Víctor M. Jiménez

Involvement of Plant Hormones and Plant Growth Regulators on in vitro Somatic Embryogenesis

In spite of the importance attained by somatic embryogenesis and of the many studies that have been conducted on this developmental process, there are still many aspects that are not fully understood. Among those features, the involvement of plant hormones and plant growth regulators on deTermining the conversion of somatic onto embryogenic tissues, and on allowing progression and maturation of somatic embryos, are far away from being completely comprehended. Part of these difficulties relies on the frequent appearance of contradictory results when studying the effect of a particular stimulus over a specific stage in somatic embryogenesis. Recent progress achieved on understanding the interaction between exogenously added plant growth regulators over the concentration of endogenous hormones, together with the involvement of sensitivity of the tissues to particular hormone groups, might help clarifying the occurrence of divergent patterns in somatic embryogenesis, and in tissue culture in general. The aspects described above, emphasizing on the effect of the concentration of plant hormones and of the addition of plant growth regulators during the different phases of somatic embryogenesis, will be reviewed in this paper. Citations will be limited to review articles as much as possible and to individual articles only in those cases in which very specific or recent information is presented.

Hormonal status of maize initial explants and of the embryogenic and non-embryogenic callus cultures derived from them as related to morphogenesis in vitro

Endogenous hormone levels (indole-3-acetic acid [IAA], abscisic acid [ABA], gibberellins (1, 3) and (20) [GAs], zeatin/zeatin riboside [Z/ZR] and N(6)[Delta(2)-isopentenyl] adenine/N(6)[Delta(2)-isopentenyl] adenosine; [iP/iPA]) were analysed in immature maize zygotic embryos of two maize (Zea mays L.) genotypes, known for their distinct ability to generate embryogenic (E) callus. No differences were found among genotypes in the hormone contents of the embryos. These embryos were also used as initial explants to establish callus cultures. E and non-embryogenic (NE) calli were obtained from the competent genotype (A188), while only NE callus was produced by the incompetent one (B73). The morphogenetic competence of each callus type was evaluated by transferring some segments to regeneration conditions. When analysing the endogenous hormone levels in the various callus types generated in each genotype, it was found that only differences in the IAA levels accounted for variations in the morphogenic properties of the calli. Higher levels of endogenous IAA were typical of embryogenic callus cultures. It was also observed, that a loss in the embryogenic competence of the calli, due to a prolonged time of culture, occurred concomitantly with a reduction in the IAA levels, practically to the levels found in the non-embryogenic calli.

Participation of Plant Hormones in Determination and Progression of Somatic Embryogenesis

In vitro culture protocols have been developed for many species, mainly using empirical approaches, to induce somatic embryogenesis from various explant types. However, the underlying biochemical mechanisms governing induction, expression and maturation during somatic embryogenesis are still poorly understood. Among the signals that participate directly in the regulation of the different phases of this process, plant hormones emerged as candidates of choice. In this chapter, studies concerning the role of exogenously added plant growth regulators in somatic embryogenesis are reviewed. In addition, we discuss possible relationships between hormonal contents in starting explants and in cultures derived from them with their embryogenic competence. Moreover, information on evolution of endogenous plant hormone levels during induction and progression of somatic embryogenesis is presented. Finally, an overview of interactions between exogenous plant growth regulators and endogenous hormones in embryogenic systems is also included.

Deposition Form and Bioaccessibility of Keto-carotenoids from Mamey Sapote (Pouteria sapota), Red Bell Pepper (Capsicum annuum), and Sockeye Salmon (Oncorhynchus nerka) Filet

The ultrastructure and carotenoid-bearing structures of mamey sapote (Pouteria sapota) chromoplasts were elucidated using light and transmission electron microscopy and compared to carotenoid deposition forms in red bell pepper (Capsicum annuum) and sockeye salmon (Oncorhynchus nerka). Globular-tubular chromoplasts of sapote contained numerous lipid globules and tubules embodying unique provitamin A keto-carotenoids in a lipid-dissolved and presumably liquid-crystalline form, respectively. Bioaccessibility of sapotexanthin and cryptocapsin was compared to that of structurally related keto-carotenoids from red bell pepper and salmon. Capsanthin from bell pepper was the most bioaccessible pigment, followed by sapotexanthin and cryptocapsin esters from mamey sapote. In contrast, astaxanthin from salmon was the least bioaccessible keto-carotenoid. Thermal treatment and fat addition consistently enhanced bioaccessibility, except for astaxanthin from naturally lipid-rich salmon, which remained unaffected. Although the provitamin A keto-carotenoids from sapote were highly bioaccessible, their qualitative and quantitative in vivo bioavailability and their conversion to vitamin A remains to be confirmed.

Biology of the Papaya Plant

Papaya is a semi-woody, usually single-stemmed plant, widely distributed in tropical and subtropical regions. The plant is singular in several aspects: short-lived perennial growth habit, large palmate leaves, rapid growth, hollow stems, petioles and fruits, and high phenotypic plasticity. Papaya plants may have three possible sexual forms: female, male, and hermaphroditic. Additionally, alterations in sexual forms and flower structure have been related to environmental constraints, which consequently modify fruit production and morphology, respectively. The climacteric fruits that are produced continuously during the adult plant life are widely commercialized and differ between female and hermaphroditic plants. The latex that the plants produce profusely contains enzymes with industrial uses and many other important compounds. These morphological and ecophysiological attributes rely on highly efficient mechanisms of resource capture, transport, and utilization. High photosynthetic rates, carbon gain, reproductive output, and growth and plasticity occur at the expense of high water and nutrient demand. Association with mycorrhiza is important for plant nutrition. Physiological acclimation capacity is evident at the shoot, root, and reproductive levels. These attributes have implications in the design of sustainable cropping systems in tropical and subtropical environments and make the papaya plant an ideal model for ecophysiological studies of growth, acclimation capacity, sex expression and longevity, and the integration with population biology and evolutionary change.

Mode of Action of Plant Hormones and Plant Growth Regulators During Induction of Somatic Embryogenesis: Molecular Aspects

UCR::Investigacion::Unidades de Investigacion::Ciencias Agroalimentarias::Centro para Investigaciones en Granos y Semillas (CIGRAS)

Effect of hydrogen cyanamide on the endogenous hormonal content of pea seedlings (Pisum sativum L.)

Hydrogen cyanamide (HC) has been used to break bud and seed dormancy and to improve rooting in several species, responses usually associated with the action of plant hormones. However, very few studies have measured endogenous hormones after HC treatment. Therefore, pea (Pisum sativum L.) seedlings with two fully developed internodes above the first leaf were sprayed with 0, 0.1 and 0.3% (v/v) HC. Endogenous concentration of indole-3-acetic acid (IAA), abscisic acid (ABA), zeatin/zeatin riboside and N 6 (∆ 2 -isopentenyl) adenine/ N 6 (∆ 2 -isopentenyl) adenosine were measured by radioimmunoassay 31 and 80 h after HC treatment. A significant increase in ABA and cytokinin (CK) levels was observed 31 h after treating the plants with 0.3% HC. Small necrotic spots were also noticed in this treatment, thus revealing a toxic effect of this treatment. Additionally, at 80 h, a significant increase in IAA was found for both HC concentrations applied. The action of HC upon ABA, CKs and IAA endogenous levels is discussed.

Carotenoids and carotenoid esters of orange- and yellow-fleshed mamey sapote (Pouteria sapota (Jacq.) H.E. Moore & Stearn) fruit and their post-prandial absorption in humans

Although different genotypes of mamey sapote with distinct pulp colors are consumed in countries from Central to South America, in-depth knowledge on genotype-related differences of their carotenoid profile is lacking. Since the fruit was found to contain the potentially vitamin A-active keto-carotenoids sapotexanthin and cryptocapsin, we sought to qualitatively and quantitatively describe the carotenoid profile of different genotypes by HPLC-DAD-MSn. Sapotexanthin and cryptocapsin were present in all genotypes. Keto-carotenoids such as cryptocapsin, capsoneoxanthin, and their esters were most abundant in orange-fleshed fruit, whereas several carotenoid epoxides prevailed in yellow-fleshed fruit. Differing carotenoid profiles were associated with different color hues of the fruit pulp, while the widely variable carotenoid content (3.7-8.0mg/100gFW) was mainly reflected by differences in color intensity (chroma C∗). Furthermore, the post-prandial absorption of sapotexanthin to human plasma was proven for the first time. Besides sapotexanthin, cryptocapsin was found to be resorbed.

Carotenoids, carotenoid esters, and anthocyanins of yellow-, orange-, and red-peeled cashew apples (Anacardium occidentale L.)

Pigment profiles of yellow-, orange-, and red-peeled cashew (Anacardium occidentale L.) apples were investigated. Among 15 identified carotenoids and carotenoid esters, β-carotene, and β-cryptoxanthin palmitate were the most abundant in peels and pulp of all samples. Total carotenoid concentrations in the pulp of yellow- and red-peeled cashew apples were low (0.69-0.73 mg/100g FW) compared to that of orange-peeled samples (2.2mg/100g FW). The color difference between the equally carotenoid-rich yellow and red colored samples indicated the presence of a further non-carotenoid pigment type in red peels. Among four detected anthocyanins, the major anthocyanin was unambiguously identified as 7-O-methylcyanidin 3-O-β-D-galactopyranoside by NMR spectroscopy. Red and yellow peel color was chiefly determined by the presence and absence of anthocyanins, respectively, while the orange appearance of the peel was mainly caused by increased carotenoid concentrations. Thus, orange-peeled fruits represent a rich source of provitamin A (ca. 124 μg retinol-activity-equivalents/100g pulp, FW).

In vitro propagation of bamboo species through axillary shoot proliferation: a review

Bamboos, very relevant plants in many countries around the world, are propagated at large scale with extreme difficulties. Use of seeds is challenging because of plant’s sporadic flowering and long flowering cycles, together with seed recalcitrance and consumption by wild animals. Vegetative propagation of bamboo is mainly conducted by cuttings and by air layering. However, these methods are only useful at small-scale because they damage the mother plants, propagation material is bulky and difficult to be transported and is only available during few months of the year. Therefore, in vitro propagation offers the opportunity to obtain large progenies from elite genotypes. In most cases, when developing protocols for in vitro propagation of plants, specific conditions for individual species, genotypes and even development stages of the donor plants must be identified by trial-and-error experiments. Because of the size of and the large diversity observed in this plant family, it usually takes several months to define most adequate culture medium, combination of plant growth regulators and of other compounds for fostering the desired development in the explants. Therefore, in this detailed review, that also puts together results from hard-to-find literature, we list all identified cases, in which development of axillary shoots was used to propagate bamboo plants, by presenting successful ways for disinfection, in vitro bud sprouting, multiplication, rooting and acclimatization.