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Maize is the staple food crop and essential for world food security. Maize plants’ water requirement is high for proper growth and development at vegetative stage and grain formation at reproductive stage. Drought is the major abiotic stress that affects almost all the growth stages of maize crop and it has a strong impact on all the physiological process of maize plants. Similarly, N metabolism is of central importance during drought stress. Nitrogen (N) is one of the macronutrients; it is a major requirement for crop growth and grain yield of maize. Therefore, nitrogen and water separately or in combination are the two most critical factors in maize production. Drought modifies source-sink relations and weakens the source and sink strength, which disturbs plant’s growth, plant’s adaptation to stress, and consequently affects crop productivity.

In the present work, tropical maize genotypes were evaluated for multiple stresses (drought × low-N and waterlogging × low-N) applied simultaneously to 30-day-old maize seedlings. Two-dimensional gel electrophoresis was used to examine the protein changes induced by combined stress, in leaves, of tolerant and susceptible genotypes. Moreover, physiological and biochemical parameters were assessed to understand the physiological status of tolerant and susceptible genotypes under combined stress. The results show that up-regulated proteins of the tolerant genotype have a significant role in activating defense response, restoration of plant growth, and to maintain metabolic homeostasis under stressful conditions. Therefore, they contribute to improve and maintain the state of acclimation of the genotype under stress. Alternatively in the susceptible genotype, the up-regulated proteins are representative biomarkers of stress or are involved in the defense against pathogens and efforts to maintain energy metabolism. Thus, protecting the survival of the genotype under multiple stress conditions. We conclude that depending on the given stress treatment, tolerant and susceptible genotypes differed in stress-enduring approaches. Therefore, the study provides insight to comprehend the response of tolerant and susceptible genotypes under combined stress conditions, which could be valuable for further research and will demonstrate that it is advantageous to select combined stress-tolerant genotypes.

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9Drought, heat, high temperature, waterlogging, low-N stress, and salinity are the major 10 environmental constraints that limit plant productivity. In tropical regions maize grown during the 11 summer rainy season, and often faces irregular rains patterns, which causes drought, and 12 waterlogging simultaneously along with low-N stress and thus affects crop growth and 13 development. The two maize genotypes CML49 and CML100 were subjected to combination of 14 abiotic stresses concurrently (drought and low-N / waterlogging and low-N). Metabolic profiling of 15 leaf and roots of two genotypes was completed using GC-MS technique. The aim of study to reveal 16 the differential response of metabolites in two maize genotypes under combination of stresses and 17 to understand the tolerance mechanism. The results of un-targeted metabolites analysis show, the 18 accumulated metabolites of tolerant genotype (CML49) in response to combined abiotic stresses 19 were related to defense, antioxidants, signaling and some metabolites indirectly involved in nitrogen 20 restoration of the maize plant. Alternatively, some metabolites of sensitive genotype (CML100) 21were regulated in response to defense, while other metabolites were involved in membrane 22 disruption and also as the signaling antagonist. Therefore, the present study provides insight into the 23 molecular mechanisms of tolerance under various stresses of maize plants, that governed on the 24 regulation of cell wall remodeling, maintain metabolic homeostasis, defense against the pathogen, 25proper signaling, and restore growth under stress conditions. 26 27 29 30 Abbrevations: 31 GC-MS-Gas chromatography mass spectrometry32 Low-N-Low nitrogen stress 33 DAS-Days after sowing 34 PCA-Principal component analysis 35 . 36 37 2 1. Introduction 38 Crop faces various stresses in their life span including abiotic and biotic. Several abiotic stresses 39 that affect crop growth, and development are drought, waterlogging, low nutrient availability, 40 salinity, high temperature and heat. The predicted changes in the global climate has accentuate in 41 the frequency and intensity of abiotic factors, most of the abiotic stresses occur in combination, for 42 instant, in tropical area's terminal drought and waterlogging occurs simultaneously during summer-43 rainy season. Although on many occasions the stresses are for shorter duration and relatively mild 44 in nature, but have a significant impact on plant growth and development. Therefore, co-occurrence 45 of abiotic stresses are more destructive to crops than their separate occurrence at different crop 46 growth stages (Mittler 2006; Prasad et al 2011). Besides, the composite responses of plants due to 47 various concurrent stresses rely on signals, these varied and contrast signals may interact with each 48 other to enhanced or obstruct one another (Vile et al. 2012; Suzuki et al. 2014). Maize is the most 49 important cereal, grown at the wide geographical ranges of latitude and longitude. In South Asia, 50 particularly in tropi...

Abiotic stresses are the major threat to crops regardless of their nature, duration, and frequency, their occurrence either singly, and or combination is deleterious for the plant growth and development. Maize is most important crop largely grown in tropical region in summer rainy season, often face a stress combination of drought and waterlogging. We previously showed under multiple stresses up-regulated leaf proteins of maize plants were involved to enhance the tolerance mechanism of tolerant genotype. Whereas, in susceptible genotypes up-regulated proteins ameliorate to survive the stressful condition. Further to understand the response of roots proteome under multiple stresses was determined using the 2DE technique. The results of the root proteome show the up-regulated proteins of CML49 genotype (tolerant) are involved in enhancing the N content, cell wall remodeling, and acclimatization during the stresses. Up-regulated proteins of CML100 genotype (sensitive) are stressed marker of roots primary and secondary metabolism. However, the root proteome of both genotypes correlates with the leaf proteome (previous). Therefore, the present study and our previous results provide comprehensive insight into the molecular mechanisms of tolerance in multiple abiotic stresses of maize plants.

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