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The expression patterns of β-1,3-glucanases (βGlu) and chitinases (Chn) were investigated during the seed germination of members of theCestroideae(threeNicotianaspecies,Petunia hybrida) and theSolanoideae(Capsicum annuum,Physalis peruviana) subgroups of Solanaceous species. Rupture of the micropylar testa (seed coat) and rupture of the micropylar endosperm, i.e. radicle emergence, were distinct and temporally separate events during the germination ofCestroideae-type seeds. βGlu accumulation in imbibedCestroideae-type seeds, occurring after testa rupture but prior to endosperm rupture, was inhibited by abscisic acid (ABA) and promoted by gibberellins (GA) and light, in strict association with germination, and appeared to be caused by transcriptional regulation of the class I βGlu genes. The micropylar cap ofSolanoideae-type seeds does not allow a distinction between testa and endosperm rupture, but βGlu accumulation occurred prior to radicle emergence of pepper andP. peruvianaseeds. ABA inhibited endosperm rupture and βGlu accumulation in the micropylar cap of pepper seeds. In contrast to tomato, βGlu accumulation in pepper seeds was not only confined to the micropylar cap, was due to distinct, tissue-specific βGlu isoforms, and was not accompanied by Chn accumulation. In conclusion, ABA inhibition of germination and βGlu accumulation in the micropylar endosperm appears to be a widespread event during the seed germination of Solanaceous species. In contrast, accumulation of Chn and distinct βGlu isoforms in the embryo, prior to germination, appears to be a species-specific phenomenon within theSolanaceae. In addition, a post-germination co-induction of βGlu and Chn in the root of the emerged seedling was found in endospermic and non-endospermic species and could represent an evolutionarily conserved event during dicot seedling development.

The Ca 2+ requirements of ethylene-dependent responses were investigated in germinating seeds of Pisum sativum L. using 1-aminocyclopropane-1-carboxylic acid (ACC) oxidase ( Ps-ACO1 ), ACC synthase ( Ps-ACS2 ) and class I b b b -1,3-glucanase as molecular markers. Ethylene biosynthesis and responsiveness are localized to the elongation and differentiation zones of the pea radicle. Ethylene treatment induced ectopic root hair formation in the cell elongation zone and promoted root hair elongation growth in the radicles of germinated seeds. Characterized Ca 2+ antagonists, including EGTA, lanthanum, verapamil, ruthenium red, W7, lithium and neomycin, were used to test for the involvement of the apoplastic and the intracellular Ca 2+ -pool, the

Class I β-1,3-glucanase (βGLU I) is transcriptionally induced in the micropylar endosperm just before its rupture prior to the germination (i.e. radicle emergence) of Nicotiana tabacum L. cv. ‘Havana 425’ seeds. Ethylene is involved in endosperm rupture and high-level βGLU I expression; but, it does not affect the spatial and temporal pattern of βGLU I expression. A promoter deletion analysis of the tobacco βGLU I B gene suggests that (1) the distal −1452 to −1193 region, which contains the positively acting ethylene-responsive element (ERE), is required for high-level, ethylene-sensitive expression, (2) the regions −1452 to −1193 and −402 to 0 contribute to down-regulation by abscisic acid (ABA), and (3) the region −402 to −211 is necessary and sufficient for low-level micropylar-endosperm-specific expression. Transcripts of the ERE-binding proteins (EREBPs) showed a novel pattern of expression during seed germination: light or gibberellin was required for EREBP-3 and EREBP-4 expression; EREBP-4 expression was constitutive and unaffected by ABA or ethylene; EREBP-3 showed transient induction just before endosperm rupture, which was earlier in ethylene-treated seeds and inhibited by ABA. No expression of EREBP-1 and EREBP-2 was detected. In contrast to βGLU I, EREBP-3 and EREBP-4 were not expressed specifically in the micropylar endosperm. The results suggest that transcriptional regulation of βGLU I could depend on: activation of ethylene signalling pathways acting via EREBP-3 with the ERE as the target, and ethylene-independent signalling pathways with targets in the proximal promoter region that are likely to determine spatial and temporal patterns of expression.

Highly sensitive kinetic studies of ethylene evolution in germinating seeds of pea (Pisum sativum L. cv Frijaune) and wheat (Triticum durum L. cv Appulo) using a laser-photoacoustic system indicated that C2H4 production started early after imbibition, and reached a maximum before mitotic activity, thus simultaneously with early radicle elongation. Most of this initial gas evolution originated from the embryonic tissue. Thereafter, a major increase in ethylene production occurred during early coleoptile growth in wheat whereas the rate of ethylene evolution tended to decrease in pea. Seed decoating, after previous imbibition at 5°C for 8 hr, accelerated germination and early root elongation of peas. Moreover, decoated peas exhibited a faster and synchronous increase in ethylene production. The results support the view that ethylene plays a regulatory role in seed germination and seedling growth pattern.

Contains fulltext : 34798pub.pdf (Publisher’s version ) (Closed access) Background and Aims The relationship between ethylene production and both seed dormancy and germination was investigated using red rice (weedy rice) as a model species. Methods Both fully dormant and after-ripened (non-dormant) naked caryopses were incubated with or without inhibitors of ethylene synthesis [aminoethoxyvinylglycine (AVG)] and perception [silver thiosulfate (STS)], or in the presence of the natural ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC). The kinetics of ethylene emissions were measured with a sensitive laser-photoacoustic system. Key Results Dormant red rice caryopses did not produce ethylene. In non-dormant caryopses, ethylene evolution never preceded the first visible stage of germination (pericarp splitting), and ethylene inhibitors completely blocked ethylene production, but not pericarp splitting. Accordingly, endogenous ACC appeared to be lacking before pericarp splitting. However, early seedling growth (radicle or coleoptile attaining the length of I mm) followed ethylene evolution and was delayed by the inhibitors, Wounding the dormant caryopses induced them to germinate and produce ethylene, but their germination was slow and pericarp splitting could be speeded up by ethylene. Conclusions The findings suggest that, in red rice, endogenous ethylene stimulates the growth of the nascent seedling, but does not affect seed dormancy or germination inception. Correspondingly, this phytohormone does not play a role in the dormancy breakage induced by wounding, but accelerates germination after such breakage has occurred.

The expression of beta-1,3-glucanase (betaGlu) and chitinase (Chn) was investigated in the testa, cotyledons, and embryonic axis of germinating Pisum sativum L. cv. 'Espresso generoso' seeds. High concentrations of betaGlu and Chn activity were found in the embryonic axis. Treatment with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornadiene showed that an early, 4-fold induction of betaGlu activity in the embryonic axis during the first 20 h after the start of imbibition is ethylene-independent. This initial increase was followed by a later 4-fold ethylene-dependent induction in the embryonic axis starting at 50 h, which is after the onset of ethylene evolution and after completion of radicle emergence. The betaGlu activity in cotyledons increased gradually throughout germination and was ethylene-independent. In contrast, the ethylene-independent Chn activity increased slightly after the onset of radical emergence in the embryonic axis and remained at a constant low level in cotyledons. Immunoinactivation assays and immunoblot analyses suggest that early betaGlu activity in the embryonic axis is due to a 54-kDa antigen, whereas late induction is due to a 34.5-kDa antigen, which is likely to be the ethylene-inducible class I betaGlu G2 described for immature pea pods. Increases in Chn in the embryonic axis were correlated with a 26-kDa antigen, whereas amounts of the additional 32- and 20-kDa antigens remained roughly constant. Thus, ethylene-dependent and ethylene-independent pathways regulate betaGlu and Chn during pea seed germination. The pattern of regulation differs from that of leaves and immature pods, and from that described for germinating tobacco seeds. The functional significance of this regulation and its underlying mechanisms are discussed.

The photoacoustic detection method for trace gases in the atmosphere is well developed towards very low limits of detection, in the last years. Due to the combination of a sensitive photoacoustic cell placed intracavity in an infrared CO2 laser we were able to detect C2H4 at ultralow (< 1:1011) concentrations within 10 seconds, C2H4 in a plant hormone which seems to play an important role throughout all the life stages of a plant, including seed germination. In addition, various types of stress have been reported to promote ethylene production from different plant tissues. As part of our ongoing research on the role of ethylene in seed germination, we have compared our laser photoacoustic set-up to a gaschromatograph for measuring C2H4 produced by germinating Pisum sativum L. seeds within the first days of imbibition. C2H4 evolution by intact seeds shows a maximum at about 25 hours of germination. Thereafter, the rate of ethylene measured by gaschromatograph continues to decrease while that measured by the laser-driven photoacoustic system shows further increases. Most of the ethylene produced by seeds is found in isolated embryonic axes. The fumigation with ozone affects the growth of seedlings and their ethylene evolution.© (1993) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A study has been made to identify the contribution of senescent changes occurring in embryonic and non-embryonic (endosperm and aleurone layer) tissues on germination of wheat (Triticum durum L. cv. Appulo) seed lots of 97, 93 and 70% viability. Measurements of germination and rates of macromolecular synthesis of embryos excised from dry seeds showed that as seed viability declined from 97 to ca 93%, there was a decrease in the capacity of embryos to grow and synthesise protein, RNA and DNA. However, no significant differences were observed between embryos from 93 and 70% viability seed stocks. Changes in nutrients, fresh and dry weights of embryonic and non-embryonic tissues and electrophoretic patterns of endosperm proteins by sodium dodecyl-sulfate polyacrylamide gel electrophoresis showed a reduced mobilisation of reserve material in 70%-viable seeds. α-Amylase (EC 3.2.1.1) production was also decreased. It is suggested that alterations occurring in non-embryonic structures play a significant role in seed viability loss. This role might be mediated by failing nutrient supply, but the involvement of some inhibitor or toxic substance is also possible.

lt is now that semolina made from different wheat varieties produces spaghetti of widely different cooking quality. On the basis of chemical and physical parameters of wheat and semolina, it has been established that among the factors regarded as possibly responsible for spaghetti cooking quality, the protein content and gluten quality are two very important factors relating to pasta cooking quality. Wheat proteolytic enzymes are generally believed to be too low to affect the quality of doughs by alteration of gluten proteins. On the other hand, it is well known that proteolytic enzymes are poorly soluble in common buffers, difficult to extract and able to change the physical characteristics of gluten proteins if present in small amounts. It has been attempted also to relate BAPA-ase, the proteolytic enzyme hydrolyzing ?-benzoyl-L-arginine-p-nitroanilide, and protease activities changes during wheat maturation to breadmaking quality of flour. In view of these considerations, is cannot be excluded that proteolytic enzymes could affect significantly the ability of semolina to produce high quality spaghetti by enzymatic breakdown of only a few peptide bonds of semolina proteins. Moreover, the literature does not provide any easily measurable charactcnstics of durum wheat varieties by which their pasta making quality could be assessed. In our laboratory, studies have been undertaken to extract and measure semolina proteolytic enzymes. In the present paper, BAPA-ase activity in semolina from five Italian durum wheat varieties from two annual crops and with different spaghetti cooking quality have been examined. In addition, in order to obtain information on changes in the level of BAPA-ase; during Pasta processing. the enzymic activity has been determined in the same semolina samples mixed with 33% water and after storage at 37°C for 15 hr ( mixed semolina).

Fusicoccin inhibits the germination of pea (Pisum sativum L. cv Progress 9) seeds by decreasing the growth of the embryonal axis and by stimulating the fresh weight increase of the cotyledons. The growth of isolated embryonal axes in the presence of sucrose and KCl is stimulated by fusicoccin. The effect of fusicoccin on the seeds is not counteracted by sucrose and KCl. Fusicoccin promotes preferentially in the cotyledons a hyperpolarization of the transmembrane electric potential and an increase in the uptake capacity, suggesting the reinforcement of the sink strength of the cotyledons in comparison with the one of the embryonal axis and therefore the inhibition of translocation from the cotyledons of some substance necessary for the growth of the embryonal axis.

Increased ethylene evolution accompanies seed germination of many species including Pisum sativum L., but only a little is known about the regulation of the ethylene biosynthetic pathway in different seed tissues. Biosynthesis of the direct ethylene precursor 1-aminocyclopropane-1-carboxylic acid (ACC), the expression of ACC oxidase (ACO), and ethylene production were investigated in the cotyledons and embryonic axis of germinating pea seeds. An early onset and sequential induction of ACC biosynthesis, accumulation of Ps-ACO1 mRNA and of ACO activity, and ethylene production were localized almost exclusively in the embryonic axis. Maximal levels of ACC, Ps-ACO1 mRNA, ACO enzyme activity and ethylene evolution were found when radicle emergence was just complete. Treatment of germinating seeds with ethylene alone or in combination with the inhibitor of ethylene action 2,5-norbornadiene showed that endogenous ethylene regulates its own biosynthesis through a positive feedback loop that enhances ACO expression. Accumulation of Ps-ACO1 mRNA and of ACO enzyme activity in the embryonic axis during the late phase of germination required ethylene, whereas Ps-ACS1 mRNA levels and overall ACC contents were not induced by ethylene treatment. Ethylene did not induce ACO in the embryonic axis during the early phase of germination. Ethylene-independent signalling pathways regulate the spatial and temporal pattern of ethylene biosynthesis, whereas the ethylene signalling pathway regulates high-level ACO expression in the embryonic axis, and thereby enhances ethylene evolution during seed germination.