Effect of Barbiturates on Rice Seedling Germination and Developmental Behaviour

Rice seedling germination and developmental behaviour were examinedin the presence of six different barbituric acid derivatives.The relationship between liquid/aqueous partition coefficientsof barbiturates and their interference with, but not completeinhibition of, normal mitochondria1 oxidative metabolism observedin animal mitochondria in vitro also appear to be factors influencingthe effects of these compounds on the germination and developmentalbehaviour of the rice seedlings described in this investigation.Evidence is presented here which points to normal oxidativemetabolism as being a necessary requisite for normal light responseand normal morphogenetic development in germinating rice seedlings.     

Mitotic activity in rice seedlings germinating under oxygen deficiency.

Rice seedlings germinating in oxygen-deficient environments do not manifest visual evidence of seminal or adventitious root growth or normal leaf growth, the coleoptile being the only seedling structure to emerge under these environmental conditions. Microscopic evidence, however, shows that mitotic activity occurs in the different tissues comprising the shoots of the seedlings germinating under oxygen deficiency. Thus evidence is presented here which shows that mitotic activity in rice seedlings germinating in oxygen-deficient environments is not confined solely to the emerging coleoptiles of the germinating seedlings.     

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.     

Oxygen as an Enviromnental Factor in Influencing Normal Morphogenetic Development in Germinating Rice Seedlings

Rice seedlings germinated in the dark in O₂-deficient and normalair environments manifest dimorphism and are designated hereas d^– and d⁺ plants. Both d^– and d⁺ seedlings lackchlorophyll but the d^– plants are stark-white whereasthe d⁺ plants are yellow or yellow-green in appearance. Riceseedlings germinated in the light under O₂ deficiency also lackchlorophyll and manifest the same developmental characteristicsas the d^– dark-germinated seedlings. Thus, in an O₂-deficientenvironment, light-germinated rice seedlings behave as thoughthey were germinated in the dark under O₂ deficiency. Exposureof the dark-germinated d^– and d⁺ seedlings and the light-germinatedd^– seedlings to normal air in the light brings about chlorophyllformation and normal morphogenetic development in all threetypes of germinating seedlings. Thus O₂ exerts a critical influenceon the response of germinating rice seedlings to light energywith respect to their normal morphogenetic development.     

Expression of 3-hydroxy-3-methylglutaryl coenzyme A reductase activity in maize tissues

The activity of the enzyme 3-hydroxy-3-methlglutaryl-coenzyme A reductase (HMGR, EC 1.1.1.34) is highly expressed in 4-day-old etiolated seedlings of normal (cv. DeKalb XL72AA), dwarf ( d ₅) and albino ( lw ₃) maize ( Zea mays L.). HMGR activity of maize seedlings appeared to be exclusively associated with the microsomal rather than the plastidic fraction of maize cells. Maize tissues with high meristematic activity such as germinating seeds, leaf bases, root tips and the site of origin of lateral roots contained high levels of microsomal HMGR activity. The activity of HMGR extracted from leaf tips of normal, dwarf and albino maize seedlings is regulated by light. Microsomal HMGR activity from leaf tips of 4-day-old maize seedlings was inhibited significantly following exposure to strong light (600 μmol m⁻² s⁻¹) for more than 10 h. By comparison, microsomal HMGR activity from leaf bases and root tips of maize was not inhibited by exposure to strong light. These results suggest that the microsomal HMGR which is highly expressed in maize may be related to sterol biosynthesis and membrane biogenesis rather than plastidic-associated isoprenoid synthesis and that light may regulate HMGR activity indirectly by increasing cell differentiation.     

Infection of tomato roots using callii of broomrape

Parasitic weeds like members of the genera Orobanche and Striga cause heavy damage to grain, vegetables and other field crops. The germinating seedlings of the parasites attack the roots of their hosts, following a series of recognition events that control germination, seedling growth and attachment to the host root. An in vitro system has been developed that allows the production of partially differentiated callii of Orobanche aegyptiaca Pers. Protrusions of subcultures of these callii behaved like radicles of germinating seeds. Using this system normal infection of tomato roots was obtained in vitro. The infection process included haustorium formation and the development of young Orobanche plants under aseptic conditions. The system developed should now permit a study of biochemical events during infection of the host by Orobanche .     

Environmental Anoxia is Unnecessary for Inhibiting Chloroplast Photomorphogenesis in Rice Coleoptiles (Oryza sativa L.)

High population densities of germinating rice seedlings in initiallyair-saturated sealed aquatic environments exhibited d^–seedling growth consisting solely of coleoptile emergence inlight and dark environments. Residual oxygen tensions of 17–23%of the initially air-saturated water containing the d^–seedlings were evident after 15 d in both the light and dark.Coleoptiles of all d^– seedlings were stark white in appearance,lacked protochlorophyllide, and contained proplastids and amyloplasts,there being no evidence of normal etioplast development in thelight or dark and no chloroplast development in the light. Thus,complete environmental anoxia was observed to be unnecessaryfor inhibiting normal chloroplast photomorphogenesis in coleoptilesof light-germinated rice seedlings. Increasing the oxygen tensionsof the 15-d-old aquatic environments of light- and dark-germinatedd^– seedlings placed in the light resulted in normal chloroplastphotomorphogenesis in coleoptiles, shoots, and roots. Key words: Oryza sativa, environmental anoxia, chloroplast photomorphogenesis, rice coleoptiles     

Enhanced attachment of Bradyrhizobium japonicum to soybean through reduced root colonization of internally seedborne microorganisms

Internally seedborne microorganisms are those surviving common surface sterilization procedures. Such microbes often colonize the radicle surface of a germinating soybean (Glycine max) seed, introducing an undefined parameter into studies on attachment and infection by Bradyrhizobium japonicum. Bacterial isolates from surface-sterilized soybean seed, cv. Williams 82 and cv. Maverick, used in our studies, were identified as Agrobacterium radiobacter, Aeromonas sp., Bacillus spp., Chryseomonas luteola, Flavimonas oryzihabitans, and Sphingomonas paucimobilis. Growth of these microbes during seed germination was reduced by treating germinating seeds with 500 micrograms/mL penicillin G. The effects of this antibiotic on seedling development and on B. japonicum 2143 attachment, nodulation, and nitrogen fixation are reported here. Penicillin G treatment of seeds did not reduce seed germination or root tip growth, or affect seedling development. No differences in nodulation kinetics, nitrogen fixation onset or rates were observed. However, the number of B. japonicum attached to treated intact seedlings was enhanced 200-325%, demonstrating that other root-colonizing bacteria can interfere with rhizobial attachment. Penicillin G treatment of soybean seedlings can be used to reduce the root colonizing microbes, which introduce an undefined parameter into studies of attachment of B. japonicum to the soybean root, without affecting plant development.     

The development of isocitric lyase activity in germinating cotton seed

In cotyledons of germinating cotton (Gossypium hirsutum L. var. Stoneville 213) seedlings, in the dark, isocitric lyase (EC 4.1.3.1) activity peaks after 2 days and thereafter slowly declines to a negligible value after 8 days. The maximum activity of this enzyme in cotyledons of 2-day-old seedlings was 16.2 μmoles of glyoxylate formed/15 min·10 cotyledon pairs. Actinomycin D at a concentration of 10 μg/ml, if added to the imbibing solution, completely prevents the development of isocitric lyase activity in these germinating seed. In cotyledons of germinating cotton seedlings, in the light, isocitric lyase activity peaks after 2 to 3 days and sharply declines to a negligible value after 4 days. The maximum activity of this enzyme in cotyledons of 2- to 3-day-old seedlings was 13.2 μmoles of glyoxylate formed/15 min·10 cotyledon pairs. Actinomycin D at a concentration of 10 μg/ml, if added to the imbibing solution, severely inhibits the development of enzyme activity.     

Shoot-derived auxin is essential for early lateral root emergence in Arabidopsis seedlings

Lateral root formation is profoundly affected by auxins. Here we present data which indicate that light influences the formation of indole-3-acetic acid (IAA) in germinating Arabidopsis seedlings. IAA transported from the developing leaves to the root system is detectable as a short-lived pulse in the roots and is required for the emergence of the lateral root primordia (LRP) during early seedling development. LRP emergence is inhibited by the removal of apical tissues prior to detection of the IAA pulse in the root, but this treatment has minimal effects on LRP initiation. Our results identify the first developing true leaves as the most likely source for the IAA required for the first emergence of the LRP, as removal of cotyledons has only a minor effect on LRP emergence in contrast to removal of the leaves. A basipetal IAA concentration gradient with high levels of IAA in the root tip appears to control LRP initiation, in contrast to their emergence. A significant increase in the ability of the root system to synthesize IAA is observed 10 days after germination, and this in turn is reflected in the reduced dependence of the lateral root emergence on aerial tissue-derived auxin at this stage. We propose a model for lateral root formation during early seedling development that can be divided into two phases: (i) an LRP initiation phase dependent on a root tip-localized IAA source, and (ii) an LRP emergence phase dependent on leaf-derived IAA up to 10 days after germination.     

光质对番茄和莴苣幼苗生长及叶绿体超微结构的影响

采用发光二极管(LED)精确调制不同光谱能量分布,以荧光灯光照为对照,研究光质对番茄和莴苣幼苗生长及叶绿体超微结构的影响.结果表明：红光下番茄、莴苣幼苗的可溶性糖、淀粉和碳水化合物含量均显著高于对照,叶片叶绿体中淀粉粒膨大显著;蓝光极显著抑制了番茄下胚轴伸长,显著提高了莴苣和番茄幼苗叶片叶绿素a和类胡萝卜素含量;红蓝光下莴苣幼苗叶片的可溶性糖、淀粉、碳水化合物、蔗糖含量和C/N均达到最大值且显著高于红光处理,番茄和莴苣幼苗的主根显著伸长,幼苗叶片中叶绿体形态正常,基粒增多,基质片层清晰,淀粉粒体积明显小于红光处理.光质对植物幼苗的光形态建成、生长、碳氮代谢及叶绿体发育有显著影响;红光下光合产物积累显著但运输受阻严重,在红光中添加适量蓝光更有利于莴苣幼苗的碳水化合物积累,并可促进幼苗根系生长,有利于同化产物输出.     

A light-independent developmental mechanism potentiates flavonoid gene expression in Arabidopsis seedlings

Throughout the plant kingdom expression of the flavonoid biosynthetic pathway is precisely regulated in response to developmental signals, nutrient status, and environmental stimuli such as light, heat and pathogen attack. Previously we showed that, in developing Arabidopsis seedlings, flavonoid genes are transiently expressed during germination in a light-dependent manner, with maximal mRNA levels occurring in 3-day-old seedlings. Here we describe the relationship between developmental and environmental regulation of flavonoid biosynthesis by examining phenylalanine ammonia-lyase (PAL), chalcone synthase (CHS), chalcone isomerase (CHI), and dihydroflavonol reductase (DFR) mRNA levels in germinating Arabidopsis seedlings as a function of light, developmental stage and temperature. We show that seedlings exhibit a transient potential for induction of these four genes, which is distinct from that observed for chlorophyll a/b-binding protein (CAB). The potential for flavonoid gene induction was similar in seedlings grown in darkness and red light, indicating that induction potential is not linked to cotyledon expansion or the development of photosynthetic capacity. The evidence for metabolic regulation of flavonoid genes during seedling development is discussed.     

Exudation of fluorescent beta-carbolines from Oxalis tuberosa L roots

Root fluorescence is a phenomenon in which roots of seedlings fluoresce when irradiated with ultraviolet (UV) light. Soybean (Glycine max) and rye grass (Elymus glaucus) are the only plant species that have been reported to exhibit this occurrence in germinating seedling roots. The trait has been useful as a marker in genetic, tissue culture and diversity studies, and has facilitated selection of plants for breeding purposes. However, the biological significance of this occurrence in plants and other organisms is unknown. Here we report that the Andean tuber crop species Oxalis tuberosa, known as oca in the highlands of South America, secretes a fluorescent compound as part of its root exudates. The main fluorescent compounds were characterized as harmine (7-methoxy-1-methyl-beta-carboline) and harmaline (3, 4-dihydroharmine). We also detected endogenous root fluorescence in other plant species, including Arabidopsis thaliana and Phytolacca americana, a possible indication that this phenomenon is widespread within the plant kingdom.     

不同比例红蓝光对番茄幼苗生长和光合作用的影响

为了探索番茄幼苗生长发育对红蓝组合光的响应机制,本试验采用发光二极管(LED)精量调制光源,以番茄品种‘SV0313TG’为试材,设红光(R)、蓝光(B)和红蓝组合光(9R1B、6R1B、3R1B、1R1B、1R3B)7个处理,以白光为对照,研究不同比例红蓝光质对番茄幼苗生长、光合色素含量、光合特性、叶绿素荧光参数及根系活力的影响.结果表明:不同比例红蓝光质处理对番茄幼苗生长的影响具有明显差异.红光显著促进幼苗株高增加,比叶面积增大,胞间CO₂浓度提高,但PSⅡ最大光化学效率(F_v/F_m)、PSⅡ实际光化学效率(Ф_PSⅡ)降低,根系生长受阻,根系活力下降,壮苗指数降低;蓝光下幼苗生长受到明显抑制,叶绿素含量降低,但叶绿素a/b 值升高;红蓝组合光有利于番茄幼苗的生长发育,3R1B处理下植株干物质量、叶绿素含量和光合性能均显著提高,幼苗生长健壮,壮苗指数最大.综上,红蓝组合光能够增加番茄幼苗叶片光合色素含量,提高光合效率,促进植株生长,尤以3R1B处理最佳.     

The impact of tocochromanols on early seedling development and NO release

Plant seeds and fruits are the main source for tocochromanols (tocopherols and tocotrienols) collectively known as Vitamin E in human nutrition. Seeds are particularly rich in gamma-tocopherol. The reason for the abundance of gamma-tocopherol in seeds is not yet clear. We analysed the influence of endogenous gamma-tocopherols on early development of seedlings from various barley cultivars. For this purpose progression of seedling development was monitored by the mean root length 48 h after imbibition. Our observations suggest that endogenous gamma-tocopherol has a negative impact on seedling development by controlling germination and postgermination events. We propose that gamma-tocopherol exerts its influence on seedling development by controlling the content of nitric oxide (NO) in germinating seeds.     

Endogenous Development of Adventitious Root Primordia in Lettuce Hypocotyls

Rudimentary adventitious root primordia were observed in optically-sectionedFeulgen-stained hypocotyls of 8-d-old lettuce seedlings germinatedin the dark and in a low light intensity environment. It issuggested that formation of these primordia may represent anaspect of normal development in the seedling. Adventitious, root primordia, hypocotyls, lettuce, Lactuca sativa     

Dark-induced and organ-specific expression of two asparagine synthetase genes in Pisum sativum.

Nucleotide sequence analysis of cDNAs for asparagine synthetase (AS) of Pisum sativum has uncovered two distinct AS mRNAs (AS1 and AS2) encoding polypeptides that are highly homologous to the human AS enzyme. The amino-terminal residues of both AS1 and AS2 polypeptides are identical to the glutamine-binding domain of the human AS enzyme, indicating that the full-length AS1 and AS2 cDNAs encode glutamine-dependent AS enzymes. Analysis of nuclear DNA shows that AS1 and AS2 are each encoded by single genes in P.sativum. Gene-specific Northern blot analysis reveals that dark treatment induces high-level accumulation of AS1 mRNA in leaves, while light treatment represses this effect as much as 30-fold. Moreover, the dark-induced accumulation of AS1 mRNA was shown to be a phytochrome-mediated response. Both AS1 and AS2 mRNAs also accumulate to high levels in cotyledons of germinating seedlings and in nitrogen-fixing root nodules. These patterns of AS gene expression correlate well with the physiological role of asparagine as a nitrogen transport amino acid during plant development.