Table 2. Quantification of changes detected in the cell structure and the organelles of untreated (0 μM) and RA-treated (175 μM) Arabidopsis roots.

Observations	7 days RA-treatment		14 days RA-treatment
	0 μM	175 μM	0 μM	175 μM
Cell wall thickness	0.12 ± 0.014	0.20 ± 0.089*	0.09 ± 0.020	0.18 ± 0.059**
Density of Plasmodesmata	2.85 ± 0.94	2.32 ± 0.66	1.98 ± 0.57	2.16 ±0.53
Density of abnormal nuclei (condensed chromatin)	0.013 ± 0.005	0.067± 0.045	0.003 ± 0.005	0.047 ± 0.015***
Density of cell wall deposits	0.035 ± 0.02	0.192 ± 0.026***	0.047 ± 0.028	0.162 ± 0.03***
Density of autolytic vacuoles	0.027 ± 0.01	0.087 ± 0.02*	0.032 ± 0.017	0.13 ± 0.053*
Density of altered vacuoles with deposits	0.12 ± 0.09	0.42 ± 0.04*	0.18 ± 0.14	0.71 ± 0.08*
Density of autophagosomes	0.013 ± 0.005	0.09 ± 0.03*	0.015 ± 0.012	0.1 ± 0.026***
Density of mitochondria	0.665 ± 0.21	1.31 ± 0.28***	0.703 ± 0.172	1.404 ± 0.303*
Density of altered mitochondria	0.044 ± 0.05	0.53 ± 0.15***	0.033 ± 0.043	0.0867 ± 0.261***

Ultrastructure measurements were expressed as: cell wall thickness (μm); Density of plasmodesmata (n° of plasmodesmata / μm of cell wall); Density of abnormal nuclei (n° of aberrant nuclei / 100 cells); Density of cell wall deposits (n° of cell wall deposits / 100 cells); Density of autolytic vacuoles (n° of autolytic vacuoles / 100 cells); Density of altered vacuoles with deposits (n° of altered vacuoles / 100 cells); Density of autophagosomes (n° of autophagosomes / 100 cells); Density of mitochondria (n° of mitochondria / 100 cells); Density of broken/altered mitochondria (n° of broken and altered mitochondria /100 cells). Data were expressed as mean ± SD. Differences between treatments were statistically analyzed through t-test with P ≤ 0.05.

* = (P ≤ 0.05)

** = (P ≤ 0.01)

*** = (P ≤ 0.001).