Subsequent Seedling Development Research Articles

GRAMINIFOLIA homolog expression in Streptocarpus rexii is associated with the basal meristems in phyllomorphs, a morphological novelty in Gesneriaceae

Streptocarpus is a genus showing great variation in vegetative plant architecture and hence provides an attractive system to study the evolution of morphological diversity. Besides species showing an orthodox caulescent plant organization, producing leaves from a conventional shoot apical meristem (SAM), there are species whose body plan is composed of units (phyllomorphs) consisting of a petiole-like structure and a lamina that has the ability of continued growth. The first of these units is the macrocotyledon, derived from the continued growth of one of the two cotyledons by the activity of a basal meristem (BM), whereas further phyllomorphs develop from a SAM-like meristem. We carried out anatomical and morphological studies on the macrocotyledon of Streptocarpus rexii showing that the lamina has a bifacial structure, whereas the petiolode is partially unifacial. YABBY transcription factors are known to be involved in organ polarity and also promote lamina growth. We characterized the expression of SrGRAM, an ortholog of the YABBY genes GRAMINIFOLIA (GRAM) and FILAMENTOUS FLOWER (FIL), in S. rexii by in situ hybridization and RT-PCR. Gene expression pattern during embryogenesis was found to be conserved between SrGRAM and FIL from Arabidopsis. During subsequent seedling development SrGRAM expression in S. rexii was closely associated with the activity of the BM of the macrocotyledon and consecutively produced phyllomorphs, whereas it was excluded from the SAM-like meristem. Our results suggest that SrGRAM acts in intercalary growth and that an altered regulation of SrGRAM may underlay the evolution of the BM in S. rexii.

Characterization of the seed reserves in Tillandsia (Bromeliaceae) and ultrastructural aspects of their use at germination

Abstract The nature and the use of the reserves accumulated in the seed of Tillandsia, a markedly epiphyte genus, are especially important in consideration of the subsequent seedling development. As a matter of fact, the embryo radicle degenerates precociously without emerging at the germination and the sole function of the root system is that of anchoring to the substratum. The present cytochemical and ultrastructural study carried out on mature seeds has highlighted the presence of proteins and lipids, in both the endosperm and in the cotyledon, which are both well–developed; in addition, the endosperm contains starch and calcium oxalate. At germination the reserves, broken–down by enzymes, are absorbed by the cotyledon in whose epidermis ultrastructural modifications, correlated with this austorial function, appear. A part of the nutrients absorbed is initially stored in the large vacuoles, of aleuronic origin, of the cotyledon parenchyma. The result is a water uptake. It is in this manner that the wat...

Achene heteromorphism in the cleistogamous species Centaurea melitensis

Centaurea melitensis is a cleistogamous annual plant displaying achene heteromorphism. Variation is linked to capitulum type: a) initial cleistogamous capitula produce thick achenes bearing a short pappus; b) in final cleistogamous capitula achenes are small with a short pappus; and c) chasmogamous capitula produce small achenes with a longer pappus. The present study, carried out in Córdoba (Spain), examines variability in achenes by analysis of morphology, timing, dispersal and germinative capacity, and monitors the subsequent development of seedlings at different densities. Results confirm the heterogeneous nature of the achenes produced, and suggest that Centaurea melitensis has developed a life history strategy (cleistogamy and achene heteromorphism) highly adapted to the unstable habitat (subnitrophilous pioneer pasture communities) in which it grows.

Involvement of peroxidase in differential sensitivity to γ-radiation in seedlings of two Nicotiana species

Mechanisms underlying differential radiosensitivity were investigated using seeds and seedlings from two Nicotiana species, Nicotiana debneyi and Nicotiana tabacum with 60Co γ-radiation up to 500 Gy. A contrasting response to radiation was found between the seeds and seedlings in these species. Seeds were more radiosensitive in N. debneyi than in N. tabacum with respect to germination rate and subsequent seedling development. Conversely, irradiation of seedlings damaged N. tabacum more than N. debneyi, as revealed by inhibition of further seedling growth, chlorophyll degradation, and abnormalities in morphology. Subsequent experiments on seedlings revealed that the amount of the radical, OH ⋅, generated in irradiated tissues did not appear to differ between the species or with increasing doses of γ-radiation and that endogenous antioxidants which might eliminate radicals non-enzymatically were not altered by irradiation in either species irrespective of radiation doses. Although radiation induced increases in the activities of some antioxidant enzymes (peroxidase, catalase and superoxide dismutase) and changed isozyme patterns, none of these features could explain the difference in response to radiation in these plants. However, activity of peroxidase in non-irradiated tissues was 5-fold higher in N. debneyi than in N. tabacum. It was thus suggested that the difference in response to radiation between these two species was ascribed to the difference in the potential activity of this enzyme to remove toxic hydrogen peroxide which was produced in irradiated tissues.

Effect of sowing date on the germination and establishment of black spruce and jack pine under simulated field conditions

We used a diurnally and seasonally realistic simulation of seedbed conditions in a controlled environment chamber to test the dependence of seedling growth during the first year on the timing of spring germination in jack pine (Pinus banksiana Lamb.) and black spruce (Picea mariana [Mill.] BSP.). Jack pine germinated poorly under cold, early season conditions compared to black spruce. Survival in seedlings that did emerge was high and fairly constant through the early season in jack pine, and increased steadily as the season advanced in black spruce. Subsequent seedling development, measured as time to shedding of the seed coat, was slowed more by early season conditions in jack pine. Earlier emerging seedlings in both species achieved greater total biomass growth through the simulated season; jack pine seedlings consistently grew more than black spruce for all sowing dates. Height growth changed little with time of seedling emergence for jack pine, but increased greatly in earlier emerging black spruce. These results suggest that early season events can be important determinants of conifer seedling establishment and may help to explain the geographic limits of these two widespread boreal trees.

Allelopathic effect of Cistus ladanifer on seed germination

1. The allelopathic effect of the exudate secreted by Cistus ladanifer leaves was tested on different plant species. Cynodon dactylon and Rumex crispus, species absent from C. ladanifer scrub (jarales), were clearly inhibited by the exudate. 2. Species present in the jarales, Medicago polymorpha and Lolium rigidum, showed no direct inhibition of germination, but the process this was delayed, and cotyledon and root size was diminished. This implies inhibition of seedling growth, and may explain the low abundance of these species inside the jarales. 3. The active constituents in the inhibition of germination are low molecular weight phenolic compounds. The flavonoids appear to exert no direct effect on germination of the species tested, but do provoke a reduction in cotyledon and root size, and could thereby inhibit subsequent seedling development.

Differences in the Rates of Metabolism of Various Triacylglycerols during Seed Germination and the Subsequent Growth of Seedlings of Dioscorea tokoro, a Perennial Herb

Differences in the rates of metabolism of various triacylglycerols (TAGs) in the reserve oil of seeds during the course of germination and seedling growth were studied in Dioscorea tokoro, an East Asian perennial herb. Eleven molecular species of TAG were determined in the reserve oil of seeds. These TAGs contained five fatty acids: palmitic acid (P); stearic acid (S); oleic acid (O); linoleic acid (L); and linolenic acid (Ln). At 20°C, levels of TAGs with one or less than one L moiety, such as OLO, OOO, PLO, POO, OLS, and OLnO, decreased rapidly during germination and the initial elongation of seedlings, whereas levels of other TAGs decreased slowly during the subsequent development of seedlings. Even though seeds were unable to germinate at these temperatures, levels of some TAGs decreased during incubation at 5°C and at 30°C. Such changes might be related to the metabolism required for the survival of seeds at these temperatures. It is also possible that they might be involved in the breaking of dormancy at low temperatures or in the induction of secondary dormancy at high temperatures. The present results provide an example of the selective utilization of the TAGs in the reserve oil of seeds during germination and the subsequent growth of seedlings.

SEEDLING ROOT AND SHOOT COMPONENTS IN RELATION TO STAND ESTABLISHMENT

Initiation, development, and subsequent growth of seedling root and shoot components can have a direct influence on the quality, adaptation, and survival of seedlings, particularly under stress conditions. Taproot, basal, lateral, and adventitious root components (common indicot plants) each have their own development sequence, growth rate, and may have separate functions for subsequent seedling growth and development. Stresses originating in root components may be expressed in shoots affecting dry matter partitioning between roots and shoots. Partitioning and development of root morphological components and root/shoot growth adaptation to stress environments will be presented for various vegetable species. Implications of root developmental differences in relation to field planting methods will be discussed. Understanding seedling morphology, physiology and assimilate partitioning during early ontogeny would assist directing strategies to improve field establishment and ultimately crop production.

D-rice seedling development in periodically stirred water in sealed environments

Summary Large numbers of germinating seedlings of two rice cultivars exhibited d- type development consisting solely of completely white coleoptile growth after 15 days in the light in both static and periodically stirred water environments in completely sealed jars. Thus, whether germinated in static or agitated water in the sealed environments, coleoptile greening and subsequent normal seedling development were inhibited by hypoxic stress caused by the large numbers of germinating rice seedlings competing for the limited environmental oxygen supply. Consequently, the evidence presented points away from the formation of unfavourable oxygen diffusion gradients in static water environments in the sealed jars as having been responsible for d type seedling development observed in previous investigations. Continuous aeration of the 15-day-old static and periodically stirred aquatic environments, respectively, resulted in complete reversal of all d seedlings into normal green plants.

ARTICHOKE SEED GERMINATION RESPONSES TO CHILLING AND GROWTH REGULATOR TREATMENTS

Three trials were conducted in 1989 to evaluate the effects of chilling, freezing, growth regulator, and acid scarification treatments on the seed germination of two artichoke varieties. Soaking seed in a 500, 1000, or 2000 ppm ethephon solution for 5 minutes significantly increased the rate and uniformity of germination. Chilling, freezing, gibberellin, and cytokinin treatments did not affect germination rate. Freezing moistened seed and acid scarification significantly delayed germination. Ethephon treatments did not affect subsequent seedling development.

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.

パフィオペディルム属における種子発芽と幼苗分化のための最適 <i>in vitro</i> 培養条件

Suitable culture medium and light condition for each step of in vitro seed germination, growth of protocorms and subsequent development of seedlings were determined in Paphiopedilum spp. The best seed germination and best growth of protocorms were obtained on Norstog medium in darkness. However, no differentiation of leaf nor root occurred in protocorms cultured on Norstog medium regardless of light condition. Although cultures on Burgeff EG-1 medium resulted in poor seed germination, germlings developed readily into seedlings with leaves and roots if cultured in light. Duration of the dark culture on Norstog medium to yield the maximal percentage of seed germination was found six weeks and longer. Healthier protocorms were produced in the culture with longer dark period. Protocorms grown to various developmental stages on Norstog medium in darkness were transplanted onto different media in different light conditions. The best development to seedlings was obtained from the protocorms with diameter 0.5 to 1.0mm transplanted onto Burgeff EG-1 medium and cultured in light.

The effects of paraquat spraying, seed placement, and pre-germination on the appearance and survival of white clover, cocksfoot, and ryegrass seedlings from spring oversowing in hill country

Abstract Some factors affecting success or failure of oversowing were examined. White clover (Trifolium repens L. ‘Grasslands Huia’), cocksfoot (Dactylis glomerata L. ‘Grasslands Wana’), and ryegrass (Lolium perenne L. ‘Grasslands Nui’) seed was placed at precise locations in a hill country sward and the appearance and survival of seedlings in response to treatments were monitored. Treatments included paraquat spraying (0.8 kg a.i./ha) before oversowing, seed placement on or below the soil surface, and pre-germination of seed. The number of seedlings established was in the order Huia > Nui > Wana, however the number of leaves per seedling was generally in the order Nui > Wana > Huia. Averaged over the three species, seedlings were larger and more abundant for sprayed treatments compared with non-sprayed treatments. Seed placed below the soil surface appeared as seedlings more rapidly than seed on the surface, but subsequent seedling development was similar for both seed placement treatments. Pre-germinate...

Effects of cotyledon removal on apple seedling growth and distribution of 14C-labelled photosynthates

In very young apple (Malus domestica Borkh.) seedlings, cotyledon dry weight decreased during the 14-day period following cotyledon separation and development. Removal of both cotyledons at the time of cotyledon separation significantly reduced subsequent seedling development as measured by leaf area and leaf fresh and dry weights, but it did not alter established 14C-labelled photosynthate transport patterns. Cotyledon removal from seedlings with fully expanded cotyledons and four unfolded expanding true leaves did not affect subsequent seedling growth. Removal of one cotyledon in very young seedlings reduced retention and export and increased apparent metabolism of 14C-labelled photosynthate. Removal of one cotyledon in older seedlings to which 14CO2 was fed to the first true leaf did not influence retention, export, or metabolism of the 14C-labelled photosynthate in the fed leaf. In the early stages of seedling growth, assimilates were directed mainly to the lower stem and root system, then to the shoot apex and immature leaves, and finally again to the root system as the first true leaf assumed the function of supplying assimilates during cotyledonary senescence.

The effect of anti‐viral thermal treatments on germination of lettuce (Lactuca sativa) seeds and subsequent seedling development

SUMMARYExperiments on the effects of virus‐inactivating high‐temperature (40d̀C) treatments (thermotherapy) of lettuce seeds partially imbibed in polyethylene glycol solution on subsequent germination and seedling development are described. Precise temperature control is shown to be important and subsequent recovery periods at lower temperature (20d̀C) may be beneficial. Fungal contamination which developed on seeds during thermotherapy was controlled, in some seedlots, by treatment in sterile conditions. The fungi were saprophytic on seeds killed by the thermotherapy. Old seed, even with high viability, was more susceptible to heat damage than fresh seed, and even fresh seed may be pushed close to its limits of tolerance by a 10‐day treatment. The techniques described may be suitable for producing small numbers of virus‐free plants for experimental or breeding purposes.

The effect of seed treatment on the germination and early growth of Euterpe edulis (family Palmae)

The germination rate of palm seeds can be improved by pre-treatment of the seed. Several methods proved effective for Euterpe edulis seed, but sulphuric acid immersion and hydrogen peroxide leaching treatments both decreased emergence of germinated seedlings and restricted plant growth up to 6 months after germination. The best overall results in germination and subsequent seedling development were from seed leached in water for 72 hours at 30°C. This treatment can be related to the natural conditions encountered by the seed in the highly leached soils of a tropical rain forest.

Effect of Temperature and Light Intensity Early in Ontogeny on Growth of Pinusresinosa Seedlings

Low temperature or low light intensity following germination of Pinusresinosa seeds greatly suppressed subsequent seedling development, with cotyledon expansion inhibited more than root expansion. A strong influence of shoot environment early in ontogeny was demonstrated on initiation of all but a few early-formed primary needle primordia and on expansion of all primary needles, including those formed early. Low temperatures or low light intensities during the cotyledon stage of development prevented initiation of most of the normal complement of primary needles. However, when seedlings were placed in a favorable environment following prolonged exposure to low temperature or low light intensity, primordia of primary needles formed readily and subsequently expanded. Following seed germination, the young seedling is a system of competing carbohydrate sinks. Early development of the seedling is an integrated continuum with the source of growth requirements shifting during ontogeny, from megagametophytes to cotyledons, to primary needles, to secondary needles. The importance of cotyledons and primary needles to early seedling development is emphasized.

The Effect of 2,4-D on Germination of Pigweed Seed

THE use of 2,4-dichlorophenoxyacetic acid (2,4-D) to control T annual weeds such as pigweed (Amaranthus retroflexus L.) is common. Abundant evidence has been published to show that 2,4-D affects germination and subsequent seedling development. Allard et al. (1) found that 2,4-D delayed germination and caused abnormalities in seedlings of 22 broadleaf and cereal species. Elongation of radicles was inhibited in mustard seedlings (7) and in both nondormant and embryo-dormant seeds (4) as well as in seeds with impermeable seed coats (4). Germination can not only be delayed but can be inhibited (4, 5, 6), although at low concentrations of 2,4-D germination may be accelerated (6). Leachates produced by rainfall coming in contact with 2,4-D in soil were deleterious to seeds of flax and corn (2). To explore further the effects of 2,4-D on seeds, germination tests were made with scarified and nonscarified seeds of pigweed and on the effect on yield and germination of seeds harvested from pigweed plants that were sprayed with sublethal doses of 2,4-D in field plots.

Irradiation of Developing Plant Embryos. I. Effects of External Irradiation (X Rays) on Barley Embryogeny, Germination, and Subsequent Seedling Development

Barley embryos in varying stages of development were subjected in situ to single doses of x radiation of 50 to 800 r. At intervals following irradiation, part of the developing grains were sampled for histologic examination; those remaining were allowed to mature so that effects of irradiation could be followed on their subsequent germination and seedling development. In the histological study, irradiation effects increased in number and severity with an increase in radiation level. Evidence from the germination- seedling study indicates the occurrence of hidden effects. (C.H.)

Germination and Development of Heather and the Hydrogen Ion Concentration of the Medium

SEVERAL workers1–3 have shown that, in the field, heather (Calluna vulgaris Salisb.) is found most frequently and attains its maximum development on soils the reactions of which are about pH 4. I have examined the germination and the subsequent seedling development of Calluna seeds planted on agar media adjusted to give a range of reactions. A quantity of 1 per cent British agar was prepared with a form of Knop's solution. This was divided equally between nine flasks. The contents of these were adjusted to pH 2, 3, 4, 5, 6, 7, 8, 9 and 10, respectively, by the addition of the requisite quantities of sulphuric acid or caustic soda. After adjustment, the agar in each flask was poured into six 1-in. boiling tubes to give a depth of agar of about 1½ in. The tubes were plugged and the agar allowed to set. A liberal sowing of Calluna seeds was then made in all tubes.