Preface Agriculture per say continue to be dependent of prevailing environmental condition and various factors of abiotic stresses are serious threats to agriculture. The situation assumes its importance in India as this country is heavily dependent on arrival, period and duration of monsoon for its agricultural production. According to FAO statistics, more than 800 million hectares of land throughout the world are currently salt-affected, including both saline and sodic soils equating to more than 6% of the world’s total land area. Continuing salinization of arable land is expected to have overwhelming global impact, resulting in a 30% loss of agricultural land over the next 25 years and up to 50% loss by 2050. Overall, it has been estimated that the world is losing at least 3 ha of arable land every minute due to soil salinity. Abiotic stress leads to a series of morphological, physiological, biochemical and molecular changes in plants that adversely affect growth and productivity. A frequent result is protein dysfunction. Understanding the mechanisms of protein folding stability and how this knowledge can be utilized is one of the most challenging strategies for aiding organisms undergoing stress conditions.  As a more comprehensive view of these processes evolves, applications to reducing plant stress are emerging.

Environmental stress can disrupt cellular structures and impair key physiological functions. Drought, salinity, and low temperature stress impose an osmotic stress that can lead to turgor loss. Membranes may become disorganized, proteins may undergo loss of activity or be denatured, and often excess levels of reactive oxygen species are produced leading to oxidative damage. As a consequence, inhibition of photosynthesis, metabolic dysfunction, and damage of cellular structures contribute to growth perturbances, reduced fertility, and premature senescence. Responses to environmental stresses occur at all levels of organization. Cellular responses to stress include adjustments of the membrane system, modifications of the cell wall architecture, and changes in cell cycle and cell division. In addition, plants alter metabolism in various ways, including production of compatible solutes that are able to stabilize proteins and cellular structures and/or to maintain cell turgor by osmotic adjustment, and redox metabolism to remove excess levels of ROS and re-establish the cellular redox balance. At the molecular level, gene expression is modified upon stress and epigenetic regulation plays an important role in the regulation of gene expression in response to environmental stress.

Climate change drastically influence water availability, salinity and several adverse soil conditions which will have direct bearing on original yields. Abiotic stress factors influence growth and secondary metabolite production in higher plants. The influences are well marked. In fact, productivities depend on the changed ecosystem also. Secondary metabolites play a major role in the adaptation of plants to the changing environment and in overcoming stress constraints. This flows from the large complexity of chemical types and interactions underlying various functions: structure stabilizing, determined by polymerisation and condensation of phenols and quinones, or by electrostatic interactions of polyamines with negatively charged loci in cell components, photoprotective, related to absorbance of visible light and UV radiation due to the presence of conjugated double bonds, antioxidant and antiradical, governed by the availability of –OH, –NH2, and –SH groupings, as well as aromatic nuclei and unsaturated aliphatic chains, signal transducing. Several plant-abiotic stress stimuli systems evidenced the multiplicity of biochemical mechanisms involved in the protective role of secondary metabolites:

Abiotic Stress in Plants               World population is growing at an alarming rate and may reach about 6 billion by the end of the year 2050. Though, the agricultural productivity is also being increased world over, yet it is not keeping pace to meet the demand of food availability. The main reasons for limiting the agricultural productivity are water shortage, depleting soil fertility and mainly various abiotic stresses and climatic change. Minimizing these loses is of primary concern for all nations to cope with the increasing food requirement. The abiotic stress is defined as the negative impact of non living factors on the living organism in a specific environment and abiotic stress is the most harm full factor concerning the growth and productivity of crops worldwide. Researches have shown that abiotic stressors are at their most harm full when they occur together in combination of abiotic stress factors (Mittler, 2006; Bianco and Defez, 2011). Numerous stresses caused by complex environmental conditions i.e. drought, too high and too low temperatures, freezing, salinity, UV light, heavy metals and recently through smog (air pollution) leading to substantial crop losses worldwide (Mahajan and Tuteja, 2005). The abiotic stresses might increase in the near future even because of global climatic change.

Plants that are affected by various abiotic stresses react differently as a result such as the reduction in organ size or a change in the antioxidant enzyme system, and while drought and heat are often studied separately, in nature they often occur together, meaning it is essential to carry out joint studies. Furthermore, and related to the above when we consider high temperature stress, one must always consider the use of water and nutrients by the plant and other physiological functions. The effects of heat stress can also be analyzed by the technique that measures lipid peroxidation in polyunsaturated acids of the plasma membrane. The accumulation of metals in plants, affects the normal processes of plant metabolism. The study shows that there is a relationship between high metal contents in plants and their modified morphology: strong reduction of leaf thickness, modified parenchyma structure, and decreased mitochondria organization were ascertained, although toxic symptoms were apparently absent. Water-deficit stress has a significant effect on plants growth and development, with primary affects on plant structure, leaf morphology and cell ultrastructure. Physiological processes such as stomatal conductance, photosynthesis and respiration are consequently impaired with further implications on the metabolic functions such as carbohydrate and energy production as well as carbohydrate translocation and utilization.

The stresses, drought, salinity, chemicals, cold and hot temperatures, have interconnected effects on plants, resulting in the disruption of protein homeostasis. Maintenance of proteins in their functional native conformations and preventing aggregation of non-native proteins are important for cell survival under stress. The heat shock proteins buffer this environmental variation and are therefore important factors for the maintenance of homeostasis across environmental regimes. Heat shock proteins are known to be expressed in plants experiencing high-temperature stress. Heat shock proteins are important in relation to stress resistance and adaptation to the environment. Their molecular function might be membrane or protein stabilization, but, for now, for most heat shock proteins the molecular function remains to be elucidated. The general observation of the response and induction of heat shock proteins following heat stress suggests that they play a fundamental role in cellular homeostasis. It is possible that heat shock proteins may be involved with the phenomenon of acquired thermotolerance. Heat stress disturbs cellular homeostasis and can lead to severe retardation in growth and development, and even death. Temperature stress can have also a devastating effect on both the plant anabolism and catabolism, initially acting on protein complexes, being the quaternary structure the first folding that is lost during heat stress or heating. Understanding the role of HSPs in relation to stress resistance in a more applied perspective as a potential indicator of stress is important. New technological developments make it possible to investigate the role of genes coding for heat shock proteins in greater detail. A combination of genomics and proteonomics will further elucidate the effects of stress on expression patterns at the DNA, RNA and protein level.