NASC at Madison 2003

- Focus on Abiotic Stress

Emma Humphreys

Abiotic Stress Topics Covered

• Phototropism

• High temperature

• Low temperature

• Drought

• Oxidative stress

• Gravitropism

http://www.union.wisc.edu/conferenceservices/arabidopsis/

Root system diversity links drought sensing with developmental plasticity

(Jonathan N. Fitz Gerald, University of Chicago)

• The developmental plasticity of plants enables them to adapt their morphology to a changing environment.

• Hypothesis: that these responses will differ in plants that have evolved in distinct environmental conditions and that exploiting this natural variation may be the best strategy for developing crop with optimized whole-plant responses to abiotic stress.

Root development: Ler v Col

• Ler on average initiates more lateral root primordia than Col and has more emerged roots

• Initiation of lateral roots is inhibited at higher osmotica, independent of background

• Percentage of lateral root emergence is inhibited at high osmotica in Col

An in-depth analysis of water stress effects on root system morphology was carried out

on various Arabidopsis ecotypes

• Lateral root growth in Columbia is inhibited by simulated drought conditions. High osmotica specifically reduce the percentage of lateral root primordia that emerge to form lateral roots in Col seedlings.

• In contrast, lateral root emergence in Landsberg erecta seedlings is insensitive to water stress.

Columbia

Landsberg

• Lateral root growth was scored in 100 Col x Ler RI lines under 3 osmotic conditions

• Three major effect quantitative trait loci (QTL) responsible for over 50% of the phenotypic variation in root system morphology were identified: EDG1-3 (elicitors of drought growth).

• EDGs are suppressors of lateral root growth.

Conclusions

• Arabidopsis exhibits root plasticity during water stress

• 3 major effect QTL contributing to root morphology in high osmotica were identified

Abiotic Stress Topics Covered

• Phototropism

• High temperature

• Low temperature

• Drought

• Oxidative stress

• Gravitropism

http://www.union.wisc.edu/conferenceservices/arabidopsis/

Root Responses to Touch & Gravity (Simon Gilroy, Pennsylvania State University )

Q. How does a root understand up and down?Sensory events occur in the collumella cells of the root tip,

so when a root is reoriented a signal is generated in these cells.

What are the signalling events?

• pH is the most likely mechanism:The pH of the root cap cytoplasm was measured before

and after root reorientation. A transient increase in pH was found to occur.

pH 7.2

pH 7.6

How do roots navigate around obstacles?

Soil

Rocks

Perhaps the touch stimulus is down regulating gravitropism…

Barrier

Touch in the root cap switches of the pH change in collumella cells

• How does the signal get from the root cap to the collumella cells?

Ca +

• An increase in calcium in the root cap signals it has touched something initiating a response

Conclusions

• pH change is important for gravitropism to occur

• Ca+ is feeding into the gravitropic response and is able to influence its activity

Further information(including time delay photography):

http://www.bio.psu.edu/Faculty/Gilroy/

Madison