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INDICE AGRARIO
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oil CROPS

SUNFLOWER


 

Capitulum and floret primordia development in plants of sunflower (helianthus annuus l.) treated with the morphactin chlorflurenol

Introduction: "Many theories to explain the generation of floret pattern in capitula of Compositae have been developed (Schwabe, 1984; Hernández, 1988; Green, 1991; Hernández and Green, 1993; Jean, 1994). Nevertheless the processes involved in the differentiation and pattern generation of floret primordia are not yet well understood.  This paper reports the changes produced in the floret pattern in the capitulum of sunflower using the morphactin Chlorflurenol (CF1: 2-Chloro-9-Hydroxy-fluorene-9-Carboxylic acid) which main action, produced by the inhibition of IAA transport (Noodén and Noodén, 1985), is the reduction of meristematic growth (Schneider, 1970)".

Author: Luis F. Hernández.  V Interamerican Electron Microscopy Congress, Venezuela, 24-28 October 1999.  Source: The Sunflower-Girasol site of Luis F. Hernández. 

 

Colchicine-induced displacement of floral organ regeneration sites in the wounded sunflower capitulum

Abstract: “As previously described a circular wounding procedure as applied to the young capitulum of the sunflower to isoalte a 1 mm diameter cylindrical plug of receptacle tissue in situ and stimulate the recapitulation on the plug surface of involucral bracts, ray and disc floret initials.  Applying 4,4 mM colchicine to the wounded wall of the plug for 5 days, subsequently resulted in a collar of meristematic-like cells forming 20-50 um from the wound site folled by the appearance of floral initials on the inside of the collar, 100-120 um distance from the plug wall, demonstrating that dedifferentation and regeneration processes are not confined to the plug rim".

Author: Luis F. Hernández and J. H. Palmer.  Published in:  Micr. Electr. Biol. Cel. (ISSN 0326-3142), vol. 14: 159-164, 1990, nº 2.   Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

Effect of foliar applications of methanol on growth and yield of sunflower (Helianthus annuus L.)

Abstract: “The effect of foliar applied methanol (Met) on growth and development of sunflower (Helianthus annuus L.) plants, grown under controlled conditions or in the field, was studied.  Foliar sprays of aqueous (30%, v/v) Met were applied at the beginning of capitulum development (23 days from seedling emergence, DFE), and every 4 days up to 41 DFE, when the floret primordia were completely differentiated on the capitulum surface.  Met treated plants grown under controlled conditions showed significant channges in vegetative growth and floral development.  Met increased stem length by 23.6%, leaf area per plant by 66.5, stem dry weight by 51.4%, number of floret primordia by 46.5% and accelerated completion of floral development by 4.5 days.  Met treated plants grown in the field did not show significant changes compared with controls, except subtle differences in vegetative development viusally detected in leaf turgor and leaf color 5 days after the treatment commenced, but these changes were not statistically significant".

Authors: L.F. Hernández, C.N. Pellegrini, L. M. Malla. Published in: fYTON, International Journal of Experimental Botany.  Vol. 66: 1-8, 2000.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

Floret differentiation in the capitulum of sunflower (Helianthus annuus L.)

Abstract: “In the capitulum of sunflower the process of generation of new floret primordia starts at the receptacle rim and continues towards its center.  Then, each floret primordium differentiates gradually over space and time, in the centripetal direction.  The florets appear in an annular generative zone first as a gentle dome and then become a two-part structure: the floret bract and the floret corolla.  This paper provides a detailed description of the beginning of the floret primordium differentiation during the floral morphogenetic process in the sunflower capitulum”.

Author:  Luis F. Hernández.  Published in: Helia vol. 20: 63-68, 1997, nº 26.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

Floret primordia differentiation in naturally wounded capitula of boron deficient sunflower (helianthus annuus l.) plants

Introduction: "Boron deficiency during floret intiation in sunflower results in damage of capitulum meristem and consequently in the appeareance of involucral bracts and ray florets in different positions at the capitulum centre (Blamey, 1976, Palmer and Marc, 1982).  Palmer and Marc (1982) reported this effect after pin prick wounding of the uncomitted receptacle surface in Floral Stage (FS) 4, 5 or 6 (Marc and Palmer, 1981). They concluded that the wound rims could provide the first sites for organ initials (Palmer and Marc, 1982, Hernández and Palmer, 1988). This paper provides a detailed sequential description of floret primordia differentiation on naturally wounded capitula from boron-deficient sunflower plants. The implications of findings presented here for organogenesis of the sunflower capitulum, have been extensively discussed (Hernández, 1988; Hernández and Palmer, 1988,1991; Hernández and Green, 1993)".

Author: Luis F. Hernández.  V Interamerican Electron Microscopy Congress, Venezuela, 24-28 October 1999.  Source: The Sunflower-Girasol site of Luis F. Hernández. 

 

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Grain yield of the sunflower capitulum promoted by surgical removal of the involucral bract primordia

Abstract: “This paper reports the effect on the sunflower capitulum development and seed yield of removing the involucral bract (IB) primordia and upper leaf primordia during early growth of the capitulum.  Plants of sunflower cv. Dekalb G100, were used grown in a controlled environment and in the field.  As a result of IB and/or upper leaves removal, the rate of floral development and the size of the treated capitula, increased significantly in both experiments.  The total number of disc floret primordia also increased significantly by up to 21.5 %.  The absence of IB during capitulum formation produced a significant increase in capitulum size and promoted grain yield measured on per plant basis.  It is concluded that the growth of the receptacle in the sunflower capitulum is highly dependent of the supply of photoassimilates coming from older mature non-growing leaves and that the younger leaves which are expanding at the time of capitulum formation and the involucral bract primordia can produced strong competition for assimilates that can result in a reduction in the potential size of the capitulum”.

Author: Luis F. Hernández.  Published in: Soil Science (Trends in Agril. Sci.) vol. 1, 127-135, 1993.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

Imbibition and germination rates of sunflower (Helianthus annuus L.) seeds according to fruit size

Abstract: "The influence of size and pericarp structure of sunflower (Heliathus annuus L.) fruits on imbibition and germination rates of the seed was investigated.  The results show a positive correlation between fruit width, pericarp thickness and fruit weight.  Germination rate was not affected by fruit size.  Nevertheless, although large fruits (more than 4.5 mm width) have a rapid imbibition rate there was a significant lag in the start of their germination in relation to that of the smaller fruits (less than 2.5 mm width)".

Authors: Luis F. Hernández and Gustavo A. Orioli.  Published in: Field Crops Research, vol. 10: 355-360, 1985.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

Morphogenesis in sunflower (Helianthus annuus L.) as affected by exogenous application of plant growth regulators

Abstract: “The effect of the plant growth regulators (PGRs) N6-benzyladenine (BA), a-Naphthaleneacetic acid (NAA) and Gibberellic acid (GA3) on morphogenesis of sunflower (Helianthus annuus L.) was studied.  PGRs were applied at the beginning of capitulum development, where floret primordia were still not determined, at dosis of 45mg of NAA day-1 during 10 days, or 45mg of BA day-1 during 10 days, or 45mg of GA3 day-1 during 5 days.  Compared with untreated plants, NAA was not able to produce any significant change.  GA3 was effective increasing the length of stem internodes and accelerating the onset of floral development by 25.0%.  BA showed the most significant effect on plant development, increasing the leaf area per plant by 38.0%, the stem dry weight by 93.0% and changing capitulum morphology and hence disc floret development.  BA-treated plants showed an increase in the numbber of floret primordia of 17.0% associated with a significant promotion of the receptacle expansion before the beginning of the floret differentiation period".

Author: L. F. Hernández.  Pubished in:  Agriscientia, vol. XIII: 3-11, 1996.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

Morphological changes in the epidermis of sunflower (helianthus annuus l.) leaves induced by uv radiation 

Introduction:  "UV radiation can affect growth, productivity and yield of different crop plants. Changes in the morphology, anatomy and development of UV exposed plants as well as the reduction of the leaf photosynthetic efficiency have been reported (Teramura and Sullivan, 1994).  The sunflower shows tolerance to low doses of UV-B radiation (Barnes et al., 1990). Nevertheless alterations in its leaf morphology and reproductive pattern in southern Argentina have been associated with recent increases in the levels of UV-B (Sunflower Breeders, pers. comm.). Previous observations using light microscopy (Hernández et al., 1999) revealed some alterations at epidermal level and in the internal structure of leaves (changes in the size and morphology of chloroplasts). The objective of this work was to study the morphology of the leaf surface of sunflower plants exposed to UV-A+B radiation using scanning electron microscopy (SEM)".

Authors: L.F. Hernández, L.I. Lindström and C.N. Pellegrini.  

V Interamerican Electron Microscopy Congress, Venezuela, 24-28 October 1999.  Source: The Sunflower-Girasol site of Luis F. Hernández. 

 

Regeneration of the sunflower capitulum after cylindrical wounding of the receptacle

Abstract: “Using the young capitulum of Helianthus annuus L., a cylindrical plug of undifferentiated receptacle tissue, 1 mm in diameter, was isolated from lateral communication with the rest of the receptacle surface by a vertical circular wound cut, while retaining continuity with the subapical meristerm.  Within 24 hr., active cell division was induced at the inner and outer surfaces of the wound and in the receptacle epidermis bordering the wound edges, creating a rounded rim at the top of the wound.  Within 3-6 days, floral initials, spaced 133-166 mm apart appeared on the flanks of both rims and later on the top of the plug and surrounding receptacle surface.  The first formed initials developed into involucral bracts or ray florets and the later ones into disc florets which were organized into contact parastichics, the number of which did not conform with the Fibonacci series.  The base of the plug developed into a stem-like structure completing the regeneration of a fully formed functional capitulum.  This operation was demonstrated for two sunflower cultivars and occurred in both long and short daylengths".

Authors: Luis. F. Hernández and John H. Palmer.  Published in: Amer. J. Bot. Vol. 75: 1253-1261, 1988, nº 9.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

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Transductions for the expression of structural pattern: Analysis in sunflower

Abstract: “The transductions to initiate and propagate pattern were investigated in the sunflower head.  The spiral pattern emerges as new florets form in regular centripetal sequence on the flat disc.  The spiral lines of florets arise as rows of simple bumps.  Each bump splits to become a small bract and a circular disc flower.  This topographical progression was described by a scanning electron microscopic technique applied to living tissue.  The suitability of various theories to explain the progression was examined.  Because no periodic cell specialization was seen by scanning electron microscopy prior to pattern emergence, a mechanism that produces pattern in uniform tissue by spontaneous physical buckling (folding) was examined further.  Key configurational changes of development were reproduced in models using the buckling assumptions.  In further testing, a young head was physically constrained to cause it to grow as an oval.  Pattern was modified as predicted.  Unexpectedly, organ character changed as well.  In localized regions, the folding was abnormal; the typical dyad floret, bract and flower, was replaced by a single large bract.  This anomally is known in mutants of sunflower; hence, the physical treatment induced a phenocopy.  We concluded that (1) buckling is a strong candidate to be the process producing organ pattern, and (2) the accompanying topographical changes can be prerequisite to organ differentiation".

Authors: Luis F. Hernández and Paul B. Green.  Published in: The Plant Cell  vol.5: 1725-1738, 1993.  Source: The Sunflower-Girasol site of Luis F. Hernández.  Find the complete paper down "some of my papers".

 

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