Alternative Oxidase Capacity of Mitochondria in Microsporophylls May Function in Cycad Thermogenesis

Abstract

Cone thermogenesis is a widespread phenomenon in cycads and may function to promote volatile emissions that affect pollinator behavior. Given their large population size and intense and durable heat-producing effects, cycads are important organisms for comprehensive studies of plant thermogenesis. However, knowledge of mitochondrial morphology and function in cone thermogenesis is limited. Therefore, we investigated these mitochondrial properties in the thermogenic cycad species Cycas revoluta. Male cones generated heat even in cool weather conditions. Female cones produced heat, but to a lesser extent than male cones. Ultrastructural analyses of the two major tissues of male cones, microsporophylls and microsporangia, revealed the existence of a population of mitochondria with a distinct morphology in the microsporophylls. In these cells, we observed large mitochondria (cross-sectional area of 2 mm 2 or more) with a uniform matrix density that occupied .10% of the total mitochondrial volume. Despite the size difference, many nonlarge mitochondria (cross-sectional area ,2 mm 2 ) also exhibited a shape and a matrix density similar to those of large mitochondria. Alternative oxidase (AOX) capacity and expression levels in microsporophylls were much higher than those in microsporangia. The AOX genes expressed in male cones revealed two different AOX complementary DNA sequences: CrAOX1 and CrAOX2. The expression level of CrAOX1 mRNA in the microsporophylls was 100 times greater than that of CrAOX2 mRNA. Collectively, these results suggest that distinctive mitochondrial morphology and CrAOX1-mediated respiration in microsporophylls might play a role in cycad cone thermogenesis.

In situ measurement of intracellular thermal conductivity using heater-thermometer hybrid diamond nanosensor

“…Internal heat is a distinctive feature of mammals and birds [1][2][3] , but also occurs in plants [4][5][6][7][8] , insects 9 , fishes 10 and possibly in dinosaurs 11 . The heat originates from intracellular biochemical sources and then flows through cells to elevate temperature of the whole body.…”

Turning Up the Heat: The Alternative Oxidase Pathway Drives Thermogenesis in Cycad Cones

“…Thermogenesis of the reproductive organs can occur in inflorescences, flowers, or cones of species from both gymnosperms and angiosperms. Approximately half of all known thermogenic species are cycads, where the male cones can heat for weeks on end (Roemer et al, 2013;Ito-Inaba et al, 2019). This is unlike many angiosperm thermogenic species, which heat for only hours to days (Miller et al, 2011).…”

Protoplast-Based Transient Expression Combined with Plant Cultivation Systems as a Valuable Tool for Floral Thermogenesis Studies in Aroids

“…Generally, thermogenic plants are de ned as species that can increase their oral or cone temperatures to at least 0.5 °C above ambient temperature. On the basis of this de nition, at least 80 plant species are considered thermogenic, half of which are gymnosperm cycads (Ito-Inaba et al 2019;Tang 1987), and the remaining are angiosperms comprising 36 species of aroids (Table 1) and a few species of Nymphaeaceae, Magnoliaceae, and Nelumbonaceae (Seymour 2010;Seymour and Matthews 2006). Many aroid species are with high heatproducing ability, and 7 species, namely giant taro (Alocasia macrorrhizos), arum lily (Arum dioscoridis), Colocasia gigantea, philodendron (Philodendron selloum), skunk cabbage (Symplocarpus foetidus and S. renifolius), and Homalomenapendula, can increase the temperature in owers (spadix, appendix, or male orets) at least 15 °C above ambient temperature (Table 1).…”