Dwi Setyati 2013

What is Plant Stress ?

Stress in biology is any change in

environmental conditions that might reduce

or adversely change a plant’s growth or

development.

Stress Physiology

Resistance : resistance is the ability adaptive or tolerant to

stresses.

Resistance includes adaptation, avoidance and tolerance

Adaptation is permanent resistance to stress in morphology and

structure , physiology and biochemistry under long-term stress

condition.

a well-developed aerenchyma in hydrophytes,

a pattern for stomata movement in CAM plant.

Tolerance is a resistant reaction to reduce or repair injury with

morphology , structure, physiology, biochemistry or molecular

biology, when plant counters with stresses.

Biotic stress◇ pathogen microbe

insectsAllelopathy

Abiotic stress◇ chilling stress ◇ freezing stress◇ heat stress◇ wet stress ◇ flood stress◇ drought stress ◇ salt stress

temperatures stress

water stress

❤Biotic and abiotic stresses can reduce average

productivity by 65%~87%

Crop Record

yield

Average

yield

Average losses Abiotic losses

(% of record

yield)

Biotic Abiotic

Corn 19300 4600 1952 12700 65.8

Wheat 14500 1880 726 11900 82.1

Soybean 7390 1610 666 5120 69.3

Sorghum 20100 2830 1051 16200 80.6

Oat 10600 1720 924 7960 75.1

Barley 11400 2050 765 8590 75.4

Potato 94100 28300 17775 50900 54.1

Sugar beet 121000 42600 17100 61300 50.7

● chilling stress

● freezing stress

● heat stress

Temperature stresses (high and low temperature)

are the major environmental factors affecting

plant growth, development and also induce

morphological, physiological and biochemical

changes in plants.

Effects of high temperature stress on plants

It induces the changes in water relations (accumulation of

compatible osmolytes, decrease in photosynthesis,

hormonal changes and cell membrane thermostability

High temperatures stress (< 40"C) can cause :

- scorching of leaves and twigs,

- sunburns on leaves,

- branches and stems,

- leaf senescence and abscission,

- shoot and root growth inhibition,

- fruit discoloration and damage and reduced yield in

plants

Formation of ROS is related to ethylene

production and lipid peroxidation and

results in membrane fluidity. Ethylene

overproduction has also been found during

or after recovery from water stress.

Leaf senescence and abscission

Heat Stress

Berries are pink to bronze where directly exposed to

sun

Berries have a pleasant, wine smell

Occurs in extreme heat at/near harvest

-Environmental stresses in plants have been

associated with production of activated forms of

oxygen , including hydrogen peroxide (H2O2),

singlet oxygen, superoxide, and the hydroxyl

radical . Through a variety of reactions, O2*-leads

to the formation of H2O2, OH* and other ROS.

- Reactive oxygen species (ROS) are produced

continuously as by products of different metabolic

pathways which are located in different cellular

compartments such as chloroplast, mitochondria

and peroxisomes.

HEAT TEMPERATURE STRESS

- The ROS comprising O2*-, H2O2, 1O

2, HO2*-, OH*,

ROOH, ROO+ and RO+ are highly reactive and toxic

and causes damage to proteins, lipids, carbohydrates

and DNA which ultimately results in cell death.

Accumulation of ROS as a result of high temperature

stress is a major cause of loss of crop productivity

worldwide.

HEAT TEMPERATURE STRESS

-induces the rapid production and accumulation of reactive

oxygen species (ROS) (Mittler, 2002 Xu et al. 2008).

- These high levels of ROS are harmful to all cellular compounds

and negatively influence cellular metabolic processes

(Breusegem et al., 2001).

- The detoxification of these ROS is very important and plants

have evolved complex strategies to deal with them (Asthir et al.,

2009).

High temperature stress in Sugarcane causes a severe

reduction :

- in the first internode length resulting in premature

death of plants.

- exhibited smaller internodes,

- early senescence,

- and reduced total biomass

The plant life cycle both vegetative and reproductive phases

are affected by the low temperature stress (Nishiyama, 1995).

During reproductive development low temperature stress :

- induces flower abscission,

- pollen sterility,

- pollen tube distortion,

- ovule abortion and reduced fruit set, which ultimately

lowers yield.

During the reproductive phase cold stress has important

economic and social consequences because the reproductive

phase products are the key components of economic yield and

are the principle source of food for entire humanity (Thakur et

al, 2010).

LOW/COLD TEMPERATURE

The reproductive phase begins with transformation of the

meristem into inflorescence and flower and, in annuals, ends

upon seed reaching maturity.

The reproductive phase consists of :

- flower initiation,

- differentiation of male and female floral parts,

- micro- and mega-sporogenesis,

- development of male and female gametophytes

(pollen grain and embryo sac),

- pollination,

- micro- and mega-gametogenesis,

- fertilization and seed development.

All these stages respond differently to cold stress but

collectively all responses are negative and reduce net yield.

Freezing injury

is caused by low

temp.<0℃

Supercooling

Intercellular crystallization

Ice crystals form between cells.

Intracellular crystallization

Ice crystals form in the cell.

Freezing Injury:

Direct injury: injury by crystal formation

Indirect injury: dehydration, suffocating

Injury mechanism:

Membrane injury

Mechanical injury

-SH theory

Strategies of increasing plant freezing tolerance:

Lower water content

Reduce photosynthesis

Increase ABA/GB

Dormant

Increase osmolytes

Caused by low temp. > 0℃

Damage

Membrane phase

Root water absorption ability

Dysfunction of respiration, accumulation of

ethanol.

Dysfunction of metabolism

Mechanism of chilling injury: membrane phase

transition:

LC phase→→G phase

LC : Liquid crystalline phase

G Phase : Gel phase

Liquid crystalline phase. The typical phase in biological membranes. The lipids have

both lateral and kinetic motion and contain membrane proteins

Gel phase. The membrane lipids have less kinetic energy and lateral motion than in

the liquid crystalline phase resulting in a regular spacing between the acyl tails

Strategies of improving plant chilling

tolerance:

Increase IUFA (index of unsaturated fatty acid),

which leads to the decrease of phase transition

temp.

Synthesis of chilling-tolerant isoenzymes.