Nuclear DNA regulates the level of ribulose 1,5-bisphosphate carboxylase oxygenase in Medicago sativa L.

The response to selection for leaf proteins was studied during three selection cycles. Selection for high total nitrogen content showed 75% heritability, and the levels of both ribulose 1,5-bisphosphate carboxylase oxygenase (Rubisco) and cytoplasmic protein were strongly under nuclear DNA control. High and low protein content were correlated with chloroplast area. Although the amounts of nuclear DNA were similar, the ratio of Rubisco/DNA and chlorophyll/DNA changed during the selection process. It can be concluded that the levels of Rubisco achieved in mature plants of M. sativa are under nuclear DNA control. The possible involvement of small subunit (SSU) genes in controlling these levels is discussed.

One large subunit of ribulose 1,5-bisphosphate carboxylase oxygenase in Medicago, Spinacia and Nicotiana.

Isoelectric focusing of subunits of ribulose 1,5-bisphosphate carboxylase oxygenase of Medicago, Spinacia and Nicotiana were investigated, using a rapid isolation technique, without S-carboxymethylation. RuBPC-ase and its subunits were isolated by gel electrophoresis. Isoelectric focusing of RuBPC-ase of M. sativa and M. falcata showed that this enzyme consists of one large subunit (LSU) polypeptide and two or three small subunits (SSU), depending on the genotype. The pl of the LSU's was identical, but the pl of SSU's of the two genotypes was different. Amino acid composition and tryptic peptide maps further supported the concept of a conserved nature of LSU and heterogeneity of SSU polypeptides in Medicago. It was also found that S. oleracea, N. tabacum, N. glutinosa and N. excelsior have a single LSU polypeptide, but they differ in respect of pl values. The SSU polypeptides appeared to be variable. S-carboxymethylation affected the number as well as the pl values of LSU and SSU polypeptides. It is suggested that one LSU polypeptide is probably the general rule in higher plants, rather than the three LSU polypeptides demonstrated by Chen et al. (1977) and Wildman (1979).

Heterogeneity of alkaline small subunits of ribulose 1,5 bisphosphate carboxylase-oxygenase from Medicago sativa and M. falcata.

The isolated leaf proteins of lucerne (Medicago sativa L. and M. falcata L.) were fractionated by Sepharose 6B column chromatography. Analysis of fractionated proteins indicated that the 2nd peak component was almost entirely ribulose 1,5 bisphosphate carboxylase-oxygenase (Rubisco) which represented 57% of the total recovered protein.Rubisco yielded one large subunit (LSU) and one small subunit (SSU) polypeptide after SDS gel electrophoresis.Isoelectric focusing of the SSU of Rubisco from genotypes of M. sativa cv. Hunter River (HR), Hairy Peruvian (HP) and of M. falcata (MF) showed two SSU components for HR and HP, and three components for MF. Most components of genotypes were located in the alkaline region of the gel. While the pIs of the SSU components of HR and HP were identical they differed from those of the SSU of MF thus demonstrating heterogeneity for SSU in Medicago.It is suggested that the alkaline nature of SSU may have some adaptive physiological significance.

Non-additive gene effects for creeping-root in lucerne (Medicago sativa L.).

Both general and specific combining abilities for creeping-rootedness of lucerne were found to be highly significant although there were substantial differences among genotypes for both parameters. These results indicate that both "additive" and "non-additive" gene effects are involved in the genetic substrate of creeping-rootedness; hence utilization of heterosis would seem to be the most appropriate procedure for further improvement in this trait.

The mechanism of aggregation of neural retina cellsin vitro.

1. The mechanism of aggregation of dissociated embryonic neural retina cells was investigated during a period of 24 hoursin vitro, and was found to consist of two distinct phases. The first phase depended on the residual cell surface material after trypsinization and was largely insensitive to cycloheximide. The second phase was sensitive to cycloheximide, indicating dependence on protein synthesis. 2. The rate of aggregation during the first hour was not eliminated by suppression of the endogenous energy source nor affected by added exogenous ATP or ADP. 3. Intercellular retina protein (I.R.P.) was isolated from neural retina tissues by EDTA treatment. The maximum rate of aggregation occurred in cultures containing 100 µg protein/ml. One µg of isolated protein was able to aggregate approximately 17000 retina cells. The process of aggregation by I.R.P. was found to be sensitive to cycloheximide. 4. I.R.P. attachment appeared to be dependent on the availability of a receptive layer on the surface of the dissociated retina cells. 5. Evidence obtained in these experiments suggested that retina cell aggregation after 24 hours depended on biosynthesis, and that macromolecules (protein or glycoprotein) were required for cell aggregation. 6. The molecular basis of cell aggregation and its role in morphogenesis is discussed.