--Kien Tjhen, J.D. Smith and D. G. Bai
Electron micrographs reveal that protein bodies in aleurone tissue, but not endosperm, are seriously degraded by 25 days after pollination (DAP) in viviparous kernels. As expected, these protein bodies appear to be intact through maturity in normal kernels.
Enzymatic activities of carboxypeptidase (CP) and endopeptidase (EP) were determined from purified extracts of aleurone, endosperm, and embryo tissue of developing maize kernels at 15, 20, 25 and 35 DAP. These ages correspond to stage 4, stage 6, mature embryos and black layer, respectively (MNL 61:40). The activities of CP and EP were investigated using routine TCA methods, at pH 5.0 with phenylalanine and at pH 5.4 with zein as respective substrates, followed by ninhydrin reaction for CP.
The CP and EP in vp/vp and normal kernels showed similar patterns of activities in all tissues. The activity of CP was about 0.06 mol/g/h and EP was about 0.1 mol/g/h during early seed development (15 DAP). The highest activity was seen in embryo tissue for CP (0.085 mol/g/h) and in aleurone tissue for EP (0.6 mol/g/h) at 25 DAP.
The activity of CP in aleurone tissue decreased significantly after 15 DAP, indicating that this enzyme was very active in aleurone tissue during early development. The activities of EP in aleurone and embryo tissues showed that this enzyme was very active at this point but turned off after 25 DAP. The endosperm tissue had low or almost negligible CP and EP activities at all stages of seed development.
Table 1. Carboxypeptidase (CP) activity in viviparous-1 and normal maize
Table 2. Endopeptidase (EP) activity in viviparous-1 and normal maize
Although some differences were observed, the similarities in the activity
patterns of these proteolytic enzymes indicate that the degradation of
aleurone protein bodies in vp/vp kernels is not due to Vp
regulation of these enzymes.
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