M. T. Smith

The occurrence of trehalose in the leaves of the desiccation-tolerant angiosperm Myrothamnus flabellifolius welw.

Summary Although the disaccharide trehalose predominates in a wide variety of desiccation-tolerant lower organisms, including some lower vascular plants, it is rare in higher vascular plants. Sucrose is suggested to have an analogous role to trehalose in stabilizing the membranes of desiccation-tolerant seeds and pollen of angiosperms. In the present study, both sucrose and trehalose were identified by capillary gas chromatography and thin layer chromatography in methanolic extracts of the leaves of the desiccation-tolerant angiosperm Myrothamnus flabellifolius Welw. Levels of sucrose in hydrated leaves were 29.3 ± 7.5 mgg −1 dry weight and those of trehalose 26.0 ± 7.2 mgg −1 dry weight. In desiccated leaves trehalose levels increased slightly (34.7 ± 4.3 mgg −1 dry weight) in contrast to a marked increase in sucrose levels in desiccated leaves (56.5 ± 6.6 mgg −1 dry weight). It is suggested that the combined sucrose and trehalose contents of the leaves of M. flabellifolius are probably sufficient to account for membrane stabilization in the desiccated state, as explained by the water replacement hypothesis.

The effect of a plant-derived smoke extract on the germination of light-sensitive lettuce seed

A simple and rapid bioassay using seeds of Lactuca sativa L. Grand Rapids has been developed for the detection of germination-enhancing compound(s) in plant-derived smoke extracts. This light-sensitive species germinates within 24 h in the dark at 20 or 25°C and shows responsiveness to smoke-derived extracts over a wide concentration range. For some seed lots where the Pfr level is high and germination in the dark is unacceptably high, a brief (10 min) exposure to far-red light, one hour after the start of imbibition in the dark, is necessary to clearly demonstrate biological activity in the smoke extracts.

Why do stored hydrated recalcitrant seeds die

A characteristic of recalcitrant seeds is that, if they are maintained under storage conditions that prevent water loss, they will ultimately lose viability. A current view is that hydrated recalcitrant seeds are metabolically active and undergo germination-associated changes in storage. Some of these changes, such as extensive vacuolation and increase in cell size, imply a requirement for water additional to that present in the seed on shedding. It is therefore suggested that, in storage, recalcitrant seeds are exposed to an initially mild, but increasingly severe, water stress. Deleterious events associated with a water stress of considerable duration are suggested to lead ultimately to the death of the tissue. The damage that occurs on prolonged storage is unlikely to be associated with an inability to form glasses or prevent membrane lipid phase changes, as absolute water contents are higher than those at which these mechanisms become important. It is considered that the most likely process leading to death of water-stressed (as opposed to dehydrated) tissue is a breakdown of co-ordination of metabolism, leading to uncontrolled free-radical-mediated oxidative damage. It is generally difficult to maintain tissue in a mild water-stressed condition for extended periods. Stored, hydrated, recalcitrant seeds may provide an ideal model system for studying the metabolic effects of prolonged mild water stress.

Identification of auxins in a commercial seaweed concentrate

Summary Compounds active in the mung bean rooting bioassay were isolated from the neutral indole fraction of a commercial seaweed concentrate by high performance liquid chromatography. A gas-chromatographicmass spectrometric analysis of the most active fractions indicated the presence of the following indoles: indole-3-acetic acid; indole-3-carboxylic acid; N,N-dimethyltryptamine; indole-3-aldehyde; and in addition, iso-indole,1,3-dione (N-hydroxyethyl phthalimide). This appears to be the first report of an indole amine and a phthalimide in algae. Attempts are currently being made to determine the efficacy of these compounds individually, and in combination, in the mung bean bioassay.

Lipid Peroxidation in Relation to Declining Vigour in Seeds of Soya (Glycine max L.) and Cabbage (Brassica oleracea L.)

Summary The relationship between the decline of seed polyunsaturated fatty acids and seed vigour was investigated in seeds of cabbage and soya bean. A decline in the levels of polyunsaturated fatty acids of both seed types was clearly associated with a decline in germination percentage. Hydroperoxide levels were highly correlated with percentage germination in both soya (r = −0.88) and cabbage (r = −0.99). In cabbage, hydroperoxide levels were also significantly correlated with seed moisture contents (r = 0.83). These results suggest that a decrease in polyunsaturated fatty acids is associated with declining seed vigour in slowly aged seeds and adds support to a recent suggestion that the mechanisms of rapid and slow ageing may not be equivalent.

Effect of gibberellic acid on carnation flower senescence : evidence that the delay of carnation flower senescence by gibberellic acid depends on the stage of flower development

Gibberellic acid at concentrations of 10−5 M and 10−4 M delayed the senescence of cut carnation flowers, when applied continuously via the stem, to flowers between the closed brush and fully open stages of development. Older flowers with reflexed petals were unresponsive. Treatment with paclobutrazol, an inhibitor of GA biosynthesis, prevented tight buds from opening fully, reduced the longevity of partially open flowers, but was ineffective when applied continuously to fully open flowers. Gibberellic acid-treated flowers did not show simultaneous petal inrolling, a known indicator of senescence, and the time to complete petal drying was extended. Gibberellic acid modified the climacteric ethylene rise in a manner consistent with the extension of longevity. These results provide evidence for a correlative role of gibberellins in flower development.

The effect of gamma radiation on the ultrastructure of the peel of banana fruits

Abstract Ultrastructural studies of the banana ( Musa acuminata Collar cv. Dwarf Cavendish) revealed that γ-irradiation at exposures above 0.2 kGy induced collapse of the peel structure, dilations between thylakoids and a loss of granal stacking; at 1 kGy granal stacking persisted although dilation of the chloroplast envelope was noted. Fruit softening and yellowing were retarded by an exposure of 0.2 kGy; the higher γ-ray exposure values accelerated these changes but none was greater than the control. A marked decrese in sensitivity to exogenously applied ethylene was evident following irradiation exposures between 0.6 and 1.0 kGy.

Effects of temperature on the desiccation responses of seeds of Zizania palustris

Seeds of wild rice ( Zizania palustris var. interior ) have been reported to show maximum survival when dehydrated at 25°C. It has also been reported that axis cells sustain least damage at this drying temperature. In the present study, a linear relationship between drying rate and dehydration temperature was established. Whereas the highest positive tetrazolium staining and lowest leakage were recorded for seeds dehydrated at 25°C, maximum germination was recorded for seeds dried at 20°C. A proportion of seeds showed glass formation irrespective of the dehydration temperatures used. Parameters of the glass to liquid transition, however, correlated with neither water content nor sugar profiles. The ratio of raffinose to sucrose was similar in all the treatments. A hydroperoxide test revealed a linear relationship between peroxide levels and drying temperature, although fatty acid amounts were not correlated with hydroperoxide amounts. Butanal amounts and total aldehydes evolved, on the other hand, showed a high negative correlation with peroxide amounts. Electron microscopy showed that the variability and relative abundance of peripheral membrane complexes (PMCs) was highest for embryonic axes dehydrated at 25°C and lowest for cells of embryonic axes of seeds dried at 10°C. Furthermore, intramembrane particles (IMPs) were evenly distributed in cells of axes dried at 25 or 37°C. In contrast, membranes of cells of axes dehydrated at 10°C showed large IMP-free areas. The relative abundance of IMPs was highest in cells of embryonic axes dried at 25°C and lowest in cells of axes dehydrated at 10°C. From these observations, it is suggested that membrane phase transitions, with the concomitant elimination of proteins, accompany dehydration of Z. palustris seeds at 10°C, whereas at 37°C peroxidation may predominate.

Infochemicals: The seed-fungus-root continuum. A review

Abstract Chemical signals in the environment may operate at levels of increasing complexity, corresponding to cells, organs, organisms, groups and communities. The micro-environment of the soil is reviewed with respect to volatiles such as O 2 , CO 2 , C 2 H 2 and HCN and the possible role these might have on seeds. Evidence is presented that the infochemicals in fire-derived volatiles are a significant cue in seed germination in many ecosystems, world wide. Some geophytes may also show dormancy-breaking by fire-derived cues. Examples are described of volatile infochemicals derived from lipid peroxidation during seed ageing, serving as germination cues for pathogenic fungi. Finally, examples of the obligate root parasites Striga and Orobanche are discussed in response to host signalling substances produced by the roots. It is concluded that practical usage of such substances may provide safer agricultural and environmental practises.

Purine cytokinin nomenclature: a working system of abbreviations

Many synonyms for the cytokinin 6-(benzylamino)purine and its metabolites have arisen in the literature despite a 1970 IUPAC-IUB directive delimiting such nomenclature. Examples of symbols and abbreviations for some classes of this cytokinin are given. The reasons for this continued synonomy are attributed to difficulties associated with the IUPAC-IUB recommendations. A modified system of abbreviations is presented in tabular form and the utility of the scheme discussed.