Comparative anatomy of leaf petioles in temperate trees and shrubs

Abstract

Petioles are important plant organs connecting stems with leaf blades and affecting light-harvesting leaf ability as well as transport of water, nutrient and biochemical signals. Despite petiole's high diversity in size, shape and anatomical settings, little information is available about their structural adaptations across evolutionary lineages and environmental conditions. To fill our knowledge gap, we investigated the variation of petiole morphology and anatomy in 95 European woody plant species using phylogenetic comparative models. Two major axes of variation were related to leaf area (from large and soft to small and tough leaves), and plant size (from cold-adapted shrubs to warm-adapted tall trees). Larger and softer leaves are found in taller trees of more productive habitats. Their petioles are longer, with a circular outline, thin cuticles without trichomes, and are anatomically characterised by the predominance of sclerenchyma, larger vessels, interfascicular areas with fibers, indistinct phloem rays, and the occurrence of prismatic crystals and druses. In contrast, smaller and tougher leaves are found in shorter trees and shrubs of colder or drier habitats. Their petioles are characterized by teret outline, thick cuticle, simple and non-glandular trichomes, epidermal cells smaller than cortex cells, phloem composed of small cells and radially arranged vessels, fiberless xylem, lamellar collenchyma, acicular crystals and secretory elements. Individual anatomical traits were linked to different internal and external drivers. The petiole length and vessel conduit size increase, while cuticle thickness decreases, with increasing leaf blade area. Epidermis cell walls are thicker in leaves with higher specific leaf area. Collenchyma becomes absent with increasing temperature, epidermis cell size increases with plant height and temperature, and petiole outline becomes polygonal with increasing precipitation. We conclude that species temperature and precipitation optima, plant height, leaf area and thickness exerted a significant control on petiole anatomical and morphological structures not confounded by phylogenetic inertia. Unrelated species with different evolutionary histories but similar thermal and hydrological requirements have converged to similar petiole anatomical structures. Our findings contribute to improving current knowledge about the functional morphoanatomy of the petiole as the key organ that plays a crucial role in the hydraulic pathways in plants.

Salivary surprise: Symmerista caterpillars anoint petioles with red saliva after clipping leaves

“…Likewise, sections of white oak petioles were stained with astra blue (0.1%) for 12 minutes followed by safranin O (0.05%) for 30 seconds. Safranin O, toluidine blue, and astra blue dye different components of cell walls [ 43 – 45 ]; they are often used to stain plant tissues, including tree petioles [ 46 ].…”

Geographic Variation in the Petiole–Lamina Relationship of 325 Eastern Qinghai–Tibetan Woody Species: Analysis in Three Dimensions

“…Thus, PCA is actually a measurement of "petiole structure, " representing the number and proportion of different tissues, e.g., vascular, storage, protective, or supportive. The proportion of these tissues in the petiole, however, is usually not fixed and varies significantly among species or environments (Givnish, 2002;Al-Edany and Al-Saadi, 2012;Gebauer et al, 2016;Maiti et al, 2016;Ray and Jones, 2018), potentially resulting in an interspecific allometric relationship between PCA and LA, whereby a larger variation in PCA than LA may attribute to a higher proportion of storage, protective, or supportive tissues in the petiole as the LA increases (Niinemets and Fleck, 2002;Klepsch et al, 2016;Filartiga et al, 2021;Sargin, 2021). Due to a significant positive relationship between lamina mass (LM) and LA (Pan et al, 2013;Lin et al, 2020), the PCA-LM relationship has been reported to be positive in some recent studies (Yamada et al, 1999;Levionnois et al, 2020).…”