Paolo Meletti

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.

Ulteriore contributo alle conoscenze sul « Denti de cani » (X Haynaldoticum sardoum Meletti e Onnis)

Abstract Further data on « Denti de cani » (X Haynaldoticum sardoum Meletti e Onnis). – The authors defin the taxonomic position of « Denti de cani » (X Haynaldoticum sardoum Meletti e Onnis). It is characterized by the presence of two forms differentiated for morphological features and behaviour.

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.

Ribonucleases in leaves and roots of Triticum durum and x Haynaldoticum sardoum submitted to low non freezing temperatures

Summary In wheat leaf and root crude extracts several RNases can be distinguished by pH optima analysis, and SDS-PAGE and activity staining. One acidic RNase (approximately 20 kD in size) and a group of neutral RNases have been identified by electrophoretic separation. Neutral RNases can be divided into salt-stimu- lated (about 24 and 26 kD) and salt-inhibited (about 27kD). Following low temperature treatment, acidic and neutral salt-inhibited RNases remain unchanged, while the neutral salt-stimulated RNases with higher mobility generally increase with respect to the control.

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.

Ribonucleases during ripening and after-ripening in Triticum durum embryos

Summary Total and polyadenylated RNA content changes during ripening and after-ripening in embryos of Triticum durum cv. Cappelli. In this work, RNase activity was studied by means of enzymatic assays and activity staining SDS-PAGE in embryos at different stages of maturation and after-ripening. Qualitative and quantitative changes of RNases were found. Of particular interest was the continuous presence of acidic RNase in embryos, and the disappearance of neutral RNase activities during after ripening. Salt-inhibited RNases disappeared 42 days after anthesis, while salt-stimulated RNases with higher mobility disappeared in fully ripened embryos. Salt-stimulated RNases with lower mobility disappeared during after-ripening. The disappearance of neutral RNase activities during ripening may be related to the different physiological status induced by dehydration.

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.

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.

Studies onxHaynaldoticum sardoum Meletti et Onnis metabolism during seed life-span: α-amylase and glutamate decarboxylase activity

Embryo GAD activity and α-amylase in the endosperm of 2 different physiological lines (CP; CV) ofxHaynaldoticum sardoum Meletti et Onnis were evaluated and different stages of seed ripening and progressively older seeds were examined. Results concerning GAD activity during ripening show differences between CP and CV seeds, the former being more active. In the ageing seeds, the GAD remains constant (CP is twice as much as CV) up to 4th year and greatly decreases at the 5th. The α-amylase activity is fairly constant during ripening in CV endosperm and increases in CP: at the fully-ripe stage, both show similar values. During seed ageing, the activity decreases progressively in CV endosperm while, in CP, values are greater but fairly constant. The results are discussed in connection with dormancy and the different physiological ageing of seeds.

Succinic semialdehyde dehydrogenase activity in durum wheat during physiological phases of seed ripening.

Summary Succinic semialdehyde dehydrogenase activity was evaluated in the wheat embryo at different phases of seed ripening (seed dehydration, dormancy and dry after-ripening). Enzymatic activity was constant from milk up to dough-ripe stage of seed endosperm and decreased at the completion of seed dehydration. Differences in the level and pattern of enzymatic activity during early germination of ripe-dormant and non-dormant seeds were also observed. Possible correlations between this enzymatic activity and the control of wheat seed germination during dormancy are discussed.