Speaker

Damini Thawait

M.Sc Ag final year

Dept of Agronomy

PRESENTATION ON

CHILLING STRESS

STRESS

•Stress in physical terms is defined as mechanical force per unit area applied to an object.• In response to the applied stress, an object undergoes a change in the dimension , which is also known as strain.•stress is an adverse force or a condition, which inhibits the normal functioning and well being of a biological system such as plants.

•Various types of stress are•freezing, chilling, heat, drought, flood, salinity, etc.

• Chilling stress – when plantsare exposed to a lowtemperature above 0 ºC

• Freezing stress – when plantsare exposed to a lowtemperature below 0 ºC

LOW TEMPERATURE STRESS

Chilling stress

Plants may develop physiological disorders when exposed to low but non-freezing temperatures. The German plant physiologist Molisch suggested the term ‘chilling injury’ as long ago as 1897 to describe this phenomenon.

Symptoms of chilling injury can differ widely between species, but usually develop rapidly in plants native to tropical and subtropical climates and almost imperceptibly slowly in plants originating in cool temperate climates.

• These plants including maize (Zea mays), soybean (Glycine max), cotton (Gossypium hirsutum), tomato (Lycopersicon esculentum) and banana (Musa sp.) are in particular sensitive to temperatures below 10–15 °C and exhibit signs of injury.

• The symptoms of stress induced injury in these plants appear from 48 to 72 h, however, this duration varies from plant to plant and also depend upon the sensitivity of a plant to cold

stress.

• Many food crops or tropical and subtropical origins are sensitive to chilling stress.

CHILLING INJURY

• Chilling injury in tropical or subtropical plants is caused by temperature above 0 ℃

• maize, cotton, rice seedling——10℃ 。

RICE POLLEN- for mother cell division 23 tem.is required ℃for O. sativa AND 20 tem. ℃Required for O. japonica.

PHYSIOLOGICAL REACTION OF PLANT TO LOW TEMPERATURE

Each plant has its unique set of temperature requirements,which are optimum for its proper growth and development.

A set of temperature conditions, which are optimum for one plant may be stressful for another plant. many plants, especially those, which are native to warm habitat, exhibit symptoms of injury when exposed to low non-freezing temperatures.

(1) Water content

Total water content decreses,bound water increases. ，(2) Unsaturated fatty acid increase in membrane &

saturated one decreases.

(3) ABA increases,GA decreases, dormancy appears.

Metabolism disorder(1) Uptake of solutes by root decreases and water balance disturbedTranspiration is more as compare to the water absorption due to that the plant loss water and leaf curls.

(2) Photosynthetic rate become low Due to low temperature the rate of photosynthesis become low & the rate of respiration is increases.

.

3 ） Aerobic respiration decreases and anaerobic respiration increases 。Cytalyse activity decreses,electron transport and phosphorylation activities decreases.

4 ） Organic substance degrades 。Protein,RNA,ATP decrease.

CHILLING INJURY SYMPTOMS

•Cellular changes : Changes in membrane structure and composition, decreased protoplasmic streaming,plasmolysis.•Altered metabolism : Increased or reduced respiration, depending on severity of stress, production of abnormal metabolites due to anaerobic condition

•Some of the more common symptoms of chilling stress areRapid wilting followed by water soaked patches which develop into sunken pits that reflect cells tissue collapse. Following warming, the sunken pits usually dry up, leaving necrotic patches of tissues on the leaf surface.

COMMON SYMPTOMS

• Reduced plant growth and• death• Surface lesions on leaves

and fruits• Abnormal curling, lobbing and

crinkling of leaves• Water soaking of tissues• Cracking, splitting and

dieback of stems• Internal discolouration

(vascular browning)• Increased susceptibility to

decay• Failure to ripen normally• Loss of vigour (potato lose

the ability to sprout if chilled)

•Cellular Membranes•The first symptom of chilling injury is the phase transition from liquid crytalline phase to solid gel state•Increase in permeability of plasmalemma results in leakage of organic and inorganic substances•Formation of crystalline deposits in root cells, epidermal, mesophyll and vascular cells of leaves -leading to tonoplast disruption.

••Cytological Changes•• Swelling of plastid membranes and mitochondrial membranes•• Swelling of chloroplast thylakoids•• Decrease in size and no. of starch grains

•Grana disintegration and increase in size and no.of plastoglobules.•Mitochondria with reduced cristae and transparent matrix.•Extensive dilation and vesiculation of smooth ER cisternae.

•Lipid composition•Ratio of Unsaturated to saturated fatty acids is higher in chilling resistant plants•Increase in activity of fatty acid was found in chilling resistant plants

EFFECTS OF CHILLING STRESS ONSeedling establishment and growth

Chilling injury is a serious problem during germination and early seedling growth and the major cause of uneven emergence and poor stand establishment

• Chilling may inhibit seed metabolic processes that are responsible for the breakdown of complex carbohydrates into simple sugars to support growth, such as germination

• During seedling (autotrophic) stage, chilling causesphotoinhibition, photosynthesis inhibition, and growthretardation

• Under severe chilling stress conditions, the seedlings (both heterotrophic and autotrophic) may die

Root growth, water and nutrient uptake

• Chilling reduces root growth, elongation, and biomass accumulation

•For many chilling sensitive plants of tropical origins(beans, maize, tomato, pepper, cotton), air or soiltemperatures of 10 to 15 ºC are near the limit for growth.

• Chilling may cause loss of leaf turgor and water deficit because of reduction in water absorption, movement,and moderate transpiration.

Plasma membrane become less fluidity and are lesspermeable to water when chilled

MEMBRANE PERMEABILITY CHANGES DURING CHILLING

• As temperatures decrease, cell membranes undergo phase transition from liquid crystalline to gel phase

•This phase transition reduces membrane permeability to small proteins, solutes,water and damages cell functions.

CHANGE IN STATE OF LIPID

MECHANISM OF CHILLING INJURY

• Plant membranes consist of a lipid bi-layer interspersed with proteins and sterols

• The physical properties of the lipid affect the activities of the integral membrane proteins

• The lipids in cold sensitive plants may have more saturated fatty acids and higher “freezing point”

•

– Chilling reduces activity of enzymes in Calvin cycle and electron transport chain & Krebs cycle , it inhibits translocation of assimilates,causes protein degradation.

• In some fruits, respiration may increase onset of injury (stimulated by ethylene) and decrease on death.

• (cont.)• Chilling causes oxidative stress

– Chilling reduces photosynthetic activity, and excess energy is directed to O2 and resulting in ROS (H2O2,etc.) accumulation. which damages membrane (lipid peroxidation), proteins, DNA, etc.

• doubled the H2O2 content in winter wheat, 4-fold increase in maize seedlings

•– Chilling causes more injury under light than in dark

CHILLING ACCLIMATION PHENOMENON

• The primary function of cold acclimation is to stabilize the membranes against freeze injury. Acclimation results in increase in proportion of unsaturated fatty acids and thereby a drop in transition temperature

• resistance to chilling stress often increases if plants are first acclimated by exposure to cool, but non-injurious, temperatures.

•

CHILLING ACCLIMATION PHENOMENON(CONT.)

• Not all plants grow best in the same temperature range.

• For example, snapdragons grow best when night time temperatures are 55°F, while the poinsettia grows best at 62°F.

• Accumulation of solutes (proline, sugars, etc.) Increase in antioxidants.

• •

ROLE OF CALCIUM IN RELATION TO COLD STRESS

• Calcium is an important messenger in a low temperature signal transduction pathway. The change in cytosolic calcium levels is a necessary first step in a temperature sensing mechanism, which enables the plant to withstand future cold stress in a better way. In both Arabidopsis and alfalfa cytoplasmic calcium levels increase rapidly in response to low temperature, largely due to an influx of calcium from extracellular stores .

METHODS TO INCREASE THE RESISTANCE TO LOW TEMPERATURE

1. Select and use chilling tolerant species/ cultivars

2. Low temperature hardening.

3. Chemical control.

4. ABA ,CCC ， PP330 ， Amo-1618).

Others.

– Proper planting dates– Artificial covers– Proper soil moisture– Plant growth regulators as ABA

.CONCLUSION•Chilling stress may affect seed germination, and cause injury to seedlings and root systems.

Chilling injury is related to membrane phase transition,metabolic disturbance, water absorption and other physiological activities etc.• Low temperatures can result in poor growth. Photosynthesis is slowed down at low temperatures. Since photosynthesis is slowed, growth is slowed, and this results in lower yields.

THANK YOU