Indoor Crop Production Exam 2

Hort 417

Non-signaling Photoreceptors

➢ Energy from absorbed photon generates electrochemical gradient

➢ Integrated into membranes

➢ E.g., reaction centers for photosystems

Signaling Photoreceptors

➢ Energy from absorbed photon activates or de-activates photoreceptors that promote or inhibit a downstream responses (e.g., phototropism)

➢ Tend to move around within a cell

➢ E.g., Phytochromes, cryptochromes, phototropins, UVR8

Positive & negative regulation (photreceptors)

Positive→ activating photo receptor
Negative → deactivating photo receptor

Photoreceptor Structure

Protein complex + a bound chromophore that absorbs photons within a certain wavelength range of light

Protein Complex: (everything but the chromophore)

The Chromophore

Active form of phyotochrome?

Phy (Pfr)← red light activates

→ far red light deactivates into →Phy pr

Inactive form of phytochrome?

Phy (pr) → far red light + temp reversion deactivates Phy (Pfr)
red light deactivates → phy (Pfr)

T/F? Phytochrome – Absorbing red or far-red light causes structural change

TRUE
The confirmational change that occurs when the chromophore absorbs a photon
(closed “arms” vs. “open“ arms as it interacts with photons)

Characteristics of Vegetational Shade:

Significant reduction in light intensity is comprised of:

Relative_______in green and far-red light
&
Relative _____ in red and blue light

➢Relative increase in green and far-red light
&
➢Relative decrease in red and blue light
*➢A reduction in the ratio of red to far-red light (R:FR)

Define: Shade Avoidance

Shade Avoidance:
A survival strategy common to shade intolerant plants comprising a set of photomorphogenic, physiological, and developmental responses enabling plants to avoid or escape vegetational shade and/or the threat of future shade by neighboring plants (competition).

Shade Avoidance: Stem Elongation

Decreasing R:FR
➢ Promotion of stem elongation (hypocotyl and internode), increased overall plant height, and reduced branching (apical dominance) 13

➢ Adaptive to increase light capture (What are the costs?)

Shade Avoidance – Locus of Perception
(Look at how planting density impacts growth behavior)

*the R:FR decreases when measured inside/under the canopy!

Shade Avoidance – Common Responses

Shade Avoidance – More Common Example

Shade Avoidance – Leaf Responses (thickness)

Shade = thinner
full sun = thicker

Phytochrome interacting factors (PIFs; transcription factors)

promote shade responses through upregulated auxin biosynthesis

Shade Tolerance:

Shade Tolerance:
A survival strategy common to shade tolerant species (e.g. forest understory plants) that has some overlap with shade avoidance (e.g., a reduction in leaf mass per unit area), but is also characterized by a lack of elongation responses to shade and heavy investment into leaf herbivory defense.

Phytochrome

Phytochrome is a photoreversible red and far-red light absorbing photoreceptor. It is the primary photoreceptor responsible for regulating shade avoidance responses.

Shade avoidance

Shade avoidance is a set of morphological, physiological, and developmental responses to escape vegetational shade or the threat thereof; these responses are generally considered adaptive

Shade avoidance considerations in CE:

plant density, placement and management of hanging baskets, and use of electric lighting with different intensities and spectral outputs can impact plant growth and development

WS (kg·m–2·h–1)

mass of water supplied

WL (kg·m–2·h–1)

mass of water vapor lost to outside

Biomass produced per unit of water transpired→

3 g of dry biomass per liter of water is low (ambient CO2; 40% RH) 6 g of dry biomass per liter of water is high (enriched CO2; 70% RH)

Photosynthesis (An) and transpiration (E)

Where are we losing water from hydroponic systems?

system evaporation

leaks

unused reservoir water to waste (crop change over)

Optimal nutrient solutions can be developed using principles of mass balance. Nutrients are in one of two places for hydroponics:

1.Nutrient solution

2. Plant

Nutrient Management by Mass Balance

Paper Review 4 – Key Points:
What is G × E?
Historically, what has been the focus for field production? 

What new opportunities do controlled environments provide in relation to G × E?

G x E:

genotype by environment.
GxE has been selected for field production ie: drought tolerance, pest resistance, stress resistance, etc.


geneotype that will proform well in CEA condition: ie traits like rapid growth, less energy, more compact plant. etc.

Paper Review 6 – Key Points

taking measurements with a smart phone photo to evaluate nitrogen content
if more red light is being reflected by the plant, chlorophyll is down (less nitrogent)

is less red light is being reflected by the plant, chlorophyll is up (more nitrogen)

R870 = infared (no relationship) aka standar

tying nitrogen content to green pigment expression.

Paper Review 7 – Key Points

Tipburn – physiological disorder during rapid plant growth involving necrosis at the leaf apex of young developing leaves

Affected crops:
¤Lettuce
¤Strawberry
¤Cabbage

¨ Tipburn is related to Ca2+ deficiency→Component of cell walls and maintains cell function as messenger signal

¤Deficiency results in cell death and necrosis ¨ Ca2+ deficiency also impacts tomato, resulting in blossom end rot

Ca2+ is also an immobile nutrient →Cannot move from sufficient to insufficient tissues

¤Deficiency symptoms seen in new foliage
-Smaller leaf area
-Lower cumulative transpiration rate compared to mature leave

¨ Inhibition of Ca2+ transfer from root to shoot
¤Ca2+ absorbed by roots and transferred via transpiration (mass flow)
¤Suppression of transpiration leads to deficiency
→High humidity nHot, dry environment resulting in stress (stomates close)
→Low root activity can also result in deficiency nWater/salinity stress nLow temperature nLow oxygen

How do we typically prevent tipburn?

¤Increase airflow
¤Decrease humidity
¤Slow plant growth rate (lower DLI and/or temperature)
¤Harvest early

What is a biostimulant?

¤Beneficial substances to plant growth and health that can be derived from chemicals, bacteria, algae, seaweed, or plants.

¤Primary functions are to improve crop yield, nutrient use efficiency, secondary metabolite accumulation, and abiotic stress tolerance.

EC and nutrient concentration→

Concentration of nutrient ions are not fixed, while an EC can be fixed, actual nutrient content can shift overtime!

→ Ionic concentration of nutrient solution changes with time

(waste and then restart for new crop, although wasteful, this makes production more accurate)