Sugars as the regulators of dormancy and sprouting in geophytes

Geophytes develop underground storage organs, which help them to survive extreme environments. Besides energy resources for plants and humans, they are widely used for vegetative propagation. Naturally, these storage organs are sink tissues during the active growth cycle of the plant, but they turn into a source during vegetative propagation. Synchronized dormancy and sprouting with the environment are crucial for plant fitness and maximum yield. The active metabolic status of an underground vegetative organ determines its developmental fate. Sugars are the main components of storage organs; thus, their dynamics play an important role in controlling the dormancy-activity cycle of geophytes. Dormant buds require carbon sources (sugar) to promote growth, and the plant adjusts sugar metabolism between storage and soluble sugars to maintain dormancy and sprouting. In recent years, sugars and their derivatives, besides energy molecules, have also been considered signaling molecules involved in several plant developmental processes, including vegetative dormancy and growth. This review discusses current knowledge on the role of sugars in regulating and controlling dormancy and sprouting in geophytes. It's regulation by external environmental factors, hormonal regulation and cross-talk. It also outlines how similar or different the regulatory mechanism controlling geophyte dormancy and sprouting is, compared to seed dormancy and germination and seasonal/annual growth in perennials that undergo dormancy-activity cycles.