ENVIRONMENTAL DEFICIENCIES Flashcards
Describe the role of essential nutrients and the effect of their deficiency on plants. Explain plant adaptations and acclimations to deficiencies i light, oxygen and essential nutrients.
ESSENTIAL MINERAL NUTRIENTS
Nitrogen (N), phosphorous (P) and sulfur (S) = part of carbon compounds (amino acids, nucleotides, enzymes cofactor…)
Phosphorous (P) and calcium (Ca) = important in structural integrity (in membranes and cell walls) and/or energy storage.
Potassium (K), magnesium (Mg), calcium (Ca), manganese (Mn), chlorine (Cl) and zinc (Zn) = elements present as ions dissolved or bound to biological compounds. Roles as enzyme cofactors, regulation of osmotic potential and messenger.
Iron (Fe), nickel (Ni), manganese (Mn), copper (Cu) and molybdenum (Mo) = metals involved in redox reactions, in particular transport.
How to know that a nutrient is essential?
without an essential nutrient, plants cannot reach reproductive stage…
it is not always easy
DEFICIENCY SYMPTOMS
Reduction in growth: Zn, N, P, S, K
Chlorosis (yellowing of leaf due to lack of chlorophyll): N, Mg, Fe, Zn, Mo
Necrosis: Cu, Zn, K, Ca
POTASSIUM DEFICIENCY
> K+ activates more than 50 enzymes, including some involved in protein synthesis and photosynthesis.
K+ acts to counteract proton charges across the thylakoid created by the proton gradient necessary for ATP synthesis.
. photosynthesis
. regulation of stomatal movement
. osmoregulation
. enzymes activation
. protein synthesis
. maintenance of cation-anion balances
AVOIDING DEFICIENCIES with FERTILISERS: limitations and drawbacks
to avoid N, P, and K deficiencies and maximise yield, farmers often use fertilisers.
> Fertilisers are costly and small scale farmers in developing countries often cannot afford them
> industrial N fixation requires lots of energy
> Nitrogenous fertilisers release greenhouse gas NO
> fertiliser leaching (N and K) leads to eutrophication
> Phosphorous is a non renewable, finite resource
ACCLIMATIONS TO NITROGEN AVAILABILITY
studying the effect of nutrient concentration in artificial growth media…
the split root system indicates that plants increase lateral root growth in regions with higher nitrogen concentration.
ACCLIMATIONS TO PHOSPHATE AVAILABILITY
LOW Pi
> inhibition of primary root growth
> increase in root hair length and number
> enhanced formation of lateral roots
> increase in lateral root length
ACCLIMATIONS TO POTASSIUM AVAILABILITY
Root hair length of seven different crops grown in containers with soils with moderate or low potassium levels…
Several crops have longer root hairs when there is a low K+ concentration in the soil.
The response to how low K+ concentration in the soil in terms of root length varies between species.
ADAPTATIONS TO LOW NUTRIENT AVAILABILITY
Root symbiosis with soil microorganisms.
Mycorrhizae facilitate access to nutrients in exchange for carbohydrates.
Plants get fixed nitrogen while the rhizobia get carbohydrates and a sheltered environment.
ROOT SYSTEM ADAPTATIONS = large root biomass and surface area (lateral rooting, root hairs)… more cortical aerenchyma.
PHOTOTROPISM
MOVING TOWARDS THE LIGHT
Light is perceived at the tip of the plant and induces the production of auxin. Auxin is transported downwards and towards the side less exposed to light. The auxin gradient promotes growth on the side and results in curvature towards the light.
In Arabiodopsis seedlings with altered auxin transport, the curvature is modified.
SHADE AVOIDANCE
Shade avoidance is the response of sun-loving plants to other plants growing over them.
Light under the canopy is enriched for far-red light wavelengths because leaves filter red and blue lights.
Shade avoidance responses include growing taller instead of branching, expand leaf blade and petiole, elevate leaf angle and flower earlier.
LIGHT RESPONSES AND PHOTORECEPTORS
Phytochromes detect red and far red, blue and UV-A. Its biological processes are shade avoidance and photomorphogenesis.
Cryptochromes detect blue waves. Its biological processes are photomorphogenesis, flowering, and the circadian clock.
Phototropins detect blue and UV-A. Its biological processes are phototropism, chloroplast movement, and stomatal opening
OXYGEN DEFICIENCY
Lack of oxygen (hypoxia/anoxia) impairs respiration: oxygen-deprived organs have to rely on fermentation to produce energy.
What can pants do to get what they need ti grow and survive?
ADAPT THEIR GROWTH PATTERN:
> expand roots to absorb essential nutrients
> increases shoot height and width and grow in the direction of light
> develop aerenchyma
INTERACT WITH OTHER LIVING BEINGS:
> collaborate with microorganisms to get nutrients
> eat insects
> outcompete neighbours for light
Many of these strategies require that plants reliably detect the availability of environmental resources. e.g. photoreceptors, nitrate sensors
GLOSSARY
Essential nutrient: nutrient required by plant to complete its reproductive cycle
Chlorosis: insufficient production of chlorophyll resulting in a yellowish coloration of the leaf
Phototropism: growth towards a light source
Hypoxia: reduced access to oxygen
Anoxia: no access to oxygen
Aerenchyma: spongy tissue characterised by gas-filled spaces
