Layer Of Seed Coat Research Articles

Ontogeny of solasodine-containing mucilage layer inSolanum viarum Dunal, ploidy types

Berries of steroid-bearingSolanum viarum Dunal are exploited commercially in India as raw material by steroid industries for solasodine, a glycoalkaloid, present in the mucilaginous exotesta of the seed. Comparative ontogeny of exotesta studied through histochemical studies in diploid, autotetraploid and trisomic plants indicated similarity in the histochemical changes occurring during ontogeny of the outermost seed coat layer which culminated in the transformation of this layer into the mucilage layer. The increased cell size in this layer in the autotetraploid plants probably accounts for the higher steroid content reported. Corroborative evidences for histochemical changes observed in the mucilage layer were obtained from studies of ultrastructure using transmission electron microscopy.

The morphological background to imbibition in seeds ofPinus sylvestris L. of different provenances

An examination was made of the structure of the coats of Scots pine (Pinus sylvestris L.) seeds of different provenance and the contribution of this factor to differences in imbibition. The seed coat layers derived from the integument, the sarcotesta, sclerotesta and endotesta did little to restrict imbibition, even though the sclerotesta of the northern provenance seeds was composed of a double multicellular layer and the sarcotesta contained large numbers of pigmented, phenol-bearing cells. In addition to the micropyle, the sclerotesta was found to possess structural openings at the chalazal end and at the ridge joining the two halves of the seed, but being covered by the pigmented cells of the sarcotesta, these did not allow water to enter any more than did the micropyle itself. Imbibition was chiefly regulated by the lipophilic covers surrounding the endosperm, which are mainly of nucellar origin, especially by the megaspore membranes nearest to the endosperm, the outer and inner exine. The nucellar cap covering the micropylar end of the endosperm proved to be impermeable to water, and its edge extended between the exine layers, which further enhanced the importance of the endosperm covers as regulators of imbibition.

Lithological control on the state of preservation of fossil seed coats of water plants

In this study 1 Eocene wood sample and 25 fossil Eocene seed coats of water plants from 6 different localities on the south coast of England are analyzed using scanning electron and light microscopy, in addition to Curie-point pyrolysis-GC(-MS) and solid state 13C NMR, in order to characterize their morphological and chemical alteration in relation to different lithologies. Results from the translucent inner seed coat layers, tegmens, reveal that these tissues consist of aliphatic type biomacromolecules similar to cutan. The tegmens remain morphologically and chemically unaltered. By contrast, the results from the outer seed coat layers, testae, show that these are composed of polyphenolic macromolecules derived from lignin-celluloses. The testae are, on average, morphologically best preserved in fine-grained sediments, whereas best chemical preservation is observed in testae from coarse-grained sediments. Testae associated with pyrite in blue or green fine-grained sediments show poor quality chemical preservation, whereas those from dark brown and grey clays with pyrite show chemical preservation more similar to that of testae from coarse-grained sediments. These results show that diagenetic alteration of organic matter is not only determined by burial history but can also be greatly influenced by differences in lithology.

Chemical and microscopic characterization of outer seed coats of fossil and extant water plants

Sclerotic outer seed coat layers (testae) of three fossil and two extant water plant species were analyzed using scanning electron and light microscopy in addition to Curie-point pyrolysis, solid state 13C NMR, and CuO oxidation. Comparison between the chemical results from the fossil and extant samples reveals that the original resistant constituents in the sclerotic testae are native lignin-celluloses which are transformed to polyphenol macromolecules recognized in the fossil samples. The combination of microscopic and chemical data provides new insights regarding the early diagenetic processes by which lignin-cellulose-containing plant remains may have been transformed. In particular, the unaltered morphology in combination with major chemical modifications is used as the basis to postulate the timing and nature of lignin transformations. The combination of pyrolysis, solid state 13C NMR, and CuO oxidation is shown to be a powerful tool to characterize the chemical structure of testae of fossil and extant water plants.

The ultrastructure of seed coat development inRanunculus sceleratus

Seed-coat development in Ranunculus sceleratus L. has been studied by electron microscopy. Three layers developed from the single integument. The outer epidermis consisted of elongated and flattened cells that were always well attached to each other. The cells were characterized by thin walls, the presence of chloroplasts and small vacuoles. The cells of the middle layer were originally closely packed. Gradually, extensive intercellular spaces were formed. The cells of the inner epidermis elongated initially, until they became cubic and developed a thick wall with numerous wall ingrowths at the side bordering the nucellus. Thus, they give rise to a mechanical layer protecting the inner part of the seed. The elongation of cells, the thickening of cell walls, the formation of wall ridges, and the formation of intercellular spaces each coincided with characteristic configurations of microtubules. Plasmodesmata were originally found between all cells of the integument but their number decreased drastically during development, especially between the three developing seed-coat layers. Well-differentiated chloroamyloplasts, present in all cells of the developing seed-coat, pointed to autotrophy during development. Maturation eventually led to the disappearance of cytoplasm in all cells, the compression of the cells of the outer epidermis and middle layers, and the formation of a mechanical layer from the inner epidermis.

Chemical and microscopical characterization of inner seed coats of fossil water plants

Inner seed coat layers (tegmens) of four different species of fossil water plants have been analyzed using light microscopy, scanning- and transmission-electron microscopy, and Curie-point pyrolysis. Microscopical analysis of the tegmens show two layers both comparable with a cuticle. Furthermore, the pyrolysates revealed the presence of highly aliphatic macromolecules comparable with cutan. The resistant constituents in the tegmens of two of the species also contained tocopheryl units which may serve as an additional source for prist-1-ene in pyrolysates of kerogens or of pristane upon natural thermodegradation.

Effect of Husk morphology on grain development and topography in rice

Kernels grown within loosened glumes in three varieties of paddy were darker in color and had a smoother surface than those grown under normal conditions. The thickness of the pericarp plus seed coat layers was 33.6 ±2.8 µm, and the thickness of the aleurone layers was 21.7 ± 2.5 µm in grains of the first type, while in the normal grains, these dimensions were 13.0 ± 1.4 and 26.9 ± 2.9 µm respectively. The kernels which developed within loosened glumes tended to taper towards the distal end. They were lighter in weight than normal grains by 32 to 67 percent, the weight loss being less in the bolder variety. The lemma-palea interlocking depth was positively correlated with the groove depth on the kernel and with the clearance between husk and kernel. All three parameters showed a positive correlation with grain breadth. A low lemma-palea interlocking depth and a smaller clearance between husk and kernel are technologically desirable characteristics in rice. The reclasping of the two glume components after pollination was essential for the normal development of the rice grain.

Dormancy in Pinusmonticola seed related to stratification time, seed coat, and genetics

The inner layer of the seed coat, a papery membrane, and physiological conditions of the gametophyte–embryo were shown to be major sites of dormancy in seed of western white pine. The hard seed coat layer was a minor site. With no stratification, 7% of the seeds were not dormant, 9% were dormant because of the hard seed coat, 34% were dormant because of the inner seed coat, and 50% were dormant because of physiological conditions of the gametophyte–embryo. These values varied with stratification times and seed lots (families).

THE LIGHT PROMOTED GERMINATION OF THE SEEDS OF CHENOPODIUM ALBUM L. VI. Pfr REQUIREMENT DURING DIFFERENT STAGES OF THE GERMINATION PROCESS

Positive photoblastic seeds of Chenopodium album need the action of the active form (Pfr) of phytochrome (P) during nearly the total length of the overall germination process. The first Pfr dependent processes require a Pfr/P ratio above the level being present in darkness. The different requirement for the length of the red irradiation indicates that these first processes have a different Pfr requirement in the individual seeds of one population. Simultaneous irradiations with narrow wavelength bands of red (643 nm) and far-red (768 nm) light, which established different Pfr/P ratios, supported this conclusion. The Pfr requirement is a function of the thickness of the seed-coat. The germination of half operated seeds (the outer seed-coat layer is removed in the area overlying the radicle) can be induced by the dark level of Pfr, being approximately Pfr/P = 0.07. The required Pfr level for the germination processes after the escape from the antagonistic effect of short far-red irradiations, decreases from 0.07 to below 0.02. Osmotic stress increases the Pfr requirement. Prolonged irradiations with far-red light inhibit the germination processes when they are already in the phase of the embryo elongation. The elongation process is supposed to consist mainly of cellular expansion. The process which induces the secondary photodormancy is only related to the first Pfr dependent processes.

THE LIGHT PROMOTED GERMINATION OF THE SEEDS OF CHENOPODIUM ALBUM L. V. DARK REACTIONS REGULATING QUANTITY AND RATE OF THE RESPONSE TO RED LIGHT

In Chenopodium album seeds the influence of the dark incubation time before a red irradiation on the subsequent germination processes was studied. During dark incubation at least two preparative reactions take place. The first one, a rehydratation of the phytochrome pigment, is both at 23 °C and 4 °C a function of the water uptake of the seeds. It regulates the rate of increase in reactivity of the seeds to red light, as measured by the final germination percentage. In the second one a reaction component for the far-red absorbing form of phytochrome (Pfr) is synthesized. This synthesis does not occur at 4 °C. The amount of this component synthesized before onset of a red irradiation, determines the reaction rate of Pfr and consequently the escape from the antagonistic effect of a far-red irradiation, which in turn determines the moment of visible germination. The processes between the moment of escape and the moment of the protrusion of the rootlet through the inner seed-coat layer are not influenced. The lower final germination percentage, after a 4 °C pre-treatment, as compared with incubation at 23 °C, is supposed to be caused by the dark conversion of Pfr to Pr in the absence, at the lower temperature, of the product of the second reaction.

THE LIGHT PROMOTED GERMINATION OF THE SEEDS OF CHENOPODIUM ALBUM L. IV. EFFECTS OF RED, FAR-RED AND WHITE LIGHT ON NON-PHOTOBLASTIC SEEDS INCUBATED IN MANNITOL

The effects of red, far-red and white fluorescent light on the germination of dark germinating seeds of Chenopodium album, incubated in a range of mannitol concentrations, have shown that the far-red absorbing form of phytochrome (Pfr) is present in these seeds. The requirement of the germination processes for Pfr increased, when the osmotic concentration of the incubation medium was increased. It is concluded that this requirement for Pfr depends on the position of a balance between promotive and inhibitory factors. Pfr influences this balance in a positive direction. It was shown that osmotic stress, a thick seed-coat and (RS)-abscisic acid can function as inhibitory factors. In its influence on the last stage of the visible germination phenomena (the protrusion through the inner seed-coat layer) white light resembles in lower osmotic concentrations red light, in higher concentrations it resembles far-red light. The earlier stages (elongation inside the seed) are influenced, in all tested concentrations, similar by red and white light. It is assumed that during the last phase of the germination process “seedling phytochrome” instead of “seed phytochrome” has a regulatory function.