Survival strategies of plants during secondary growth: barrier properties of phellems and lenticels towards water, oxygen, and carbon dioxide

Abstract

Ever since plants began to conquer the terrestrial environment, a simple but effective evolutionary strategy has been employed to cope with the combined necessities of preventing an excessive loss of water via the aerial surface while also supporting the vital exchange of CO(2) and O(2) for photosynthesis and respiration. Large areas of the primary above-ground surface of plants are covered by a hydrophobic, non-cellular cuticle which effectively minimizes evaporation and very strongly reduces exchange of CO(2) and O(2). Hence, gas exchange is controlled by regulating stomatal apertures. Upon wounding or entering into secondary growth, however, the epidermis, cuticle, and stomata are replaced by a phellem (cork), which is produced by a lateral cambium, the phellogen. Former stomata are replaced by lenticels, which are multicellular structures and functionally analogous to stomata. In the secondary plant body, phellems effectively prevent the loss of water from the cortex of the stem while lenticels support the exchange of vital gases such as CO(2), O(2), and water vapour. The permeance of these gases via the lenticels reaches a maximum during July and is minimal during autumn and winter. In contrast to stomatal control, gas exchange through phellems is regulated by long-term structural changes. The permeances of cuticles, phellems, and lenticels are compared and discussed.

Diverging temperature response of tree stem CO2 release under dry and wet season conditions in a tropical montane moist forest

“…Attempts to explain deviations from the common temperature-respiration relationship or high between-tree variations in stem CO 2 release mainly focussed on four physiological phenomenon: (1) on time lags between temperature variation and CO 2 release (Ryan 1990;Lavigne 1996;Stockfors and Linder 1998), (2) the significance of stem photosynthetic activity (Sprugel and Benecke 1991;Gansert 1995;Pfanz 1999;Strobel 2004), (3) the CO 2 transport with xylem sap flux (Edward and Hanson 1996;Levy and Jarvis 1998;Teskey and McGuire 2002;Gansert and Burkdorf 2005) and/or (4) on differences in the diffusion resistance to gas by xylem, cambium and the bark (Sorz and Hietz 2006, Lendzian 2006. In three of our trees (Cr, Ge, Hm; Table 1), the correlation coefficients between diurnal T T and R S were higher when a time lag of 1.5-2 h was considered in the analysis (data not shown).…”

“…In three of our trees (Cr, Ge, Hm; Table 1), the correlation coefficients between diurnal T T and R S were higher when a time lag of 1.5-2 h was considered in the analysis (data not shown). At least in two of the stems (Cr, Ge), R S might indeed show a delayed temperature response, which should be related to the bigger tree size prolonging the radial diffusion pathway of CO 2 (Lavigne 1996) or a higher bark resistance to gas diffusion (Sorz and Hietz 2006;Lendzian 2006;Steppe et al 2007). In the smaller stem, a lowered thermal conductivity could be the reason for the observed time delay (Hm) (Gries 2004).…”

“…From a biomechanical point of view, the resistance to radial gas diffusion as controlled by xylem, cambium or the bark layers (Sorz and Hietz 2006;Lendzian 2006;Steppe et al 2007) can significantly influence the apparent stem CO 2 release. Bark structural properties differed between species and these differences could explain much of the between-species variation in the velocity of oxygen diffusion in wood segments in a laboratory study by Sorz and Hietz (2006).…”

A comparative transcriptomic approach to understanding the formation of cork

“…The development of covering tissues is essential in land plants to protect them from the surrounding environment, preventing excessive water loss, the entrance of pathogens and, in aerial parts, ultraviolet irradiation (Lendzian 2006). In secondary (mature) stems and roots, tubers, fruit and healing tissues, this protection is provided by the periderm, a complex structure composed of three distinct stratums, the phellem at the outer side, the phellogen or cork cambium in the middle, and the phelloderm at the inner part (Waisel 1995;Lendzian 2006).…”

“…In secondary (mature) stems and roots, tubers, fruit and healing tissues, this protection is provided by the periderm, a complex structure composed of three distinct stratums, the phellem at the outer side, the phellogen or cork cambium in the middle, and the phelloderm at the inner part (Waisel 1995;Lendzian 2006). The activity of the meristematic phellogen cells is asymmetrical with many more cell layers being produced outwardly than inwardly, resulting in a thicker phellem.…”