In response to winter conditions, carbohydrates in dormant buds are synthesized from the reserves accumulated during the growing season. During dormancy, carbohydrate dynamics are restricted to bud tissues, and a sugar deficit is the cause of growth cessation and bud dormancy. A dormant bud’s capacity to release is tightly linked to its supply of carbohydrates. Carbohydrate metabolism plays an important role in the process of bud break by acting as the primary source of carbon and energy. Interestingly, it has been found that some plants can remember their prior chill accumulation for example, vernalized henbane plants were grown in noninductive photoperiods (where they cannot flower), and when they were exposed to inductive photoperiods, they flowered. Plants that are sensitive to photoperiods do not have to rely on warm temperatures alone, thus protecting them when freezing weather returns (Keskitalo et al., 2005). Another environmental factor is photoperiods. For plants with a winter annual life history, sufficient chill accumulation may be a critical step for bud break, and after bud break takes place, a period of mild temperature is required for growth resumption. In recent decades, many studies have been conducted on this issue, and many factors have been identified in temperate and boreal trees, with winter chilling being the key environmental factor that controls their phenology. In the context of global warming, knowledge of the physiological, biochemical, and molecular bases of bud break in perennial fruit trees is of crucial importance because the timing of bud break directly affects flowering quality and uniformity. There are three different stages that determine the quality of bud dormancy release, flowering, and fruit yield: (1) paradormancy, where growth inhibition arises from another part of the plant (2) endodormancy (or true dormancy), which is triggered by internal factors and (3) ecodormancy, which is controlled by environmental factors. Therefore, understanding the genetic and physiological bases of bud break is of great importance to control longan fruit yield to establish regular annual cropping levels and to alleviate the production constraints associated with biennial bearing.īud dormancy is a biological characteristic and a necessary physiological process that enables plants to store more energy to survive for long periods under adverse conditions. These adverse environmental conditions lead to longan bud break and flowering at inappropriate times. There are many environmental conditions that can trigger the irregular flowering of longan, such as spring frost accompanied by flower damage and high temperature and moisture in winter, which causes flowering reversion. However, the irregular flowering habit of longan as a biennial fruit tree often affects its production and leads to erratic yields. A stable annual yield is the most important factor affecting the healthy development of the longan industry. Longan ( Dimocarpus longan) is a subtropical perennial crop, and it is best known for its nutritious fruit, which has a relatively high medicinal value. Our results present a dynamic picture of the bud break of longan, not only revealing the temporal specific expression of key candidate genes and proteins but also providing a scientific basis for the genetic improvement of this fruit tree species. In addition, catalase isozyme 1, an important enzyme in the redox cycle, and RuBisCO, a key enzyme in the Calvin cycle of photosynthetic carbon assimilation, might be the key DAPs for SJ bud break. In addition, light, rather than a high sugar content or chilling duration, might act as the key signal for triggering bud break. Compared to those of “SX”, the primary inflorescence, axillary inflorescence, floral primordium, bract, and prophyll of “SJ” (“Sijimi”) were weaker. Combined with our previous transcriptome data, it was observed that sucrose synthase 6 (SS6) and granule-bound starch synthase 1 (GBSSI) might be the key DAPs for “SX” bud break. “SX” (“Shixia”), a common longan cultivated variety that needs an appropriate period of low temperatures to accumulate energy and nutrients for flower induction, had a strong primary inflorescence, had a strong axillary inflorescence, and contained high contents of sugars, and most DAPs during the bud break process were enriched in assimilates and energy metabolism. In total, 3180 unique proteins were identified in 18 samples, and 1101 differentially abundant proteins (DAPs) were identified. To obtain new insights into the underlying regulatory mechanism of bud break in longan, a comparative analysis was conducted in three flower induction stages of two longan varieties with opposite flowering phenotypes by using isobaric tags for relative and absolute quantification (iTRAQ). The timing of bud break is very important for the flowering and fruiting of longan.
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