The mobilization of defence mechanisms in the early stages of pea seed germination against Ascochyta pisi

Ascochyta pisi is a necrotrophic pathogenic fungus, which mainly survives between seasons through infected seeds. Defence responses of pea embryo axes to A. pisi were investigated in the heterotrophic phase of seed germination and during the transition from the heterotrophic to the autotrophic phase. Germinated pea seeds, both non-inoculated and inoculated with A. pisi, were cultured in perlite for 96 h. Polarographic studies performed on intact embryo axes of germinating pea seeds infected with A. pisi showed a high respiratory intensity in time from 48 to 96 h after inoculation. Forty-eight-hour embryo axes of germinating pea seeds exhibited the highest respiration rate, which in infected axes was maintained at the following time points after inoculation. Moreover, at 72 and 96 h after inoculation, respiratory intensity was by 64% and 73% higher than in the control. Electron paramagnetic resonance analysis revealed a higher concentration of semiquinone free radicals with g values of g _||?=?2.0031?±?0.0004 and g _⊥?=?2.0048?±?0.0004 in infected axes than in the control. Generation of superoxide anion radical was also higher in infected axes than in the control but stronger at 72 and 96 h after inoculation. Starting from 72 h after infection, the level of Mn²⁺ ions in infected axes decreased in relation to the control. At the same time, the highest activity of superoxide dismutase (EC 1.15.1.1) and catalase (EC 1.11.1.6) was observed in 72-h infected axes. In turn, the activity of peroxidase (EC 1.11.1.7) up to 72 h after infection was lower than in the control. In 48-h infected embryo axes, a very high level of pterocarpan pisatin was observed. Infection of germinating pea seeds with A. pisi restricted mainly the growth of the epicotyl, but did not inhibit the increase in length and fresh weight of root embryo axes versus cultivation time. These results indicate that in pea during the stages of seed germination and early seedling growth, protective mechanisms are induced in embryo axes against A. pisi.     

The role of seed coat in early stages of soybean germination

The presence of the seed coat delays the early stages of germination of soybean embryos. This retardation seems to be due to the seed coat acting as a mechanical barrier to seedling. Although entire soybean seeds are insensitive to light, removal of the seed coat induces a light requiring condition. The early germination of naked seeds or isolated embryonic axes is enhanced by darkness. Red light produced a similar effect as white, providing evidence for the effective wavelength of the photo-inhibition. Far-red light acted similarly to darkness in promoting the early germination of the embryos. It is suggested that possibly light may act through phytochrome by the high irradiance system.     

Legumin and albumin of pea cotyledons during seed germination

During 6 days of pea seed germination the depletion of legumin with mol. m. 390 000 from protein bodies was observed. SDS-PAGE indicated that the legumin subunits with mol. m. 41 700 and 21 000 were prevailing. Only the former of these, probably corresponding to α-subunit, was degraded rapidly during 6 days of germination. Water-soluble proteins (albumins) prepared from pea cotyledons were separated by preparative IEF into proteins with pI 7.1, 6.5, 6.0, 5.4, 5.0, and 4.6. During 6 days the components of albumin with pI 7.1, and 6.5 were dramatically depleted. Major fractions with pI 6.5, 6.0, and 5.4 were subjected to SDS-PAGE and their subunit composition was determined. Moreover, albumin of pea cotyledons was resolved into 13 components by SDS-PAGE. Mobilization of albumin began from the degradation of components with higher mol. m. during germination.     

Polymorphism in rice amylases at an early stage of seed germination

A polymorphism in rice amylases at an early stage of seed germination is analyzed by zymogram. In non-glutinous cultivars of rice, alpha-amylase isozymes are mainly confirmed in germinating seeds. However, in glutinous cultivars, beta-amylase isozymes, which are not confirmed in nonglutinous cultivars, make up the major part of the total amylase activity and the expression of alpha-amylases are repressed.     

Ribosomal RNA integrity and rate of seed germination

The integrity of ribosomal RNA (the percentage of complete, un-nicked molecules) in seeds was studied by electrophoresis under denaturing conditions. Two batches of carrot seed, harvested at different stages of maturity, and four batches ofNicotiana seed stored for various times were used. Within each species, there was a correlation between the integrity of the rRNA of the dry seed and the rate of germination of that seed. In carrot seed, there was extensive degradation of existing rRNA in both the embryo and endosperm during the first two days of imbibition.     

Gibberellin-like activity in cotyledons and embryonic axes during pea seed germination

Endogenous gibberellin-like activity was determined in dry pea seeds (Pisum sativum cv. Bördi), in cotyledons and axes of germinating pea seeds and also in excised cotyledons and axes. During the first two days of pea seed germination, neither the embryonic axes nor the cotyledons show a mutual influence on gibberellin activity, but this appears after 72–96 h of germination. The gibberellin-like activity m cotyledons and axes of germinating seeds increased during the same period, but it decreased in isolated axes and excised cotyledons.     

Polyadenylation of RNA in immature oocytes and early cleavage of Urechis caupo

The poly(A) content of RNA extracted from four stages of immature oocytes, mature oocytes, and cleavage embryos through the eight-cell stage was determined by hybridization with [³H]-poly(U). During oogenesis the poly(A) content per cell gradually increases from 0.007 pg of poly(A)/cell in the 10- to 39-μm oocytes to 0.20 pg of poly(A)/cell in the 125-μm mature oocytes. After fertilization there is an additional increase to approximately 1.1 pg of poly(A)/embryo at the two-cell stage which is followed by a slight decline between the two- and eight-cell stages. Most of the increase in poly(A) after fertilization occurs in a 45-min interval coincident with the appearance of the polar bodies. The size distribution of the poly(A) in RNA from the different stages of development was determined based on the length of RNase-resistant poly(U) obtained from poly(U)-poly(A) hybrids. The size distribution of the poly(A) sequences is constant through each stage of development which indicates that the increase in the poly(A) content of the cells is the result of polyadenylation of new RNA sequences.     

Plastid biogenesis in embryonic pea leaf cells during early germination

Summary The ultrastructure of embryonic pea leaf cells was examined during the first 24 h of imbibition of dry seeds. Special attention was paid to plastids, which underwent two interesting interactions during this period. The first was a close physical association between the endoplasmic reticulum and plastids. The second was an association of numerous lipid bodies with the surface of plastids. The functional implications of these associations are considered.Abbreviations CCF conventional chemical fixation - ER endoplasmic reticulum - HPF-FS high-pressure freezing and freeze substitution Dedicated to Professor Eldon H. Newcomb in recognition of his contributions to cell biology     

Polyadenylation of nascent RNA during the embryogenesis of Ilyanassa obsoleta.

It has been demonstrated that specific changes in carbohydrate-containing cell surface lectin receptor sites occur with differentiation and maturation of sea urchin embryo cells. In this study, evidence is presented, using a quantitative electronic particle counter assay to measure agglutination, which indicates that concanavalin A (Con A) mediated agglutination of dissociated $\text{32}\text{64}$ cell sea urchin embryos differs dramatically with respect to specific cell populations. The migratory cell type, the micromere, is significantly more agglutinable with Con A than the other cell types and colchicine treatment markedly increases sea urchin embryo cell agglutinability. The results indicate that like many malignant cells which display extensive migratory behavior, specific migratory populations of embryonic cells are agglutinable with Con A. The results are discussed with respect to the possible nature of lectin receptor sites on specific populations of embryonic cells and the possible role of colchicine-sensitive structures in controlling the display patterns of these sites.