Yoh Iwasa

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Yoh Iwasa is a mathematical biologist. He has repeatedly found that the same mathematical and computational methods are applicable to diverse branches of biology, and similar concepts are able to give insights in different subfields of life sciences.

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Suresh K Ghimire

Tribhuvan University

Dorian Q Fuller

University College London

Caroline J . Tully

University of Melbourne

Andrew Mathews

University of California, Santa Cruz

Freddy Bravo

Universidade Estadual de Feira de Sanana

Flavia Landucci

Masaryk University

Silvio Nihei

Universidade de São Paulo

Chris Martine

Bucknell University

djordjije milanovic

University of Banja Luka

Juana María Coronado-Blanco

Universidad Autónoma de Tamaulipas

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Optimal seasonal schedule for the production of isoprene, a highly volatile biogenic VOC

Scientific reports, May 29, 2024

The leaves of many trees emit volatile organic compounds (abbreviated as BVOCs), which protect th... more The leaves of many trees emit volatile organic compounds (abbreviated as BVOCs), which protect them from various damages, such as herbivory, pathogens, and heat stress. For example, isoprene is highly volatile and is known to enhance the resistance to heat stress. In this study, we analyze the optimal seasonal schedule for producing isoprene in leaves to mitigate damage. We assume that photosynthetic rate, heat stress, and the stress-suppressing effect of isoprene may vary throughout the season. We seek the seasonal schedule of isoprene production that maximizes the total net photosynthesis using Pontryagin's maximum principle. The isoprene production rate is determined by the changing balance between the cost and benefit of enhanced leaf protection over time. If heat stress peaks in midsummer, isoprene production can reach its highest levels during the summer. However, if a large portion of leaves is lost due to heat stress in a short period, the optimal schedule involves peaking isoprene production after the peak of heat stress. Both high photosynthetic rate and high isoprene volatility in midsummer make the peak of isoprene production in spring. These results can be clearly understood by distinguishing immediate impacts and the impacts of future expectations. Keywords Volatility, Marginal value of leaf area, Pontryagin's maximum principle, Post-risk enhancement, Immediate impact, The impact of future expectations Trees produce a diversity of volatile organic compounds (abbreviated as BVOCs) to protect their leaves from various damages, including heat stress, herbivory, and pathogens 1 . The amount of BVOC production is very large 2 , and the BVOC may modify the local and global climates . BVOCs have protective functions 1 . Isoprene enhanced the heat tolerance of leaves by facilitating recovery after heat stress of leaves through the rapid suppression of reactive oxygen species and stabilizing cell membrane . Monoterpenes and sesquiterpenes functions as repellents of herbivorous insects. In addition, trees attacked by herbivorous insects emit BVOCs which attract predatory insects that remove the herbivores . In this context, BVOCs functions as infochemicals, calling for predators to guard the trees. Thanks to the recent rapid advancement of technique in handling genomics and genome-wide gene expression data (e.g., for genes controlling flowering timing of plants ), information about the genes involved in the production of BVOCs has become increasingly available. For example, both Quercus glauca and Lithocarpus edulis are trees of the Fagaceae family living in warm temperate regions of the Japanese islands. In both species, the genes related to isoprene production show high expression in the middle of the summer . The gene expression does not necessarily imply the production of respective chemicals, as it is often subject to additional regulatory processes. One possible interpretation is that the tree prepares for the arrival of the season with a high risk of heat stress by activating biochemical pathways needed for producing isoprene, becoming ready to produce the chemical upon the sudden arrival of detrimental heat stress. In this study, we examine a mathematical model to determine the optimal seasonal pattern of isoprene production for a tree. Isoprene is highly volatile and is not able to stay on leaves, and is able to enhance leaves' resistance to heat stress. We approach this as an optimal control problem, seeking for the profitable seasonal schedule of isoprene production. The tree is considered as a player aiming to maximize its total net photosynthesis, defined as the total carbon produced by the photosynthesis of a cohort of leaves until their shedding, minus the cost of isoprene production. We assume that the risk of heat stress, photosynthetic rate, and the effectiveness of BVOCs may vary seasonally.

Yoh Iwasa

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