Growth towards light as an adaptation to high light conditions in Chara branches

Abstract

Summary• Growth of plants or plant organs towards more light is commonly interpreted as an adaptation to low light conditions. Here, we show for the first time, in a study of charophyte branches, a growth-based orientation towards light functioning as a mechanism to protect the plant from excessive light.• Two Chara species were exposed to five different intensities of photosynthetically active radiation and species traits and pigmentation were measured.• Branches of plants exposed to higher light intensities were convergent and pointed steeply upwards, whereas those exposed to lower light intensities grew nearly straight and were less inclined. Only branches that increased in length during the experiments reacted to differences in light intensity. This indicates that branch orientation is determined by a light-dependent growth reaction. Orientation of charophyte branches towards light is accompanied by a decrease in chlorophyll a (Chl a ) content and a lower Chl a : carotenoid ratio, which clearly indicates that the plant is taking protective measures against potentially damaging excess light conditions.• We suggest that the growth-based orientation of Chara branches towards light may protect sexual organs, which grow on adaxial branch sides, from light damage. In addition, the upward orientation of branches might lead to increased light transmission within dense charophyte beds, thus enabling an enhanced gross production.

Morphological and reproductive differences among three charophyte species in response to variation in water depth

“…In addition, not all charophyte species alter their chl a/chl b ratio in response to the changes of light in the environment. For example, no significant difference in the chl a/chl b ratio was found among varied light intensities in Chara canescens (Küster et al 2004) and C. intermedia Braun (Schneider et al 2006). In the present study, the chl a/chl b ratio of C. braunii did not significantly vary with increasing depth.…”

“…Considering the high light intensity in shallow water, we reasoned that the reduced weight increases of C. vulgaris and N. gracilens in shallow water may have resulted from high light stress, leading to photoinhibition. Convergent and steeply upward pointing branches of the plants that were found in shallow water may be a mechanism to protect the plant from damage by high light intensity (Schneider et al 2006, Wang et al 2008.…”

“…For example, charophytes can morphologically adapt to either high water levels or low light availability by elongating their stems toward the water surface (Andrews et al 1984a, Casanova 1994, Casanova & Brock 1999a, Blindow & Schütte 2007, Wang et al 2008. Conversely, acclimation of charophytes to low water levels or high light intensity can result in stunted stems, impacted apices, and in creased branchlet growth toward the apex as a way to protect the gametangia (Schneider et al 2006, Wang et al 2008, Schneider et al 2015. Charophytes can also photosynthetically acclimate to different amounts of light by regulating pigment content and pattern (Andrews et al 1984b, Czeczuga 1986, Schagerl & Pichler 2000, Küster et al 2000, 2005, Wang et al 2008.…”

The role of charophytes in a Mediterranean pond created for restoration purposes

“…Another resource related to C. hispida growth dynamics is light availability (de Winton et al, 2004;Schneider et al, 2006), which is related to the shadow effect of the seston.…”

Genetic and morphological data fail to differentiate Chara intermedia from C. baltica, or C. polyacantha and C. rudis from C. hispida

“…When working with charophytes, we should remember that different species commonly grow in close proximity and that some populations may show local adaptations, producing slightly different morphologies. Furthermore, Schneider et al (2006) showed that changes in branch form occur in C. hispida and C. intermedia in response to different light conditions, and Blindow & Schütte (2007) concluded that morphological differences between freshwater and brackish water populations of C. aspera were at least partly explained by plastic responses to salinity rather than genetic differences. Thus, phenotypic plasticity and genetic adaptation to different environmental conditions underlie the morphological variability seen in many charophyte species, which in turn provides the basis for natural selection to drive macroevolution by natural selection; this developmental diversity is the basis of plant taxonomy and phylogeny (Cronk, 2001).…”