N.A.C. Brown

Smoke as a germination cue: a review

Slow combustion or burning of dry or green plant material from many sources produces volatile compounds that are water soluble and that stimulate the germination of many seeds with different dormancy strategies. The active principals are apparently produced around 160ndash;200 deg;C and are volatilized at higher temperatures. Once dissolved in water the active compounds also stimulate rooting, seedling growth and flowering. The positive effects of smoke have resulted in it being used as a seed pre-treatment for enhancing conservation of threatened or rare species, the horticultural exploitation of desirable plants and in the reclamation of mine spoils and disturbed land. Presently the identity of the active molecules is unknown but their remarkable effect on seed germination is, already widely utilized.

Plant-derived smoke and smoke extracts stimulate seed germination of the fire-climax grass Themeda triandra

Abstract Plant-derived smoke and aqueous extracts of smoke stimulate germination of dormant seed of the important fire-climax grass Themeda triandra (redgrass). The positive germination response to smoke increased as the state of seed imbibition increased. Furthermore, aqueous smoke extracts significantly increased seed germination at optimum and sub-optimum germination temperatures. Ethrel and ethylene, at a wide range of concentrations, failed to increase T. triandra seed germination, indicating that ethylene is not the active component of plant-derived smoke. Similarly, ash or aqueous ash extracts failed to stimulate germination. In contrast, aqueous smoke extracts prepared from burning fynbos vegetation and grass leaf material stimulated T. triandra seed germination. The bioactive component of plant-derived smoke may originate from a commonly occurring source, possibly being a thermal breakdown product of hemicellulose or cellulose.

Butenolide from plant-derived smoke enhances germination and seedling growth of arable weed species

We tested the applicability of the recently identified major germination cue from smoke (a butenolide 3-methyl-2Hfuro[2,3-c]pyran-2-one) on 18 weed species from non-fire prone environments. For the study species we compared the relative effectiveness of alternating temperatures, KNO3, GA3, smoke water and the butenolide on germination percentage, germination rate and seedling mass. We found that while smoke stimulated germination in a number of species it also had negative impacts on other species. In addition, the butenolide was effective on the widest range of species in terms of enhancing germination percentage, rate and seedling mass. However, none of the treatments, including butenolide were effective on all species. Our data demonstrate that butenolide may have wide applicability as a germination and seedling growth stimulant irrespective of whether the species come from fire-prone habitats.

Patterns in the seed germination response to smoke in plants from the Cape Floristic Region, South Africa

De Lange and Boucher (1990) discovered the germination enhancing effect of plant-derived smoke on seed of fynbos species. This finding has been applied to horti- culturally important fynbos species and to date 301 species have been tested for a response to smoke. Germination in 150 (49.8%) of these was significantly improved by smoke treatment; the remaining 151 species showed no significant response. Families in which species showed a significant response included the horticulturally important Asteraceae (everlastings), Bruniaceae (brunias), Crassulaceae (crassulas), Ericaceae (ericas), Geraniaceae (pelargoniums), Mesembryanthemaceae (mesembs), Proteaceae (pro- teas) and Restionaceae (restios). No species responded in the families of geophytes such as Amaryllidaceae and Hyacinthaceae and in the Iridaceae the majority of species studied (also geophytes) did not respond. Further analysis of the germination results using ordinal logistic regression confirmed that the geophytic growth form was a robust predictor of response to smoke; geophytes exhibited a very low germination response to smoke. In addition, the analysis indicated that serotinous species had seeds that were less likely to respond to smoke than non-serotinous species, presumably as a consequence of their seeds not being in the soil when fire occurs. It also indicated that plants with some capacity to re-sprout were less likely to respond to smoke than obligate seeders.

Some chromatographic characteristics of germination stimulants in plant-derived smoke extracts

Plant-derived smoke extracts stimulate the germination of many different seeds. the present report explains steps to determine some of the chemical characteristics of the compounds concerned. Grand Rapids lettuce seeds were used as a bioassay because smoke-derived extracts overcome their light-sensitivity. The active compounds were partitioned into ethyl acetate, separated by various TLC systems and fractionated by reverse phase HPLC. They are stable surviving a series of chromatographic steps and are very active biologically. In order to ascertain their chemical properties it was necessary to use a range of dilutions after each isolation step. It would appear that similar types of compounds are present in smoke extracts derived from different plant material.

Ultrastructure of dry viable and non-viable Protea compacta embryos

Summary An investigation of Protea compacta seed revealed that a number of ultrastructural differences exist between viable and non-viable embryos. The most conspicuous difference is that the lipid bodies of non-viable embryos coalesced, probably as a result of the rupturing of the «membranes» that enclosed them. On the basis of the size of the globoids present, three different types of protein bodies could be distinguished both in viable and non-viable embryos. Protein bodies containing a large number of small globoids were present mainly in the vicinity of the embryonic root tip while those with a few large globoids were found predominantly in the cotyledonary cells.

Environmental and hormonal regulation of seed dormancy and germination in Cape fynbos Leucospermum R.Br. (Proteaceae) species

The endogenous levels of abscisic acid (ABA), cytokinins (CKs) and gibberellins (GA1/GA3 combined) in Leucospermum glabrum embryos were monitored in axes and cotyledons separately during normal germination. Plant growth substance changes were correlated with known morphological, structural and ultrastructural events in the embryo of Proteaceae. The effect of exogenous application of 6-benzyladenine (BA) and GA4+7 under three known dormancy-enforcing environmental conditions were studied in L. glabrum and L. cordifolium. The endogenous levels of the hormone classes GAs and CKs changed phasically during normal germination under a single alternating temperature regime. GA1/GA3 levels increased in cotyledons within 3 d of hydration while at the same time initial CK levels decreased. Following this transient peak GAs fell to a low level throughout the germinative period. Subsequently the CKs, Z and ZR, and to a lesser extent their dihydro-derivatives, appeared in both the axes and the cotyledons as fluctuating, transient peaks. Early increases in GAs are thought to control the induction of the germination process. The CK pattern suggests that CKs control at least three major processes of germination sensu stricto following induction: 1) early mobilization of protein and lipid reserves in the axis and later in cotyledons, 2) cotyledon expansion which causes the endotesta to split permitting radicle protrusion and 3) later, radicle growth.Our results indicate that dormancy in intact Leucospermum seeds is enforced by embryo anoxia, regulated by the impermeable exotesta. In addition synthesis of or tissue sensitizing to both hormone classes GAs and CKs depends on moderately low temperature as the primary environmental requirement. For GA synthesis a secondary, daily pulse of high temperature is required. Inhibitory hormones, specifically ABA, appear not to play a role.

The effect of temperature and various gases on the germination and endogenous hormone levels of seed of Leucadendron daphnoides

Summary Germination of seed of Leucadendron daphnoides was increased 50% by chilling at 5 °C and 400% by incubation in high oxygen concentrations Incubation at 25°C depressed germination markedly and in nitrogen no germination occurred. Poor germination is apparently due to a lack of germination promoters rather than to, the presence of inhibitors. Both chilling and oxygen incubation brought about a four-fold increase in the level of butanol-soluble cytokinins. The latter apparently play the primary role in promoting germination. The greater effectiveness of high oxygen tensions in improving germination appears to be due to the additional effect oxygen has in stimulating the production of acidic gibberellin-like substances to a level 30 times higher than with chilling. Gibberellins do not appear to have a primary role in promoting germination in this species, but their effect is additive in the presence of an elevated level of butanol-soluble cytokinins. Germination does not appear to depend on phasic changes in hormone levels.

Growth of enset (Ensete ventricosum) suckers under different horticultural practices

The influence of three propagation practices and three corm types of enset on the production of suckers was investigated. After removal of apical buds, mother corms were uprooted and immediately replanted, not uprooted from original positions and uprooted and transferred to new planting holes three months later. Three corm types: whole, halved and quartered corms were used. Suckers were harvested one year after removal of apical buds. After harvest, the suckers were sorted into three size groups: undersized, small and medium to large. The number of suckers produced per plot, from four planting holes, ranged from 40 to 141 depending on the treatments. Halved and quartered mother corms, when transferred to new planting holes three months after removal of apical buds, produced fewer suckers. On the other hand, the halved corms, when uprooted and replanted immediately after removal of apical buds or not uprooted from their original growing sites, gave earlier differentiation of buds and produced more suckers. The halved corms also gave more medium to large suckers than whole and quartered corms when evaluated across all the propagation methods. An increase in the number of vigorous suckers from halved corms is possible because of elimination of the strong apical dominance while leaving reasonable portions of the mother corm to sustain initiation, growth and development of suckers. Therefore, halved corms uprooted and immediately replanted or left in situ can be used to produce more suckers with better growth.