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ARTICLE

Is the abaxial palisade parenchyma in phyllaries of the sunflower (Helianthus annuus L.) capitulum a missing trait in modern genotypes?

by Hernández LF, MV Rosetti

1 Laboratorio de Morfología Vegetal. Depto. de Agronomía, UNSur, San Andrés 800, Bahía Blanca, 8000, Argentina.
2 Comisión de Investigaciones Científicas de la Pcia. de Buenos Aires (CIC). La Plata, 1900, Argentina.

Address correspondence to: L.F. Hernández, e-mail:

Phyton-International Journal of Experimental Botany 2016, 85(all), 291-296. https://doi.org/10.32604/phyton.2016.85.291

Abstract

The involucral bracts (IB or phyllaries) of the sunflower (Helianthus annuus L.) capitulum constitute an example of photosynthesizing organs that contribute to the photosynthesis budget during the generation of crop yield. The anatomy of IB was analyzed in two domesticated primitive sunflower genotypes, Havasupai and Hopi, in the sunflower line HA89B, in the wild Helianthus annuus ssp. annuus, in the sunflower male-fertile line R013 and in the commercial hybrid DKOP3845. Stomata and trichomes were counted on the adaxial and abaxial epidermis. In all cases, the IB showed a one-layered adaxial and abaxial epidermis, secretory ducts and parenchymatic cells with abundant chloroplast. The vascular system was similar to that of the nomophylls; however, their bundles were smaller, with an abaxial surface showing abundance of glandular and non-glandular trichomes and stomata. IB of Havasupai, Hopi and the male-fertile line strain showed higher number of adaxial hypodermic strata than those of HA89B, DKOP3845 and wild sunflower (2-3 vs. 1), and one mesophyll with inverted polarity with respect to a foliage leaf: the presence of a spongy parenchyma on the adaxial side was observed with a rudimentary palisade parenchyma on the abaxial side. Stomatal density of the IB was significantly higher in Hopi and Havasupai than in HA89B and DKOP3845, with values ranging from 132 to 156 vs 73 to 110 stomata/mm2, respectively. Like the modern commercial hybrid, the IB of male-fertile line showed lower stomatal density (83 stomata/mm2) and scarce abaxial trichomes. The anatomical studies of phyllaries in Asteraceae remain relatively poor in the literature. From the functional point of view, sunflower breeding produced undesired changes in the IB anatomy. Future studies for comparing the physiological (photosynthesis and respiration) and biochemical activities of the RuBisCO among the IB of the primitive (Havasupai and Hopi), male-fertile lines and modern sunflower genotypes will help to define the magnitude of their importance as a morphological trait to be considered in future plans of sunflower breeding.

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