and tissue affected by the stress. This may be due to the variance in metabolic
adjustments to stress that are different in different tissues and genotypes of the
same plant. The metabolic tuning of plants is usually triggered by number of defense
molecules that enhance protection [5]. Although plant responses are unique to
different extremes, they utilize the common components and signaling pathways
to trigger defense. Recent research has revealed nitric oxide (NO) as one of the
critical components in several plant acclimation responses to both biotic and abiotic
stress conditions [2]. Literature demonstrated that various abiotic factors induce NO
generation that lead to the activation of cellular processes for protection against
oxidative stress and metabolic adjustments for survival.
1.1
Introduction to NO
NO is a lipophilic gaseous signaling molecule having versatile functions in both
plants and animals. The first discovery in 1772 by Joseph Priestley described NO as
an air-polluting “nitrous air” without any specific color and odor. After two centuries, Klepper observed NO emission by air purging of herbicide-treated Glycine max
leaves followed by other observations on NO as a bacterial metabolic by-product [6].
A breakthrough study by Robert F. Furchgott, Louis J. Ignarro, and Ferid Murad
turned up the signaling functions of NO in mammalian species and secured the
Nobel Prize at Physiology in 1998. From that point, there were many parallel
investigations on exploration of NO generation and NO signaling in both plants
and animals. However, the investigations on NO in mammals were much rapid
wherein the role of NO was well demonstrated in many physiological processes
including muscle relaxation, neural communication, immune responses, and programmed cell death.
A bit later, NO has been accepted as multitasking molecule with innumerable
functions even in plants. The lipophilic and diffusible nature of NO makes it
perfectly suitable for several signaling processes in plants [7]. NO also plays an
active role in modifying the activity of enzymes and some key signaling components
via posttranslational protein modifications (PTMs). NO also plays a duel role as
an antioxidant and as oxidant depending on the cellular concentration and plant
species and many other factors. Endogenous NO levels have been reported to get
triggered by abiotic stress conditions in diverse plant species. NO play a vital role
in increasing plant adaptation to stressful conditions by modifying various physiological processes. There has been sufficient data suggesting NO as an endogenous
signal that mediates plant responses to various abiotic stimuli. Nevertheless NO also
acts as a critical messenger during stimulation of hypersensitivity response to
pathogens.
1.1.1 Functions of NO
Albeit NO is recognized as a toxic gas for plant foliage by early discoveries, later
it was treated as a powerful signaling molecule in plant defense during pathogen
infestation. NO is actively involved in a plethora of plant development responses
596
P. Santisree et al.
adjustments to stress that are different in different tissues and genotypes of the
same plant. The metabolic tuning of plants is usually triggered by number of defense
molecules that enhance protection [5]. Although plant responses are unique to
different extremes, they utilize the common components and signaling pathways
to trigger defense. Recent research has revealed nitric oxide (NO) as one of the
critical components in several plant acclimation responses to both biotic and abiotic
stress conditions [2]. Literature demonstrated that various abiotic factors induce NO
generation that lead to the activation of cellular processes for protection against
oxidative stress and metabolic adjustments for survival.
1.1
Introduction to NO
NO is a lipophilic gaseous signaling molecule having versatile functions in both
plants and animals. The first discovery in 1772 by Joseph Priestley described NO as
an air-polluting “nitrous air” without any specific color and odor. After two centuries, Klepper observed NO emission by air purging of herbicide-treated Glycine max
leaves followed by other observations on NO as a bacterial metabolic by-product [6].
A breakthrough study by Robert F. Furchgott, Louis J. Ignarro, and Ferid Murad
turned up the signaling functions of NO in mammalian species and secured the
Nobel Prize at Physiology in 1998. From that point, there were many parallel
investigations on exploration of NO generation and NO signaling in both plants
and animals. However, the investigations on NO in mammals were much rapid
wherein the role of NO was well demonstrated in many physiological processes
including muscle relaxation, neural communication, immune responses, and programmed cell death.
A bit later, NO has been accepted as multitasking molecule with innumerable
functions even in plants. The lipophilic and diffusible nature of NO makes it
perfectly suitable for several signaling processes in plants [7]. NO also plays an
active role in modifying the activity of enzymes and some key signaling components
via posttranslational protein modifications (PTMs). NO also plays a duel role as
an antioxidant and as oxidant depending on the cellular concentration and plant
species and many other factors. Endogenous NO levels have been reported to get
triggered by abiotic stress conditions in diverse plant species. NO play a vital role
in increasing plant adaptation to stressful conditions by modifying various physiological processes. There has been sufficient data suggesting NO as an endogenous
signal that mediates plant responses to various abiotic stimuli. Nevertheless NO also
acts as a critical messenger during stimulation of hypersensitivity response to
pathogens.
1.1.1 Functions of NO
Albeit NO is recognized as a toxic gas for plant foliage by early discoveries, later
it was treated as a powerful signaling molecule in plant defense during pathogen
infestation. NO is actively involved in a plethora of plant development responses
596
P. Santisree et al.