Physiological Response of
Plant to the Environment
Solar Radiation
The ultimate source of energy for photosynthesis and
bio-productivity is solar energy.
- solar radiation also influences the plant's growth
and development in what are referred to as
photomorphogenic,
Phototropic
 and photoperiodic responses.
Temperature
Effects of heat stress on plant physiological responses. Upward-pointing arrows indicate activated/upregulated
physiological indices. Downward-pointing arrows indicate deactivated/downregulated physiological indices.
Abbreviations: HS, heat stress; PSII, photosystem II; Rubisco, ribulose-1,5-bisphosphate carboxylase/oxygenase;
ROS, reactive oxygen species.
Temperature
Photosynthesis
Generally, high temperature reduces photosynthetic efficiency, thus
shortening the plant life cycle and diminishing productivity.
photosystem II (PSII) activity is greatly reduced or even stops under
HS because PSII complex is the most heat-intolerant
influences chloroplast structure and the thermal stability of
components of the photosynthetic system, reducing ribulose-1,5bisphosphate carboxylase/oxygenase (Rubisco) activity, amounts of
photosynthetic pigments, and the carbon fixation capacity
Temperature
Cell Membrane Thermostability
Membrane dysfunction is the main physiological consequence of
plant exposure to HS.
Under extreme HS, the increased kinetic energy and movement of
biomolecules across membranes loosens chemical bonds, leading to
disintegration of membrane lipids and increasing membrane fluidity
Temperature
Oxidative Damage
Plants exposed to HS show accumulation of ROS—singlet oxygen
(1O2), superoxide radical (O2−), hydrogen peroxide (H2O2), and
hydroxyl radical (OH−)—generating oxidative stress
Temperature
Other Physiological Responses
Plant water status is generally erratic under changing temperatures. Heat
stress causes dehydration and affects plant growth and development.
Water potential and relative water content are substantially decreased
upon exposure to HS, reducing photosynthetic productivity .
However, under transient or mild HS, plants regulate the rate of respiration
and transpiration to balance water loss and heat dissipation.
The level of soluble sugars and proteins are also altered during HS to
regulate osmotic pressure within the cell.
Finally, HS reduces the yield of cultivated crops, including cereals, legumes,
and oil crops.
WIND
- Causes mechanical stress to plant
- Affects leaf microclimate
- Wind often enhances water stress by reducing leaf boundary layers
and reduces plant temperature by transpiration cooling.
Water
• Water stress adversely impacts many aspects of the physiology of
plants, especially photosynthetic capacity. If the stress is prolonged,
plant growth, and productivity are severely diminished.
Water
STOMATAL SIGNALING DURING WATER
STRESS MEMBRANE
In response to a water deficit
stress, ion - and water transport
systems across membranes function to
control turgor pressure changes in
guard cells and stimulate stomatal
closure.
Stomatal response, ROS scavenging, metabolic changes, and photosynthesis are all
affected when plants are subjected to water stress. These collective responses lead to
an adjustment in the growth rate of plants as an adaptive response for survival.
Growing Degree Days
- What are Growing Degree Days? Growing Degree Days (GDD),
also known as Growing Degree Units (GDU), are a way researchers and
growers can estimate the development of plants and insects during a
growing season.
- help growers and researchers track the development of plants
and pests.
For example, a cool-season crop like alfalfa uses a threshold
temperature of 41 degrees Fahrenheit and a starting date of March 1,
whereas a warm-season crop like corn uses a threshold temperature of
50 F and the planting date as the starting date.
The threshold, or base temperature, is the temperature under
which no significant crop development is expected.
Crops don’t grow any more at temperatures greater than 86 F
than they do at temperatures less than 86 F.
Calculating GDD
Method 1: Temperature averaging
Degree-day accumulation = [(Maximum Temperature + Minimum
Temperature) / 2] - Base Temperature
Remember: Since plants don’t grow any more at temperatures greater
than 86 F than they do at temperatures less than 86 F, we use 86 F as
the maximum temperature for any temperature greater than 86 F. Also,
negative values are recorded as zero.