Potassium Role In Altering Cotton Leaves Physiology To Acclimate And Recover Drought Stress At Flowering Stage

The maintenance of high plant functions at low plant water status,and the recovery of plant functions after water stress are the major physiological processes that can contribute to the sustainability of high yield under sporadic drought events.Leaf has a pivotal role in plant energy capture and carbon assimilation and therefore,has built-in potential to acclimate the prevailing environmental stresses.A two year pot experiment was conducted to evaluate whether potassium(K)application can enhance cotton(Gossypium hirsutum L.)potential to maintain plant functions under drought and recover after re watering conditions.Two cotton cultivars,low K-sensitive(Siza 3)and-tolerant(Simian 3),were exposed to severe drought stress at flowering and bolling stages under three K rates(0,150,and 300 K2O kg ha’1),and then rewatered for recovery.Under drought stress,cotton plants showed a severe decline in leaf photo-physiological activities,carbon and nitrogen metabolism,dry matter partitioning and enhanced lipid peroxidation as compared to well watered plants.However,plants under K application not only showed lower decline in these traits but also facilitated the plants to recover their functions more efficiently as compared to plants without K application.The plants with K application showed lower lipid peroxidation and higher carbon and nitrogen metabolizing enzymes activities and enhanced osmotic adjustment under drought stress as compared to plants without K application.Additionally,Siza 3 exhibited more constructive effects of K application than Simian 3.The results suggest that K application enhances cotton potential to maintain higher plant functions under drought and to recover after rewatering.The main results are as follows:1.Potassium improves acclimation to and recovery from drought stress in functional leaf photo-physiological activities of cotton(Gossypium hirsutum L.)To investigate whether potassium(K)application enhances cotton potential to maintain plant functions during drought and recovers after rewatering,the low K-sensitive(Siza 3)and-tolerant(Simian 3)cotton cultivars were exposed to severe drought stress at flowering and bolling stage under three K application rates(0,150,and 300 K2O kg ha-1),and then rewatered for recovery.Under drought stress,cotton plants showed a severe decline in leaf water potential,stomatal conductance,photosynthetic rate,and maximum and actual efficiency of PSII,resulting in higher photoinhibition and lipid peroxidation as compared to the well watered plants.However,plants under K application not only showed lower decline in these traits but also facilitated the plants to recover their functions more efficiently as compared to the plants without K application.The plants with K application showed lower lipid peroxidation and higher enzymatic antioxidant activity with higher proline accumulation as compared to the plants without K application.Siza 3 performed better under higher K application than Simian 3 and significant relationships between rate of recovery of photo-physiological activities and K application rates were observed.The results suggest that K application enhances cotton potential to maintain higher photo-physiological activities under drought and to recover after rewatering.2.Potassium fertilizer improves drought stress alleviation potential in cotton by enhancing photosynthesis and carbohydrate metabolismUnder drought,limited photo-assimilates synthesis and their poor partitioning is a main constraint to final yield production in cotton(Gossypium hirsutum L.).In this section we explored the potassium(K)role in photo-assimilation and carbohydrate metabolism under drought stress in two different cotton cultivars.Plants were exposed to well-watered[(75-80%soil relative water content(SRWC)]and water stress(35-40%SRWC)conditions for a week followed by re-watering to the level of well-watered plants.The results showed that water-stressed plants under K deficiency(K0)exhibited significant decline in net photosynthesis,stomatal conductance,intercellular CO2 concentration and ribulose-1,5-bisphosphate carboxylase(Rubisco)activity resulting in reduced photo-assimilates synthesis and partitioning towards reproductive organs in both cultivars.Conversely,K application decreased the decline in photosynthesis,Rubisco activity and dry matter production and translocation.The positive effects of K application increased as the rate of K fertilization increased,and that was more pronounced in Siza 3 than Simian 3 during both years.Drought stress decreased starch but increased sucrose content;whereas,K application maintained higher concentration of sucrose in leaves of water-stressed plants through the regulation of higher sucrose phosphate synthase(SPS),sucrose synthase(SuSy)and lower soluble acid invertase(SAI)activities.The results of the study concluded that K application regulated the photo-assimilation and translocation process along with the related enzymes activities in cotton.The study suggests that K nutrient management strategy has the potential to minimize the impacts of drought stress on cotton.3.Potassium application regulates nitrogen metabolism and osmotic adjustment in cotton(Gossypium hirsutum L.)functional leaf under drought stressThe aim of this part of above work was to look into whether potassium(K)maintains nitrogen metabolism and osmotic adjustment development of cotton functional leaves to sustain growth under soil drought and rewatering conditions;the plants of Siza 3(low-K sensitive)and Simian 3(low-K tolerant)were grown under three different K rates(K0,K1 and K2;0,150 and 300kg K2O ha-1,respectively)and exposed to severe drought stress at 40±5%soil relative water content(SRWC)at flowering stage by withholding water for eight days followed by rewatering to well watered level(75±5%SRWC).Plants of both cultivars showed a decrease in leaf relative water content and osmotic potential of the functional leaves and developed osmotic adjustment with an increase in the contents of free amino acids,soluble sugars,inorganic K and nitrate under drought stress as compared to well watered plants.In drought stressed plants,nitrogen metabolizing enzymes activities of nitrogen reductase(NR),glutamine synthetase(GS)and glutamate synthase(GOGAT)were diminished along with decreased chlorophyll content and soluble proteins.However,drought stressed plants under K application not only exhibited higher leaf water status and osmotic adjustment with greater accumulation of osmolytes but also regulated nitrogen metabolism by maintaining enzyme activities,soluble proteins and chlorophyll content in functional leaves as compared to the plants without K application.Low-K sensitive cultivar of Siza 3 showed better stability in enzymes activities,especially in GS and GOGAT under higher K rates than low-K tolerant of Simian 3.The results of the study suggested that K application enhances cotton plants’ potential of sustaining high nitrogen metabolizing enzymes activities and related components to supplement osmotic adjustment under soil drought conditions.