Developmental Expression of Genetically Defined Peptidases in Maize

Abstract

The activities of genetically defined amino-and endopeptidases of maize were compared in pericarp, endosperm, and embryonic tissue of the maize kernel from 5 days postpollination until harvest. Activities were highest in the immature stages and declined as drying progressed. The expression of some of the peptidase genes contributed by the pollen parent was examined during early endosperm development in an F1 cross. The paternaly contributed peptidase variants could first be detected 7 days after pollination.During germination and early seedlng growth the peptidase activities continued to decline in the endosperm but maintained high levels in the scutelium. The maize peptidases probably have no direct role in hydrolysis of endosperm storage proteins during germination and growth.The peptidase isozymes were associated with the soluble cytoplasmic fraction of the maize scutelum during early growth. Only one tissue specificity was found for the peptidases. Occurrence of a particular aminopeptidase isozyme, AMP2, is limited to endosperm tissue during kernel maturation.Developmental studies of peptidases in Zea mays were undertaken in order to elucidate possible physiological functions of these enzymes. The work reported here is part of a larger project to characterize the peptidases with respect to genetic control, developmental occurrence, biochemical properties, and physiological function. Limited proteolysis serves as a control mechanism in the activation of zymogens and in other posttranslational modifications. Proteases and peptidases are of course involved in protein turnover, mobilization of protein reserves, and senescence.The genetic bases of maize peptidases have been reported previously. Aminopeptidase (AMP) variation is coded by four structural genes-Amp], Amp2, Amp3, and Amp4-each having two or more allelic variants (18). Maize endopeptidase (ENP) is the product of a single genetic locus, Enpl, which has five known allelic variants (14). Purification procedures, molecular weights, substrate specificities, and other biochemical properties of the maize peptidases have also been reported elsewhere (17,25).Briefly, the peptidases all have slightly alkaline pH optima in the range 7.5 to 8.2 and isoelectric pH values from 4.0 to 4.5. The mol wt of endopeptidase is 55,000 and aminopeptidases range from 63,000 to 70,000.

Changes and induction of aminopeptidase activities in response to pathogen infection during germination of pigeonpea (Cajanas cajan) seeds

“…Enzyme was also significantly cleaved ApNA whereas the activity of enzyme with VpNA was found to be negligible. Results were consistent with previous findings for AP activities in barley (Strelec et al, 2009), with substrate specificities of partially purified maize seed APs (Vodkin and Scandalios, 1979), as well as with AP zymograms of pea (Pisum sativum) seeds (Elleman, 1974). However AP activity with LpNA as substrate decreased during maize seed germination (Vodkin and Scandalios, 1980), this is inconsistent with our findings.…”

Changes in nutrient composition and in vitro ruminal fermentation of total mixed ration silage stored at different temperatures and periods

“…The proteolytic activity of grains during ensiling remains unknown. It has been reported that protease activities in grains gradually decline during maturation, whereas they drastically increase after germination . These findings suggest that protease activities in grains used as TMR ingredients are low because the grains are well matured and have not germinated.…”

Effects of Replacing Ensiled-Alfalfa with Fresh-Alfalfa on Dynamic Fermentation Characteristics, Chemical Compositions, and Protein Fractions in Fermented Total Mixed Ration with Different Additives

“…This finding was inconsistent with the result of the present study, in which LP and MOL+LP in F-FTMR had lower AN and PA NPN contents than the control at 60 d of fermenting. Protease activities are lower when grains are used as TMR ingredients because they are well-matured and un-germinated [ 46 , 47 ]. In the present study, there were no fresh forages but hay, silages, and grains in E-FTMR, and they were not beneficial for microorganisms and protease activities in E-FTMR diets.…”