Procyanidin b1

Extraction and quantification of total soluble and insoluble PAs were performed as previously described by Pang et al. (2008) . Briefly, approximately 0.5 g of freeze-dried tissues was extracted using 5 ml of 70% acetone solution (v/v) containing 0.1% (w/v) ascorbic acid by vortexing, and then sonicated at 4 °C in the dark for 1 h. For quantification of soluble PAs, 1 ml of DMACA reagent (2% w/v p-dimethyl-amino-cinnamaldehyde (DMACA) in methanol–3 M HCl) was added to 1 ml of fluid under test. After reaction for 30 min, the total soluble PA levels was calculated spectrophotometrically at 640 nm, with (+)-catechin as the standard (Yuanye Bio-Technology, Shanghai, China). Quantification of insoluble PAs (with butanol–HCl) was performed as described previously (Pang et al., 2008 ). Absorbance values were converted into PA equivalents with procyanidin B1 as a standard (Yuanye Bio-Technology). The Arabidopsis seeds and citrus calli were stained with 0.2% DMACA in methanol: 6 M HCl (1:1) for at least 30 min and then washed in ethanol: acetic acid (75:25) for visualization of PAs under UV light on a universal fluorescence microscope (Olympus BX61, Tokyo, Japan).