CHARACTERIZATION OF TISSUE-SPECIFIC SEED PROTEINS IN PISUM

PNL Volume 12 1980 RESEARCH REPORTS 57

Muller, H.P. Institute of Genetics, University of Bonn, West Germany

A realistic estimation of an expected increase in protein quantity and

quality of crop plants depends on an understanding of the genetic control

of protein structures as well as of the regulatory processes during the

incorporation of functional units involved in the synthesis, processing, and

deposition of seed proteins.

A study for elucidating some of the problems indicated involves detailed

biochemical and physiochemical analysis and characterization of the proteins

available in seeds. This implies that not only the total nitrogen content

of seeds but also the enzymatically active proteins as well as the storage

proteins have to be analyzed.

For an assessment of the genetic component in the overall process,

suitable genotypes have to be available for analysis. One may either compare

different varieties with one another or compare mutant lines derived from

one variety (and therefore genetically closely related).

The water soluble seed protein fraction of leguminous seeds contains

many different proteins. The separation of this fraction into distinct

subunits by means of gel-electrophoresis opens the possibility to characterize

their polypeptide pattern. We have studied the subunit patterns of the

albumin fraction extracted from mature seeds of different genotypes. In

our investigations we concentrated on analysis of tissue-specific enzymes

of restricted substrate specificity.

The results obtained for the aminopeptidase and the malate dehydrogenase

extracted from the cotyledons of different genotypes are illustrated in Fig. 1.

The genotypes have the following characteristics: mutants 17 A and 488

are each homozygous for a reciprocal translocation; the seeds of No. 239(5)

carry a double trisomy in chromosomes 4 and 7; those of 239(11) have an

additional copy of chromosome 7. These genotypes should help to gain insights

into position effects as well as gene-dosage effects.

With respect to the patterns of the aminopeptidase, an enzyme which

is closely involved in the mobilization of the seed reserve proteins during

germination, and which also can be regarded as true "marker enzyme", we found

marked differences between the genotypes in the number of isozymes and in

the staining intensity of comparable bands. Since all protein preparations

were carried out under highly standardized conditions, the pattern can be

regarded as representative for aminopeptidase. More drastic changes in the

isozyme pattern were found for malate dehydrogenase, which seems to be involved

in reactions concerning the enzymatic adaption. The electropherograms for

the trisoinic lines in particular deviate strongly from the other genotypes.

There are some common bands, but others are lacking or are additionally

detectable. The results show that considerable heterogeneity of aminopeptidase

and MDH-isozymes, as judged by variance in the polypeptide patterns, is

produced by or associated with the genetic differences. There are some

indications of structural modifications of enzymes. Polymorphic forms of

enzymes seem to have adaptive significance. Furthermore, the knowledge of

the presence of enzymatically active proteins found in seeds should constitute

a useful basis for studying the metabolic events during seed germination.



58 RESEARCH REPORTS	PNL Volume 12	1980



Tg. 1. Aminopeptidase and malate dehydrogenase banding patterns in seeds of different pea genotypes.