Thermal Adaptation - Heat Acclimation in Plants

The survival and reproduction of plants is dependent on availability of water, nutrients and sunlight. Increased environmental temperature can put significant pressures on plants, affecting osmoregulation and photosynthetic ability of the cells (Berry & Bjorkman 1980). Plants inhabiting hot climates possess adaptations to the impacts of heat stress (excessive water loss, chlorosis, increased respiration) (McWilliam & Naylor 1967). Physiological stress in plants as a result of temperature reduces reproductive and individual growth. This blog post will discuss some adaptations allowing plant survival in high temperatures. 

Fig. 1 - Diagram showing processes of photosynthesis and respiration in plant cells
(Morholt & Brandwein)

Plant respiration is the oxidization of glucose in the mitochondrial organelles of plant cells, resulting in production of carbon dioxide (CO²) and water (Fig. 1). Global circulation models (GCM) have suggested that increased environmental temperature increases respiration in plants, resulting in water loss of leaves and roots, photosynthetic inhibition of leaves, and weakened roots (especially with increased soil temperature) (Atkin et al 2005). Increased respiration would also increase atmospheric CO², contributing to the existing greenhouse effect. Atkin et al (2005) contradicted GCM and found that increased environmental temperature does not always result in increased plant respiration and adaptations exist to balance regular CO² production with increased environmental temperature. These adaptations are both intra-cellular and physiological, depending on the species concerned and the niche conditions for its habitat.

Fig. 2 - Representation of the temperature response of respiration in warm-grown (Hot), cool-grown (Cold) and warm grown type plants acclimated to cooler and hotter temperatures
(Atkin et al 2005)

Desert plants reduce respiration and water loss by reducing surface area of leaves. Plants inhabiting Death Valley, California, retained photosynthetic ability up to 43°C before experiencing damage to the chloroplast membranes (Seemann et al 1984). Atkin et al (2005) found that some plants can regulate concentration/amount of enzymes involved in plant respiration, and vary mitochondrial protein concentration, thus changing rates of respiration. Simplified, this means cold-adapted plants can increase respiration with increased temperature, and warm-adapted plants can decrease respiration to reduce water loss and CO² output (Fig.2). This would balance the production of CO² by plants in the atmosphere. However, the ratio of cold-adapted plants to warm-adapted plants in global populations would impact total vegetative CO² output.

Plants inhabit areas of highly varied temperature, light and water availability in different global biomes. This post has listed some plant survival adaptations, as well as impacts of increased temperature on plants and the world. The likely increase in global temperature is an effect of anthropogenic increase in CO² emissions. Studies have shown that plants can somewhat modify respiration and osmoregulation as a result of temperature increase, and these processes may impact the effects of global warming.

References:

Atkin, O. Bruhn, D. Hurry, V. Tjoelker, M. 2005, ‘The hot and the cold: unravelling the variable response of plant respiration to temperature’, Functional Plant Biology, Vol. 32, pp 87-105

Berry, J. Bjorkman, O. 1980, ‘Photosynthetic response and adaptation to temperature in higher plants’, Annual Review of Plant Biology, Vol. 31, pp 491-543

McWilliam, J.R. Naylor, A.W. 1967, ‘Temperature and Plant Adaptation; Interaction of Temperature and Light in the Synthesis of Chlorophyll in Corn’, Plant Physiology, Vol. 42, pp 1711-1715

Seemann, J. Berry, J. Downton, W. 1984, ‘Photosynthetic Response and Adaptation to High Temperature in Desert Plants: A Comparison of Gas Exchange and Fluorescence Methods for Studies of Thermal Tolerance’, Plant Physiology, Vol. 75, No. 2, pp 364-368

Figures:

Figure 1 - E. Morholt, P.F. Brandwein, (date unknown), A Sourcebook for the Biological Sciences

Figure 2 - Atkin, O. Bruhn, D. Hurry, V. Tjoelker, M. 2005, ‘The hot and the cold: unravelling the variable response of plant respiration to temperature’, Functional Plant Biology, Vol. 32, page 88 (Fig.1)