| Research Abstract |
We have studied about two modulations : aspartic proteinase in soybean and cysteine proteinase inhibitor in rice seeds. First, we isolated and characterized two genes coding for aspartic proteinases (Aps) in soybean Glycine max. These encoded enzymes, soyAP1 and soyAP2, shared 57% amino acid sequence identity. Northern blot analysis demonstrated that soyAP1 was expressed specifically in seeds, especially in dry seeds, while the expression of soyAP2 took place in various tissues such as roots, stems, leaves and flowers, but not in dry seeds. SoyAP1 was highly expressed even at an early stage of germination, with a subsequent decrease in expression intensity. However, SoyAP2 mRNA level increased when 48 hours elapsed after imbibition at room temperature. At the root tip, SoyAP1 was expressed in immature tracheary elements disappeared when the elements were still immature. These results suggest that soyAP1 is expressed in immature tracheary elements and sieve tubes, and may be involved in programmed cell death.
We cloned four kinds of cDNAs for wheat cystatins, WC1, WC2, WC3 and WC4, from the seed. All were expressed in the seed at an early stage of maturation and, after that, their quantities decreased gradually. However, each of the mRNAs was again expressed one day after the start of germination and the expression continued for the following five days. WC1 seemed to be expressed always at higher level compared to WC2 and WC4. Immunostaining study showed that both WC1 and WC4 existed in the aleuron layer and embryo, whereas in the endosperm the only existing species was WC1. Differences in mRNA level and tissue localization found for the WCs may suggest their differential physiological roles.
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