Plant Physiology: Drought Stress

7/21/2019 Plant Physiology: Drought Stress

http://slidepdf.com/reader/full/plant-physiology-drought-stress 1/20

Plant Stress Physiology: Drought Stress

A Simple Paper

Presented to

Charisse Mae R. Ibañez

Faculty of the Natural Sciences Department

School of Arts and Sciences

Ateneo de Zamboanga University

Zamboanga City, Philippines

In Partial Fulfillment

of the Requirements of Botany 203

Plant Physiology

Final Examination

By

Betlee Ian T. Barraquias Jr

BS Biology III – A



Plant Stress Physiology: Drought Stress

By:

Betlee Ian T. Barraquias Jr.

Chapter I: Introduction

A. Background of the Study

B. Objectives

C. Significance of the Study

D. Definition of Terms

Chapter II: Discussion and Review of Related Literature A. Physiological Importance of Water in Plants

i. Plant Structure

ii. Plant Growth

iii. Nutrient and Mineral Medium

iv. Nutrient Uptake

v. Fluid Movement

vi. Thermoregulation

vii. Biochemical Processes

B. Stress Physiology of Plant Water Deficiency

i. Homeostasis and Stressii. Adaptive Mechanisms

i. Stress Resistance

ii. Acclimation and Phenotypic Plasticity

iii. Stress Avoidance

iii. Drought Stress

iv. Effects of Drought Stress

v. Physiological Response Mechanisms

i. Cell and Tissue Water Conservation

ii. Antioxidant Defense

iii. Hormones and Root Signaling

Chapter III: Summary, Conclusion, and Recommendation

Bibliography



Chapter I

Introduction

As life on earth dates back from millions of years, it has been continually subjected to

changes and stresses that disrupted its essential equilibrium. This has consequently led

to the extinctions of many life forms. However, there are some that have persisted by

means of adaptation to the changes and stresses in the environment. And one of these

most successful groups is the plants.

Plants are among the earliest biotic elements present on earth. They have faced

countless stresses such as exposure to drought, extreme temperatures, and oxidative

stresses that have insulted their essential equilibrium. This essential equilibrium, or

what we call homeostasis, is an absolute requirement for life. This ensures that

conditions are ideal for certain life processes be systematically carried out.

However, in spite of these stresses, plants have persisted as a group, and as a species.

Plants have their own coping mechanisms, or adaptations, such as stress-driven

pathways, that enable them to live through such stresses. Furthermore, these

adaptations may have given them a degree of resistance against these stresses

through the process of evolution. This, in turn, made them an even more persistent

species that lives on up to today.

A branch of science, botany, and its sub-discipline, plant physiology, studies about

plants and their mechanisms on how they function. Another narrower sub-discipline,

plant stress physiology, studies about the response of plants that are subjected tophysiological stresses. One of the most common plant stresses is droughts, or water

shortages.

Water is an absolute requirement for plant life. It is inarguably important as it serves

many fundamental functions in plant processes. Water serves as a solvent or a medium

through which nutrients and hormones are channeled throughout the plant. Water

constitutes more than ninety percent of the weight of plants and also plays a key role in

maintaining plant cell turgidity. Furthermore, water is also a critical element that donates

an electron and a proton for photosynthetic reactions to occur (Hasegawa, & Jenks,

2005; Khanna, 2012; Lisar, et. al., 2012; Vince, & Zoltan, 2011). Water also plays a rolein the mechanism of fluid channeling throughout the plant. And it also serves a

thermoregulatory function that prevents overheating that disrupts homeostasis by

straying away to the stability-driving optimal temperature (Ewers, n.d.; Khanna, 2012;

Plants and Soil Sciences e-library, n.d.; Vince, & Zoltan, 2011).



With the functions of water, its deficiency, indeed, leads to the disruption of plant

homeostasis that may lead to plant death. However, water deficiency also leads to

cascade of effects that further increase the adverse influence of such stress (Farooq,

2008; Hasegawa & Jenks, 2005; Lisar, et. al., 2012; Vince, & Zoltan, 2011). So, in this

connection, as this paper is intended to discuss about plant stress physiology, it seeks

to specifically tackle about the stress physiology of drought stress and water deficiency

in plants. The paper shall proceed by focusing on:

1. the discussion of the physiological importance of water to plants;

2. the basic concepts of plant stress physiology:

a. Homeostasis;

b. Adaptive Mechanisms;

c. Physiological Response Mechanisms;

3. the discussion of the effects of water deficiency;

Significance of the Study

Plants, in nature, continually face environmental stresses throughout their lives. One of

the most common stresses brought about by the environment is drought, or water

shortage. Plants have evolved as a group, and as a species to persist through these

environmental stresses. Considering the nature of plants, having to continually lose

water due to natural mechanisms (e.g. fluid movement, photosynthesis), the paper

seeks to understand these mechanisms that help them adapt to such detrimental and

stressful situations. This study proves relevant to the course, plant physiology, as it,obviously, studies a branch of the subject, plant stress physiology.

Definition of Terms

Abiotic Stress: Stress induced by the non-living environment (e.g. light, temperature,

water shortage) (Vince, & Zoltan, 2011).

Avoidance: The action of making void, or of having no effect (Lisar, et. al., 2012).

Biological Stress: Environmental modulation of homeostasis.

Biotic Stress: Stress induced by biotic elements (e.g. insects, infections) (Vince, &

Zoltan, 2011).

Dehydration: The loss of water from a cell. Plant cells dehydrate during drought of water

deficit (Lisar, et. al., 2012).



Drought Avoidance: The avoidance of drought impact by utilizing adaptations that limit

the perception of water deficit by the protoplasm (Lisar, et. al., 2012).

Drought Tolerance: The ability to withstand suboptimal water availability by utilizing

adaptations that permit metabolism to occur at low water potential (Lisar, et. al., 2012).

Drought: The limitation of water over a prolonged period of time. It denotes the loss of

water from plant tissues and cells (Lisar, et. al., 2012).

Phenotypic plasticity: The capacity of a single genotype to exhibit variable phenotypes

in different environments is common in insects and is often highly adaptive (Whitman, &

Agrawal, n.d.).

Plant Stress: Adverse effect on plant physiology induced upon by a sudden transition

from optimal to suboptimal condition that disrupts homeostasis (Vince, & Zoltan, 2011).

Scavenging: is the deactivation of certain substances by the addition or reaction ofanother chemical substance (Campbell, et. al. 2008).

Strain: Changes or damages as a consequence of a stress or difficulty (Beck, et. al.,

2005).

Stress: A difficulty such as water deficiency (Beck, et. al., 2005)

Tolerance: The ability to withstand some particular environmental condition (Lisar, et.

al., 2012).

Turgor: Is the normal state of turgidity and tension in living cells (EncyclopediaBritannica, n.d.).

Water Potential: It is the measure of the potential energy in water as well as the

difference between the potential in a given water sample and pure water (Boundless,

2014).



Chapter II

Review of Related Literature and Discussions

Physiological Importance of Water in Plants

The physiological importance of water in plants is best appreciated by looking into the

roles that water play in various plant systems. Water plays a part in many fundamental

processes that occur in plants, while also being the main constituent of plant structure.

Plant Structure

Plants are made up of more than ninety percent of water. Each individual plant cell is

composed of 80 to 90 percent of water contained within its central vacuole. This large

composition of water in plant cell provides pressure to the cell that gives the cell its

turgidity, which would in turn support the plant to stand erect (Ferguson, 1959; Khanna,

2012; Whiting, 2014).

Plant Growth

As growth in plants occurs, water enters the cell in response to an osmotic driving force

and pressure. Though proteins, carbohydrates, and other metabolites are deposited

during growth, water uptake makes for most of the increase in cell volume, and hence,

growth (University of California, n.d.).

Nutrient and Mineral Medium

Water serves as a solvent for plant nutrients and minerals. Plants, normally, cannot

absorb these nutrients and minerals, and water is needed to dissolve them so to be able

for them to be channeled throughout the plant (Khanna, 2012).

Nutrient Uptake

Furthermore, water also plays a role in mineral nutrient uptake that occurs on the roots.

As plants cannot normally absorb raw, dry mineral nutrients, water is needed for these

to be dissolved and able to be transported to the plant through the epidermis of the

roots (Ferguson, 1959; Kimbal, 2013).



Fluid Movement

Fluid movement within the plant is described by the cohesion-tension theory. According

to this theory, the driving force of fluid movement is transpiration. It details that

transpiration and water uptake in plants work in tandem to produce fluid movement

within the plant (Ewers, n.d.; Lisar, et. al., 2012).

Water molecules cohere and are pulled up in the plant by the tension, or by a pulling

force that is exerted by transpiration on the leaf surface. Transpiration occurs as a result

of concentration gradients (molecules tend to move from higher concentrations to lower

concentrations). Concentration of water molecules in the atmosphere tends to be less

than the concentration of water molecules in the leaves of plants. This concomitantly

drives transpiration where water moves from the leaves of the plant to the environment.

This would further cause cascading effects on the stem, and roots, where water tends to

move from the stem to the leaves, roots to the stem, and soil to the roots (Ewers, n.d.;

Lisar, et. al., 2012).

Thermoregulation

Water plays, yet, another significant role in plants, thermoregulation. Through

transpiration, plants release water vapors to regulate temperature. An optimal

temperature is necessary for the functionality of many biomolecules since temperature

is a factor for proper configurations of certain molecules (e.g. proteins and enzymes).

Thermoregulation, then, contributes to the maintenance of the correct configurations of

biomolecules that consequently allow them to work systematically for the overall

homeostatic condition of plants (Ferguson, 1959; Tamil Nadu Agricultural University,

n.d.).

Biochemical Processes

An aqueous environment is necessary for the functionality of many important

biomolecules. Lipids, proteins, and enzymes use water as a medium to interact with

other substances for reaction. Water also plays a role in buffering pH, where such

affects the configuration and functionality of biomolecules (Ferguson, 1959).

Aside from water’s role in the functionality of biomolecules, water also serves as a basic

material for most metabolic or biochemical reactions in the plant system. One example

is photosynthesis where water is being utilized as the primary electron and proton donor

for the photosynthetic process to be carried out (Ferguson, 1959).



Stress Physiology of Plant Water Deficiency

As water is inarguably important and vital to plant life, another equally important

element is the maintenance of the structural organization of plants. In order for plant life

to continue and persist, it must maintain its structural organization for essential

processes to be able to systematically carried out. The structural organization isretained through the maintenance of favorable, optimal conditions that allow for

essential processes to proceed. This state of maintaining a stable and optimal condition

is referred as homeostasis (Vince, & Zoltan, 2011).

Homeostasis and Stress

Homeostasis and stress are two opposing concepts. Plants in nature continually face

environmental stresses that concomitantly disrupt homeostasis as stresses implicate

adverse physiological effects (Ahmad Anjum, et. al., 2011; Vince, & Zoltan, 2011).

Plant stress can be divided into two primary categories: Abiotic, and biotic stresses;

abiotic stress, as its name suggests, is induced by physical and chemical factors such

as light, temperature, and water limitations, while the latter is induced by other life forms

such as insects and/or infections by bacteria (Vince, & Zoltan, 2011).

Moreover, abiotic stress may induce primary and secondary effects on plants. A primary

effect causes a cascade of physiological changes that may give rise to secondary

effects. A primary effect, such as water deficiency affects various physical and

biochemical properties of cells. These influences, usually detrimental, give rise tosecondary effects such as reduced metabolic activity, ion cytotoxicity, and production of

toxic chemicals (Lisar, et. al., 2012; Vince, & Zoltan, 2011).

Plants may be strained by a stress that adversely affects overall plant functionality by

disrupting normal physiological processes that occur under optimal conditions (Vince, &

Zoltan, 2011). However, the effects of strains vary and depend on certain factors such

as strain severity and duration (Beck, et. al., 2005; Vince, & Zoltan, 2011).

The effect of environmental stress on plant survival revolves around the concepts of

avoidance, resistance, and susceptibility. Plant survival according to stress avoidance

can be illustrated by the life cycle of ephemeral plants. Ephemeral plants complete their

life cycles during periods of adequate moisture and form dormant seeds before the

onset of dry seasons. This allows them, in spite of stress exposure, to avoid strain

impact and survive in the form of dormant seeds. Stress resistance, on the other hand,

is achieved through tolerance to stress. This is accomplished by the plant’s ability to

adapt and tune its physiological processes to be able to induce homeostatic conditions



under sub optimal circumstances. While stress avoidance, and resistance ultimately

leads to plant survival, stress susceptibility leads to plant death. This occurs when the

stress strains the plant to a degree of beyond repair or irreversibility (Farooq, et. al.,

2009; Lisar, et. al., 2012; Vince, & Zoltan, 2011).

Adaptive Mechanisms

As a successful groups and species, plants have developed various adaptations against

environmental stresses. The two main general concepts under the adaptive

mechanisms of plant are resistance or tolerance, and avoidance.

Stress Resistance

Stress resistance or tolerance can be attained through various modes. Plants undergo

acclimation that allows them to operate and induce homeostatic state under sub-optimal

conditions by altering and tuning physiological processes. (Farooq, et. al., 2009; Lisar,

et. al., 2012; Vince and Zoltan, 2011).

Acclimation and Phenotypic Plasticity

Acclimation is the process by which an individual organism undergoes adjustment to a

gradual change in its environment. Acclimation results to an acclimated-homeostaticstate, where such homeostatic state is induced in sub-optimal conditions through

multiple physiological processes and changes that are integrated over time –

acclimation period (Vince, & Zoltan, 2011).

Acclimation may involve short- or long-term processes. Short-term processes are

initiated within seconds or minutes upon exposure to stress. Short-term processes may

be transient in nature, where it is detected soon, but rather disappear rapidly. Long-term

processes are less transient and exhibit long-term effects. However, these processes

overlap in time such that short-term processes serve to be the initial response to stress,

while the long-term processes are usually detected later in the acclimation process. Thisindicates that the attainment of an acclimated state is a complex and time-nested

response to stresses (Vince, & Zoltan, 2011).

Acclimation usually involves the expression of specific genes that are associated with

stress exposure. Various plants may exhibit mechanisms where they alter their

physiologies and morphologies to shift and induce optimal conditions during stress.

These mechanisms are achieved with underlying evolutionary processes, where



favorable genes that make plants resistant to stress are conserved through natural

selection. However, these mechanisms may not involve genotypic mutation or

modifications. Certain set of genes can act to express various phenotypic expressions

according to environmental conditions. Such capacity is referred to as phenotypic

plasticity (Vince, & Zoltan, 2011).

However, though the mechanism of the exhibitions of various phenotypic expressions

without any genotypic alteration changes plant morphology, they only represent

temporary changes. Restoration of the normal environmental conditions reverses the

process and brings back the original phenotypic expression under normal conditions

(Vince, & Zoltan, 2011).

Stress Avoidance

Another mechanism that leads to plant survival under stress is avoidance. Stress

avoidance mechanisms are achieved by some groups or species of plant through their

life cycles. As cited earlier, an example would be ephemeral plants where they have a

shortened life cycle to avoid the drought stresses (Farooq, et. al., 2009; Vince, & Zoltan,

2011).

Stress avoidance can also be achieved through mechanisms that minimize strain

induction by stresses. One such mechanism is achieved through morphological

changes such as reduced stomatal conductance, decreased leaf area, and

development of extensive root/shoot ratios during drought stress (Lisar, et. al., 2012;

Turner, et. al., 2001, & Kavar, et. al., 2007, as cited in Farooq, 2009)

Drought Stress

In nature, plants are continuously exposed to various biotic and abiotic stresses. Among

these stresses, drought stress is one of the most adverse and common (Ahmad Anjum,

2011). As water plays various fundamental roles in plant life, its deficiency leads to the

impairing and disruption of whole plant system which would ultimately lead to plant

death (Hasegawa, & Jenks, 2005; Khanna, 2012; Lisar, et. al., 2012; Vince, & Zoltan,

2011). However, plants have developed various mechanisms and physiological

response pathways to maintain its structural organization intact while slowly adapting

and becoming resistant to strains induced by stress.



Effects of Drought Stress

Drought stress implicates a cascade of effects that prove detrimental to plant life. These

effects further aggravate the adverse influence of plant stress leading to growth

inhibition, reproductive failure, and ultimately, plant death (Lisar, et. al., 2012). Water

stress in plants reduces the plant cell’s turgidity. As a consequence, the plant will tendto slightly wilt due to the loss of pressure that was used to be provided by water.

Furthermore, it also has its effects on plant growth; water deficiency would lead to

inhibition of growth as water uptake during growth makes up for most of the plant cell

volume. Nutrient uptake, thermoregulation, and biosynthesis of certain substances in

plants are also impaired due to water deficiency (Ferguson, 1959; Kimbal, 2013; Lisar,

et. al., 2012).

These effects brought about by drought stress are further aggravated by secondary

effects. Stomatal closure due to drought stress causes a carbon dioxide deficiency that

inhibits photosynthetic reaction. This, in turn, leads to the production, due to theaccumulated energy in the photosystems, of reactive oxygen species (ROS) that

involves hydrogen peroxide and free radicals which brings oxidative damage to

proteins, DNA, and lipids (Ahmad Anjum, 2011; Lisar, et. al. 2012).

Furthermore, as stomatal closure affects the rate of transpiration, it also has negative

effects on the uptake of mineral nutrients from the soil. As described by the cohesion-

tension theory, transpiration and the cohesion-tension system of water are the

underlying mechanisms of fluid movement and nutrient uptake of plants. Stomatal

closure by water stress would, then, further lead to consequences in growth and

structural integrity of plants due to malnutrition and impaired nutrient transport (Lisar, et.al., 2012).

Physiological Response Mechanisms

Plants have developed various pathways that allow them to adapt through stresses. Cell

and tissue water conservation, antioxidation and scavenging defense system, and

hormones and root signaling have been the most important mechanisms responsible for

drought tolerance (Ahmad, Anjum, et. al., 2011; Farooq, et. al., 2009).

Cell and Tissue Water Conservation

Osmotic adjustment allows the cell to decrease osmotic potential which concomitantly

increases the gradient for water influx and maintenance of turgor. This is achieved

through the osmotic adjustment in cell wall elasticity (Farooq, et. al., 2009).



Abscisic acid, and other unidentified substances maintain high tissue water potential.

This, in turn, confers resistance to strains brought by drought stress (Turner, et. al.,

2001, as cited in Farooq, et. al., 2009). Furthermore, Ahmad Anjum, et. al. (2011), and

Morgan (1990), in Farooq, et. al. (2009), explained that osmotic adjustment is also

aided by active accumulation of solutes such as proline, sucrose, soluble

carbohydrates, and glycinebetaine in the cytoplasm. This maintains cell water balance,

minimizing the harmful effects of drought.

Antioxidant Defense

As drought stress brings about the production of reactive oxygen species that may

potentially damage cell tissues, the plants undergo a specific pathway that produces

antioxidants and other scavenging substances that work against the reactive

species(Gong, et. al., 2005, as cited in Farooq, et. al., 2009; Hasegawa, & Jenks,2005).

Antioxidants compose of substances of both non-enzymatic and enzymatic nature

(Gong, et. al., 2005, as cited in Farooq, et. al., 2009; Hasegawa, & Jenks,

2005).Enzymatic components usually are involved in the breakdown of reactive oxygen

species. These antioxidant enzymes are the most efficient mechanism against oxidative

stress (Farooq, et. al., 2009). Examples under enzymatic components include

superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, and glutathione

reductase (Gong, et. al., 2005, as cited in Farooq, et. al., 2009). However, some

enzymatic components are involved in the scavenging of reactive oxygen species(Fazeli, et. al., 2007, as cited in Farooq, et. al., 2009).Non-enzymatic components, on

the other hand, include carotenoids and various other compounds such as abietane

diterpenes, play a role in the antioxidant defense system through scavenging. (Deltoro,

et. al., 1998, as cited in Farooq, et. al., 2009).

Furthermore, oxidative damage in plant tissues are alleviated by the actions of both

enzymatic and non-enzymatic antioxidant systems. Beta-carotenes, ascorbic acid,

alpha-tocopherol, reduced glutathione, and enzyme including superoxide dismutase,

peroxidase, ascorbate peroxidase, catalase, polyphenol oxidase, and glutathione

reductase play a role in the alleviation of oxidative damage (Hasegawa, & Jenks, 2005;Prochazkova, et. al., 2001, as cited in Farooq, 2009).



Hormones and Root Signaling

Auxins, gibberellins, cytokinins, ethylene, and abscisic acid are the five major plant

hormones. These hormones have their roles on drought stress resistance. Under

drought stress, auxins, gibberellins and cytokinins usually decrease, while abscisic acid

and ethylene increase (Nilsen, & Orcutte, 1996, as cited in Farooq, 2009).

During drought stress, an extensive root system is an advantageous adaption to extract

water from soil layers (Ahmad Anjum, et. al., 2011; Lisar, et. al., 2012). Though the

exact effect of drought stress on roots have remained controversial, Jaleel, et. al.

(2008), as cited in Ahmad Anjum, et. al. (2011), reported an increased root growth in

Catharanthus roseus under drought stress. While Sacks, et. al. (2007), as cited in

Ahmad Anjum, et. al. (2011), reported an insubstantial inhibitory effect on root growth

under drought stress in maize (Ahmad Anjum, et. al., 2011).

As drought stress is induced upon plants, the root to shoot ratio increases since rootsare less sensitive from growth inhibition due to low water potentials (Lisar, et. al., 2012;

Wu, & Cosgrove, 2000, as cited in Ahmad Anjum, et. al., 2011). Under drought stress,

roots induce a signal cascade to the shoots that cause physiological responses that

eventually determines the level of adaptation to stress (Ahmad Anjum, et. al. 2011;

Lisar, et. al., 2012).

Abscisic acid (ABA), cytokinins, ethylene, and other unknown factors have been

identified in the root-shoot signaling. This signaling induces stomatal closure, which is a

known adaptation to limited water supply. ABA promotes the efflux of potassium ions

from the guard cells, which results to loss of turgor pressure leading to stomatal closure(Ahmad Anjum, et. al., 2011).



Chapter III

Summary, Conclusion, and Recommendation

Summary

The physiological importance of water in plants can be best appreciated by turning to

the roles it plays in various plant systems. Water plays a part in many fundamental

processes such as plant growth, nutrient and mineral uptake, fluid movement,

thermoregulation, and various biochemical processes (e.g. photosynthesis) that occurs

in plants. Water also is the main constituent of plant structure, comprising eighty to

ninety percent of every individual plant cell that provides pressure that provides turgidity

to the plant which concomitantly supports the plant to stand erect.

While water is inarguably essential and vital to plant life, another equally important

element is the maintenance of the structural organization of plants. In order for plant life

to continue, it must maintain this structural organization so normal plant processes be

systematically carried out. The structural organization is retained through the

maintenance of favorable, optimal conditions that allow for essential processes to

proceed. This state of maintaining a stable and optimal condition is referred to as

homeostasis.

However, plants in nature are continually threatened by stresses that disrupt its

homeostasis. Stresses can induce strains that damage plant structure that consequently

lead to the impairment of various physiological processes. This would, in turn, adversely

affect the overall homeostatic condition of plants.

But as plants are a successful group and species, they have developed various

adaptive mechanisms that allow them to persist in spite of stress. Stress resistance, and

stress avoidance are two of the general adaptive mechanisms a plant undergoes to

survive through a stress.

While there are multiple causes of plant stress, one of the most common and adverse

environmental stress is drought stress. Drought stress is caused by water shortage.

Drought stress can cause an array of effects ranging from plant stunted growth to plantdeath. But initially, drought stress brings upon a cascade of effects including reduced

turgor, production of reactive oxygen species, carbon deficiency, photosynthetic

inhibition, and mineral uptake impairment.

However, plants have developed various pathways that deal with such type of stress.

One pathway or physiological response mechanism is cell and tissue water



conservation, where it involves the maintenance of water turgor through adjustment in

cell wall elasticity and through influx and accumulation of solutes. Another physiological

response is antioxidant defense where plants produce antioxidant and scavenging

substances against reactive oxygen species that potentially harm plant proteins, DNA,

and lipids. Finally, plants also use hormone and root signaling, especially abscisic acid

to induce specific changes in the physiology and morphology (e.g. stomatal closure) of

plants for adaptation.

Conclusion

The objectives of the paper, discussion of the (1) physiological importance of water to

plants, (2) basic concepts of plant stress physiology, (a) homeostasis, (b) adaptive

mechanisms, (c) physiological response mechanisms, and (3) effects of water

deficiency, has been successfully met as evident in the summary and discussions inChapter II.

Recommendation/s

Considering the time given for the making of the paper, and the load of the researcher,

the researcher believes that this paper is limited as it failed to integrate certain plant

stress physiology concepts. But nevertheless, the paper has achieved its objectives in

discussing its focuses.

Terminologies

The researcher believes that there are certain terminologies on the underlying concepts

discussed on the paper that have not been integrated due to diverse literatures that

used different terminologies on referring to certain concepts. Because of this, it is

recommended that these terminologies be investigated and be integrated in case of

future improvement.

Research Integrations

The researcher wanted to integrate recent advancements regarding the subject.

However, due to lack of time and load of the researcher, the researcher only focused on

discussing the fundamentals of the stress physiology of drought stress in plants.



Therefore, for future improvements, it is recommended that these recent researches be

looked upon and integrated.

Peer Review

While the paper has met its objectives, it has not been peer reviewed. Hence, peer

review is recommended to further add credence to the paper.

Further Discussions

The researcher admits that there could be concepts that have been missed in

discussing the topic. Therefore, it is recommended that this paper be reviewed and

improved upon.

Detailed Explanations

The researcher wanted to make detailed explanations underlying physiological

phenomena. The researcher wanted to discuss the topic on many levels: organism,

organ, tissue, cellular, and molecular levels. However, due to lack of time and to the

loads of the researcher, the paper did not put much detail on each level. Therefore, it is

recommended that these details be looked into and integrated on the paper.



References

Acclimization. (2014, December). Wikipedia. Retrieved on March 21, 2015,

fromhttp://en.wikipedia.org/wiki/Acclimatization

Ahmad Anjum, S., et. al. (2011, April). Morphological physiological, and biochemicalresponses of plants to drought stress. Retrieved on March 20, 2015, from

http://www.academicjournals.org/article/article1380900919_Anjum%20et%20al.p

df

Ali, A., et. al. (2011, March). Mechanism of drought tolerance in plant and its

management through different methods. Wilolud Journals. ISSN: 2141 – 4203.

Ali, O. A. M., & Hammad, S. A. R. (2014, June). Physiological and biochemical studies

on drought tolerance of wheat plants by application of amino acids and yeast

extract. Retrieved on March 20, 2015, from

http://www.sciencedirect.com/science/article/pii/S0570178314000190

Armstrong, S. (2015, January). How does water affect plant growth. Retrieved on March

20, 2015, from http://www.gardeningknowhow.com/special/children/how-does-

water-affect-plant-growth.htm

Aroca, R. (2012). Plant responses to drought stress from morphological to molecular

features. Retrieved on March 21, 2015,

fromhttps://books.google.com.ph/books?id=seJW3tx3BM8C&pg=PA138&lpg=PA

138&dq=plant+acclimation+to+water+drought&source=bl&ots=o0XvokhCDh&sig

=bUhsNuRWpUPFE2uW6qTjxuwW0B4&hl=en&sa=X&ei=RSwNVc7lH8e7mAWmxIJQ&ved=0CFkQ6AEwCA#v=onepage&q=plant%20acclimation%20to%20wat

er%20drought&f=false

Batra, N. G., Kumari, N., & Sharma, V. (2014, March). Drought-induced changes in

chlorophyll fluorescence, photosynthetic pigments, and thylakoid membrane of

proteins of Vigna radiata. Retrieved on March 21, 2015,

fromhttp://www.tandfonline.com/doi/full/10.1080/17429145.2014.905801#abstrac

t

Beck, E., Muller-Hohenstein, K., Schulze, E. D. (2005). Environment as stress factor:Stress physiology of plants. Retrieved on March 20, 2015, from

http://www.springer.com/978-3-549-20833-4

Boundless. (2014, November). Water and solute potential. Retrieved on March 21,

2015, from https://www.boundless.com/biology/textbooks/boundless-biology-

textbook/plant-form-and-physiology-30/transport-of-water-and-solutes-in-plants-

183/water-and-solute-potential-696-11921/



Campbell, N. A., et. al. (2008). Biology (8th ed.).

Charng, Y.(2008). Stress physiology. Retrieved on March 20, 2015, from

http://www.dls.ym.edu.tw/s46/(06-09-2008)Plant%20Physiol%20Ch26.pdf

Chaves, M. M., et. al. (2002, February). How plants cope with water stress in the field:Photosynthesis and growth. Retrieved on March 21, 2015,

fromhttp://aob.oxfordjournals.org/content/89/7/907.full

Ewers, F. (n.d.). Water movement in plants. Retrieved on March 20, 2015, from

http://www.biologyreference.com/Ve-Z/Water-Movement-in-Plants.html

Farooq, M., et. al. (2009, January). Plant drought stress: Effects, mechanisms, and

management. Retrieved on March 20, 2015, from

https://hal.inria.fr/file/index/docid/886451/filename/hal-00886451.pdf

Ferguson, M. H. (1959). The role of water in plant growth. Retrieved on March 20, 2015,from

http://www.puricare.co.za/UserFiles/File/The%20Role%20of%20Water%20in%20

Plant%20Growth.pdf

Flexas, J., et. al. (2009, February). Photosynthesis limitations during water stress

acclimation and recovery in the drought-adapted Vitis hybrid Richter-110.

Retrieved on March 21, 2015,

fromhttp://jxb.oxfordjournals.org/content/60/8/2361.full.pdf

Hasegawa, P. M., & Jenks, M. A. (2005). Plant abiotic stress. India, Pondicherry: Kolam

Information Services Pvt. Ltd.

Khanna, B. (2012). What is the role of water in plants. Retrieved on March 20, 2015,

from http://www.preservearticles.com/201101032317/role-of-water-in-plants.html

Kimball, J. W. (2013, September). Kimball’s biology pages. Retrieved on March 20,

2015, from http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/R/Roots.html

Kron, A. P., Ribeiro, R. V., & Souza, G. M. (2008). Water deficiency at different

developmental stages of Glycine max can improve drought tolerance. Retrieved

on March 20, 2015, fromhttp://www.scielo.br/scielo.php?script=sci_arttext&pid=S0006-

87052008000100005

Lawlor, D. W. (2012, October). Genetic engineering to improve plant performance under

drought: Physiological evaluation of achievements, limitations, and possibilities.

doi:10.1093/jxb/err313.



Lidon, F. C., & Zlatev, Z. (2012). An overview on drought induced changes in plant

growth, water relations, and photosynthesis. Retrieved on March 21, 2015,

fromhttp://ejfa.info/index.php/ejfa/article/viewFile/10599/5380

Lisar, S. Y. S., et. al. (2012, January). Water stress in plants: Causes, effects, and

responses. University of Tabriz, Tabriz, Iran. Retrieved on March 20, 2015, fromhttp://cdn.intechopen.com/pdfs-wm/27305.pdf

Nezhadahmadi, A., Prodhan, Z. H., & Faruq, G. (2013, November). Drought tolerance

on wheat. Retrieved on March 20, 2015, from

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3844267/

Phenotypic plasticity. (2014, December). Wikipedia. Retrieved on March 21, 2015,

fromhttp://en.wikipedia.org/wiki/Phenotypic_plasticity

Plants and water. (n.d.). University of California: Department of Plant Sciences

Retrieved on March 20, 2015, from

http://www.plantsciences.ucdavis.edu/plantsciences_Faculty/Bloom/CAMEL/Plan

tsWater.pdf

Role of water for growth and development of crops. (n.d.). Tamil Nadu Agricultural

University. Retrieved on March 20, 2015, from

http://agritech.tnau.ac.in/agriculture/agri_irrigationmgt_roleofwater.html

Role of water in plant growth – hydrological cycle – water in soil – plant – atmosphere

continuum – absorption of water and transpiration. (n.d.). Retrieved on March 20,

2015, from http://agridr.in/tnauEAgri/eagri50/AGRO103/lec02.pdf

Transpiration – water movement through plants. (n.d.). Plant and Soil Sciences e-

Library. Retrieved on March 20, 2015, from

http://passel.unl.edu/pages/informationmodule.php?idinformationmodule=109285

3841&topicorder=3

Vince, O., & Zoltan, M. (2011). Plant physiology. Retrieved on March 20, 2015, from

http://www.tankonyvtar.hu/en/tartalom/tamop425/0010_1A_Book_angol_01_nov

enyelettan/ch04s05.html

Water potential theory. (n.d.). Retrieved on March 21, 2015, from

http://www.decagon.com/education/water-potential/

Water Potential. (n.d.). Pearson Education. Retrieved on March 21, 2015, from

http://www.phschool.com/science/biology_place/labbench/lab1/watpot.html

Whiting, D., et. al. (2014, October). Plant growth factors: Water. Retrieved on March 20,

2015, from http://www.ext.colostate.edu/mg/gardennotes/144.html



Whitman, D. W., & Agrawal, A. A. (n.d.). Phenotypic plasticity and why is it important.

Retrieved on March 21, 2015, from

http://webcache.googleusercontent.com/search?q=cache:Of7BTFp0194J:www.re

searchgate.net/profile/Anurag_Agrawal5/publication/228731603_What_is_phenot

ypic_plasticity_and_why_is_it_important/links/00b7d51ba5a0d028e0000000.pdf+

&cd=6&hl=en&ct=clnk&gl=ph

Documents

Plant Physiology: Drought Stress