Correlation between seed longevity and RNA integrity in the embryos of rice seeds

The mature embryos of rice seeds contain translatable mRNAs required for the initial phase of germination. To clarify the relationship between seed longevity and RNA integrity in embryos, germinability and stability of embryonic RNAs were analyzed using the seeds of japonica rice cultivars subjected to controlled deterioration treatment (CDT) or long periods of storage. Degradation of RNA from embryos of a japonica rice cultivar “Nipponbare” was induced by CDT before the decline of the germination rate and we observed a positive relationship between seed germinability and integrity of embryonic RNAs. Moreover, this relationship was confirmed in the experiments using aged seeds from the “Nipponbare”, “Sasanishiki” and “Koshihikari” rice cultivars. In addition, the RNA integrity number (RIN) values, calculated using electrophoresis data and Agilent Bioanalyzer software, had a positive correlation with germinability (R²=0.75). Therefore, the stability of embryonic RNAs required for germination is involved in maintaining seed longevity over time and RIN values can serve as a quantitative indicator to evaluate germinability in rice.     

Proteomic analysis of RNA-binding proteins in dry seeds of rice after fractionation by ssDNA affinity column chromatography

In proteomic analysis, one of the major limitations is the detection of low-abundance proteins. To detect low-abundance RNA-binding proteins in mature dry seeds of rice, fractionation by single stranded DNA (ssDNA) affinity column chromatography was carried out before analysis by two-dimensional gel electrophoresis (2-DE). Proteomic analysis of the ssDNA-binding fraction revealed the existence of three types of RNA-binding proteins, including a K homology (KH) domain containing protein, a putative RNA-binding protein and a glycine-rich RNA-binding protein, in mature seeds. In addition, decreases in the putative RNA-binding protein and glycine-rich RNA-binding protein after absorbing water in seeds appear to be associated with seed germination.     

Chloroplast Ribonucleoproteins (RNPs) as Phosphate Acceptors for Casein Kinase II: Purification by ssDNA-Cellulose Column Chromatography

Using ssDNA-cellulose column chromatography, a 34 kDa ribonucleoprotein(p34) has been purified from a 0.4 M KCl crude extract of spinachchloroplasts as an effective phosphate acceptor for casein kinaseII (CK-II) in vitro. Monomeric and oligomeric CK-IIs were copurifiedwith p34 by the column chromatography and the kinases were separatedfrom p34 by means of Mono Q column chromatography. It was foundthat (i) the purified p34 (pi 4.9) was phosphorylated specificallyby CK-II in vitro; and (ii) similar polypeptides, such as p35(pI 4.7) and p39 (pI 4.9) in maize and p33 (pI 4.7) in liverwort,were detected as ssDNA-binding chloroplast proteins phosphorylatedby CK-II in vitro. The findings suggest that (i) RNPs that functionas phosphate acceptors for CK-II exist commonly in chloroplastsamong plant cells; and (ii) the physiological activity of RNPsis regulated by their specific phosphorylation by CK-II in chloroplasts. (Received July 3, 1995; Accepted October 5, 1995)