Potassium nutrition of maize:Uptake,transport,utilization,and role in stress tolerance

Potassium(K) is an essential macronutrient for plant growth and development and influences yield and quality of agricultural crops.Maize(Zea mays) is one of the most widely distributed crops worldwide.In China,although maize consumes a large amount of K fertilizer,the K uptake/utilization efficiency(KUE)of maize cultivars is relatively low.Elucidation of KUE mechanisms and development of maize cultivars with higher KUE are needed.Maize KUE is determined by K+uptake,transport,and remobilization,which depend on a variety of K+channels and transporters.We review basic information about K+channels and transporters in maize,their functions and regulation,and the roles of K+in nitrogen transport,sugar transport,and salt tolerance.We discuss challenges and prospects for maize KUE improvement.

The Potassium Transporter AtKUP12 Enhances Tolerance to Salt Stress through the Maintenance of the K^(+)/Na^(+)Ratio in Arabidopsis

Potassium(K^(+))is a necessary nutrient for plant growth and crop production.The K^(+)transporter plays crucial roles in the absorption and transport of K^(+)in plants.Most K^(+)transporters in Arabidopsis have been reported,but AtKUP12,which is a member of the KT/KUP/HAK family,has not yet been the subject of relevant in-depth research.In the present study,we demonstrated that AtKUP12 plays a crucial role in K^(+)uptake in Arabidopsis under 100μM low-K^(+)and 125 mM salt stress conditions.AtKUP12 transcripts were induced by K^(+)deficiency and salt stress.We analyzed the K^(+)uptake of AtKUP12 using the K^(+)uptake-deficient yeast R5421 and Arabidopsis mutant atkup12.Transformation with AtKUP12 rescued the growth defect of mutant yeast and atkup12 mutant plants at the low-K^(+)concentration,which suggested that AtKUP12 might be involved in high-affinity K^(+)uptake in low-K^(+)environments.In comparison to the wild-type(WT)and atkup12-AtKUP12 complementation lines,atkup12 showed a dramatic reduction in potassium concentration,K^(+)/Na^(+)ratio,and root and shoot growth on 12-day-old seedlings under the salt conditions;however,there was no significant difference between the complementation and WT lines.Taken together,these results demonstrate that AtKUP12 might participate in salt tolerance in Arabidopsis through K^(+)uptake and K^(+)/Na^(+)homeostasis.

PtHAK5, a candidate for mediating high-affinity K^+ uptake in the halophytic grass, Puccinellia tenuiflora

Puccinellia tenuiflora is a typical salt-excluding halophytic grass with strong salt-tolerance, which enhances tolerance by restricting Na^+influx as well as having a strong selectivity for K^+ over Na^+. The HAK5 K^+ transporters generally modulate effective K^+acquisition in plants, especially under low K^+ condition. In this study,Pt HAK5 from P. tenuiflora was isolated by RT-PCR and characterized using yeast complementation. The results showed Pt HAK5 consisted of 784 amino acids and shared over 80% homology with the identified high-affinity K^+ transporter HAK5 from other higher plants. The expression of PtHAK5 rescued the K^+ -uptake-defective phenotype of yeast strain CY162. In conclusion, PtHAK5 is a candidate for mediating high-affinity K^+ uptake under low K^+ conditions.

Introduction of Bacillus thuringiensis(Bt)gene does not reduce potassium use efficiency of Bt transgenic cotton(Gossypium hirsutum L.)

Background:Potassium(K)deficiency has become a common field production problem following the widespread adoption of Bacillus thuringiensis(Bt)transgenic cotton(Gossypium hirsutum L.)worldwide.The purpose of this study was to clarify whether the introduction of Bt gene directly reduces the K-use efficiency of cotton to induce K deficiency.Results:The cotton variety,Jihe 321(wild type,WT)and its two Bt(Cry1Ac)-transgenic overexpression lines(OE-29317,OE-29312)were studied in field with low soil-test K+(47.8 mg·kg^(−1)).In the field with low soil-test K+,only OE-29317 had less biomass and K+accumulation than the WT at some growth stages.Both Bt lines produced similar or even greater seed cotton yield than WT in the field.When the Bt gene(~70%)in OE-29317 and OE-29312 plants was silenced by virus-induced gene silencing(VIGS),the VIGS-Bt plants did not produce more biomass than VIGSgreen fluorescent protein(control)plants.Conclusions:The introduction of Bt gene did not necessarily hinder the K use efficiency of the cotton lines under this study.