ABSTRACT
Abstract. Soil salinity is one of the major environmental constraints to crop production, restricting the efficient utilization of agricultural land worldwide. Most plants will come in contact with Na+ at some stage during their life cycle, although their level of exposure may vary greatly. All plants tested so far have been shown to take up Na+ in the low affinity range. Salt stress is a complex phenomenon in plants imposing hyperionic and hyperosmotic stress, ionic imbalance, disrupting several major metabolic activities and thus limiting crop productivity. The osmotic stress and ionic excess arise in sequence with two distinct phases, with genotypic differences in salt tolerance. The tolerance
mechanism toward salt stress is to minimize ion disequilibrium or osmotic stress or alleviate the consequent secondary effects caused by these stresses. The activation of the SOS signaling pathway is well recognized as a key mechanism for Na+ exclusion and ion homeostasis control at the cellular level. Similarly, polyamines also function as stress messengers during plant responses to salinity stress signaling. Polyamines bind to and regulate the activity and subcellular localization of target proteins implicated in salt and osmotic stress signaling and development. Salt stress promotes the production of reactive oxygen species such as hydrogen peroxide and the superoxide anion. Increasing evidence indicates that
4.1 Introduction / 52 4.2 Osmotic and Ionic Stress / 53 4.3 Response of Crops to Salt Stress / 53 4.4 Salt Uptake, Partitioning, and Remobilization / 56 4.5 Osmotic Adjustment and Osmoprotection / 58 4.6 Signaling Pathways for Ion Homeostasis / 59
4.6.1 SOS Pathway of Na+ Exclusion, Remobilization, and Partitioning / 59 4.7 Signaling Pathways for Osmotic Adjustment and Osmoprotection / 60
4.7.1 Polyamine Accumulation and Stress Response / 60 4.7.2 ABA Signaling / 61 4.7.3 ROS Signaling / 62 4.7.4 Phosphatidic Acid Signaling / 63 4.7.5 Calcium Signaling / 65 4.7.6 MAPK Signaling / 66
4.8 Cross Talk between Different Signaling Pathways: Salinity and Other Biotic and Abiotic Stress Signaling Cross Talk / 67
4.9 Conclusion and Future Prospects / 68 Acknowledgments / 69 References / 69
lipid signalling is an integrative part of the complex regulatory network in plant response toward salinity stress. Besides this, calcium has been recognized as an important secondary messenger in plants under various developmental cues, as well as salinity. Secondary messengers such as Ca2+, cGMP, and reactive oxygen species show rapid increase after elevation in the salt concentration. Salt-and hyperosmosis-induced secondary messengers activate various members of the MAPK family, which play
pivotal roles in the plant’s responses. The knowledge of salinity stress was greatly enhanced by identifying the convergent and divergent pathways between salinity and other abiotic stress responses. This chapter gives an overview of different salt stress signaling pathways and discusses their specificity and cross talk during signaling responses.
