ANALYSIS OF CYCLES OF DORMANCY AND GROWTH IN PEA AXILLARY BUDS BASED ON MESSENGER-RNA ACCUMULATION PATTERNS OF CELL CYCLE-RELATED GENES

Axillary buds of pea (Pisum sativum L. cv. Alaska) do not grow on inta ct plants. Dormant axillary buds can be stimulated to grow rapidly aft er decapitation. Here, we isolated cDNAs of PCNA, cyclinB, cyclinD, an d cdc2 from pea. The mRNA expression levels of these genes were very l ow in dormant axillary buds, whereas they remarkably increased after d ecapitation. Based on the mRNA accumulation patterns of these genes, w e found that most cells in dormant axillary buds are arrested at the G (1) phase in the cell cycle. There are four buds at the second node on pea seedlings. After decapitation, mRNAs became abundant in the large and small buds and were kept during the following 3 d. After 4 d, mRN As were still present in the large bud, but not in the small bud. Howe ver, after removal of the large bud, the mRNA levels started to increa se again in the small bud. These mRNA accumulation patterns were the s ame as those after the first decapitation, These results suggested tha t most cells in axillary buds at the second node are arrested at the G (1) phase again and have the capacity to undergo multiple cycles of do rmancy and growth. Moreover, in situ hybridization analyses demonstrat ed that PCNA mRNA increased in all parts of the axillary buds after de capitation.