Evaluation of cold stress of young industrial chicory (Cichorium intybus L.) by chlorophyll a fluorescence imaging. II. Dark relaxation kinetics

Industrial chicory, Cichorium intybus L., has rather poor early vigour under the typical early spring morning conditions of low temperatures and high light intensity. Screening tools are being developed to assess the cold tolerance/sensitivity of young industrial chicory plants under these conditions. Refinement of such tools requires better understanding of the plants' physiological responses. In this paper we discuss the effects of growth temperature (GT), measurement temperature (MT), and measuring light intensity (ML) on the relaxation of the Kautsky curve. We chose the chicory variety 'Hera', as it is known to possess a good average early vigour. Young plants of the variety 'Hera' were grown at three temperatures (GT): 16A degrees C (reference), 8A degrees C (intermediate), and 4A degrees C (cold stress). The dark relaxation kinetics were analyzed at different light intensities (ML) in combination with different measurement temperatures (MT). The three components of the nonphotochemical quenching process (NPQ(E), NPQ(T), and NPQ(I)) were determined. NPQ(E) was not affected by GT but was significantly affected by MT and ML. NPQ(T) and NPQ(I) were affected by all factors and their interactions. An acclimation effect for plants grown at low GT was detected. Acclimation resulted in lower NPQ(T) and NPQ(I) values. The halftime of the inhibition depending on NPQ (NPQ(I)) was not affected by any of the factors investigated. Based on the data generated, we conclude that NPQ(I) is a valuable parameter for screening the cold sensitivity of young industrial chicory plants.