Abstract
Sorghum metabolism continually adapts to environmental temperature as thermal patterns modulate diurnally and seasonally. The degree of adaptation to any given temperature may be difficult to determine from phenotypic responses of the plants. The present study was designed to see if the efficiency of quantum yield of photosystem II could be used as a measure of how well leaf tissue metabolism was able to withstand a prolonged respiratory demand caused by elevated temperatures. The efficiency of quantum yield values of Pioneer 84G62 and Northrup King KS585 commercial sorghum hybrids showed that when the hybrids were grown in a 28°C/20°C day/night cycle in the greenhouse or the field, Pioneer hybrid 84G62 withstood subsequent elevated thermal challenges better than Northrup King KS585. The same hybrids grown in a 39°C/32°C day/night cycle showed similar efficiency of quantum yield values when thermally challenged. Water-deficit stress increased the heat resistance of the tissue raising the efficiency of quantum yield of both lines to the same level. Upon recovery from the water deficit stress the differential efficiency of quantum yield values between the two lines re-appeared. The data provided in this study suggest a metabolic advantage of Pioneer 84G62 to environmental thermal challenges compared with the Northrup King KS585.
Highlights
Enzyme adaptations to temperature occur constantly as temperature patterns modulate diurnally, seasonally, or over centuries
The current study investigated the level of genetic diversity of two commercial sorghum hybrids to thermal and water variability
To evaluate how well-watered Pioneer 84G62 and Northrup King KS585 sorghum hybrids cope with distinct thermal regimes, plants were grown in greenhouses set to maintain air temperatures at either a 28 ̊C/20 ̊C or 39 ̊C/29 ̊C day/night cycle
Summary
Enzyme adaptations to temperature occur constantly as temperature patterns modulate diurnally, seasonally, or over centuries. The concept of thermal kinetic windows (TKW) arose from a desire to investigate temperature stresses in plants and the realization of a lack of knowledge about how to identify the optimal temperatures for metabolism. Thermal kinetic windows of optimal enzyme function were defined as the temperature range over which the value of the apparent Km was within 200% of the minimum apparent Km value observed for the enzyme [1]. The purpose of the thermal kinetic window was to provide a general indicator of the range of temperatures in which the optimal temperature for metabolism was located. Because Thermal Kinetic Windows are only 5 ̊C to 8 ̊C in breadth, plants may be outside their optimal thermal range a large portion of every day
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