Abstract
Temperate woody perennials survive to low temperatures in winter entering a dormant stage. Dormancy is not just a survival strategy, since chilling accumulation is required for proper flowering and arbitrates species adaptation to different latitudes. In spite of the fact that chilling requirements have been known for two centuries, the biological basis behind remain elusive. Since chilling accumulation is required for the normal growth of flower buds, it is tempting to hypothesize that something might be going on at this particular stage during winter dormancy. Here, we characterized flower bud development in relation to dormancy, quantifying changes in starch in the flower primordia in two sweet cherry cultivars over a cold and a mild year. Results show that, along the winter, flower buds remain at the same phenological stage with flower primordia at the very same developmental stage. But, surprisingly, important variation in the starch content of the ovary primordia cells occurs. Starch accumulated following the same pattern than chilling accumulation and reaching a maximum at chilling fulfillment. This starch subsequently vanished during ecodormancy concomitantly with ovary development before budbreak. These results showed that, along the apparent inactivity during endodormancy, flower primordia were physiologically active accumulating starch, providing a biological basis to understand chilling requirements.
Highlights
Woody perennials, in temperate and boreal regions, cease growth and enter into a dormant stage to survive to low winter temperatures (Considine and Considine, 2016)
Flower primordia started developing at the end of the summer showing incipient verticiles: sepals, petals, anthers, and pistil (Figure 2A)
Flower buds increased in size, and papilla started to develop in the stigma (Figure 2G)
Summary
In temperate and boreal regions, cease growth and enter into a dormant stage to survive to low winter temperatures (Considine and Considine, 2016). Dormancy is not just a survival strategy, since cold winter temperatures are required for proper flowering (Rohde and Bhalerao, 2007; Kurokura et al, 2013), and these chilling requirements are the main drawback to cultivate temperate trees in warmer latitudes (Campoy et al, 2011). Since this paradoxical chilling requirement was early noticed (Knight, 1801), it has been subsequently widely confirmed in a number of species and circumstances for temperate fruit tree production. In temperate fruit trees, the regulation by physiological factors inside the affected structure is referred as endodormancy, and the regulation by environmental factors is referred as ecodormancy (Lang et al, 1987), but other terms have been coined around dormancy in different species and the subject has been recently comprehensively reviewed (Considine and Considine, 2016)
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