Supplemental data

Methods

In previous experiment, six of wucai cultivars were used as materials, and the heat-sensitive and heat-tolerant culativars were selected according to the value of semi-lethal temperature.

Electrical conductivity (EC) was measured as described by Nautiyal et al. (2008) with slight modifications. The well-grown seedlings with four to five true leaves of uniform size were used as experimental materials. For each cultivar, the fully expanded third seedling leaves were washed thoroughly with distilled water and wiped the water off. Then they were punched into discs of 8 mm in diameter and randomly blended. Three leaf discs were placed in an individual test tube containing 3 cm3 of distilled water. These tubes were capped with aluminium foil, exposed to 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C and 60°C in water baths for 1 h and then allowed to cool at room temperature, after which the first electrical conductivity (EC1) was recorded. The samples were subsequently boiled at 100 °C for 30 min to ensure the complete disruption of the cell membrane and then cooled at room temperature. After this, the final electrical conductivity (EC2) was recorded. Relative electrical conductivity (REC) was calculated as follows: REC [%] = EC1/EC2 × 100. The relationship between REC and temperature (T) was described by a sigmoid curve, which was fitted using the following logistic function: REC = k/(1+ae-bT), where k is the maximum percentage of cell damage, a and b are equation parameters. According to the regression analysis, the inflection point of temperature (ln a/b) in the equation was the semi-lethal temperature (LT50).

Results

The REC of all cultivars increased with increasing temperature (Fig. 1). The LT50 of WS-6 and WS-1 was 38.02°C and 42.27°C, respectively, at minimum and maximum value, according to REC and logistic function (Table 1).

Fig. 1. REC measured in wucai seedling leaves under different temperature treatments (25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C and 60°C). Values represent the mean ± S.E. (n = 3).

Table 1

Parameters of logistic equation, correlation coefficient (R2) and the semi-lethal temperature (LT50) of the six wucai cultivars.

Cultivar / Parameters of Logistic equation / Correlation coefficient (R2) / LT50 (°C)
a / b
WS-6 / 127.6510 / 0.1278 / 0.9800 / 38.02
TDW-2 / 127.7659 / 0.1248 / 0.9881 / 38.86
JHX / 137.2494 / 0.1253 / 0.9833 / 39.28
XHW / 129.8266 / 0.1190 / 0.9855 / 40.89
TDW-1 / 108.9512 / 0.1134 / 0.9913 / 41.37
WS-1 / 152.8719 / 0.1190 / 0.9859 / 42.27

Reference

Nautiyal PC., Rajgopal K, Zala, PV, Pujari DS, Basu M, Dhadhal BA, Nandre BM (2008) Evaluation of wild Arachis species for abiotic stress tolerance: 1. Thermal stress and leaf water relations. - Euphytica 159: 43-57