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ABIOTIC PLANT STRESS

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PLANT STRESS

1. Any external factors that negatively influence plant growth, productivity, reproductive capacity or survival

2. Any change in environmental conditions that produce a less than ideal plant response

3. Any change in environmental conditions that Have a potentially adverse effect on a plant’s survival, growth, and reproduction

4. Any change in environmental conditions that have a devastating impact on crop yields in agriculture

Abiotic StressesEnvironmental, non-biological Stress

Water (high/low)Oxygen

NutrientsTemperature (high/low)

Salt RadiationPollutants

Excess or deficit

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WATER STRESS• Drought leading to water stress is a major problem in reducing

agricultural productivity especially in tropical, semi-arid and arid regions of the world

• Water deficits result from low and erratic rainfall, pooor soil water storage and when the rate of water transpiration exceeds water uptake

• The cellular water deficits resulr in the concentration of solutes, loss of turgor, change in cell volume, disruption of water potential gradients, change in membrane integraty, denaturation of proteins and several physiological and molecular components

• The stress effects depend on the degree and duration of stress, developmental stage of plant, genotypic capacity of species and environmental interaction

FLOODING STRESS• Soil water logging and submergence (collectively termed

flooding) influence species composition and productivity in numerous plant communities world wide

• Hydrological patterns can determine the vegetation in natural and man-made wetlands, since this is dependent on ecophysiological responses of species to flooding

• In Rice farming, flooding regimes are manipulated or are accommodated by genotype’s selection to secure much of the world production of this staple crop

• For most crops, excess water is a major constraint to productivity , adversely affecting grain yields

• A major constraint from excess water, at least for poorly adapted species is an inadequate supply of oxygen to submerged tisuue

SALT STRESS• Salinity affects agricultural production and its quality in

arid and semiarid regions, where rainfall is limited and is not sufficient to transport salts from the plant root zone

• Salinity arises due to increase in the concentration of salts like sodium chloride, sodium carbonate, sodium sulphate or salts of magnesium. The dominant salts are either sodium chloride or sodium sulphate or mixtures of them.

• The effect of salinity of plant is complex and its adverse effects include ion toxicity, water deficits and nutrient imbalance and deficiencies

SALT STRESS• The saline soil management includes crop selection,

crop stand establishment, leaching requirement, drainage and other reclamation practices

• Salt tolerance mechanisms are highly complex since the effect are diverse and are controlled by a number of genes or group of genes

• Salt tolerance is generally associated with regulated ion uptake compartmentation of ion and gene product including stress proteins

• Ion homeostasis is important component of salt tolerance

HIGH TEMPERATURE STRESS• The global mean temperature increased by 0.6 C between 1990 to

2000 and is projected to increase by another 1.4 to over 5 C by 2100

• Plants suffer the ups and downs of temperature of their environment and estimate decrease in crop yield range up to a 17% for each degree Celcius increase

• The effect of temperature to plants is strongly dependent on ambient air temperature and radiant energy fluxes

• All organisms when exposed to rapid increase in external temperature generally 5 to 10 C above normal temperature for a period of few minutes to a few hours exhibit synthesis of an elite set of protein called heat shock proteins (HSP)

• HSP proteins are involved in cellular repair, rescue, clean up and/or protection during stress and from its recovery

PHOTOOXIDATIVE STRESS• Light stress is one of the important environmental

constraint that limit the efficiency of photosynthesis and plant productivity

• Plant when absorbed light energy exceeds the capacity for light energy utilization in plant photosynthesis, the photosynthetic efficiency will be reduced due to the formation of AOS which can damage photosynthetic apparratus and chloroplast components

• Plants are believed to develop certain strategies of tolerance mechanisms

NUTRIENT STRESS

• Plant growth and development and yield are contributed by 17 essential elements

• Nutrient stress and associated metabolic disorders decrease plant growth and yield

• Plant growth and metabolism is also affected by heavy metal stress

• Developing nutrient stress tolerance may help to extend agriculture to unexplored harsh and nutrient poor soil

Macroelements Microelements

Element Symbol Element Symbol

Nitrogen N Chlorine Cl

Phosphorous P Iron Fe

Potassium K Boron B

Manganese Mn

Calcium Ca Zinc Zn

Magnesium Mg Copper Cu

Sulfur S Molybdenum Mb

Nickel Ni

Nutrient DeficiencyA lack of one or more essential elements needed by plants

for optimum growth lead to plant stress.

HEAVY METAL STRESS1. Supra optimal concentration of heavy metals such as

Cd, Pb, Hg, Cu, Zn and Ni affect growth, development and yield of plants, though Cu, ZN, and Ni are essential micronutrients at low concentration

2. Heavy metals affect several physiological and metabolic processes

3. Plants have developed several mechanisms that control and responds to the uptake and accumulation of both essential and non essential heavy metals

HEAVY METAL STRESS1. Tolerance mechanisms vary from species to

species and their genetic background

2. The important heavy metal tolerance mechanism include metal binding to wall, reduced transport across cell membrane, active efflux of metals, compartementation , chelation and sequestration of heavy metal by particular ligands such as phytochelatins and metallothioneins

14Stress is the driving force behind the process of adaptation and evolution

Plant Stress Response

Stresses cause responses in metabolism and developmentInjuries occur in susceptible plants, can lead to impeding flowering, death

Preferable!

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Plant Stress Responses

High temperature Stress

Phosphorus deficiency

SULFUR DEFICIENCY

NITROGEN DEFICIENCY

STRATEGY TO COPE WITH ABIOTIC STRESS

• Agronomy by managing or manipulating the environment

• Plant Breeding using tolerant cultivar

Importance of Plant breeding?

Increases in yield are derived both from improved varieties and from improved

management.It suggests about a 50-50 of crop yield split

between genetic gain and gain attributed to management.

Planting material is the most important input in agriculture

An improved cultivar is the most economic and least laborious input for crop cultivation

I. Producing initial variation (crossing of diverse

material)

II. Development, testing, and selection of potential

cultivar

III. Testing experimental varieties and selection and

multiplication of the best

General Breeding Procedure

Plant Breeding in the 21th Century

Selection breeding methods

In vitro breeding methods

Molecular breeding methods

Transgenic breeding methods

Outline

a. Abiotic Stressb. Agronomic aspect of Abiotic stress

c. Physiologocal aspect of Abiotic Stress

d. Molecular Biological aspect of Abiotic Stress

e. Conventional Breeding f. In vitro breeding

g. . Transgenic breedingh. Molecular Breeding