Phenylpropanoid deficiency affects the course of plant acclimation to cold

The effects of phenylpropanoid deficiency on plant growth, photosynthetic efficiency of the photosystem II and freezing tolerance of leaves were studied during acclimation of winter oilseed rape plants ( Brassica napus L. var. oleifera L. cv Jantar) at low temperature. Application of 2-amino-2-indanophosphonic acid inhibited phenylalanine ammonia-lyase (E. C. 4.3.1.5) activity by about 90%. This was followed by a marked reduction of soluble phenolics ( in particular hydroxycinnamic acids) and anthocyanins in leaves. Inhibition of the cold-promoted incorporation of ferulic acid into cell walls was also observed. The reduction of phenylpropanoid contents was associated with: (1) partial abrogation of the cold-induced growth effects, such as inhibition of leaf fresh weight increments and accumulation of dry matter, proteins and cell walls; (2) decreased photochemical efficiency of photosystem II in low temperature-affected leaves; and (3) decreased ability of leaves to develop tolerance to the extracellular formation of ice. These findings are discussed in terms of phenylpropanoids' role in plant responses to cold (>0degreesC) and freezing temperatures.