Flooding responses Flashcards
in every habitat, what is a powerful discriminator of plant distribution?
tropics water table levels and their fluctuations
– strongly influences the zonation of neighbouring communities.
how can flooding vary?
seasonal
long/short duration
confined to rooting zone or total immersion of shoot too.
this variation requires plants to have different adaptations
what dangers does flooding pose to plants due to lack of oxygen?
3 levels
Crawford and Braendle 1996 hypoxia - low oxygen anoxia - no oxygen LEVEL1: 1. Deprivation of oxygen to plant organs 2.production of toxic ions in soil 3. changes to hormone distribution 4. faciltiates microbial pathogens LEVEL 2:1. anoxic injury 2. post flooding dev injury eg root dieback causes wind to throw trees. LEVEL3: 1. reduced ATP gen 2. Depletion of Carbohydrate reserves 3. hydrolysis of cyanogenic glycosides 4. accumulation of toxic metabolites.
what do Global environment change models suggest
incidences offlooding likelyto increase in S america, SE asia, C Africa.
what wereestimated insurance payouts to farmers due to flooding damage between 2001 and 2011 in US?
Voesenek and Bailey-Serres 2015
averaged $24 billion / yr-1
what is one morphological response to flooding
eg in bulrush, Typha latifolia
Formation of aerenchyma
gas filled spaces called lacunae which connect, extending from below the ground and up through stems creating an internal aeration system. allows plant to survive when o2 deficient, like a snorkel.
even with aerenchyma, why might plant not survive flooding?
oxygen diffuses from the root - Radial Oxygen Loss.
to prevent this, suberin is laid down in hypodermal cells of root to prevent ROL.
how is suberiztion controlled?
ethylene builds up in response to flooding
induces transcription of many genes, one being RCN1, resulting in suberin synthesis inbetween epidermal and hypodermal cells.
suberized hypodermal cells from exodermis, and results in reduced ROL
what is the mechanism for aerenchyma formation?
3 mechanisms, one better understood.
forms lysigenous aerenchyma, uses programmed cell death, triggered by flood induced ethylene accumulation and involves Ca2+ signalling, ROS (ca2+ activates enzyme RBOH to form ROS), increases SOD expression and expression of wall loosening enzymes, resulting in cell wall degradation.
what is involved in the ethylene transduction cascade.
ethylene receptors (5 members, on the ER).
activate CTR1 protein kinase enzyme, in the absence of ethylene.
PK enzyme inhibits EIN2 transmembrane protein, activating transcription factors causing ethylene responses.
what are 2 strategies plants use when facing total submergence?
- low oxygen escape strategy
2. low oxygen quiescent strategy
what happens in the low oxygen escape strategy
shoots elongate, keep some leaf material above water.
Ethylene induces snorkel1 and 2 gene expression. Encode TF known as ethylene response factor, ERF. Promotes giberellin production, stimulating elongation growth.
what happens in the low oxygen quiescent strategy?
reduces metabolism to maintain energy so that growth can be resumed after flooding subsides.
ethylene induces expression of SUBMERGENCE1A (SUB1A-1) gene.
Ethylene also induces ERF (ethylene response factor) which promotes GA production. SuB1A-1 inhibits GA action, and induces degredation of DELLA transcription factors so DELLA is expressed and growth inhibited.
SUB1A-1 minimises decline of a DELLA called SLENDER RICE-1 (SLR1).
example of variety modified in green rev
in the green revolution, rice variety LG was extensively cultivated. thrived in shallow paddies but dies within a week of submergence, lacked SUB1A-1. using non GM breeding, SUB1A-1 has been introduced into these varieties and have tolerance to extended submergence.
also SUB1A-1 introgressed from FR13A flooding tolerant variety into Swarna which then maintains yield after flooding.
how are ERF - ethylene response factors, regulated in arabidopsis?
stabilised under hypoxia (reduced oxygen) but are targeted for degradation under normoxia
Uses N end rule pathway, regulated by oxygen levels
regulates ERF half life based on presence of specific AA and N terminal. if recognised sequence, targets protein for destruction.
