2.4 Chlorophyll (Chl) content measurements
Chl content was determined according to Porra et al. (1989). Leaf segments (0.1 g) were first washed with distilled water and then kept in 1 ml acetone (80%) at 4°C for one to two weeks. Then samples were centrifuged at 13,000 g for 5 min and subsequently their absorbance was monitored at 663 and 645 nm using a UV visible spectrophotometer (50 Bio Varian, Varian Inc., Walnut Creek, CA). Total Chl content was calculated according to the following equation: total Chl (mg·L−1) = (8.02 × OD663) + (20.21 × OD645), where OD stands for optical density. The results of the Chl content were expressed as mg per gram fresh weight (mg g−1 fresh weight (FW)) and calculated based on the extinction coefficients and the equations given by Porra et al. (1989).