Cytological changes of ‘Cara Cara’ navel orange ( Citrus sinensis Osbeck) spring shoot during self-pruning process by paraffin section and TEM analysis. Stages A–F occur before self-pruning, (A–F) 45 days, 35 days, 25 days, 15 days, 7 days, and 3 days before self-pruning of shoot tips, respectively. (G) 3 days before self-pruning of lateral bud; (H) 20 days after self-pruning; (I) lobular of shoot tips begin to fall (before self-pruning); (J) the appearance of the AZ; stages L–P occur after self-pruning, (K) visible AZ; (L, M) shoot tip begins to fall; (N) shoot tips after self-pruning; (O) before formation of protective layer of AZ; (P) after protective layer of AZ formed. Bars are 50 μm in L–P, and 100 μm in other photographs. Red arrows represent AZ.