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.

Plant Growth,Yield Components,Economic Responses,and Soil Indigenous K Uptake of Two Cotton Genotypes with Different K-Efficiencies

HG103,a high K-efficiency cotton cultivar with high-yield potential,and LG122,a low K-efficiency cotton cultivar with low-yield potential were used to study the genotypic variation on yield,economic responses,and soil indigenous K exploitation for cotton in pot and field conditions in 2006 and 2007.Results indicated that both the cultivars differed significantly in the rate of translocation of dry matter into reproductive organs and the time of running into reproductive stage.Cotton yield and economic parameters of HG103 were much better than LG122.Potassium content in cotton shells reached the highest level at maturity stage for both genotypes.Results also showed that the K content in each plant part of HG103 was lower than that of LG122.The two genotypes showed different efficiencies and abilities on absorbing soil rapidly available K and slowly available K.LG122 showed higher absorption of K rate than HG103 after K fertilization,but on the contrary,HG103 uptake more soil indigenous K than LG122 in no K fertilization treatment.This result indicated that HG103 could tolerant and absorb more soil indigenous K than LG122,under condition of soil K stress.LG122 could grow well and absorb more K nutrient when soil K supply is sufficient.Our results demonstrated that higher K content in plant tissues and higher K uptake by plant may not an exclusive condition for high yield planting with K fertilization.Earlier translocation of more dry matters into reproductive organs is one of the key mechanisms of high K use efficiency in cotton.

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.

Mechanistic Analysis of AKT1 Regulation by the CBL-CIPK-PP2CA Interactions

Arabidopsis K＋ transporter I （AKT1） participates in K＋ uptake in roots, especially under Iow-K conditions. We recently identified a Ca2＋ signaling pathway consisting of multiple calcineurin B-like calcium sensors （CBLs） and multiple target kinases （CBL-interacting protein kinases or CIPKs） that phosphorylate and activate AKT1, whereas a specific PP2C-type phosphatase inactivates CIPK-dependent AKT1 activity. In this study, we analyzed the interactions between PP2Cs and the CBL-CIPK pathway and found previously unsuspected mechanisms underlying the CBL-CIPK-PP2C signaling processes. The interaction between the CIPKs and PP2Cs involves the kinase domain of the CIPK component, in addition to the protein phosphatase interacting motif （PPI） in the regulatory domain. Furthermore, specific CBLs physically interact with and inactivate PP2C phosphatases to recover the CIPK-dependent AKT1 channel activity. These findings provide fur- ther insights into the signaling network consisting of CBL-CIPK-PP2C interactions in the activation of the AKT1 channel.