Metabolism and transcriptome of two petunia cultivars with contrasting chilling tolerance indicate important functions of source-sink relationships and abscisic acid

Abstract

The use of chilling-tolerant cultivars of Petunia hybrida would allow reduction of heating temperatures in greenhouses and thereby contribute to save energy. In contrast to the plant reaction to severe cold close to freezing temperatures, the genetic control of tolerance to mild temperature reduction and of associated physiological processes are hardly known. Within the frame of the AgroCluster WEGA, the cultivar ‘Ultra Blue‘ was identified as chilling-tolerant, showing a significantly lower growth depression by cultivation at 12 °C versus 16 °C when compared with the sensitive cultivar ‘Sweet Sunshine Williams‘. By analysis of plant hormone levels, carbohydrate metabolism and plant transcriptome at the two temperatures we investigated, whether the two cultivars reveal specific metabolic and molecular patterns. Differences in sugar and plant hormone concentrations and in activities of sucrolytic enzymes in source-leaves and the shoot apex between both cultivars, together with the response of chilling-induced growth depression to chemical manipulations of abscisic acid (ABA) level, suggest that a higher transport and utilisation of carbohydrates and higher ABA levels in the growth sinks of the tolerant cultivar have protective functions against chilling. The metabolic data corresponded to the results of a Petunia-microarray. This showed cultivar-specific hybridisation of sequences belonging to genes putatively controlling key enzymes of sucrolysis, glycolysis, citrate cycle and the carotinoid pathway upstream of ABA biosynthesis. Further using the recently sequenced parental genomes of Petunia hybrida and modern tools of molecular genetic, the role of newly identified candidate genes putatively controlling chilling tolerance in petunia can be tested and identified control genes can be implemented into respective breeding programs.