WATER STRESS

Fábia Guimarães Dias

Global warming

Rio Negro increased 30 meters this year

Drought in the northeast state

The importance of water

Water is a essential substance for plant life It influences various functions in plants:

As structure, growth and metabolism.  Corresponding 90% of the dry weight of many

organs.

Como estrut

StressesAbiotic stress

Water

DroughtFlooding

Temperature

ColdFreezing

High

Light

LowHigh

Chemical/Soil

Salt or salinityMineral deficiency

Acid soilAir pollutantsElevated CO2

Biotic stress

Infection by Pathogens

virus, bacterias, fungi, nematodes and

insects

The number of publications per year related to abiotic stress

Drought

It is one of the most common limitations affecting the growth (causing metabolic changes)

Drought induces complex responses to adaptation of plants to limiting environments

Transcriptional regulatory network

ABA is a central regulator of plant responses

Adaptation X acclimation

Plant adaptation: Genetic resistance, acquired by the selection

process for many generations

Plant acclimation: Increased tolerance as a result of previous

exposure to stress

Mechanisms of drought resistance

The mechanisms of drought resistance can be grouped into three categories:

Escape drought Avoidance drought Tolerate drought

Adaptation mechanisms

Escape drought It is defined as the ability of a plant to complete their

life cycle before the start of the drought period This mechanism involves the rapid phenological

development (early flowering and maturity) and plasticity (variation in duration of growth depending on the extent of the drought).

Avoidance drought Ability of plants to maintain turgor and cell volume

By absorption of water by an abundant root system and reduce the loss by transpiration through stomatal closure.

Adaptation mechanisms

Tolerate drought It is a mechanism that allows the plant to keep

the metabolism, even with the reduction of tissue water potential, mainly due to the accumulation osmolytes protein.

Response of plant growth to stress

Response of plant growth to stress onset is often characterized by a rapid and acute (‘acute response’) inhibition, followed by recovery and adaptation to the new condition (‘adaptation response’)

Growth rate

adaptation

“acute”

Tempo

Inicio do estresse In barley leaves, the leaf elongation rate decreased close to zero within seconds after salt addition to the roots, followed by recovery of LER to approximately 46% and 70% of the non-stressed plants within minutes and days, respectively

Response of plant growth to stress

While the acute response prepares plants for possibly more severe conditions, the adaptive response can be seen as the establishment of a new steady state to prolonged and stable stress.

Drought reduces leaf growth by affecting cell division and expansion In dicotyledonous plant species, such as

Arabidopsis, leaf growth results from the proliferation and subsequent expansion of founder cells, recruited from the SAM.

Leaf development

Time (day)

Initially leaf growth is driven exclusively by cell proliferation (P, red shading).

Within several days and starting from the leaf tip, cells exit the mitotic cell cycle and start to expand (E, green shading).

After a few days, leaf growth is steered solely by cell expansion. Again starting at the tip, cells become mature (no shading), coinciding with growth cessation

The drought reduces leaf growth and affects cell division and expansion The drought affects growth in Arabidopsis

Skirycz et al. 2010

25mM de manitolWT

50% reduction in leaf sizer

Rolled and narrow leaves

Arabidopsis seedlings were germinated and grown on medium with or without mannitol up to 22 after stratification.

The drought reduces leaf growth and affects cell division and expansion Cellular changes during osmotic stress in

Arabidopsis

Não foi significativo em 9 DAS

Skirycz et al. 2010

Processes involved in regulating the growth of plants under drought

Dry soil is detected in the roots by activating a combination of chemical signals and hydraulic

The chemical signals are transported via the xylem to the leaves, where they initiate numerous mechanisms of tolerance: avoid / tolerate

The TFs regulating genes encoding enzymes in the catabolism of gibberellin (GA2ox) reducing the levels of GA, which stabilizes DELLA proteins, leading to inhibition of growth.

DELLA proteins are restricted to nuclear proliferation and cell expansion in plant

The gibberellin stimulates growth by inhibiting DELLA protein

Leaf growth

The growth regulation mediated by DELLA proteins is conserved in different stresses and promotes a convergence between the classic stress hormones.

Leaf growth

Flooding Stress

Main responses to flooding

What happen in flooded soil ? Absence of O2 in the soil: Roots needs to

breathe to grow O2 available to the root is originally the soil

pore spaces

Hypoxic (low oxygen)

Anoxic (without oxygen)

Main responses to flooding

The flooding causes O2 deficiency, CO2 excess and excess ethylene

The O2 deficiency decreases the rate of aerobic respiration, which causes accumulation of metabolic toxins such as methane.

Main responses to flooding

The flooding can cause an immediate reduction in gas exchange between plant and environment

Affecting plant growth

Planting sunflowers in flooding

Main responses to flooding

Piptadenia gonoacantha

Espécie arbórea da mata de galeria

Seedlings of P. gonoacantha showed rapid growth under field capacity, while flooding reduced the growth roots and shoot

Ferreira et al (2001)

Hypotheses for the reduced growth of seedlings of P.gonoqchathaa) Low production of ATP,b) Decrease in the rate of CO2 assimilation due to stomatal closure,c) Reduction in the synthesis and translocation of growth regulating substances such as gibberellins and cytokinins.

Main responses to flooding

Seedlings with two days of age grew up in sand completely flooded with water

The elongation of the hypocotyl was suppressed during the flooding

Nanjo et al 2011

WTFlooding

Gene expression inducible by flooding

Expression of genes that encode small proteins in soybean

Of the 100 genes induced in the microarray analysis, only three showed fold change greater than 500 time

qPCR dos três genes

These genes encode unknown or hypothetical proteins

Gene expression in specific organs and tissues

All the organs were subjected to flooding during 6h

How do plants tolerate flooding

Nénufar

Morphological adaptations

Aerenchyma is a specialization of the parenchyma. Spaces filled with gas.

Development of aerenchyma in the apical region of maize seedlings

Development of aerenchyma in roots of maize seedlings

Morphological adaptations

Negative geotropism