Fig 1.
Meteorological data at the experimental plot of the Apple Research Institute, Gunwi (lat. 36.28°N, long. 128.47°E).
(a) Change in daily minimum, mean, and maximum temperature during May of 2018. (b) Comparison of daily mean temperatures to 10-year annual mean.
Table 1.
Metabolomic profile of young apple fruit/pedicel mixed tissues undergoing abscission.
Fig 2.
Morphological changes of an excised Hongro/M9 apple tree subunit after ex vivo cold shock followed by 168 hr of incubation at 25 °C.
(a) Comparison of pedicel tissues containing the abscission zone (AZ) (left: normal, before the incubation; middle: treatment, cold shock followed by the incubation; right: control, after the incubation). (b) Transmission electron microscopy images of the AZ cortical cells at proximal tissues in the pedicel (top: cold treatment, 168 hr of incubation following initial 2 hr of cold shock; bottom: control, 168 hr after incubation without cold shock). Samples were observed with a LIBRA 120 transmission electron microscope at an acceleration voltage of 120 kV, magnification of 4 k (left, middle) and 6.3 k (right). Arrows indicate the development of cytoplasmic vesicles.
Fig 3.
Spatial expression patterns of target genes involved in hormone metabolism and stress response in cold-stressed apple subunit consisting of fruit, branch, and pedicel.
(a) abscisic acid (ABA) hormone biosynthesis, catabolism, and signal transduction; (b) Cold stress; (c) Drought stress; (d) Abscission-zone (AZ) formation; (e) Ethylene; (f) Auxin; (g) Gibberellin. MDP0000336547 was used as reference gene. Data are mean ± standard error (6 ≤ n ≤ 8). * indicate significant difference in relative expression between cold treatment and control at p < 0.05 by Student’s t-test.
Fig 4.
Spatial expression patterns of genes involved in metabolic responses.
(a) Cold response, (b) abscisic acid (ABA) transport, (c) ethylene biosynthesis, and (d) cell wall modification in apple subunits consisting of a branch, pedicel, and fruit. Samples were grouped by treatments as follows: Control (water); ABA (125 mg/L of ABA); Cold (initial cold shock at 4 °C for 2 hr); Cold + ABA (125 mg/L ABA followed by initial cold shock at 4 °C for 2 hr). MDP0000336547 was used as reference gene. Data are mean ± standard error (n = 6). Data were analyzed using two-way ANOVA. Values with different letters differ significantly from each other at p < 0.05.
Fig 5.
A scheme of the abscission signaling induced by cold stress in early developing apple.