Abstract
Elevated growth temperatures are known to affect foliar organic acid concentrations in various plant species. In the current study, citrate, malate, malonate, fumarate and succinate decreased 40 to 80% in soybean leaflets when plants were grown continuously in controlled environment chambers at 36/28 compared to 28/20 °C. Temperature effects on the above mentioned organic acids were partially reversed three days after plants were transferred among optimal and supra-optimal growth temperatures. In addition, CO2 enrichment increased foliar malate, malonate and fumarate concentrations in the supra-optimal temperature treatment, thereby mitigating effects of high temperature on respiratory metabolism. Glycerate, which functions in the photorespiratory pathway, decreased in response to CO2 enrichment at both growth temperatures. The above findings suggested that diminished levels of organic acids in soybean leaflets upon exposure to high growth temperatures were attributable to metabolic impairment and to changes of photorespiratory flux. Leaf development rates differed among temperature and CO2 treatments, which affected foliar organic acid levels. Additionally, we report that large decreases of foliar organic acids in response to elevated growth temperatures were observed in legume species.
Highlights
Various adaptive mechanisms make it possible for terrestrial plants to acquire thermotolerance and to survive high and acutely high growth temperatures [1,2]
Organic acids perform vital functions in respiratory, photorespiratory and photosynthetic metabolism, and these compounds are normally synthesized from the oxidation of soluble sugars and lipids [18,19]
Organic acids serve as substrates for amino acid and secondary product formation and shuttle protons among subcellular compartments to manage energy balance and cellular pH
Summary
Various adaptive mechanisms make it possible for terrestrial plants to acquire thermotolerance and to survive high and acutely high growth temperatures [1,2]. Especially under field conditions, involves complex processes that stabilize membranes and proteins in order to preserve cellular function. Heat stress induces reactive oxygen species (ROS), which oxidize cellular constituents and damage membrane integrity [3]. The control of ROS is an important strategy in attaining thermotolerance. Specific proteins, known as heat shock proteins (HSPs), are synthesized in response to elevated growth temperatures. Many plant metabolites alleviate environmental stress by functioning as osmolytes or compatible solutes and by assisting in the removal of ROS [6,7,8]. Elevated growth temperatures affect rates of important metabolic processes, including photosynthetic CO2 assimilation, dark respiration and photorespiration [9]. Acclimation to enhanced growth temperatures involves wholesale changes of plant metabolism
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