Plant-Derived Smoke and Karrikin 1 in Seed Priming and Seed Biotechnology

Plant-derived smoke and smoke water (SW) can stimulate seed germination in numerous plants from fire-prone and fire-free areas, including cultivated plants and agricultural weeds. Smoke contains thousands of compounds; only several stimulants and inhibitors have been isolated from smoke. Among the six karrikins present in smoke, karrikin 1 (KAR1) seems to be key for the stimulating effect of smoke. The discovery and activity of highly diluted SW and KAR1 at extremely low concentrations (even at ca. 10−9 M) inducing seed germination of a wide array of horticultural and agricultural plants have created tremendous opportunities for the use of these factors in pre-sowing seed treatment through smoke- or KAR1-priming. This review presents examples of effects exerted by the two types of priming on seed germination and seedling emergence, growth, and development, as well as on the content of some compounds and enzyme activity. Seed biotechnology may involve both SW and KAR1. Some examples demonstrate that SW and/or KAR1 increased the efficiency of somatic embryogenesis, somatic embryo germination and conversion to plantlets. It is also possible to stimulate in vitro seed germination by SW, which allows to use in orchid propagation

Znaczenie etylenu w ustępowaniu spoczynku i kiełkowaniu nasion

The role of ethylene in the release of dormancy and the germination of non-dormant seeds is considered. In many species, exogenous ethylene, or ethephon — an ethylene-releasing compound — stimulates seed germination that could be inhibited because of embryo or coat dormancy, adverse environmental conditions or presence of inhibitors (e.g. abscisic acid, jasmonate). The inhibition of germination of those seeds is usually related to the lack, or low level, of ethylene production. This can be associated with the insufficient content of 1 -aminocyclopropane-1 -carboxylicacid (ACC) and/or the ACC oxidase activity. The inhibition of germination of such seeds can be eliminated by exogenous ethylene or ethephon. Thus, the level of ethylene seems to be a limiting factor of seed germination. It has been shown that exogenous ethylene may act separately or together with other plant growth regulators, thus an additive or synergistic relationship is possible. The requirement for ethylene may also be essential for the stimulatory action of other plant growth regulators

The gibberellins biosynthesis pathway in higher plants.

<p>The cellular localizations of metabolites are in plastids, endoplasmic reticulum and cytoplasm. Plant bioactive gibberellins are GA₄, GA₇, GA₁, GA₃, GA₅ and GA₆. Enzymes catalyzing subsequent reactions indicated in bold, abbreviations: <i>ent</i>-CDP, <i>ent</i>-copalyl diphosphate; (CPS), <i>ent</i>-copalyl diphosphate synthase; (KS), <i>ent</i>-kaurene synthase; (KO), <i>ent</i>-kaurene oxidase; (KAO), <i>ent</i>-kaurenoic acid oxidase; (GA13ox), Gibberellin 13-oxidase; (GA20ox), Gibberellin 20-oxidase; (GA3ox), Gibberellin 3-oxidase. Adapted from [<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182055#pone.0182055.ref007" target="_blank">7</a>, <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182055#pone.0182055.ref008" target="_blank">8</a>].</p

Relative gene expression of genes coding <i>GA20oxidases</i> in late steps of gibberellin biosynthesis.

<p><i>Medicago truncatula GA20ox (Gibberellin 20-oxidase)</i> gene expression during induction phase (21 days) of <i>Medicago truncatula</i> non-embryogenic genotype (M9) and variant with embryogenic phenotype (M9-10a). Expression in both lines measured relative to lowest observed expression set to 1. Two-way ANOVA with post-hoc Tukey-Kramer’s test with 0.05 confidence interval, significance between groups indicated with **** for P≤ 0.0001. Bars indicate +/- SD (n = 3).</p

Gene expression and metabolite profiling of gibberellin biosynthesis during induction of somatic embryogenesis in <i>Medicago truncatula</i> Gaertn

<div><p>Gibberellins (GAs) are involved in the regulation of numerous developmental processes in plants including zygotic embryogenesis, but their biosynthesis and role during somatic embryogenesis (SE) is mostly unknown. In this study we show that during three week- long induction phase, when cells of leaf explants from non-embryogenic genotype (M9) and embryogenic variant (M9-10a) were forming the callus, all the bioactive gibberellins from non-13-hydroxylation (GA₄, GA₇) and 13-hydroxylation (GA₁, GA₅, GA₃, GA₆) pathways were present, but the contents of only a few of them differed between the tested lines. The GA₅₃ and GA₁₉ substrates synthesized by the 13-hydroxylation pathway accumulated specifically in the M9-10a line after the first week of induction; subsequently, among the bioactive gibberellins detected, only the content of GA₃ increased and appeared to be connected with acquisition of embryogenic competence. We fully annotated 20 <i>Medicago truncatula</i> orthologous genes coding the enzymes which catalyze all the known reactions of gibberellin biosynthesis. Our results indicate that, within all the genes tested, expression of only three: <i>MtCPS</i>, <i>MtGA3ox1</i> and <i>MtGA3ox2</i>, was specific to embryogenic explants and reflected the changes observed in GA₅₃, GA₁₉ and GA₃ contents. Moreover, by analyzing expression of <i>MtBBM</i>, SE marker gene, we confirmed the inhibitory effect of manipulation in GA_s metabolism, applying exogenous GA₃, which not only impaired the production of somatic embryos, but also significantly decreased expression of this gene.</p></div

Relative gene expression of genes coding enzymes in intermediate steps of gibberellin biosynthesis.

<p><i>Medicago truncatula CYP714</i> gene (<i>Cytochrome 450 family</i>, known also as <i>Gibberellin 13-oxidases</i>, <i>GA13ox)</i> expression profiles during induction phase (21 days) of <i>Medicago truncatula</i> non-embryogenic genotype (M9) and variant with embryogenic phenotype (M9-10a). Expression in both lines measured relative to lowest observed expression set to 1. Two-way ANOVA with post-hoc Tukey-Kramer’s test with 0.05 confidence interval, significance between groups indicated with ** for P≤ 0.01,*** for P≤ 0.001 and **** for P≤ 0.0001. Bars indicate +/- SD (n = 3).</p