Henk Gude

The effects of abscisic acid on growth and respiratory characteristics of potato tuber tissue discs

Incubation of potato tuber tissue discs on B5 medium supplemented with 1-naphtyl-acetic acid (NAA) led to callus formation, irrespective of the presence of kinetin; without NAA no callus formation occurred. Incubation in the presence of abscisic acid (ABA) reduced the increases in fresh weight and dry weight both in callus-forming and in non-callus-forming tissue. Mitochondrial respiration was lowered by ABA as well. The induction of the alternative, CN-resistant pathway was inhibited by the presence of ABA, especially in mitochondria from non-callus-forming tissue.The in vivo respiration of the callus-forming tissue was higher than that of the non-callus-forming tissue. Total respiration, cytochrome pathway activity and the capacity of the alternative pathway were all lowered in callus-forming tissue by treatment with ABA. The in vivo activity of the alternative pathway was low in all tissue types, especially after ABA-treatment. The slight stimulation by hydroxamates of the oxygen uptake of callus-forming tissue incubated on medium with NAA and ABA indicates the involvement of a hydroxamate-activated peroxidase in the oxygen uptake of this tissue; this peroxidase seemed not to participate in the oxygen uptake of the other tissues types.In non-callus-forming tissue the oxygen uptake of ABA-treated tissue was very low and almost completely resistant to the combined addition of inhibitors of both the cytochrome and the alternative pathway, indicating that the in vivo activity of the mitochondria in the oxygen uptake of the tissue was very low. The possible causes for this ABA-effect are discussed. In non-callus-forming tissue the treatment with ABA creates a situation which is comparable with that observed in intact potato tubers. This situation is characterized by a tissue respiration lower than that of the isolated mitochondria and an alternative pathway capacity that is low or absent.

The Role of Some Phytohormones in the Regulation of Respiratory Pathways in Potato Tuber Tissue

Incubating potato tuber tissue discs on nutrient media with various phytohormones makes it possible to manipulate the development of the tissue and is thus a useful tool for assessing the role of phytohormones in development and concomittant physiological changes. In the present study tissue discs were forced into two major directions of development: callus-forming discs and non callus-forming discs. In these two types of tissue the role of the phytohormones ethylene and abscisic acid (ABA) with respect to their regulation of the induction and functioning of respiratory pathways (in particular alternative oxidase) was studied.

Hydroxamate-Activated Peroxidases: Interference with Determination of Respiratory Pathway Activity ?

In many studies on plant respiration, hydroxamates are an important tool in the determination of the flow through the “efficient” cytochrome path and the “inefficient” alternative path (Laties,1982). A complete and specific inhibition of the alternative pathway by these hydroxamates is a prerequisite for such an use of this type of inhibitors. In this paper the properties of a peroxidase will be described, that causes an increased oxygen uptake after addition of hydroxamates.