Polyamine metabolism during seedling development in rice

The main free amines identified during growth and development of rice seedlings were agmatine, putrescine, spermidine, diaminopropane and tyramine. Amine composition differed according to tissue and stages of development. Conjugated amines were only found in roots. We present evidence that arginine decarboxylase (ADC) regulates putrescine during the development of rice seedlings. When ADC action was blocked by DFMA (-DL-difluoromethylarginine, a specific irreversible inhibitor of ADC), polyamine titers and seedling development were diminished; when agmatine or putrescine was added, normal polyamine titers and growth were restored. The effects of DFMA were concentration dependent. DFMO (-DL-difluoromethylornithine, a specific irreversible inhibitor of ornithine decarboxylase or ODC) promoted growth and development at concentrations below 2 mM. This effect was probably related to its unexplained, but consistently observed slight enhancement of rice ADC. When the increase in the concentration of spermidine was prevented by CHA (cyclohexylammonium sulfate), the number of roots increased and the increase in length of leaves and roots was strongly inhibited. The addition of exogenous spermidine at the time of treatment with CHA reversed the inhibition by CHA.Abbreviations ADC arginine decarboxylase - ODC ornithine decarboxylase - DFMA -DL-difluoromethylarginine - DFMO -DL-difluoromethylornithine - CHA cyclohexylammonium sulfate     

One-carbon metabolism during the menstrual cycle and pregnancy

Many enzymes in one-carbon metabolism (OCM) are up- or down-regulated by the sex hormones which vary diurnally and throughout the menstrual cycle. During pregnancy, estradiol and progesterone levels increase tremendously to modulate physiological changes in the reproductive system. In this work, we extend and improve an existing mathematical model of hepatic OCM to understand the dynamic metabolic changes that happen during the menstrual cycle and pregnancy due to estradiol variation. In particular, we add the polyamine drain on S-adenosyl methionine and the direct effects of estradiol on the enzymes cystathionine β-synthase (CBS), thymidylate synthase (TS), and dihydrofolate reductase (DHFR). We show that the homocysteine concentration varies inversely with estradiol concentration, discuss the fluctuations in 14 other one-carbon metabolites and velocities throughout the menstrual cycle, and draw comparisons with the literature. We then use the model to study the effects of vitamin B₁₂, vitamin B₆, and folate deficiencies and explain why homocysteine is not a good biomarker for vitamin deficiencies. Additionally, we compute homocysteine throughout pregnancy, and compare the results with experimental data. Our mathematical model explains how numerous homeostatic mechanisms in OCM function and provides new insights into how homocysteine and its deleterious effects are influenced by estradiol. The mathematical model can be used by others for further in silico experiments on changes in one-carbon metabolism during the menstrual cycle and pregnancy.     

Regulation of seed germination and polarity in seedling development inOrobanche aegyptiaca by growth substances

InOrobanche aegyptiaca PEES. (Orobanchaceae) the mature seed is tiny and contains a subglobose embryo which is not differentiated into radicle, hypocotyl, plumule, and cotyledons. In aseptic seed cultures on medium TB supplemented with yeast extract or coconut milk, both roots and shoot originated from the morphological radicular pole of the embryo (monopolar pattern). The bipolar mode of seedling formation, that is a shoot originating from the plumular pole and roots from the radicular pole, ensued on the basal medium THS and on TB supplemented with certain concentrations of IAA, kinetin, GA3, or strigol.     

Cell wall storage polysaccharides in cotyledons ofLupinus angustifolius L. II. Mobilization during germination and seedling development

Summary During germination and early seedling development, cotyledons of seeds ofLupinus angustifolius were modified from thick-walled, fleshy storage organs to leaf-like, expanded photosynthetic organs by the controlled collapse of groups of mesophyll cells.Cotyledon cell walls of imbibed seeds are PAS-negative, have a strong affinity for calcofluor, and a dense fibrillar ultrastructure. The first visible sign of the mobilization of cell wall polysaccharides occurs 5 days after imbibition, with the appearance of PAS-positive maculae in ordered rows on the inner surface of the thickened walls. These correspond in orientation and frequency with the folds and radial striations found in walls of mature seeds, and with areas with poor affinity for calcofluor. In the electron microscope, the maculae appear as electron-lucent, wedge-shaped areas of loosely-arranged fibrils which, as germination proceeds, spread throughout the walls. The evidence suggests that storage polysaccharides are mobilized from the matrix of the walls by the action of hydrolytic enzymes leaving a framework of structural components, and not by the erosion of cracks and fissures.Most of the experimental work was carried out at the former ARC Unit of Development Botany, Cambridge.     

Specificity of fungal associations of Pyroleae and Monotropa hypopitys during germination and seedling development

Mycoheterotrophic plants obtain organic carbon from associated mycorrhizal fungi, fully or partially. Angiosperms with this form of nutrition possess exceptionally small ‘dust seeds’ which after germination develop ‘seedlings’ that remain subterranean for several years, fully dependent on fungi for supply of carbon. Mycoheterotrophs which as adults have photosynthesis thus develop from full to partial mycoheterotrophy, or autotrophy, during ontogeny. Mycoheterotrophic plants may represent a gradient of variation in a parasitism–mutualism continuum, both among and within species. Previous studies on plant–fungal associations in mycoheterotrophs have focused on either germination or the adult life stages of the plant. Much less is known about the fungal associations during development of the subterranean seedlings. We investigated germination and seedling development and the diversity of fungi associated with germinating seeds and subterranean seedlings (juveniles) in five Monotropoideae (Ericaceae) species, the full mycoheterotroph Monotropa hypopitys and the putatively partial mycoheterotrophs Pyrola chlorantha, P. rotundifolia, Moneses uniflora and Chimaphila umbellata. Seedlings retrieved from seed sowing experiments in the field were used to examine diversity of fungal associates, using pyrosequencing analysis of ITS2 region for fungal identification. The investigated species varied with regard to germination, seedling development and diversity of associated fungi during juvenile ontogeny. Results suggest that fungal host specificity increases during juvenile ontogeny, most pronounced in the fully mycoheterotrophic species, but a narrowing of fungal associates was found also in two partially mycoheterotrophic species. We suggest that variation in specificity of associated fungi during seedling ontogeny in mycoheterotrophs represents ongoing evolution along a parasitism–mutualism continuum.     

Pyruvate metabolism in mitochondria from cucumber cotyledons during early seedling development

Mitochondria were isolated from cucumber cotyledons during earlyseedling growth, and their capacity for pyruvate metabolisminvestigated. The rate of pyruvate oxidation was low. Evidenceis presented that suggests that this is due to low activitiesof the pyruvate transporter. Key words: Cotyledon, cucumber, germination, pyruvate oxidation     

Response of adenine and pyridine metabolism during germination and early seedling growth under arsenic stress in Brassica juncea

Adenine and pyridine nucleotides play vital roles in virtually all aspects of plant growth. This study analyzed the response of adenine and pyridine metabolism during germination and early seedling growth (ESG) of Brassica juncea exposed to two doses of arsenate (AsV), 100 and 250 μM, having non-significant or significant inhibitory effects, respectively, on germination and ESG. The ratio of NAD/NADP and NAD/NADH showed no significant change in control and 100 μM AsV, but increased significantly at 250 μM AsV during initial 24 h and also at 7th day. The activity of enzymes of NAD metabolism, viz. NAD kinase, NADP phosphatase, nicotinamidase and poly(ADP-ribose) polymerases showed significant change mostly at 250 μM AsV. Further, significant decrease was observed in the ratio of ATP/ADP and in the activities of adenylate kinase and apyrase at 250 μM AsV at 7th day. External supply of ATP (1 mM) to 100 and 250 μM AsV significantly improved germination percentage and germination strength of the seeds as compared to AsV treatments alone. The study concludes that with the increase in concentration of AsV, the balance of NAD/NADP, NAD/NADH and ATP/ADP and the activities of enzymes of adenine and pyridine metabolism were significantly altered and that these changes may be responsible for inhibitory effects of AsV on germination and ESG.     

Ureide metabolism during seedling development in French bean (Phaseolus vulgaris)

French bean ( Phaseolus vulgaris ) is a legume that transports most of the atmospheric nitrogen fixed in its nodules to the aerial parts of the plant as ureides. Changes in ureide content and in enzymatic activities involved in their metabolism were identified in the cotyledons and embryonic axes during germination and early seedling development. Accumulation of ureides (ca. 1300 nmol per pair of cotyledons) was observed in the cotyledons of dry seeds. Throughout germination, the total amount of ureides slightly decreased to about 1200 nmol, but increased both in cotyledons and in embryonic axes after radicle emergence. In the axes, the ureides were almost equally distributed in roots, hypocotyls and epicotyls. The pattern of ureide distribution was not affected by the presence of nitrate or sucrose in the media up to 6 days after imbibition. Ureides are synthesized from purines because allopurinol (a xanthine dehydrogenase inhibitor) blocks the increase of ureides. Allantoin and allantoate-degrading activities were detected in French bean dried seeds, whereas no ureidoglycolate-degrading activity was detected. During germination, the levels of the three activities remain unchanged in cotyledons. After radicle emergence, the levels of activities in cotyledons changed. Allantoin-degrading activity increased, allantoate-degrading activity decreased and ureidoglycolate-degrading activity remained undetectable in cotyledons. In developing embryonic axes, the three activities were detected throughout germination and early seedling development. The embryonic axes are able to synthesize ureides, because those compounds accumulated in axes without cotyledons.     

Biochemical changes during germination and seedling growth in Cuscuta campestris

Changes in the contents of starch, protein, DNA, RNA, total phosphorus, acid soluble phosphorus and inorganic phosphorus, and in the activities of some enzymes of carbohydrate, amino acid, nucleic acid and phosphate metabolism were studied during the germination of Cuscuta campestris seeds. The results are expressed on per seed basis.
Starch content in Cuscuta seeds showed a steady decline with most of it depleted by the end of the eighth day of germination. Protein content increased with germination up to 48 h and then decreased. RNA and DNA contents increased to a maximal level on the fourth day of germination and then decreased. Total phosphorus in the seeds remained almost unchanged during the period of study. Both trichloroacetic acid soluble and inorganic phosphorus increased until the third day and then decreased. Phytin was rapidly hydrolyzed with little being detectable by the seventh day of germination. Glucose-6-phosphate dehydrogenase increased with germination, while fructose bisphosphate aldolase which is indispensable for glycolysis, decreased with germination. Ribonuclease and deoxyribonuclease increased till the third and fourth day, respectively, and then decreased. Aspartate and alanine aminotransferases showed a maximum on the second day and then decreased. Activities of alkaline fructose-1,6-bisphosphatase and phytase were absent in the dry seeds and appeared only on the second day of germination. Both α- and β-amylase activities were present in the dry seed.     

Thioredoxin h overexpressed in barley seeds enhances selenite resistance and uptake during germination and early seedling development

The uptake, distribution and metabolism of selenite were examined in germinating homozygous barley (Hordeum vulgare L.) grain with thioredoxin h overexpressed in starchy endosperm. Results were related to the null segregant in which the transgene had segregated out during crossing. Compared with the null segregant, the homozygote showed enhanced germination and root and shoot growth in the presence of 1 and 2 mM sodium selenite. The rate of incorporation of selenite by the homozygote was approximately twice that of the null segregant. Based on X-ray absorption spectroscopy, the major products in both cases were selenomethionine-like species and the red, monoclinic form of elemental selenium, a derivative not previously reported in green plants. Selenite and selenate made up the balance. The distribution of the products formed differed as to the tissue — root, shoot, aleurone, endosperm — but the ratios were similar in the homozygote and null segregant. The results provide evidence that, in addition to the accelerated germination observed previously in water, barley grain overexpressing thioredoxin h are resistant to the inhibitory effects of selenite. These properties raise the possibility that plants overexpressing thioredoxin h could find application in the remediation of polluted environments.     

RNA synthesis during spore germination in Bacillus subtilis.

Summary We have analyzed the RNA synthesized during spore germination in Bacillus subtilis. Early in germination there is little incorporation of [³H]uridine into RNA. A large increase in incorporation into RNA was found at 45–60 min into germination which was in part due to increases in the specific activity of the UTP pool. When corrected for specific activity changes, the instantaneous rate of RNA synthesis showed a seven to tenfold increase between 30 and 45 min of germination. Polyacrylamide gel electrophoresis studies showed that the RNA synthesized during germination appeared very similar to the RNA made during vegetative growth. DNA-RNA hybridization studies indicated that mRNA and rRNA were synthesized throughout germination. Their relative proportions remained constant and were very similar to the composition of RNA synthesized during vegetative growth.In partial fulfillment of the requirements for the doctoral degree by A.S. in the Department of Microbiology at the New York University School of Medicine     

The role of the sucrose transporter, OsSUT1, in germination and early seedling growth and development of rice plants

Using expression analysis, the role of the sucrose transporter OsSUT1 during germination and early growth of rice seedlings has been examined in detail, over a time-course ranging from 1 d to 7 d post-imbibition. Unlike the wheat orthologue, TaSUT1, which is thought to be directly involved in sugar transfer across the scutellar epithelium, OsSUT1 is not expressed in the scutellar epithelial cell layer of germinating rice and is, therefore, not involved in transport of sugars across the symplastic discontinuity between the endosperm and the embryo. OsSUT1 expression was also absent from the aleurone cells, indicating it is not involved in the transport of sucrose in this cell layer during germination. However, by 3 d post-imbibition, OsSUT1 was present in the companion cells and sieve elements of the scutellar vascular bundle, where it may play a role in phloem loading of sucrose for transport to the developing shoot and roots. This sucrose is most likely sourced from hexoses imported from the endosperm. In addition, sucrose may be remobilized from starch granules which are present at a high density in the scutellar ground tissues surrounding the vasculature and at the base of the shoot. OsSUT1 was also present in the coleoptile and the first and second leaf blades, where it was localized to the phloem along the entire length of these tissues, and was also present within the phloem of the primary roots. OsSUT1 may be involved in retrieval of sugars from the apoplasm in these tissues.