Mitogen Activated Protein Kinase: Function and Responses to Different Stresses in Plants

Mitogen Activated Protein Kinase (MAPK) pathway is the most commonly studied signaling mechanisms, consisting of different groups of protein kinases that participate in regularly connecting interpretation of external stimuli that can change in gene expression or cellular organization within eukaryotic systems. The MAP kinase pathways functions in plants cell signaling (intra- and extra). MAPK cascades follow a response system. MAP kinases are the component of kinase constituents that deliver signals from sensors to responders in eukaryotes including plants. Several pathways are activated under different environmental stresses. Stimulating agents may be biological (biotic) like microbial infections or environmental (abiotic) like temperatures threshold, high salt concentration, drought, heavy metal, Ultra-violet radiation, ozone gases and reactive oxygen species (ROS). The involvement of MAPK signaling pathway in different stresses has been widely studied. In this review we also try to highlight MAPK cascades, its regulation, functions and recent findings in various cellular processes against stress conditions.

N-Zn Dynamics under Different Rice Production Systems

Water scarcity and nutrient availability constraints rice production and interact mutually to affect potential crop yields. Two field studies were conducted during 2008-09 to monitor N-Zn dynamics under alternate wetting and drying (AWD) and direct seeded aerobic rice (DSR) in comparison to conventional transplanting (TPR). It comprised of application of recommended N (143 kg ha-1) in two or three splits and soil or foliar Zn (25 kg ha-1; ZnSO4, 21%) at basal or transplanting, tillering and panicle initiation in experiment No. 1 & 2 for each of the rice system respectively. Crop response in terms of soil N and Zn, plant uptake, improved growth, chlorophyll contents, yield and quality was better in 2008 than 2009. Soil NH4+-N or NO3--N contents, total plant N and its translocation into leaf, stem and panicles was high with application of three (1/2 basal+1/4 tillering+1/4 anthesis) or 1/3 (at basal+tillering+ anthesis) and two N splits (1/2 basal+1/2 anthesis) than other splits in TPR, AWD and DSR during both seasons respectively. Total dry matter accumulation, LAI, pre and post-anthesis LAD, CGR and NAR were also higher in DSR with two equal (1/2) splits (basal+anthesis) and were followed by TPR and AWD for three splits (1/2 basal+1/4 tillering+1/4 anthesis) during 2008. During 2009, total dry matter accumulation was high in DSR and was followed by TPR and AWD while Chl contents, LAI, LAD, CGR and NAR were higher in TPR followed by AWD and DSR with three or two equal (1/3) splits at (basal+tillering+ anthesis) or transplanting+tillering and 1⁄2 (basal+ anthesis) in TPR, AWD and DSR respectively. Improved N nutrition with three or two splits resulted in increased leaf water potential with greater osmotic potential and high turgor maintenance in 2008 than 2009 with lower values of plant water relations. Similar response was found for improved yield and yield components Nonetheless, effect on 1000-kernel weight in 2008 and sterile spikelets were non-significant in 2009 respectively. Kernel and straw yields while harvest index were also higher with application of three or two equal N splits in DSR, TPR and AWD in 2008 while response was opposite in 2009 with order of increase in straw and kernel yield and harvest index in TPR>AWD>DSR respectively. Regarding kernel quality, effect for abortive and chalky kernels was non-significant among the production systems in 2008. However, percentage of opaque, chalky and abortive kernels was high in DSR decreasing normal kernel percentage in both seasons than AWD and TPR with improved kernel quality. Kernel length in both seasons while kernel width was non- significant during 2008 and 09 respectively with significant interaction and kernel water absorption ratio, kernel proteins were high with low amylose contents with three or two N split applications in all three cultivation systems. High water productivity was observed in AWD and DSR than TPR during 2008 and for AWD in 2009 with two or three splits. Due to increased kernel yield, farmer’s profitability in terms of benefit: cost benefit ratio was also high with three or two splits in TPR, AWD and DSR during both seasons. In case of experiment No. 2, soil Zn application at tillering or panicle initiation increased the plant or soil Zn contents in TPR, AWD and DSR respectively during 2009 and increased Zn distribution from leaves or stem towards panicle in comparison to high soil and plant Zn contents with soil application at transplanting and tillering in AWD and DSR while for foliar applied Zn in TPR respectively. Soil applied Zn at seeding in DSR also increased crop field emergence while high dry matter accumulation, Chl contents, LAI, pre- and post-anthesis LAD, CGR and NAR was the result of soil applied Zn at tillering and transplanting in AWD and DSR while for foliar applied Zn in TPR during 2008. However, soil Zn application at tillering or panicle initiation resulted in better crop growth in all three rice systems in 2009. Similar trend was observed for yield and yield components and spikelet sterility was also reduced with soil Zn application at transplanting and tillering or foliar applied Zn at panicle initiation in AWD, DSR and TPR during 2008 than 2009. Straw and kernel yield and harvest index were also high during 2008 than 2009 with similar response among the rice systems. Zn application at these stages also improved the plant water status with maintenance of high turgor. Soil Zn application improved the filled kernels percentage with reducing spikelet sterility and improved kernel, length width and kernel water absorption ration and protein contents while reduced amylose contents. However, response was more pronounced in DSR with soil Zn application. Crop water productivity was also for soil applied Zn at tillering or panicle initiation with benefit:cost ratio when soil Zn was applied at these stages due to increased crop yield. It is concluded that for better crop growth, yield response and profitability application of N in three splits (1/2 at basal/transplanting+1/4 or 1/3 (tillering+anthesis) in TPR and AWD while 1⁄2 at basal + 1⁄2 anthesis in DSR can be recommended. Similarly soil Zn application at tillering or panicle initiation in all three rice systems for increased tillering, reduced panicle sterility and improved yield and grain Zn contents.