Cell Membrane Stability and Relative Cell Injury in Response to Heat Stress during Early and Late Seedling Stages of Diverse Carrot Germplasm

Leaf samples were collected for cell membrane stability estimation 30 days (Early Seedling (ES) developmental stage) or 52 days after planting (Late Seedling (LS) developmental stage).

Cell membrane stability of heat-treated and nontreated plants of each accession was estimated by measuring electrolytic leakage from cellular membranes of leaves following the method of relative conductivity (Ibrahim and Quick, 2001) with some modifications. Briefly, five leaves of ~3.5 cm length were collected from each of five heat-treated and five nontreated plants of each accession-replicate. Leaf samples were washed with tap water, rinsed with double distilled water, and placed in vials containing 10 ml of deionized water for 18 h at 10 °C. Then the control accession vials were moved to 25 °C; whereas heat-treated accession vials were heated in a water bath at 52 °C for 1 h. All leaf samples of control and heat-stressed plants were again incubated at 10 °C for 24 h for diffusion of electrolytes from leaf tissue to aqueous media, brought to room temperature, shaken by hand, and initial conductance (E₁) was measured. Samples were then autoclaved at 0.10 MPa and 121 °C for 15 min to kill plant tissue and release electrolytes. Samples were cooled to 25 °C, contents shaken, and final conductance (E₂) was measured.

Relative cell injury was calculated with the formula reported by Ibrahim and Quick (2001):
Cell membrane stability (CMS) (%) = 1 – (E₁/ E₂) × 100
Relative cell injury (RCI) (%) = [(1 – CMS₂) / (1 – CMS₁) × 100]
While CMS₁ is cell membrane stability for control samples, CMS₂ is for heat-treated samples.

Observed RCI values for each germplasm accession were then ranked from lowest (1) to highest (215)