has little or no change, DNA methylation and histone modifications are very susceptible to those in vitro environmental conditions. In the present review, we highlight the most used in vitro systems such as organogenesis and SE in plants and discuss how epigenetics plays a pivotal role in the phenotype outcome. Furthermore, we discuss the big role that the small RNAs have during cell division and propagation and propose different challenges and opportunities to study epigenetics in plant cell tissue and organ cultures.

In vitro culture: an epigenetic challenge for plants

Plantlets grown in vitro might be easily impaired by sudden changes in environmental conditions after ex vitro transfer. They usually need several weeks under shade and gradually decreasing air humidity to acclimate to the new conditions and to correct all abnormalities in their anatomy and physiology induced by special conditions of in vitro culture. For plant survival, the most important changes include development of cuticle, epicuticular waxes, and effective stomatal regulation of transpiration leading to stabilization of water status. For plant growth, changes in photosynthetic parameters (chlorophyll content, chloroplast ultrastructure, efficiency of photosystem 2, net photosynthetic rate) ensuring fully autotrophic growth with the rate corresponding to naturally grown plants are the most important. Acclimation can be speeded up by hardening of plantlets in vitro or after transplantation by decreasing the transpiration rate by antitranspirants including abscisic acid, or by increasing photosynthetic rate by elevated CO2 concentration.

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Acclimation of Plantlets to Ex Vitro Conditions: Effects of Air Humidity, Irradiance, CO2 Concentration and Abscisic Acid (a Review)

Plantlets of Nicotiana tabacum L. cv. Petit Havana SR1 were grown in vitro on Murashige and Skoog medium containing 2% saccharose, and then transplanted ex vitro into pots with coarse sand and Hewitt nutrient solution. In the first day after transplantation, the anti-transpirant abscisic acid (ABA; 0.01, 0.05 or 0.10 mM) was added to the substrate. Leaf stomatal conductance (g s ), which was high in plants during the first days after transplantation similarly as in plantlets grown in vitro, was considerably decreased by ABA-treatment. However, in the further days g s decreased more quickly in control than in ABA-treated plants, and after 2 or 3 weeks g s was significantly lower than that of plantlets grown in vitro but similar in control and ABA-treated plants. Two weeks after transplantation, net photosynthetic rate, chlorophyll a +b content, maximal photochemical efficiency, and actual quantum yield of photosystem II in plant leaves were higher in comparison with those in plantlets grown in vitro. ABA-treatment had slight positive or insignificant effect on photosynthetic parameters and enhanced plant growth. Thus ABA application can alleviate 'transplant shock' and speed up acclimation of plantlets to ex vitro conditions.

/pdf/acclimation-of-tobacco-plantlets-to-ex-vitro-conditions-as-5474veouj9.pdf

Acclimation of tobacco plantlets to ex vitro conditions as affected by application of abscisic acid

In vitro plant regeneration of Agave fourcroydes Lem. (Agavaceae) is described. Results suggest that the NO3
-:NH4
+ balance in the culture medium is a key factor controlling callus growth and organogenesis in rhizome cultures. Stem callus showed limited organogenic capacity, but high cytokinin concentrations induced adventitious shoot formation on stem explants. When these shoots were excised and subcultured, new callus formed at their base from which new shoots arose. The shoots from stem explants and rhizome callus formed extensive root systems in vitro and were transferred to pot culture with a 90% survival rate.

In vitro propagation of Agave fourcroydes Lem. (Henequen)

Experiments were designed to assess the capacity of an in vitro cultured CAM plant to control water loss and to examine the response of their stomata to various factors. Detached leaves of micropropagated Agave tequilana plants lost water at similar rates as did field-grown plantlets when dehydrated in air. This was consistent with the fact that stomata from micropropagated plants show similar morphology than field-grown plantlets. In addition, stomata from micropropagated plants responded to various factors in a manner similar to those from field-grown plantlets. It appears that in vitro culture does not affect the capacity of leaves to control water loss nor does it alters the nocturnal stomatal opening of this CAM plant.

Stomatal physiology of a micropropagated CAM plant; Agave tequilana (Weber)

Resumen en: The pattern of diseases produced by phytopathogens in some areas of cultivation are changing drastically due, among other causes, to new market trends th...

José Luis Herrera Herrera

Papers

In vitro propagation of Agave fourcroydes Lem. (Henequen)

Stomatal physiology of a micropropagated CAM plant; Agave tequilana (Weber)

Microbial Diseases Affecting Henequen (Agave fourcroydes Lem.) in Yucatan, Mexico