The presence of two types of beta-cyanoalanine synthase in germinating seeds and their responses to ethylene (original) (raw)
Related papers
Plant and Cell Physiology, 1996
Nitrogenous inhibitors of respiration, namely, KCN, NaN 3 and NH 2 OH, which promote the germination of cocklebur {Xanthium pennsylvaniicum Wallr.) seeds, enhanced the accumulation of cyanogenic compounds. Urea and cyanamide, which were ineffective, did not. Part of the exogenously applied KCN was converted to cyanogenic glycosides and lipids, but these compounds were only produced at low levels in NaN 3-treated seeds. Exposure to NH 2 OH caused a slight accumulation of both types of cyanogenic compounds. Thiourea, effective in stimulating germination, did not increase the cyanogenic compounds, which suggests that the mechanism of its effect on germination is different from that of other nitrogenous compounds. Thiocyanate had a slightly promotive effect and caused minor increases in the levels of cyanogenic compounds. Ethylene increased the metabolic utilization of the accumulated cyanogens in response to KCN or NaN 3. The response to ethylene of seeds in secondary dormancy was restored only after pre-treatment with KCN or NaN 3. The response occurred once the level of cyanogens had increased. By contrast, enhancement of the effects of KCN and NaN 3 on germination by propyl gallate or benzohydroxamate, inhibitors of CN-resistant respiration, was accompanied by the increased accumulation of cyanogens within the seeds that had been exposed to KCN or NaN 3 in combination with the other types of respiratory inhibitors. Thus, it is suggested that endogenous cyanogens might be involved in the germination of cocklebur seeds.
Promotion of Cocklebur Seed Germination by Allyl, Sulfur and Cyanogenic Compounds
Plant and Cell Physiology, 1996
The effects of allyl, sulfur and cyanogenic compounds on the germination of upper cocklebur (Xanthium pennsylvanicum Wallr.) seeds were examined. Mercaptoethanol and methylmercaptan as well as KCN, substrates for pcyanoalanine synthase (CAS), and H 2 S and thiocyanate, the products of the CAS catalyzing reaction, were effective in promoting germination, suggesting the involvement of CAS in germination. Most of allyl compounds, especially allylthiourea, as well as ethylene which activated CAS [Hasegawa et al. (1994) Physiol. Plant. 91: 141], promoted the germination in an abnormal type which occurred by the predominant growth of cotyledons as did C 2 H 4 [Katoh and Esashi (1975) Plant Cell Physiol. 16: 687]. However, they failed to activate CAS unlike ethylene, and to liberate free ethylene during an incubation period. It was thus possible that an C 2 H 4-like double bond within allyl compounds can act to promote seed germination.
Agrociencia, 2008
The establishment and progress of the cell cycle are important events for the germination of seeds. In maize the auxins and the exogeniously added cytokinins stimulate the synthesis of DNA during the early hours of germination, and this effect depends, to a greater or lesser extent, on the presence of sucrose in the imbibition buffer. However, in the absence of exogeniously added hormones, the presence or absence of sucrose does not affect the synthesis of DNA at early or late times of germination. Therefore, the effect of the phytoregulators would be more related to the stimulation of a mitogenic action, than to the germinative process per se. When measuring the presence of specific proteins of the phases G1 and S of the cell cycle, in the presence of auxins, it was evident that markers of G1 such as the cyclins D2;1 and D4;1, or markers of the S phase such as cyclin A1 or PCNA, did not change their levels during germination. Besides, the levels of a marker of G1, the cyclin D5;2 and a marker of the S phase, the DNA polymerase a, increased visibly in response to the addition of auxins. This response and in particular that of DNA polymerase a, could explain the increase in the synthesis of DNA caused by the addition of auxins in embryonic axes during germination.
Plant and Cell Physiology, 1998
The activity of ^-cyanoalanine synthase (CAS, EC 4.4.1.9) in cotyledons of cocklebur seeds (Xanthium pennsylvanicum Wallr.) was detected both in the soluble and particulate fractions. The CAS activity of the soluble fraction (cytosolic CAS activity) was 10 times higher than that of the particulate fraction. The CAS activity of the particulate fraction was confirmed to be localized in the mitochondria. Both enzymatic activities were clearly separated by non-denaturing PAGE. The enzyme with cytosolic CAS activity has been extensively purified and separated into three different forms designated as cyt-1, cyt-2, and cyt-3. According to the SDS-PAGE analysis, the three enzymes are estimated to be a homodimer composed of 35-kDa subunits. The purified enzymes showed CS activity. Partial amino acid sequences of cyt-1 were determined and had a high homology with cysteine synthases (CS, EC 4.2.99.8) from other plant sources. The catalytic action of the purified CSs in converting cyanide and cysteine into H 2 S and ficyanoalanine was confirmed by the detection of significant M CN incorporation into /J-cyanoalanine. These results indicated that cytosolic CAS activity is due to cytosolic CS and suggested that the CAS activity of CS is likely to be involved in cyanide metabolism in plant tissues.
Development, Dormancy and Germination of Seeds Metabolism, Hormonal Control and Genetic Control
International Journal of Agriculture, Environment and Bioresearch, 2022
The seed is an important stage in the life cycle of higher plants, thus ensuring its survival. It is the plant's dispersal unit, which is able to survive the period between seed maturation and the establishment of the next generation as a seedling after germination. For this survival, the seed is mainly in a dry state, and well equipped to withstand long periods of adverse conditions. To optimize germination, the seed goes into a dormant state. Dormancy prevents germination before harvest. This seed dormancy allows the seeds to overcome unfavorable periods for seedlings. Several processes are known to be involved in the induction of dormancy and in the transition from dormant to germinal state. Many studies have been done to better understand how germination is controlled by various endogenous and exogenous factors. Thus, the biochemical and physiological factors linked to dormancy and the germination process as well as the role of phytohormones and genes involved in different tissues are described and discussed in this article.
2008
The aim of this study was to identify the genetical, biochemical, morphological and anatomical modifications induced by some biologically active substances with stimulator effect on Raphanus sativum L. seedlings, cultivated in laboratory conditions. There were tested three substances (caffeine, kinetine, 2, 4-dichlorophenoxyacetic acid) in concentrations recognized as producers of some functional effects in culture plants, as follows: modifications of cellular division (mitotic index and frequency of the appearance of chromosomal aberrations); the dynamic of the activity of oxidative enzymatic complex (superoxid dismutase, catalase, peroxidase) and the total protein content; morphoanatomical aspects regarding the germination process (biometric measurements and interpretations of the structure of seedling organs). The applied treatments influence, in generally, the entire process of seed germination and seedling ontogenesis (translated by the cytogenetical, morpho-anatomical and biochemical effects mentioned above), depending on the type and concentration of the utilized substance. The results of this study reveal the complexity of the metabolical transformations of the treated culture plants, whipping up to new explorations of some aspects of practical interest.
Possible involvement of volatile compounds in the after-ripening of cocklebur seeds
Physiologia Plantarum - PHYSIOL PLANT, 1994
The mechanism of emergence from primary dormancy, the process of after-ripening, in cocklebur (Xanthium pennsylvanicum) seeds was examined in relation to the involvement of volatile compounds and to the relative humidity (RH) in which the seeds were stored. The after-ripening of these seeds proceeds only at water contents between 7 and 14% which are conditioned under RHs of 33% to 53% and are identified with water-binding region II. After-ripening of cocklebur seeds occurred even in water-binding region I. imposed by 12% RH. when exposed to HCN gas during the storage period. Exposure of dormant seeds to acetaldehyde (ethanal) retarded after-ripening. even in water-binding region II. thus decreasing germinability. This decrease of germinability by ethanal was found also in the after-ripened seeds, suggesting that ethanal accelerates seed deterioration rather than retarding the after-ripening. The contents of ethanal. ethanal and HCN were high only in the dormant seeds held at 12% RH. Regardless of RH. a possible conversion of ethanal to ethanol. perhaps via alcohol dehydrogenase. was far larger in dormant than in non-dormant seeds. In contrast, the reverse conversion of ethanol to ethanal was more profound in non-dormant seeds. Pre-exposure of both types of seeds to HCN reduced the contents of both ethanal and ethanol at 12% RH. The contents of various adenylales including ATP in seed tissues were higher in dormant seeds stored at 12% RH than in non-dormant seeds after-ripened at 44% RH. It is suggested that emergence of cocklebur seeds from primary dormancy by HCN treatment at 12% RH may result from the reduction in the contents of ethanal via an unknown mechanism incurring the consumption of ATP. This implies involvement of volatile compound metabolism at the water-binding region II in the after-ripening process of cocklebur seeds.
The onset of cellular synthetic activity in roots of germinating corn
Experimental Cell Research, 1969
The onset of cellular synthetic activities in roots of the germinating corn embryo was studied by autoradiographic techniques. It was found that thymidine is exclusively incorporated in the cytoulasm during the first 33 h of germination. Later. thvmidine is also incornorated into the nuclei. Digestion controls show that <he incorporated thymidine-both cytoplasmic and nuclear-is in DNA. Combining a nulse of 3H-thvmidine and a long chase it was found that thvmidine which was incorporatedexclusively into cytoplasmic DNA-at the beginning of the "chasing" period is also incorporated into nuclear DNA at the end of this period. This and other results suggest that there is a moving of the cytoplasm-incorporated thymidine to the nucleus. SH-Uridine is exclusively incorporated in the chromatin at the beginning of the germination process. The chromatin-dependent RNA synthesis is the first recorded event during reactivation in roots of germinating corn. The resumption of RNA synthesis in the nucleolus and the first appearance of a cytoplasmic labeling after aH-uridine incorporation occur a few hours later.
Detection of auxinic compounds in germinated seeds
Revista de Ciencias Agrícolas, 2021
ryptophan (TRP) is a metabolite from which several important metabolic syntheses arise in plants, animals, and humans. In bacteria and fungi, it is a precursor of Indole Acetic acid (IAA) using various metabolic pathways. The objective of this study is the detection of intermediate metabolites in the synthesis of IAA in seeds of several species in the germination process. In the study, seeds of plant species grown in deionized water were placed in order to stimulate germination and samples were taken every 24 hours. High performance liquid chromatography (HPLC) was used for the detection of the compounds. The results show that the pH of the medium is altered and there is no pattern of behavior. Regarding the detected compounds, in addition to TRP, there is indole-3-acetamide (IAM), 3-indoleacetonitrile (IAN), tryptamine (TRM), which are part of the TRP-dependent routes, since they use this amino acid as a precursor. Anthranilic acid (AA) and kynurenine (KYN), which are part of the Independent TRP pathway, were also detected. IAA and TRP were also detected during the germination process of the studied seeds (Sorghum bicolor, T aesativum, Zea mayz, Phaseolus vulgaris, G. hirsutum, Cucurbita maxima). Finally, it was observed that the seeds, due to weight loss, suffer physical wear during the germination process, since there is a difference between the initial dry weight and the weight of the seeds at the end of the study.