Research content
During my student days, I studied bacterial cell surface proteins. At that time, I was very surprised to hear about plants that generate heat in their flowers. This great surprise still fuels my motivation for research today. Currently, my laboratory conducts research on plants that generate heat in their flowers and on the aging of flowers in common ornamental plants. Broadly speaking, these are the following:
Research on the thermogenic molecular mechanisms in plant flowers (including inflorescences and cones)
The first record of thermogenic plants can be found in "Flora Français" (1778), a book by the renowned French naturalist Lamarck. In it, Lamarck reports that a certain species of plant in the genus Arum (probably Arum lily) generates heat. Subsequently, thermogenic phenomena were reported in Philodendron (1) in 1972 and in Symplocarpus renifolius (2) in 1974. In the late 1980s and early 1990s, cyanide-tolerant respiratory enzyme (AOX) was isolated and identified from a thermogenic plant called Voodoo lily as a protein that plays a crucial role in heat generation (3, 4). AOX is considered an important protein for heat generation because it plays a role in dissipating excess energy on the mitochondrial membrane and its expression and activity are high in heat-generating tissues. AOX has since been found to play an important role in general plants as well, and has been actively researched, particularly in the field of plant environmental stress responses. Its three-dimensional structure was reported in 2012 (5). Another well-known molecule involved in heat generation in plants, besides AOX, is salicylic acid. Salicylic acid was reported in 1989 as a "calorigen" that induces fever in the voodoo lily (6, 7). However, there are no reports of salicylic acid acting as a calorigen in other fever-inducing plants. One of our research goals is to identify a true calorigen that can replace salicylic acid.
With advancements in temperature measurement technologies such as infrared thermography, numerous instances of heat generation in plants have been reported. To date, approximately 80 species have been reported, and this number is expected to increase further. Nevertheless, among the hundreds of thousands of plant species that inhabit the Earth, the existence of heat-generating plants remains unique. However, just as the heat-stable DNA polymerase widely used in PCR was found in thermophilic bacteria (8), and the fluorescent protein GFP was found in the jellyfish Aequorea victoria (9), there are many examples of important molecules being discovered in organisms with special abilities. Therefore, in future research, another important molecule besides AOX may be discovered in heat-generating plants. Furthermore, the endless questions about the mechanisms supporting heat generation, the mechanisms for sensing temperature, and the evolutionary origins of heat-generating plants are also part of the appeal of heat-generating plant research.
Research on the aging of cut flowers and techniques for preserving their quality.
The aging of cut flowers is induced by a complex interplay of many factors, either individually or in combination, including the depletion of internal components through respiration, decreased transpiration and absorption capacity, accelerated aging by ethylene, and physiological changes based on fluctuations in other plant hormones such as abscisic acid and cytokinins. For this reason, there are a wide variety of techniques for preserving the freshness of cut flowers, including quality-preserving agents such as silver thiosulfate (STS) and antibacterial agents, low-temperature storage, techniques for maintaining appropriate moisture levels, and methods for physically reducing the effects of ethylene. In addition, because there are many types of flowers and the condition of cut flowers often varies depending on the season, in practice, multiple freshness-preserving techniques are combined to enhance the vase life of cut flowers.
Among the many freshness preservation techniques, low-temperature storage is one of the most versatile techniques that can be used regardless of the type of cut flower. Generally, storing cut flowers at low temperatures suppresses the consumption of carbohydrates through respiration, as well as wilting of leaves and petals due to transpiration, decay by microorganisms, and ethylene production. In practice, low-temperature storage is widely used in many retail stores and mass retailers that handle flowers, but because the effects of low temperatures on plants are wide-ranging, there are many cases where low temperatures are not used effectively. On the other hand, studies using model plants have shown that STS, an ethylene inhibitor, acts on the ethylene receptor to stop the normal progression of the ethylene signaling pathway and suppress the expression of genes involved in ethylene biosynthesis, but there have been few examples of systematically investigating the effects of low temperatures on flowers at the molecular level.
Statistics reported to the United Nations indicate that cut flowers have a global trade value of $4 billion, with Europe, the United States, and Japan being the major consumers of flowers in this market (10). Furthermore, according to the Ministry of Finance's "Trade Statistics," the value of cut flower exports from Japan has been on the rise in recent years, with exports to the United States in FY2017 increasing fivefold compared to five years prior. Needless to say, the quality of Japanese flowers is highly regarded worldwide, and we hope to contribute through our research to delivering beautiful Japanese cut flowers to many people both domestically and internationally.
(References) (1) Nagy et al., Science 1972. (2) Knutson, Science 1974. (3) Elthon and McIntosh, PNAS 1987. (4) Rhoads and McIntosh, PNAS 1991. (5) Shiba et al., PNAS 2013. (6) Raskin et al., Science 1987. (7) Raskin et al. al., PNAS 1989. (8) Chien et al. J. Bacteriol 1976. (9) Shimomura et al., J Cell Comp Physiol 1962. (10) Hoppen et al., Sci Rep 2019.