In Vitro Propagation of Three Date Palm (Phoenix dactylifera L.) Varieties Using Immature Female Inflorescences.

Immature female inflorescences are promising materials for use as explants for the tissue culture of date palm. Four types of MS media were used in this study during the four micropropagation stages-starting media (SM), maturation media (MM), multiplication media (PM) and rooting media (RM)-to micropropagate three elite date palm varieties, Amri, Magdoul and Barhy using the immature female inflorescences as explant. The highest percentage of callus induction in all the varieties studied was obtained on the SM1 (9 µM 2,4-D + 5.7 µM IAA + 10 µM NAA). Culturing on the MM1 (4.5 µM 2,4-D + 9.8 µM 2-iP + 1.5 AC) allowed us to obtain the best value in terms of callus weight. After culturing on the PM1 (4.4 µM BA + 9.8 µM 2-iP) produced the highest numbers of somatic embryos and shoots. The explants on RM2 (0.5 µM NAA + 1.25 µM IBA + 3 g AC) showed the highest root numbers and root lengths, while the highest shoot length was achieved on RM3 (0.5 µM NAA + 0.5 µM IBA + 3 g AC). The Amri variety presented the best response among the three varieties in all parameters, followed by the Magdoul and Barhy varieties. In all the stages of micropropagation, the analysis of variance revealed highly significant variations among varieties and culture media, and a significant difference in the number of roots during the rooting stage. The results also showed non-significant differences in the interaction between varieties and culture media, except for shoot length in the rooting stage. The results also reveal the broad sense heritability ranging from low to high for the measured parameters. It can be concluded that the immature female inflorescences can be used as a productive explant source for successful date palm micropropagation using the SM1, MM1, PM1 and RM2 culture media. It can also be concluded that the success of date palm micropropagation not only depends on the concentrations of growth regulators, but also on their types.

Analysis of Global Gene Expression in Maize (Zea mays) Vegetative and Reproductive Tissues That Differ in Accumulation of Starch and Sucrose.

Carbon allocation between vegetative and reproductive tissues impacts cereal grain production. Despite great agricultural importance, sink-source relationships have not been fully characterized at the early reproductive stages in maize. Here, we quantify the accumulation of non-structural carbohydrates and patterns of gene expression in the top internode of the stem and the female inflorescence of maize at the onset of grain filling (reproductive stage R1). Top internode stem and female inflorescence tissues of the Puma maize inbred line were collected at reproductive stage R1 (without pollination) and non-structural carbohydrates were quantified by spectrophotometry. The female inflorescence accumulated starch at higher levels than the top internode of the stem. Global mRNA transcript levels were then evaluated in both tissues by RNA sequencing. Gene expression analysis identified 491 genes differentially expressed between the female inflorescence and the top stem internode. Gene ontology classification of differentially expressed genes showed enrichment for sucrose synthesis, the light-dependent reactions of photosynthesis, and transmembrane transporters. Our results suggest that sugar transporters play a key role in sugar partitioning in the maize stem and reveal previously uncharacterized differences between the female inflorescence and the top internode of the stem at early reproductive stages.

Direct Organogenesis from Immature Female Inflorescence of Date Palm by Gradual Reduction of 2,4-D Concentration.

Inflorescences represent an alternative explant source for superior date palm trees, especially those that do not produce offshoots. They provide large numbers of explants free of fungal and bacterial contamination for successful tissue culture initiation. Furthermore, they are characterized by the capacity of plant regeneration within a short time as compared to other explant types. This chapter focuses on the procedures employed for plant regeneration by direct organogenesis using immature female inflorescence explants, including initiation of adventitious buds, differentiation, multiplication, shoot elongation, rooting, and acclimatization. Adding 5 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D) into the initiation medium and gradually reducing it to 1 and then to 0.5 mg/L in the subsequent 2 subcultures, respectively, are determining factors in direct adventitious bud formation from the inflorescence. Bud differentiation is obtained on MS medium containing 0.25 mg/L kinetin (Kin), 0.25 mg/L benzyladenine (BA), 0.25 mg/L abscisic acid (ABA), 0.1 mg/L naphthaleneacetic acid (NAA), and 0.2 g/L activated charcoal (AC). Regenerated shoots exhibit sufficient root formation on MS medium supplemented with 2 mg/L indole butyric acid (IBA) and 1 mg/L NAA and subsequent survival in the greenhouse.

Histological Evidence of Indirect Somatic Embryogenesis from Immature Female Date Palm Inflorescences.

Rapid production of somatic embryogenesis and date palm regeneration is achieved by culturing immature female inflorescence explants. Inflorescence explants are soft, creamy in color, average 6-7 cm in length, and cultured on Murashige and Skoog (MS) medium containing 1 mg/L thidiazuron (TDZ). Callus induction occurs after 4-5 weeks of culture on the callus induction medium. Subsequently, callus develops embryogenic calli on MS medium supplemented with 0.1 mg/L naphthalene acetic acid (NAA). Histological samples were collected successively at the culturing time and during morphogenetic changes throughout the developmental stages of somatic embryos. Initiation of callus and different successive developmental stages for somatic embryos including two-celled, four-celled, globular, bipolar, and fully developed cotyledonary somatic embryos were observed. Mature somatic embryos develop within 10-12 weeks after culture establishment.

Direct Organogenesis and Indirect Somatic Embryogenesis by In Vitro Reversion of Mature Female Floral Buds to a Vegetative State.

This protocol describes in vitro plant regeneration from mature female inflorescence explants of date palm (Phoenix dactylifera L.) by reversion of floral state (reproductive phase) to the vegetative state. The mature female inflorescence (fully developed) is cultured on MS induction medium containing 10 mg/L 2,4-dichlorophenoxyacetic acid (2,4-D), 3 mg/L 2-isopentenyladenine (2iP), and 2 mg/L paclobutrazol (PBZ) or 2 mg/L abscisic acid (ABA). The basal part of the petals has meristematic cells, which can be induced to initiate callus or direct shoot formation depending on the plant growth regulator amendments. Callus forms on the induction medium supplemented with PBZ after 12 weeks, whereas it differentiates into somatic embryos on a medium containing 0.1 mg/L naphthaleneacetic acid (NAA). Direct shoots are regenerated on the induction medium amended with ABA after 24 weeks. Procedures for plant regeneration from mature female inflorescence explants are described, and histological changes which occur during the reversion process are presented.