| Self-pruning, also known as self-cutting of the terminal bud, is a natural process that branches of plants shed from the plant body, which also is a biological phenomena in the nature. Self-pruning exists in many plants, in herbaceous plants such as tomatoes and peppers, in woody plants, such ascitrus, pomegranate, persimmon, peash, plum tree, meratia praecox and so on. In previous studies people found that self-pruning has a close relationship with flower differentiation in precocious and wild-type trifoliate orange. For both precocious and wild-type trifoliate orange, self-pruning is a developmental boundary of all kinds of shoots. For the flowering-capable shoots, flower buds form after self-pruning; for the flowering-incapable shoots, leaf bud form after self-pruning.Abscission occurs at specific sites called abscission zones (AZs). The development and functioning of AZs are complex and precise processes which involve many genes. Degradation of cell wall and middle lamelia at AZs causes cell separation and leads to shedding of distal organs. Self-pruning is a kind of organ abscission which may play an important role in plant growth and crop cultivation. In this study, we investigate the self-pruning features of Cara Cara navel orange in detail and try to study the molecular mechanism of these features.From the morphology point of view, self-pruning belongs to organ abscission. Organ abscission is a ubiquitous phenomenon in the plant kingdom. Organ abscission exists widely in nature. So far, the studies of plants’organ abscission has been a lot, its physiological and biochemical processes has also made a deep understanding, but the study on self-pruning is still in the initial stage of the research. This research explain the the structure of organizations from the cellular level, and explain the mechanism and function from the molecular level. The main results are as follows:1. In order to understand what is self-pruning from the macro point, we discovered that the site shedding is not fixed, since the shear length of shoot and number of nodes is very different, a short shoot is only 4cm long and has 3 nodes, and the long shoot is up to 60cm and has 20 nodes or so. Adult citrus and young citrus has clear difference from the shear length and shoot nodes. But, Shoots from the pruning site is relatively fixed, most of them remain in the axillary of some foreleaf.2. Abscission occurs at specific sites called abscission zones (AZs). The development and functioning of AZs are complex and precise processes which involve many genes. Degradation of cell wall and middle lamelia at AZS causes cell separation and leads to shedding of distal organs. The abscission zones already differentiated from the base area before the shedding of organs, and later the further differentiation of the protective layer from the area, AZ is composed of 5-20 layers of small cells throughout the cell layer, dense cytoplasm, intercellular spaces small. As for Cara Cara, the abscission layer cells is smaller than adjacent cells, mostly rectangular, after 1-3 days of the separation occurs did appear self-pruning.3. By microarray, some EST associated with programmed cell death has increased its expression. Apoptosis analysis by TUNEL found that, green fluorescence was detected at different levels at locations of bud removal and leaf removal, indicating the occurrence of the self-pruning of the citrus occurred along with programmed cell death.4. By microarray, we found that, when self-pruning happens, the content of some pathogenesis related protein such as chitinase and 0-1,3 glucanase has been down-regulated, and up- regulated after self-pruning. The possibility is that the plant promotes self-pruning by decreasing resistance.5. in situ hybridization with CiCEN, CiAPl, CiFLC, the results showed that they had no direct relationship with self-pruning in citrus, there did not detect the due signal in the shedding parts of the organs, with whose expression more concentrated in the shoot of apical meristem (SAM) and axillary meristem, while the previous research on CiCEN, CiAPl expression is that they appeared visible down-regulated expression though semi-quantitative PCR, the results perhaps can be greater interpretation because CiCEN, CiAPl had close relationship associated with vegetative growth the SAM, since the self-pruning leads to the reduction of vegetative growth, thereby causing the downregulated. |
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