Plant Nucleases: VI. GENETIC AND DEVELOPMENTAL VARIABILITY IN RIBONUCLEASE ACTIVITY IN INBRED AND HYBRID CORN ENDOSPERMS

The nuclease activity of developing corn endosperms was found to consist mainly of plant RNase I during the period of major deposition of dry weight. The RNase concentrations in most inbred lines and hybrids increased throughout development, but there were large differences among genotypes in the enzyme levels at all stages. Crosses were made among inbreds classified as containing high or low RNase levels. In most cases, the general patterns of enzyme levels during development of the hybrid endosperms were not changed greatly, or showed intermediate levels of activity compared to the inbred parents. When Oh43 was used as a maternal parent, two contrasting developmental patterns were produced by using two low RNase inbreds as pollen parents. There appear to be genetic controls not only on the gross RNase levels, but also on the timing of RNase synthesis and on its stability after the cells mature. Environmental influences on RNase levels in the endosperm were noted one year.At 18 days after pollination, the RNase levels in the endosperm crown were as much as 10 times higher than in the base. By 35 days after pollination, the enzyme levels were generally uniform; at 50 days, the basal tissue usually contained the highest levels. In some genotypes, however, the enzyme levels fell in the crown while they rose in the base. These changes suggest that RNase may be associated with developmental controls that operate as the different portions of the endosperm cease cell division and begin synthesis of starch and zein.