C. Floris

Rate of synthesis of spermine and spermidine in germinating seeds of Glycine, Helianthus and Triticum.

The spermine, spermidine, and the total protein content of embryos or embryonic axes from Triticum durum, Helianthus annuus, and Glycine max seeds at different times of early germination was evaluated. Mitotic activity of root-tip meristems from germinating seeds was also determined. The hypothesis is suggested that differences in polyamine and protein pattern during early germination could be correlated with the onset of mitotic activity and with the different characteristics of the seeds assayed.

Metabolism in Seed Ripening: Protein and poly(A)+ RNA Pattern in developing embryos of Triticum durum

Abstract Pattern of proteins and poly(A) + RNA synthesis in Triticum durum embryos during their development and in after-ripened seeds was studied. The aim was to evaluate differences as to the polyadenylated RNA in relation to the ripening and dormancy of caryopses. Developing embryos show a progressive increase of protein and poly(A) + contents while, during the after ripening period, a decrease of both occurs. With these events a syncronous incorporation pattern of labeled precursors does not coincide: therefore it is possible that, during embryo development, a progressive utilization of both proteins and poly(A) + RNA occurs. Moreover, the poly(A) + RNA of dormant dry embryos exhibits a template capability higher than of the after-ripe ones. On the contrary, when the after ripe embryos are from imbibed seeds, their transla-tional capability is higher. Some hypotheses about the different messengers for proteins probably involved in the maintaining of seed dormancy are discussed.

Metabolism in Wheat Seed Dormancy: Polyamine Content during Early Germination

Summary Spermine and spermidine content of embryos from dormant and non-dormant wheat seeds, during the early phases of germination was analyzed. Treatment of dormant seeds with GA3 and of non-dormant seeds with GA3 and ABA was also performed to verify, at a metabolic level, the consequences of the stimulating effects of GA3 on dormant and the inhibitory activity of ABA on non-dormant seeds. Polyamine content of treated and control seeds in relation to protein content, physiological state of seeds and treatment with plant growth regulators are discussed.

Metabolic Activity Distribution in the Embryo of Naturally Aged Seeds of Durum Wheat

Summary The control of metabolic activity in old seeds was carried out with the aim to evaluate whether embryos from seeds which had lost their viability contain tissues still able to perform certain synthetic processes. Using labelling experiments with [ 3 H]-thymidine, [ 3 H]-uridine and [ 3 H]-lysine, analysis was conducted on DNA, RNA and protein synthesis of different areas from non-germinating embryos in comparison with young viable ones. Light microscope studies of sectioned autoradiographed tissues give evidence for the persistence, in some areas of aged embryos (first node and scutellum), of a marked synthetic activity similar to that of young embryos whereas other areas (shoot apex) have lost or reduced this capability. The results obtained allow to conclude that the loss of germination capacity due to a general damage in aged seeds is not accompanied, in all embryonic tissues, by the failure of synthetic capacities. The internal areas of embryo appear to be more isolated and less sensitive to damaging effects of external ageing factors.

Polyamines and RNA content in wheat embryos from seeds of different age

Abstract The content of polyamines and RNA in isolated embryos from dry resting seeds of durum wheat has been determined. This, with the aim to investigate the variations of the polyamines and RNA amounts during the ageing process and to correlate them with the loss of germination capacity of the seeds. The results showed that the total polyamines increase while the RNA content decreases during the ageing of the embryos. Since no great difference exists as to the polyamine content between the embryos from seeds capable and incapable to germinate, it appears to be lacking a close relationship between the polyamine content and the germination capacity of the examined seeds. The decrease of the RNA content and the corresponding increase of the polyamine-N/RNA-nucleotide ratio, seem to suggest that the loss of germination capacity of the wheat seed could be related to impaired regulation properties during the ageing process.

Polyamine accumulation in aged wheat seeds

The present work was conducted to evaluate the content of the main polyamines (Spm, Spd, Put) in a series of naturally aged durum-wheat seeds as well as the activities of the enzymes ODC and ADC involved in their biosynthesis. In dry seeds the content of polyamines, especially that of Spd, rose during ageing till 6 years and then declined sharply. However, an increase of PA content upon imbibition was observed only with the youngest seeds, while a decrease was found in the older ones.The activities of ODC and ADC differed in aged seeds, the ODC activity being constant and lower than the ADC in the course of seed ageing. The ADC increased till the early ageing and decreased then in the very old, ungerminating seeds. Imbibition increased both enzyme activities in the youngest seeds only, in the older ones rather a decrease and changed ADC/ODC ration was found.The obtained results are discussed in relation to the participation of these enzymes in the biosynthesis of polyamines during seed ageing and in the course of plant senescence or stress.

Effects of GA3 treatment on the synthesis of poly(A)-rich RNA in wheat dormant embryos

Summary Gibberellic acid (GA 3 ) is capable to improve seed germination and seedling growth of dormant (D) wheat seeds. Total RNA content and synthesis rate of D embryos, lower than in non-dormant ones (ND), do not increase when GA 3 is applied during early 10 h of seed soaking. Synthesis of poly(A)rich RNA is stimulated after 8 h of hormonal treatment, but the response to GA, is similar for both D and ND embryos. Dry D embryos exhibit a content of poly(A)-rich RNA higher than ND embryos, and differences in the rate of synthesis exist during early germination. This pattern and the effects of GA 3 treatment in relation to different physiological state of seeds are discussed.

Influence of Age and Storage Temperature on RNA Metabolism in Durum Wheat Seeds

Summary Pattern and metabolic activity of embryo RNA from wheat seeds of different ages (2, 6, 9 year-old seeds) with a different germination capacity in relation to storage conditions has been studied. The embryos from 9 year-old seeds stored at laboratory conditions show a degraded RNA which is also incapable of incorporating ( 3 H)-adenosine. Storage at 10°C permits the 9 year-old seeds to maintain embryo RNA classes which are similar to those of younger seeds, and a poly(A) + rich RNA fraction with a high ( 3 H)-adenosine incorporation. The 6 year-old embryos from seeds stored at laboratory conditions have a high germination capacity but low germination energy. They show a degraded RNA, with a prevalence of a light class of RNA, and an ( 3 H)-adenosine incorporation which is lower than in the case of the controls (2 year-old seeds). Storage at 10°C shows that the RNA of the 6 year-old embryos maintains characteristics and an incorporation capacity which are similar to unaged seeds. The experiments also show the protective action of low temperature against degradation processes during storage and ageing. The paper also discusses the relationships between the structural and functional stability of RNA and seed germination and seedling growth.

Variation of glutamate decarboxylase activity andγ-amino butyric acid content of wheat embryos during ripening of seeds

GAD activity and γ-ABA content of wheat embryos at 7 ripening stages were verified with the aim of studying the metabolic activity of embryo during dehydration and quiescence of caryopsis. Data showed that in the early stage of ripening GAD activity is very low, increases rapidly at dough-stage, remaining constant up to waxystage, and decreases in the last fully-ripe embryos. γ-ABA content appears to be roughly parallel to the variations of GAD activity.

Biological activity of fractions from embryo extracts ofDurum wheat at different phases of ripening

Bioassay of fractions from wheat embryos revealed that, at all ripening phases, they posses natural substances which stimulate hypocothyl growth. The fullyripe and the after-ripe embryos exibited a very effective fraction for depressing seed germination and seedling root growth; the other fractions stimulate root growth. The results are discussed in relation to current hypotheses of physiological balance between antagonist growth substances.