Strigolactones (SL) fulfil important roles in plant development and stress tolerance. Here we characterised the role of SL in the dark chilling tolerance of pea and Arabidopsis by analysis of mutants that are defective in either SL synthesis or signalling. Pea mutants (rms3, rms4, rms5) had significantly greater shoot branching with higher leaf chlorophyll a/b ratios and carotenoid contents than the wild type. Exposure to dark chilling significantly decreased shoot fresh weights but increased leaf numbers in all lines. However, dark chilling treatments decreased biomass (dry weight) accumulation only in rms3 and rms5 shoots. Unlike the wild type plants, chilling-induced inhibition of photosynthetic carbon assimilation was observed in the rms lines and also in max3-9, max4-1, max2-1 mutants that are defective in SL synthesis or signalling. When grown on agar plates the max mutant rosettes accumulated less biomass than the wild type. The synthetic SL, GR24 decreased leaf area in the wild type, max3-9 and max4-1 mutants but not in max2-1 in the absence of stress. Moreover, a chilling-induced decrease in leaf area was observed in all the lines in the presence of GR24. We conclude that SL plays an important role in the control of dark chilling tolerance.
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