The Importance of Genetically Determined Seed Coat Characteristics to Seed Quality in Grain Legumes

Comparisons of five pairs of isogenk lines of peas, differingonly in the A gene for seed coat colour showed that white seeds(genotype aa) imbibed more rapidly than coloured seeds (AA),suffered greater imbibition damage revealed by dead tissue onthe cotyledons, and higher solute leakage. Seed-coat pigmentationwas closely associated with slow water uptake, since when expressionof the A gene was suppressed by the recessive pollens gene,the resulting white seeds {palpal AA) imbibed rapidly. The slowwater uptake by coloured seeds was not due to the restrictionof water entry by the seed coat since the differences in imbibitionrate were maintained when a portion of the seed coat was removedand seeds were imbibed with the exposed cotyledon in contactwith moist filter paper. Imbibition of similarly treated seedsby immersion in polyethylene glycol solutions (1–4%) whichincreased the seed/solution wettability, had little effect onthe water uptake of coloured seeds compared to imbibition inwater whereas that of white seeds increased in the first 10mins imbibition. Poor wettability of the inner surface of colouredseed coats did not therefore explain the slow imbibition ofthese seeds. The white seed coats loosened rapidly during imbibitionwhilst the coloured seed coats remained closely associated withthe cotyledons suggesting that the adherence of the seed coatto the cotyledons and therefore the ease of access of waterbetween the testa and cotyledons determines the rate of imbibition.The rapid water uptake by white-coated seeds and the subsequentimbibition damage may explain the high incidence of infectionof these seeds by the soil-bome fungus Pythhan after 2 d insoil. Improved seed quality and emergence may therefore be achievedby breeding for seed coat characteristics leading to reducedrates of imbibition Pisum sativum, isogenic lines, A gene, seed coat colour, imbibition, imbibition damage, wettability, pollens gene, seed quality, grain legumes     

Development of seed coat-imposed dormancy during seed maturation in Cynoglossum officinale

The relationship between seed phenolics and appearance of seed coat–imposed dormancy during seed development in Cynoglossum officinale L. was studied. Up to 24 days after anthesis, seeds failed to germinate upon imbibition in Petri dishes at 25°C. At 44 days after anthesis, seeds were fully germinable; removal of seed coats did not improve their germination or O₂ uptake. At 72 days after anthesis, mature seeds at the base of the cyme did not germinate unless their coats were removed. Removal of seed coat also stimulated O₂ uptake at this harvest date. The methanol-soluble phenolic content of the seeds increased during the early stages of seed development, in both the seed coat and the embryo. As seed development continued, the methanol-soluble phenolic content of the embryo stabilized, but that of the seed coat declined. This decline was associated with an increase in the thioglycolic acid–soluble phenolics, presumably lignins, in the seed coat. These results suggest that polymerization of methanol–soluble phenolics into lignins in the seed coat during later stages of seed development renders the seed coat of C. officinale impermeable to 03, and thus keeps the seed dormant.     

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.     

Reactive oxygen species release, vitamin E, fatty acid and phytosterol contents of artificially aged radish (Raphanus sativus L.) seeds during germination

Seeds of Raphanus sativus L. subjected to accelerated ageing were investigated for reactive oxygen species (ROS) release and for content of vitamin E (tocopherol, TOC, and tocotrienol, TOC-3), fatty acids and phytosterols in seed coats, cotyledons and embryonic axes during germination. In unaged seeds, ROS release occurred mainly in seed coats of non-imbibed seeds and in seedlings (48?h of imbibition). TOC and TOC-3 were mainly represented by the ??-isoform, abundant in embryonic axes. Fatty acids were mainly found in cotyledons. In seed coat and embryonic axis, phytosterols consisted mainly of sitosterols. The effects of ageing were mainly visible in embryonic axes at 48?h of imbibition. Deterioration was associated with a decrease in fresh weight increase percentage, germination percentage, ??-TOC and total fatty acid content. An increase in ROS release from seed coats and in ??-TOC, ??-TOC, ??-TOC-3 content in embryonic axis was also observed. The use of ??-TOC and total fatty acids in embryonic axis as parameters of seed quality evaluation during storage was suggested.     

红松种子休眠与种皮的关系

本文探讨红松(Pinus koraiensis)种子休眠与其种皮之间的关系。夹破中种皮后,种子萌发率很低。在离体胚培养基中外加 ABA 及经 ABA 溶液浸泡种子的萌发实验表明,ABA也不是导致休眠的关键因素。试验确认红松种子存在透气障碍,即中、内种皮对氧气的进入都有阻碍作用。经低温砂藏后,种皮的阻碍作用明显减小。种皮的透气性障碍可能是诱导休限的主导因素。     

Hypoxia and Imbibition Injuries to Aging Seeds

The development of hypoxia and primary injuries were examined during the imbibition of aging pea seeds (Pisum sativum L., cv. Nemchinovskii). The distribution of air-dry pea seeds by their room-temperature phosphorescence revealed the presence of two fractions (I and II) in a seed lot with 72% germinability and three fractions (I, II, and III) in a seed lot with 50% germinability. The water uptake during imbibition was slower in the fraction I seeds than in the fraction-II seeds. The fraction-I seeds produced normal seedlings, whereas the fraction-II seeds either produced seedlings with morphological defects (abnormal) or did not germinate at all. The fraction-III seeds were all dead. The phosphorescence of endogenous porphyrins, emitted only at low O₂ content, was measured after 20-h seed imbibition. The fraction-I seeds emitted no discernible phosphorescence. The fraction-II comprised highly phosphorescent seeds incapable of radicle protrusion and moderately phosphorescent seeds producing abnormal seedlings. The fraction-II seeds experienced hypoxia during the imbibition because of rapid oxygen consumption by the embryo and restrictions to O₂ diffusion imposed by the seed coat. In the fraction-I seeds, the rate of oxygen consumption by the embryo was slower and the seed coat resistance to oxygen diffusion was lower than in the fraction-II seeds. Therefore, hypoxia did not arise in the fraction-I seeds. The submergence of seeds in water caused lethal injuries. The imbibition of seeds without any contact with water caused no lethal damages but did not reduce the percentage of seeds dying of hypoxia. A slow imbibition of seeds in the media containing either an osmoticum (PEG) or an inhibitor of aquaporin channels (p-chloromercuribenzoate) prevented the lethal injuries at early stages of seed hydration and retarded the appearance of oxygen deficiency in fraction-II seeds. Different rates of water uptake by fraction-I and fraction-II seeds were controlled by permeability of cell membranes rather than by permeability of seed coat. It is proposed that low permeability of plasma membranes to water in fraction-I seeds results from the predominantly closed aquaporin channels, whereas a higher permeability of weak seeds (fraction II) is due to open channels.     

The effect soaking pea seeds with or without seedcoats has on seedling growth

Pea seeds (Pisum sativum L. `Alaska') with intact seedcoats (WC) and with seedcoats removed (WOC) were soaked in distilled water for 24 hours at 20°. The water, containing the pea diffusate, was decanted after the second, fourth, sixth, eighth, twelfth, and twenty-fourth hour and analyzed for total nitrogen, α-amino nitrogen, carbohydrate, and total solute dry weight. The seeds were germinated at 20° in a 16 hour photoperiod of 300 foot candles. Stem lengths and dry weights of roots, shoots and cotyledons were determined after 4, 11, and 18 days of growth. WOC seeds imbibed more water than WC seeds during the 24 hour imbibition period. Diffusates from WOC seeds always contained more solute than diffusates from WC seeds. Maltose, glucose, and fructose were not detected in the early diffusates from WOC seeds but were found in WC seed diffusates at all times. Seedlings from WC seeds had longer stems than those from WOC seeds. The dry weight of stems and roots of WC seedlings was greater than those from WOC seedlings. The dry weight of cotyledons from 18 day-old WC seedlings was less than from WOC seedlings. Water absorption by WC seeds was slower than by WOC seeds. Removal of the seedcoat allowed rapid imbibition resulting in seed injury presumably because of the loss of solutes which included monosaccharides, disaccharides, amino acids, and other nitrogen containing compounds. These results are consistent with the hypothesis that rapid imbibition disrupts membrane organization leading to reduction of seedling growth.     

Imbibition of Swietenia macrophylla (Meliaceae) seeds: the role of stomata

BACKGROUND AND AIMS: The occurrence of stomata in seed coats is uncommon and there is limited information about their function(s). The aim of this study was to verify the distribution of stomata in seed coats of Swietenia macrophylla and to relate it to the imbibition process and aspects of the structure of the outer integument layers. METHODS: For the structural and ultrastructural studies, the seeds were processed using the usual techniques and studied under light and scanning electron microscopes. Histochemical tests were employed to identify the cell wall composition in the different seed coat portions. To assess the role of the stomata in the imbibition, non-impervious seeds were compared with partially impervious ones, in which only the embryo, median or hilar regions were left free. Further, the apoplastic pathway marker was employed to confirm the role of the stomata as sites of water passage during imbibition. KEY RESULTS: A positive relationship was observed between seed coat thickness and stomata density. The stomata were devoid of movement, with a large pore. They occurred in large numbers in the embryo region and extended with lower frequency towards the wing. Imbibition rates were related to stomata density, suggesting that the stomata act as preferential sites for water entry in the S. macrophylla seeds. CONCLUSIONS: At maturity, the stomata in the seed coat play a significant role in seed imbibition. The data may also infer that these permanently opened stomata have an important role in gas exchange during seed development, aiding embryo respiration.     

Exudation of an allelopathic substance lepidimoide from seeds during germination

Lepidimoide promotes growth of the cockscomb hypocotyl. It is exuded from germinating seeds of various plant species into their culture environment. The mode of exudation of lepidimoide from seeds into the culture solution, using sunflower and buckwheat seeds, was studied in relation to seed germination. In the dry seeds, about 75% of the lepidimoide was found in the seed coat and about 25% in the kernel. Upon water imbibition it was released into the culture solution. However, the quantity of lepidimoide detected in the seed exudate was more than three times the total amount in dry and imbibed seeds, suggesting that lepidimoide was also produced de novo in the seeds and subsequently released. When seed coats or kernels were imbibed separately, the quantity of lepidimoide released from the seed coats into the culture solution was much the same as that in the dry seeds, but the amount of lepidimoide detected in the exudate of kernels was about 16 times that in the dry kernels. These results suggest that lepidimoide, already present in dry seeds, as well as that newly produced in the kernels following imbibition, was released into the environment.     

Functional aspects of mature seed coat of theCannaceae

Cannaceae seeds have been analysed regarding seed coat structure, germination and macromolecular composition of the seed coats. Data of several mass spectrometric techniques were combined with those of microscopic and histochemical techniques to acquire insight into the functions of the seed coat.Cannaceae seeds have an exotestal layer of Malpighian cells with a hydrophobic and a hydrophilic part. The hydrophobic part is mainly responsible for the impermeability of the seed and contains silica, callose, lignin as water repellent substances. Water can only enter the seed after a certain temperature-induced opening of an imbibition lid. During imbibition the hydrophilic part of the Malpighian cells swells and the seed coat ruptures due to differences in pressure in the upper and lower part of the Malpighian cells.     

Fungi growing on stored soybeans and their significance in lipid breakdown*

US Grade 2 soybeans contain about 20% cracked and split seeds, 3% damaged seeds and 2% foreign material. Examination by scanning electron microscopy showed that intact seeds were externally almost free of microorganisms. In cracked seed coats and in damaged areas on broken soybeans, profusely developing fungal mycelia were frequently observed. Fungi penetrated the beans through these cracks and through the micropyle. Penetration through the hilum was observed only in cases where the seed coats showed pronounced signs of damage. No penetration through pore-like structures in the seed coat could be observed. Light microscope observations of sections of naturally infested soybeans showed little penetration into the underlying cell layers. Sections of soybeans kept at 99% r.h. and 26d?C for 4 days revealed profusely developing fungi colonising both seed coat tissue and cotyledons. In the cotyledonous tissue hyphae did not penetrate into the cells but developed only in the intercellular spaces. In inoculated, detached seed coats, fungi developed better on the inner than on the outer side. On cotyledons free of seed coats, fungal development was better than in the seed coat itself. In broken soybeans of commercial stock origin, free fatty acids (FFA), mould count and respiration rate increased 3.5-, 3.5-and 5.0-fold, respectively as compared with intact ones. When broken and intact soybeans were mixed there was no increase in the rate of deterioration. It is concluded that fungi are involved in the increase of FFA in soybeans during storage and that this process is significantly faster in the broken bean fraction.     

种壳厚度对鼠类种子扩散行为及种子命运的影响

种子扩散是植物更新和扩大分布区的一种重要途径。鼠类采取不同的种子扩散和贮藏策略,以应对食物短缺,同时也促进了植物种子扩散。为应对鼠类对植物种子的过度取食,种子进化出了一系列物理、化学等防御特征。其中种壳厚度作为一种物理防御策略,是影响鼠类贮藏行为和种子命运的关键因素。本研究拟通过去除天然栓皮栎（Quercus variabilis）种子的外壳,再在种仁外包被1、2、4、6不同层数的聚乙烯薄膜,模拟种壳厚度,准确控制种壳厚度。2020年10月—2021年1月,在四川都江堰森林生境中释放人工种壳包被的种子,研究人工种壳厚度对鼠类介导的种子扩散和命运的影响。结果表明：（1）鼠类优先扩散种壳较薄（1层薄膜包被）的人工种子;随着种壳厚度的增加,扩散速率逐渐降低,种壳最厚（6层薄膜包被）的种子扩散最慢（P < 0.001）;（2）鼠类喜好分散贮藏1层、2层薄膜包被的种子;当种壳厚度增加至包被4层、6层薄膜时,分散贮藏比例显著降低（P < 0.05）;（3）鼠类偏好集中贮藏4层薄膜包被的种子（P < 0.05）;（4）不同种壳厚度的种子扩散距离无显著差异（P > 0.05）;（5）种壳较薄（1层薄膜包被）的种子分散贮藏率在3 m范围内比例较高。采用聚乙烯薄膜包被是模拟种子外壳的可行方法,并可用于评估种壳厚度对鼠类种子贮藏行为和种子命运的影响等相关研究。     

Patterns and kinetics of water uptake by soybean seeds

Soybean [Glycine max (L.) Merr.] plants produce some seeds (called stone or impermeable seeds) that do not take up water for long periods of time. The present investigation confirmed that the stone seed trait is a feature of the seed coat: isolated embryos from both stone and permeable seeds took up water equally quickly. A whole, permeable seed typically imbibed water initially through its dorsal side, forming wrinkles in the seed coat and delivering water to the underlying cotyledons. Later, some lateral movement of water through the coat occurred, presumably through the air spaces of the osteosclereid layer. Imbibition by seeds was a two-phase process, the first dominated by hydration of the seed coat and the second by hydration of the cotyledons, which was rate-limited by the coat. When hydrated, coats of stone seeds were permeable to water but their hydraulic conductivity, as measured with a pressure probe, was smaller than that of coats from permeable seeds by a factor of five. Hydrated coats of both permeable and stone seeds showed weak osmometer properties.     

The significance of structure for imbibition in seeds of the Norway spruce,Picea abies (L.) Karst.

Since the observations of those regularly handling Norway spruce [Picea abies (L.) Karst.] seeds with regard to their imbibition frequently disagree with earlier opinions that this process is markedly inhibited by the seed coat, we decided to examine the morphological factors influencing imbibition in seeds of different colour and different provenances. The seed coat, consisting of the sarcotesta, sclerotesta and endotesta, was found to have little influence on the passage of water, despite the presence of sclereids full of wax lamellae. No differences in seed coat structure were observed between provenances or colours of seeds. The cells of the endotesta were lignified in the area of the micropyle, however, and stood out lip-like on the outer surface of the micropyle after imbibition. An opening in the sclerotesta filled with parenchyma cells was also seen at the chalazal end of the seed. Neither of these openings, which were covered by accumulations of wax, served as the main route for the passage of water, though the micropyle opened up slightly after only 24 h incubation, when the lignified cells bordering it swelled differently from the rest of the endotesta. The progress of water into the seed soon discontinued, however, as the tip of the nucellar cap, covered with wax and crystals, effectively plugged the micropyle. This opening of the micropyle may be the reason why the IDS method does not always succeed in separating viable from non-viable spruce seeds sufficiently well by their density. Imbibition was mostly regulated by the lipophilic layers surrounding the endosperm, which are mainly of nucellar origin, and particularly the megaspore membranes, the outer and inner exine. Imbibition was further hampered by the impermeable nucellar cap, which covered about 3/4 of the length of the endosperm and had merged with the outer exine at its edges. Deposits of wax were observed both between the exines and between the endotesta and the nucellar layers at the edges of the nucellar cap. Waxes may serve as a defence against diseases at the sites of water penetration, while simultaneously increasing the significance of the nucellar endosperm covers as regulators of imbibition.     

Physical dormancy and histological features of seeds of five Acacia species (Fabaceae) from xerophytic forests in central Argentina

Physical dormancy (impermeability of seed coats to water) is related to histological features of the seed coat. This mechanism has ecological importance since it determines the time and space of germination. The aim of the present study was to compare the histology and impermeability of the seed coat in five Neotropical Acacia species from xerophytic forests of central Argentina: Acacia aroma, A. caven, A. atramentaria, A. gilliesii and A. praecox. An imbibition experiment was performed to determine the presence or absence of physical dormancy. Seed coat structure was studied through histochemical analysis. The seeds of A. gilliesii and A. praecox were treated with ammonium ferrous sulfate to identify the sites of water entry. Acacia aroma, A. caven and A. atramentaria exhibited physical dormancy; the seed coat was very thick and compact, with a wide, sclerified parenchyma and a “water gap” for water uptake. Seed coat impermeability in these species was mainly attributed to characteristics of the lignified epidermis. By contrast, A. gilliesii and A. praecox did not have physical dormancy and showed thin seed coats with a much narrower sclerified parenchyma. Water entered the seeds of A. gilliesii and A. praecox not only through the hilar zone but also through the entire surface of the seed coat. Differences in the seed coat structure among species could be related to different regenerative responses to environmental conditions that would facilitate the coexistence of these Acacia species in the xerophytic forests of Córdoba, Argentina.     

A subtilisin-like serine protease essential for mucilage release from Arabidopsis seed coats

During Arabidopsis seed development large quantities of mucilage, composed of pectins, are deposited into the apoplast underneath the outer wall of the seed coat. Upon imbibition of mature seeds, the stored mucilage expands through hydration and breaks the outer cell wall that encapsulates the whole seed. Mutant seeds carrying loss-of-function alleles of AtSBT1.7 that encodes one of 56 Arabidopsis thaliana subtilisin-like serine proteases (subtilases) do not release mucilage upon hydration. Microscopic analysis of the mutant seed coat revealed no visible structural differences compared with wild-type seeds. Weakening of the outer primary wall using cation chelators triggered mucilage release from the seed coats of mutants. However, in contrast to mature wild-type seeds, the mutant's outer cell walls did not rupture at the radial walls of the seed coat epidermal cells, but instead opened at the chalazal end of the seed, and were released in one piece. In atsbt1.7, the total rhamnose and galacturonic acid contents, representing the backbone of mucilage, remained unchanged compared with wild-type seeds. Thus, extrusion and solubility, but not the initial deposition of mucilage, are affected in atsbt1.7 mutants. AtSBT1.7 is localized in the developing seed coat, indicating a role in testa development or maturation. The altered mode of rupture of the outer seed coat wall and mucilage release indicate that AtSBT1.7 triggers the accumulation, and/or activation, of cell wall modifying enzymes necessary either for the loosening of the outer primary cell wall, or to facilitate swelling of the mucilage, as indicated by elevated pectin methylesterase activity in developing atsbt1.7 mutant seeds.     

MOISTURE AND TEMPERATURE IN RELATION TO SEED STRUCTURE AND GERMINATION OF SUGAR PINE (PINUS LAMBERTIANA DOUGL.)

The typical, irregular, delayed germination of sugar pine seeds was studied under different conditions of environment and seed dissection. Individual seeds showed a 3-phase pattern of water uptake which was obscured when average values for groups of seeds were used. Stratification at 5 C slowed the rate of imbibition as well as the growth rate, but when followed after 3 months by return to 20 C, germination was uniformly rapid. Complete removal of the seed coats yielded prompt germination without stratification. The thin layer of the inner coat was a critical factor. Slitting this layer indicated less significance for gas exchange or mechanical restraint than for a restriction upon the rate of water uptake. Regardless of the method of seed treatment, the visible stages of germination consistently occurred within well-defined levels of water uptake. The delicate balance between water entry and use as well as the internal distribution of water within seed components should be evaluated, rather than a mere expression of the total amount of water in a seed.     

Patterns of adenine metabolism and caffeine biosynthesis in different parts of tea seedlings

Contents of purine alkaloids in different parts of tea ( Camellia sinensis L. cv. Yabukita ) seedlings, seeds and tissue cultures were determined with high-performance liquid chromatography. More than 99% of the caffeine detected was in the leaves of the 4-month-old seedlings. The amount expressed per g fresh weight was higher in older leaves. Theobromine, a precursor of caffeine biosynthesis, was found only in younger leaves. Zero or only trace amounts of theophylline, a degradation product of caffeine, were found in the seedlings. Almost all the caffeine in tea seeds was found in the seed coats. Theobromine and theophilline could not be detected in any part of the seeds.
Tracer experiments using [8-¹⁴C]-adenine indicate that (i) caffeine biosynthesis from [8-¹⁴C]-adenine occurs only in younger leaves,(ii) "salvage" of [8-¹⁴C]-adenine for nucleic acid synthesis takes place in all parts of the seedlings, (iii) considerable degradation of [8-¹⁴C]-adenine by conventional purine degradation pathway via uric acid takes place in roots and lower parts of stem tissue.
The results strongly suggest that caffeine is synthesized in younger leaves and accumulated within the leaves. Both caffeine contents and its synthetic activity from adenine were extremely low in tissue culture of tea.     

A Seed Coat Bedding Assay to Genetically Explore In Vitro How the Endosperm Controls Seed Germination in Arabidopsis thaliana

The Arabidopsis endosperm consists of a single cell layer surrounding the mature embryo and playing an essential role to prevent the germination of dormant seeds or that of nondormant seeds irradiated by a far red (FR) light pulse. In order to further gain insight into the molecular genetic mechanisms underlying the germination repressive activity exerted by the endosperm, a "seed coat bedding" assay (SCBA) was devised. The SCBA is a dissection procedure physically separating seed coats and embryos from seeds, which allows monitoring the growth of embryos on an underlying layer of seed coats. Remarkably, the SCBA reconstitutes the germination repressive activities of the seed coat in the context of seed dormancy and FR-dependent control of seed germination. Since the SCBA allows the combinatorial use of dormant, nondormant and genetically modified seed coat and embryonic materials, the genetic pathways controlling germination and specifically operating in the endosperm and embryo can be dissected. Here we detail the procedure to assemble a SCBA.