Mechanisms of constraints: the contributions of selection and genetic variance to the maintenance of cotyledon number in wild radish

Abstract

The evolutionary mechanisms underlying the maintenance of invariant traits are poorly understood, partly because the lack of variance makes these mechanisms difficult to study. Although the number of cotyledons that plant species produce is highly canalized, populations of plants frequently contain individuals with abnormal cotyledon numbers. In a garden study with 1857 wild radish plants from 75 paternal half‐sibling families, 89 (almost 5%) had cotyledon numbers less or greater than two. We found evidence for direct selection on cotyledon number, but no evidence for additive genetic variation for cotyledon number. In spite of the very large sample size, our power to detect variation and selection was hampered by the small number of individuals (10) producing more than two cotyledons. Thus, our results provide support for both a lack of genetic variation and selection as reasons for the current lack of variation in wild radish cotyledon number.

Seed germination and abnormality of cotyledon of Peganum harmala populations in Mongolia

“…The present study discuss canalization of cotyledon number and bifurcation or lobbing as cause of more than two cotyledons formation (Conner and Agrawal, 2005;Chandler, 2008).…”

“…Previous studies reported more and less than two cotyledons in the family Aceraceae, Juglandaceae, Rubiaceae, Pedaliaceae, Protaceae, Ranunculaceae, Papaveraceae, Brassicaceae, Fabaceae, Geraniaceae, Chenopodiaceae, Onagraceae, Solanaceae, Scrophulariaceae, Salicaceae and Euphorbiaceae (Gates, 1910;Went, 1944;Harrison, 1964;Dessureaux, 1967;Magsar and Tsagaanmaam, 1984;Rajora and Zsuffa, 1986;Taylor and Mundell, 1999;Graz, 2001;Conner and Agrawal, 2005;Chandler, 2008). The present results show three, four cotyledons and different shape dicotyledons in Peganum genus (Peganaceae), in addition to above mentioned families.…”

“…Qin and Zhao (2007) showed that βGlcY affects cotyledon formation of Nicotiana tabacum L. Recent studies explain abnormality of cotyledons as a lack of genetic variation (Conner and Agrawal, 2005) but researchers still argue on factors and genetic reasons of abnormality of cotyledons (Chandler, 2008).…”

“…Previous studies supposed that cotyledon number range is related to hormonal asymmetric distribution and maternal effects (Liu et al, 1993;Mayer et al, 1993;Hadfi et al, 1998;Al-Hammadi et al, 2003;Orlova et al, 2006;Swarup et al, 2004), some kind of selection (Taylor and Mundell, 1999), lack of genetic variation (Conner and Agrawal, 2005), etc. Experimental studies reported that arabinogalactan proteins (AGPs) play functional roles in embryo development and cotyledon formation on Nicotiana tabacum (Qin and Zhao, 2007).…”

Nutrients in Two and Three Cotyledon Seedlings of Peganum harmala L. Under Soil Salinity

“…External such as drought, salinity as well as endogenous factors such as phytohormones, proteins, transcription and other substances can affect embryogenesis (Unnikrishnan et al, 1990;Khorolsuren & Jamsran, 2005;Umehara et al, 2007). Previous studies reported that salinity effects on seed germination and early seedling growth (Rahman & Ungar, 1990;Gulzar et al, 2001;Bayuelo-Jimenez et al, 2002;Jamil et al, 2005Jamil et al, , 2006Lombardi & Lupi, 2006;Cordazzo, 2007;Necajeva & Ievenish, 2008;Bybordi & Tabatabaei, 2009;Sivasankaramoorthy et al, 2010;Akbarimoghaddam et al, 2011), and approved that the formation of three cotyledons is related with embryogenesis (Taylor & Mundell, 1999;Al-Hammadi et al, 2003;Conner & Agrawal, 2005).…”