Morphophysiological dormancy and germination ecology in diaspores of the subtropical palm Phoenix canariensis Chabaud

The timing of germination is a crucial event in a plant’s life cycle. Seed dormancy and germination mechanisms are important factors regulating seedling emergence. Since detailed experimental evidence for germination pattern of Phoenix canariensis colonizing sub-tropical climate is scarce, we investigated seed dormancy and germination ecology of P. canariensis. We found that the embryo is underdeveloped at the time of dispersal and doubles in size before the cotyledonary petiole (CP) protrudes through the operculum. The primary root and plumule emerge from the elongated CP outside the seed. In light/dark at 30/25°C, the CP emerged from 8% of the diaspores within 30 days and from 76% within 14 weeks. Thus, 8% of the diaspores have MD and the others MPD. Removal of the pericarp and operculum resulted in 100% germination within 5 days in light/dark at 30/25°C. Cold and warm stratification as well as treatment with GA3 significantly increased the germination speed, but the final germination percentage was not significantly increased. Seed germination was synchronized in early summer when seed dormancy was released by cold stratification in the soil over winter. A remote-tubular germination type and intricate root system provide an ecological advantage to the seedling establishment.

Germination ecology of Trachycarpus fortunei (Arecaceae), a species with morphophysiological and shoot dormancy

Beyond strong inference that most of the 2600 known species of Arecaceae produce diaspores with an underdeveloped embryo and therefore have morphological (MD) or morphophysiological dormancy (MPD), little is known about the specific dormancy class or sub-class, and how dormancy-break occurs under ecological conditions. Here, we found that mature seeds of Trachycarpus fortunei collected at the time of natural dispersal had an underdeveloped embryo that was 10% of total seed length. No diaspores germinated over a wide range of temperatures in either light or darkness. Cold-stratification at 4 °C for 1, 2, and 3 months or treatment with 100, 500, and 1000 ppm gibberellic acid (GA3) improved germination percentages, with 3 months cold-stratification or 1000 ppm GA3 resulting in highest germination. The embryo grew inside the seeds during cold-stratification. However, warm stratification did not improve germination. Therefore, seeds of T. fortunei have intermediate complex MPD. Cold stratified seeds moved to spring conditions (15/20 °C) had cotyledonary petiole (CP) elongated, but leaves developed only when the CP elongated seeds were moved to summer temperatures (25/30 °C), suggesting the presence of shoot dormancy. The seedlings are remote-tubular type. This is the first report for Arecaceae indicating the presence of complex MPD.

Intermediate Epicotyl Physiological Dormancy in the Recalcitrant Seed of Quercus chungii F.P.Metcalf with the Elongated Cotyledonary Petiole

Control of seed germination and dormancy is important in seed plant adaptation and evolution. When studying seed dormancy of Quercus species, we observed a substantially delayed shoot emergence following a fast root emergence in Quercus chungii F.P.Metcalf. Since epicotyl physiological dormancy (PD) has not been reported in Quercus section Cyclobalanopsis, we examined seed morphology and germination in Q. chungii and aimed to document epicotyl PD in the seeds. The embryo was fully developed in fresh ripe seeds. The elongating cotyledonary petiole pushed the embryo axis out of the seed during germination, which differed from observations in other Quercus species. Shoots emerged from seeds with developing roots after 3 months of warm stratification (35/25 °C), reaching the highest percentage of shoot emergence in seeds after 5 months. Seeds were recalcitrant and displayed a yet unreported epicotyl PD type, for which we propose the formula Cnd(root) ‒ Cp’’ 2b(shoot). Early emergence and development of the root system in Q. chungii seeds with epicotyl PD appears to be a mechanism to maintain a constant water supply to the shoot during plumule development and emergence. Our documentation of seed germination will provide guidance for the conservation and restoration of this species from seeds.

Morpho-anatomical characterization of diaspores and seedlings of Livistona rotundifolia

Livistona rotundifolia (Lam.) Mart. (Arecaceae) is an ornamentally important species used for landscaping and commonly grown as a potted plant. However, seedling production is hindered by the lack of information available about the species germination process and it could be subsidized by seed and seedling anatomical and morphological studies. Therefore, this study aimed at describing L. rotundifolia diaspore morphology in addition to seedling morphology and anatomy. Germination is tubular remote and begins with the opening of a circular operculum in the fruit endocarp through which the cotyledonary petiole is emitted. The endosperm is consumed as cotyledonary petiole grows. Eophyll is covered by two leaf sheaths and the first L. rotundifolia leaves are simple and lanceolate, with longitudinal and parallel veins. The developing cotyledonary petiole presents root hairs and a typical stem structure. The cotyledonary petiole/root transition region shows secondary root emission, parenchyma cells, and groups of fiber bundles. Roots present a well-defined cortex with polyarc vascular cylinder. Cortex and vascular cylinder are not well-differentiated in the root apex. The results of this study will contribute to the overall biology of L. rotundifolia, as well as to seedling production and species identification, subsidizing regeneration and conservation studies.

Morphophysiological dormancy in seeds ofConvallaria keiskeiand a proposal to recognize two types of double dormancy in seed dormancy classification

Convallariamajalishas double dormancy and hypogeal germination, but no information is available on embryo growth or on the effects of light and gibberellic acid (GA3) on germination in this genus. Therefore, we investigated embryo growth and other germination features in seeds ofC. keiskeiand compared the data with those ofTrillium camschatcensein another study. Until now, in seeds with double dormancy, embryo growth and germination (epigeal) have been studied in detail only for seeds ofT. camschatcense. Phenology of embryo growth and emergence of cotyledonary petiole/root (hereafter root) and shoot in seeds ofC. keiskeiwere monitored outdoors. Effects of temperature, light and GA3on embryo growth and root and shoot emergence were tested under laboratory conditions. Roots emerged the first spring following seed dispersal in autumn. The embryo grew soon after root emergence, and germination was hypogeal. Seeds with an emerged root formed buds from which a shoot (leaf) emerged above ground during the second spring. Alternating temperatures and light had negative effects on root emergence, and GA3did not substitute for cold stratification in root emergence. Seeds ofC. keiskeihave double dormancy, but it differs from that inT. camschatcense. Based on differences in embryo growth before (T. camschatcense) versus after (C. keiskei) root emergence, and on epigeal (T. camschatcense) versus hypogeal (C. keiskei) germination, we suggest that two types of deep simple double morphophysiological dormancy (MPD) be recognized. Since embryo growth inC. keiskeidoes not fit the standard definition of MPD, we propose to expand this definition.

Organogenesis during plant regeneration in cotyledon culture of Trifolium michelianum Savi

Shoots of <em>Trifolium michelianum</em> Savi. could be induced directly from the cotyledonary petiole or through petiole-derived callus on EC6 medium (Mahewswaran and Williams 1984) supplemented with BAP at 4.4, 8.8 and 22.2 µM. The mode of caulogenesis highly depended on cytokinin concentration in the medium. Most of the shoots regenerated into mature plants when transplanted to half-strong MS (Murashige and Skoog 1962). The time of caulogenic determination was set for the first day of culture. The induction of determination for caulogenesis was accompanied by the loss of competence toward root formation. SEM studies revealed that caulogenesis was restricted to the distal end of the cotyledonary petioles, very close to but not at the site of excision. The sites of shoot regeneration were limited to abaxial and lateral surfaces of the petioles.