Heat Stress, Freezing, and GDD

How do plants gain better tolerance to hot temperatures?

Plants respond to high temperatures by acclimation, such as by making protective substances, e.g. “heat shock proteins” (HSP).

How do HSPs function in plants?

They help to repair (re-fold proteins back into their functional 3-D configuration), or eliminate damaged proteins caused by high temperatures.

Name the three processes that underlie situations of sensitivity to modestly high temperatures (below temperatures that cause protein denaturation) in plants. Give at least one example from one of these processes and describe how the plant is affected.

(1) Pollen production (during early meiosis stage), (2) night time respiration (and the imbalance this creates in carbohydrate supply vs demand), and (3) high rates of transpiration which exacerbates drought. In pollen production, crops are unable to set seed because the delicate cell division process is disrupted. In night time respiration, warm nights speed up the rate of carbohydrate consumption causing an imbalance between production and consumption. In drought, high temperature increases the rate of water loss.

Which types of plants in our region are most capable of tolerating extremely low freezing temperatures? Which types survive cold winters even though their tissues cannot tolerate temperatures much below freezing?

Woody-plant above-ground tissues such as buds and bark are the most tolerant to freezing; they are directly exposed to our most extreme cold temperatures. In contrast, perennial herbaceous plants like forages, range grasses, and winter cereal crops are able to avoid getting exposed to extreme temperatures by having their overwintering growing points at or below the soil surface, insulated by snow cover and plant debris and kept warmer than the air temperature due to the thermal mass of the ground.

What location of ice formation in plants is the most lethal?

Intracellular ice formation.

Acclimation to cold generates accumulation of what three substances in plants?

Osmotic solutes (contributes to a lower freezing point), antifreeze proteins, and stability factors like compatible solutes and desiccation-related proteins that stabilize membranes and proteins to desiccation stress.

Name techniques farmers use to mitigate the effects of subzero temperatures on

overwintering forages and winter grains.

Leave stubble of previous crop and use no-till to leave debris that captures snow and plant debris which insulate such that growing points that are below the soil surface remain at mildly cold temperatures will survive.

What does GDD stand for?

Growing Degree Days, which is the sum over an indicated period of days of the daily temperatures in excess of a base temperature. (better to describe as an equation)

What is the equation for calculating GDD?

[(Maximum temp+Minimum temp)/2]-50