Analysis of cycles of dormancy and growth in pea axillary buds based on mRNA accumulation patterns of cell cycle-related genes.

Axillary buds of pea (Pisum sativum L. cv. Alaska) do not grow on intact plants. Dormant axillary buds can be stimulated to grow rapidly after decapitation. Here, we isolated cDNAs of PCNA, cyclinB, cyclinD, and cdc2 from pea. The mRNA expression levels of these genes were very low in dormant axillary buds, whereas they remarkably increased after decapitation. Based on the mRNA accumulation patterns of these genes, we found that most cells in dormant axillary buds are arrested at the G1 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, mRNAs were still present in the large bud, but not in the small bud. However, after removal of the large bud, the mRNA levels started to increase again in the small bud. These mRNA accumulation patterns were the same as those after the first decapitation. These results suggested that most cells in axillary buds at the second node are arrested at the G1 phase again and have the capacity to undergo multiple cycles of dormancy and growth. Moreover, in situ hybridization analyses demonstrated that PCNA mRNA increased in all parts of the axillary buds after decapitation.