Abstract
Polyamines (PA) have a protective role in maintaining growth and development in Scots pine during abiotic stresses. In the present study, a controlled liquid Scots pine embryogenic cell culture was used for studying the responses of PA metabolism related to potassium deficiency. The transcription level regulation of PA metabolism led to the accumulation of putrescine (Put). Arginine decarboxylase (ADC) had an increased expression trend under potassium deficiency, whereas spermidine synthase (SPDS) expression decreased. Generally, free spermidine (Spd) and spermine (Spm)/ thermospermine (t-Spm) contents were kept relatively stable, mostly by the downregulation of polyamine oxidase (PAO) expression. The low potassium contents in the culture medium decreased the potassium content of the cells, which inhibited cell mass growth, but did not affect cell viability. The reduced growth was probably caused by repressed metabolic activity and cell division, whereas there were no signs of H2O2-induced oxidative stress or increased cell death. The low intracellular content of K+ decreased the content of Na+. The decrease in the pH of the culture medium indicated that H+ ions were pumped out of the cells. Altogether, our findings emphasize the specific role(s) of Put under potassium deficiency and strict developmental regulation of PA metabolism in Scots pine.
Highlights
Potassium (K+ ) deficiency is a common practical problem in drained peatlands in Finland
We found that transcription level regulation altered the cellular PA contents under potassium deficiency leading to the accumulation of Put like previously observed in adult Scots pine trees suffering from potassium stress [4], and young Scots pine seedling exposed to severe drought [36]
The growth of the cell mass was highest under the 100% and 150% potassium treatments and decreased linearly with the potassium content (Figure 1b, Supplementary Table S3)
Summary
Potassium (K+ ) deficiency is a common practical problem in drained peatlands in Finland. Every fourth forested stand growing on drained peatland suffers from a severe potassium shortage, and imbalances in nutrition are most common in deep-peated and nitrogen-rich sites [1]. The severe shortage may lead to dieback or even death of trees on drained peatlands [2], which enhanced further studies [3,4] on foliar nutrient diagnosis to determine the critical levels for potassium and responses to varying forest fertilization treatments. Potassium is an essential nutrient and the most abundant cation in plants [6]. The role of potassium is related to functioning as a cofactor of enzymes and maintaining ion homeostasis by improving cell membrane stability and osmotic adjustment ability [6]. Due to the several functions of potassium, its intracellular content and intercellular and organ level transport are strictly regulated
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