Proline and Polyamine Involvement in Chilling Tolerance of Maize Suspension Cultures

Abstract

We have assessed the effect of various medium supplements in promoting the ability of maize (Zea mays L.) inbred FR27rhm suspension cultures to grow following a period of 4 °C chilling stress. Following a 4 week exposure to 4 °C in culture medium without proline, no cell growth occurred upon subsequent incubation at 28°C for 2 weeks. This inhibition was reversed when 3 to 48 mol m−3 proline or 0.1 mol m−3 putrescine or 0.01 mol m−3 spermidine were present in the medium during the chilling stress. On the other hand, suspensions were made more sensitive to 4°C by blocking polyamine biosynthesis with 1.0 mol m−3 methylglyoxal bis (guanylhydrazone) (MGBG) or a combination of 1.0 mol m−3 difluoromethylornithine (DFMO) and 1.0 mol m−3 difluoromethylarginine (DFMA). The addition of 10 mol m−3 putrescine to the suspension containing DFMO and DFMA prevented the increased chilling sensitivity. Electrolyte leakage studies conducted to assess membrane integrity after 4 weeks at 4°C and a 2 week regrowth period showed that cells treated with no polyamines (control), 0.01 mol m−3 spermidine, 1.0 mol m−3 putrescine, or 1.0 mol m−3 MGBG lost 43, 32, 14, and 100% of the total electrolyte pool, respectively. These results suggest that proline and polyamines are beneficial for inducing chilling tolerance in FR27rhm suspension.