Stomatal plugs and their impact on fungal invasion in Agathis robusta

Abstract

The hypothesis that stomatal wax plugs in Agathis robusta (C. Moore ex F. Muell.) F. Muell. (Araucariaceae) protect leaves against fungal invasion by preventing hyphae entering the stomatal pore was tested. Leaves with intact wax plugs and leaves from which wax plugs had been experimentally removed were inoculated with either Botrytis cinerea (De Bary) Whetzel or Alternaria solani (Ellis & G. Martin) L.R. Jones & Grout. Interactions of fungal hyphae with stomata were subsequently analysed by scanning electron microscopy. Wax plugs blocked the penetration of fungal hyphae into stomata of A. robusta in 100% of encounters. In contrast, hyphae readily penetrated stomata of leaves from which wax plugs had been removed or where the wax plugs were damaged. On rare occasions, hyphae were also observed to penetrate directly through the cuticle. Florin rings around the external surface of stomata also acted to deflect fungal hyphae from the stomatal opening. Formation and degradation of wax plugs was also examined to assess the period over which they offer protection from fungal invasion. Wax plugs formed in young leaves in spring and were complete by summer. There was subsequent degradation of wax plugs in the following winter, and they then regenerated again in spring. However, regeneration of wax plugs appeared to decline after the leaves reached 2 years of age. The data are discussed with reference to the adaptive significance of wax plugs in conifers and other plants.

Oldest record of Metrosideros (Myrtaceae): Fossil flowers, fruits, and leaves from Australia

“…As well as being potentially valuable diagnostically, cuticle characters are also potentially valuable as palaeoclimate indicators. For instance, peristomatal rings may play a similar role to the ‘Florin rings’ described by Mohammadian et al (2009) on the cuticles of extant Agathis (Araucariaceae), as a physical stomatal defense from hyphal infection. These Florin rings were found to influence the growth of hyphae on fungus inoculated leaves by directing them away from the stomatal pore.…”

Rice Stomatal Mega-Papillae Restrict Water Loss and Pathogen Entry

“…In the short term, these processes can be regulated via alterations to stomatal pore aperture, and over longer durations, via changes to stomatal size and/or density (Zeiger et al, 1987;Lake and Woodward, 2008;Martin-StPaul et al, 2017;Dutton et al, 2019;Ye et al, 2020). A number of other specialized epidermal adaptions have also evolved that influence airflow and/or pathogen entry in and around stomata, and these include papillae outgrowths (Barthlott et al, 1998;Hückelhoven et al, 1999;Wakte et al, 2007;Mohammadian et al, 2009;Ensikat et al, 2011;Müller et al, 2017). To find beneficial stomatal or other epidermal traits that might lead to improved rice performance, we screened the flag leaves of 164 different rice varieties.…”

Evolutionary and ecological significance of photosynthetic organs inPhyllocladus(Podocarpaceae)

“…Florin rings are common in xeromorphic conifer leaves and may reduce stomatal transpiration (Buchholz & Gray, 1948;Florin, 1951;Oladele, 1983;Yoshie & Sakai, 1985;Hill & Pole, 1992;Stockey, Ko & Woltz, 1992;Kunzmann et al, 2006;Kunzmann, 2007;Kim et al, 2011). Florin rings have also been recorded in extremely wet environments, where they assist in diverting fungal hyphae away from the stomatal pore, a feature that may be important in retaining the photosynthetic function of the long-lived phylloclades (see Mohammadian, Hill & Watling, 2009 for a similar argument in the conifer genus Agathis Salisb.). Florin rings may also be important in stopping liquid water from entering the stomatal pore from the general surface of the phylloclade.…”