Lecture 4: How Plants Communicate

Question 1

Intra-plant communication: Root-to-Shoot Signaling

Answer 1

Works via the cohesion-tension theory (transportation of water via the xylem)

Transpiration in the leaves led to water being drawn in roots
-Transportation +photosynthesis are closely interconnected (stomata opening and closing)
-When there is high transpiration there is high water availability in the roots (plant can control their water-use efficiency)

In a drought: low transpiration due to low water availability

Question 2

Transpiration

Answer 2

When water is taken up from the soil, up the root system, through the plant, and then evaporated from the leaf surface

Question 3

Role of roots when sensing water availability

Answer 3

Roots can senses soil water availability through endogenous signals and control stomata with it.
1.) Abscisic acid (ABA): hormone that controls stomatal opening and closing

2.) When there is water stress: ABA increases in roots and moves to leaves (Root-to-shoot).
-ABA pools stored in leaves becomes available, and when reaching a threshold, stomata closes

-Water potential in leaves determine stomatal resistance: the more negative the leaf water potential, the higher the stomatal resistance and ABA content in the leaf

Question 4

Role of ABA

Answer 4

1. ABA binds to receptor at guard cell membrane
2. Stimulates opening of calcium channels in guard cells
3. Ca2+ enters the cell, acting as a second messenger
4. Calcium binds to receptor, activating anion channels: anions leave the cell, causing polarization
5. Due to polarization, K+ leaves cell, depolarisation occurs
6. Exit of ions reduces turgor pressure in guard cell: stomatal closure
7. Stoma opens again when: ABA concentrations reduce and turgor pressure returns.

Question 5

Inter-plant communication: Competitive interactions

Answer 5

-Shape vegetation composition and control biodiversity
-Need to be able to rapidly detect neighbours and respond:
–Defensive strategies: avoidance of competitive interactions
–Offensive strategies: inhibition of competitor’s performance

-Need to be capable of self-recognition (identity+kin) to avoid accidentally fighting themselves or plants of the same species.

Question 6

Self-recognition

Answer 6

1.) Identity recognition in root growth:
-Plants can alter their root growth and sense the presence of other roots
-Can change direction, grow more/less

2.) Kin recognition: ability to distinguish between genetically related and unrelated individuals
-Kin: sibling plants from same mother plant
-Cooperation with kin can save resources: e.g increasing self-shading to avoid shading of other kin plants, competing with non-kin instead.

Question 7

Shade avoidance

Answer 7

Competition for light can induce changes in plants to avoid being shaded
-Shaded plant canopy exhibits low red to far-red ratios
-Causes an increased growth of stems and/or petioles
-Redirection of leaf growth vertically and/or horizontally
-Plants want to reach better red to far-red ratio

Question 8

Inter-specific communication: Volatile Organic Compounds (VOCs)

Answer 8

Play a crucial role for different plant functions:
-Plant reproduction (attraction of pollinators)
-Plant defines
-Plant communication
-Interaction with environment

Question 9

Inter-specific communication: Communication with pollinators (goals)

Answer 9

To produce a lot of offspring, plant requires:
-Maximum reproductive fitness
-Maximum pollen dispersal
-Avoid stigma’s clogging
-Avoid wasting energy

Question 10

Insects as pollen distributors

Answer 10

-short+quick stay on flower
-moves fast between individuals
-stays within one plant species
-doesn’t consume too much

Plants compete for attention of pollinators (evolution of flower traits according to pollen vectors)

Question 11

Pollen vectors

Answer 11

-Color
-Shape
-Scent
-Reward

Question 12

Communication+symbiosis

Answer 12

1.) Bacteria (rhizobium): nitrogen-fixing organisms that are ‘bound’ to root nodules
-Bacteria attracted by flavonoids which induce nod genes in Rhizobium
-synthesis of nod factors: encourages rhizobium to colonise plant’s root hair
-symbiotic relationship: bacteria feeds on sugar+plant relies on nitrogen-fixed by bacteria

2.) Fungi: mycorrhizae

Question 13

Plants vs Pathogens

Answer 13

-Requires hormones+VOCs to fight off microorganisms (Can be abiotic or biotic stress)

-Plants have direct and indirect defence:
–Direct: Fight off herbivorous insects
–Indirect: signal other plants about danger

-Plant’s ‘immune system’: Systematic Acquired Resistance (SAR)
–response to an attack by bacteria+fungi+viruses
–Provides parts of the plants with long-lasting protection against pathogens
-Involved molecules: salicylic acid+jasmonic acid