Transcriptional and Metabolic Responses of Maize Shoots to Long-Term Potassium Deficiency

AimsPotassium is important for plant growth and crop yield. However, the effects of potassium (K+) deficiency on silage maize biomass yield and how maize shoot feedback mechanisms of K+ deficiency regulating whole plant growth remains largely unknown. Here, the study aims to explore the maize growth and transcriptional and metabolic responses of shoots to long-term potassium deficiency.MethodsThe growth of silage maize and its biomass were analyzed with K+ treatment in field and hydroponic experiments. Furthermore, transcriptional and metabolic profiles of shoots were investigated for their effects on maize development under K+ deficiency condition. ResultsUnder K+ insufficiency condition, the biomass yield of silage maize decreased by 14%-17% in two-year field trials. The transcriptome data showed that there were 390 differently expressed genes overlapping and similarly regulated in the two varieties and they were considered as the fundamental responses to K+ deficiency in maize shoots, with many stress-induced genes involved in transport, primary and secondary metabolism, regulation, and other processes involved in K+ acquisition and homeostasis. Metabolic profiles indicated that most amino acids, phenolic acids, organic acids, and alkaloids were accumulated in shoots under K+ deficiency condition and part of the sugars and sugar alcohols also increased. ConclusionOur results suggested putrescine and putrescine derivatives were specifically accumulated under K+ deficiency condition, which may play a role in feedback regulation of shoot growth. These results confirmed the importance of K+ on silage maize production and provided a deeper insight into the responses to K+ deficiency in maize shoots.

Grafting Tobacco onto Nutrient-efficient Rootstocks Improves Photosynthesis

Potassium deficiency is a major problem limiting tobacco (Nicotiana tabacum) growth, and grafting has the potential to alleviate it. To compare the photosynthetic performance of grafted tobacco under different potassium levels, tobacco Yunyan 87 (main cultivar) and Wufeng No. 2 (potassium high-efficiency cultivar) were selected to conduct mutual grafting trials in the form of hydroculture with two potassium supply levels (5 mmol·L−1 K and 0.5 mmol·L−1 K). The plant growth, gas exchange parameters, chlorophyll a fluorescence, and the initial ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO) activity were measured. The results showed that potassium deficiency could significantly decrease the net photosynthetic rate, stomatal conductance (gS), and transpiration rate in the tobacco leaves, resulting in nonstomatal restriction. Grafting could effectively alleviate this problem. The actual quantum yield of photosystem II (PSII) photochemicals in ‘Yunyan 87’ increased 29.4% and 20.3% by grafting, respectively, under normal and low potassium levels. Compared with nongrafted ‘Yunyan 87’, grafting also effectively improved the electron transfer efficiency of PSII in the tobacco leaves under low potassium stress by reducing nonradiation energy dissipation and enhancing the initial activity of RuBisCO. From this study, it can be known that grafted tobacco plants can improve their photosynthesis by alleviating the nonstomata restriction of leaves under potassium stress and improving the electron transfer efficiency of PSII.

Polyamine Metabolism in Scots Pine Embryogenic Cells under Potassium Deficiency

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.