Post-germination Seedling Research Articles

Differential regulation of the expression in transgenic tobacco of the gene for beta-glucuronidase under the control of the 5'-upstream regions of two catalase genes from castor bean.

The regulatory functions of the 5'-flanking regions of two genes for catalase (cat1 and cat2) from castor bean were analyzed in transgenic tobacco plants that carried fusion constructs that included the gene for beta-glucuronidase (GUS) for Escherichia coli. Dry mature seeds from transgenic plants carrying the CAT1-GUS or CAT2-GUS constructs, in which the GUS gene was fused to the 5'-flanking region of cat1 or cat2, respectively, contained significant GUS activity, indicating that the promoters of cat1 and cat2 were active during seed development. GUS activity increased in response to germination in the seeds of transgenic tobacco that carried CAT1-GUS, as well as in those that carried CAT2-GUS. During the post-germinative stage the GUS activity directed by CAT2-GUS increased still further, whereas that directed by CAT1-GUS decreased. The changes in GUS activity in the transgenic tobacco plants that carried CAT1-GUS and CAT2-GUS were similar to the changes in the levels of transcripts of cat1 and cat2, respectively, in castor bean. The results suggest that the expression of cat1 and cat2 in the germinating seeds and post-germinative seedlings is regulated mainly at the level of transcription. However, the distribution of GUS activity among the organs of the transgenic tobacco seedlings and plantlets, which was examined by histochemical staining and by enzymatic assays of tissue extracts, was not identical to that of transcripts of cat1 and cat2 in castor bean. Histochemical analysis also revealed the interesting spatial regulation of the expression of the promoter of cat2 in the transgenic tobacco seedlings.

Embryogenesis in Higher Plants: An Overview.

The sporophytic generation of higher plants is initiated with the double fertilization event that results in the formation of a single-celled zygote and a progenitor cell of the endosperm. Embryogenesis describes the subsequent period of development, during which the zygote undergoes a complex series of morphological and cellular changes resulting in the formation of a developmentally arrested mature embryo comprised of an embryonic axis with shoot and root poles and cotyledon(s), which often contains high levels of storage macromolecules such as proteins and lipids. Thus, the events that occur during embryonic development establish the organization of the plant body and prepare the embryo for both dormancy and germination. Higher plant embryogenesis has been studied intensively during the past century. Studies using light and electron microscopy have provided detailed descriptions of the morphological and anatomical changes that characterize embryonic development (Maheshwari, 1950; Wardlaw, 1955; Natesh and Rau, 1984; Raghavan, 1986). Cellular differentiation has been studied largely in relationship to the biosynthesis and accumulation of storage proteins, lipids, and starch, macromolecular reserves that ultimately serve as nutrients for postgerminative seedlings (Jenner, 1982; Slack and Browse, 1984; Casey et al., 1986; Shotwell and Larkins, 1989). The focus of attention on these reserves reflects their agricultura1 importance and the fact that the abundance of these macromolecules facilitates studies of their accumulation. By contrast, much less is known about the processes that underlie embryo morphogenesis, although increasing attention is being devoted to this area. In this review, we will provide an overview of the processes that occur during embryonic development, focusing primarily on dicotyledonous plants. Additionally, we will discuss some of the critical processes involved in embryo formation, about which relatively little is known. This review is meant to provide a conceptual summary of embryonic development rather than to cover all aspects of embryogenesis in detail or to describe events that occur in all species of plants. Readers are referred to other reviews on embryogenesis for additional coverage of the topic (Natesh and Rau, 1984; Dure, 1985; Raghavan, 1986; Crouch, 1987; Goldberg et al., 1989; Meinke, 1991a; De Jong et al., 1993; Lindsey and Topping, 1993).

Changes in Protein Synthesis upon Cytokinin-Mediated Adventitious Bud Induction and during Seedling Development in Norway Spruce, Picea abies

A pulse-treatment of embryos of Picea abies (L.) Karst with cytokinin efficiently and reproducibly induces the coordinate de novo formation of bud primordia from subepidermal cells. The cytokinin treatment also affects the germinative development of the embryo; chloroplast maturation is delayed, and cell elongation is completely suppressed. We have analyzed the protein patterns in developing spruce embryos with the aim of identifying proteins which are differentially synthesized during early bud-differentiation and germination. In addition to a set of major seed storage proteins and a large set of constitutively synthesized proteins, we distinguish two sets of proteins that showed different patterns of synthesis in relation to germination. One was synthesized at high rates during germination, and the second set during post-germinative seedling development. Twenty-two proteins were differentially synthesized in the bud-induced versus the germinating embryos. Interestingly, all 22 belonged to either the germination phase-abundant or the seedling protein sets, whereas the constitutively synthesized proteins were unaffected by the treatment. Proteins synthesized exclusively in bud-induced embryos were not found. In total, the bud-induction treatment caused a maintenance of a protein synthesis pattern typical for the germination phase in the nontreated embryos, and the de novo formation of buds was not preceded by a major change in gene expression in the tissue.

Seed Reserves and Seedling Development in Winter Wheat

AbstractSeed reserves are essential for germination of cereals including wheat, but the contributions of the endosperm and its associated aleurone layer to postgermination seedling development remain to be elucidated. Winter wheat (Triticum aestivum L. em Thell. ‘Stephens’) was grown for 36 d in a controlled environment from kernels of three sizes, and from kernels where part of the endosperm had been excised prior to sowing to study the contributions of seed reserves to seedling development. Excision of endosperm delayed the first two phyllochrons, prevented outgrowth of the coleoptilar tiller, and slightly delayed the appearance of the next two tillers. Plant dry weight, leaf numbers and dimensions, number of nodal roots, and total number of tillers were all affected by endosperm excision. The combined area of the first two leaves was linearly correlated with aleurone area for all seed treatments. Areas of later‐formed leaves and final dry weight of seedlings were directly related to the areas of the first two leaves. Thus, the aleurone layer, in addition to seed reserves, is important for the enlargement of the first two leaves, with subsequent seedling development controlled by the size of the first two leaves under the conditions used in this study.

ELECTROCARDIOGRAM OF THE MONTH

Copper (Cu) contamination dramatically affects crop growth and thus threatens crop production; while applications of melatonin (MT) serve as an effective way to tolerate Cu stress for plant development, the underlying mechanism remains largely unknown in rice. Here, we found that Cu toxicity remarkably decreased germination rates and seedling growth compared to the untreated control (CK), while seed priming with a solution of 100 μM MT significantly alleviated the adverse effects on Cu-stressed seeds. In addition, the MT treatment decreased the accumulation of Cu in seedlings at 7 days after imbibition (DAI), possibly through enhanced Cu sequestration, and improved reserve mobilization through the promoted activity of α-amylase and protease in seeds under Cu stress. Interestingly, gibberellin (GA) synthesis was restored to or even exceeded the CK levels in the MT presoaking treatment, while the abscisic acid (ABA) content decreased compared to those of the Cu-stressed seeds, suggesting crosstalk between MT and other phytohormones, e.g., GA and ABA. More importantly, MT pretreatment also significantly promoted the growth of postgermination seedlings. This was largely ascribed to the MT-ameliorated antioxidant system, which consequently reduced the accumulation of Cu stress-induced oxidative products, e.g., hydrogen peroxide (H2O2), malondialdehyde (MDA), and superoxide (O2·_). Collectively, these results demonstrate that seed priming with MT could greatly mitigate the adverse effects of Cu stress on seed germination and subsequent postgermination growth through crosstalk among various defensive response pathways. This study provides vital guidance for applications of MT in agronomic production.