Some differential properties of alpha-amylase isozymes in growing and germinating seed of wheat

Kozo NISHIKAWA, Yoshihiko FURUTA, Yasuhiko HINA and Shigeto FUJI

Faculty of Agriculture, Gifu University, Kakamigahara, Gifu-ken 504, Japan

All the genes so far identified for alpha-amylase isozymes of germinating seed of common wheat and Aegilops squarrosa locate on the chromosomes belonging to either homoeologous group 6 and 7, namely the genes for Band 1, 7 and 9 on chromosome 6D, Band 2 on 6A, Band 3 and 10 on 6B, Band 11 on 7D, Band 13 on 7A and Band 15 on 7B (NISHIKAWA and NOBUHARA 1971, NISHIKAWA et al. 1976, unpublished). In spite of the same substrate specificity, alpha-amylase isozymes specified by the genes on the chromosomes of homoeologous group 6 (group 6 isozymes) differ from those by the chromosomes of group 7 (group 7 isozymes) in some aspects.

As well known, homoeologous chromosomes have been derived from one and the same pivotal chromosome and so called homoeoallelic genes on the respective chromosomes of the same group. The isozyme by definition, no matter whether specified by the allelic or homoeoallelic genes can not tolerate gross modifications of its polypeptide chain. This means in turn that changes of its physical properties, such as isoelectric point, must be within a limited extent. Group 6 isozymes (Band 1 to 10) were higher than group 7 isozymes with regard to isoelectric point, the former being within the zone of about pH 7.1 to 6.1, while the latter within the zone of about pH 5.7 to 5.3. It is evident that the two pI zones do not overlap with each other. Then, in addition to chromosome locations of the genes concerned, non-overlapping zone of pI of group 6 and 7 isozymes proves that group 6 isozymes are specified by a group of homoeoallelic genes and group 7 isozymes by another group of homoeoallelic genes.

In growing seed of common wheat (cv. Chinese Spring) 1 to 21 days after anthesis, weak activity of group 7 isozymes could be detected, but none of group 6 isozymes occurred, as shown in Fig. 1. Band 15 appeared a few days later than two others.

Group 6 isozymes, on the other hand, were activated in the earlier stage of seed germination than group 7 isozymes as shown in Fig.2. 1 day after seed imbibition, group 6 isozymes, Band 1 to 9 (Band 10 does not occur in cv. Chinese Spring) started to be detected and with the lapse of time their catalytic activity increased and continued up to about 10 days after imbibition. While group 7 isozymes were activated about 2 days behind the group 6 isozymes and kept the higher avtivity for at least 10 days thereafter. When small seed was used, in which group 6 isozymes could keep their relatively higher activity for only a few days the alternation of alpha-amylase activity from group 6 to group 7 isozymes was obvious.

From differential activity both in growing and germinating seed as mentioned above, functional differentiation of starch degradation activity of two groups of alpha-amylase isozymes can be reasonably pressumed.