Siegfried Zerche

Transcriptomic analysis reveals ethylene as stimulator and auxin as regulator of adventitious root formation in petunia cuttings.

Adventitious root (AR) formation in the stem base (SB) of cuttings is the basis for propagation of many plant species and petunia is used as model to study this developmental process. Following AR formation from 2 to 192 hours post-excision (hpe) of cuttings, transcriptome analysis by microarray revealed a change of the character of the rooting zone from SB to root identity. The greatest shift in the number of differentially expressed genes was observed between 24 and 72 hpe, when the categories storage, mineral nutrient acquisition, anti-oxidative and secondary metabolism, and biotic stimuli showed a notable high number of induced genes. Analyses of phytohormone-related genes disclosed multifaceted changes of the auxin transport system, auxin conjugation and the auxin signal perception machinery indicating a reduction in auxin sensitivity and phase-specific responses of particular auxin-regulated genes. Genes involved in ethylene biosynthesis and action showed a more uniform pattern as a high number of respective genes were generally induced during the whole process of AR formation. The important role of ethylene for stimulating AR formation was demonstrated by the application of inhibitors of ethylene biosynthesis and perception as well as of the precursor aminocyclopropane-1-carboxylic acid, all changing the number and length of AR. A model is proposed showing the putative role of polar auxin transport and resulting auxin accumulation in initiation of subsequent changes in auxin homeostasis and signal perception with a particular role of Aux/IAA expression. These changes might in turn guide the entrance into the different phases of AR formation. Ethylene biosynthesis, which is stimulated by wounding and does probably also respond to other stresses and auxin, acts as important stimulator of AR formation probably via the expression of ethylene responsive transcription factor genes, whereas the timing of different phases seems to be controlled by auxin.

Seed Potassium Concentration Decline During Maturation Is Inversely Related to Subsequent Germination of Primrose

Abstract It has been reported previously that seed potassium (K) concentrations were negatively correlated with the seeds germination capacity in randomly sampled commercial seed lots of primrose (Primula vulgaris Huds.). To explain this relationship, hypotheses about a causal role for the seed maturation level at harvest date and the possible environmental and genetic stability of the correlation were explored. Mineral composition and quality of Primula seeds were investigated (1) as to how they were affected by maturation stage with weekly seed harvests from the 7th to the 15th week post-anthesis (WPA), and (2) using a nutrient solution culture of gonophores varying in K supply (0, 1.5, 3, and 6 mmol K L−1) during reproductive growth. Concentrations of minerals [K, nitrogen (N), phosphorus (P), calcium (Ca), and magnesium (Mg)] in leaves and whole seeds were analyzed, as were selected seed characteristics (embryo and endosperm development, seed mass, viability, and germination) of two parental lines (pin and thrum morph of genotypes 45 and 48) for hybrid-seed generation. Leaf-mineral composition and vegetative growth were mostly affected by K supply. In contrast, mineral concentrations per gram dry seed mass of seeds harvested at mature stage (15 WPA) were not influenced (i.e., K, Mg), or only slightly so (i.e., N, P, Ca), by differential K supply to gonophore plants. However, seeds harvested at the premature stage (8 WPA) revealed concentrations of K, Ca, and Mg at evidently increased levels, with K and Mg clearly reflecting the differential K availability. During further maturation, the seed N and P concentrations remained relatively constant in respect to the considerable growth in single seed mass. In contrast, concentrations of K, Ca, and Mg decreased markedly and simultaneously with rapid seed growth. Irrespective of the different growth rates of seed mass between the genotypes, the decreasing seed concentrations (31% decline) strongly correlated with increasing percentage germination (40% rise) from 9 to 14 WPA (r = −0.81; n = 21; p < 0.01). However, weaker negative correlations between germination and seed Ca or Mg concentrations resulted from pronounced genotypic differences in levels of these two seed elements. Taken together, seed K concentration is the most reliable measure to indicate maturity and to act as a marker for low germination capacity due to premature seed harvest. In addition, possible interactions between climate impact, phytohormones, and seed mineral dynamics during maturation should be explored.