Analysis of inflorescence organogenesis in eastern gamagrass, Tripsacum dactyloides (Poaceae): the wild type and the gynomonoecious gsf1 mutant

Inflorescence organogenesis of a wild-type and a gynomonoecious (pistillate) mutant in Tripsacum dactyloides was studied using scanning electron microscopy. SEM (scanning electron microscope) analysis indicated that wild-type T. dactyloides (Eastern gamagrass) expressed a pattern of inflorescence organogenesis that is observed in other members of the subtribe Tripsacinae (Zea: maize and teosinte), family Poaceae. Branch primordia are initiated acropetally along the rachis of wild-type inflorescences in a distichous arrangement. Branch primordia at the base of some inflorescences develop into long branches, which themselves produce an acropetal series of distichous spikelet pair primordia. All other branch primordia function as spikelet pair primordia and bifurcate into pedicellate and sessile spikelet primordia. In all wild-type inflorescences development of the pedicellate spikelets is arrested in the proximal portion of the rachis, and these spikelets abort, leaving two rows of solitary sessile spikelets. Organogenesis of spikelets and florets in wild-type inflorescences is similar to that previously described in maize and the teosintes. Our analysis of gsf1 mutant inflorescences reveals a pattern of development similar to that of the wild type, but differs from the wild type in retaining (1) the pistillate condition in paired spikelets along the distal portion of the rachis and (2) the lower floret in sessile spikelets in the proximal region of the rachis. The gsf1 mutation blocks gynoecial tissue abortion in both the paired-spikelet and the unpaired-spikelet zone. This study supports the hypothesis that both femaleness and maleness in Zea and Tripsacum inflorescences are derived from a common developmental pathway. The pattern of inflorescence development is not inconsistent with the view that the maize ear was derived from a Tripsacum genomic background.     

Suppressor of sessile spikelets1 (Sosl): a dominant mutant affecting inflorescence development in maize

Suppressor of sessile spikeletsl (Sos1) is a dominant mutant of maize that blocks branching of the spikelet-pair primordium to form the sessile spikelet during ear development. As a result, Sos1 mutant ears and tassels possess single spikelets as opposed to the normal condition of paired spikelets, one sessile and the other pedicellate. Sos1 also causes a reduction in the number of tassel branches and the number of orthostichies (or cupule ranks) in the ear. The sos1 genetic locus maps to the short arm of maize chromosome 4. The Sos1 single spikelet phenotype appears similar to the single spikelet phenotype found in teosinte, the probable progenitor of maize. This similarity invites the hypothesis that sos1 had a role in the evolution of maize from teosinte. However, genetic mapping data and a comparison of the developmental basis of the single spikelet condition in the Sos1 mutant and teosinte demonstrate that their similar phenotypes result from distinct genetic-developmental mechanisms. These results indicate that sos1 was not involved in the evolution of maize and caution against drawing conclusions of homology based solely on similar adult phenotypes.     

Early ontogenetic development of the pistillate inflorescence in a diploid perennial teosinte (Zea diploperennis, Poaceae)

CAMARA-HERNANDEZ J. & GAMBINO, S., 1991. Early ontogenetic development of the pistillate inflorescence in a diploid perennial teosinte (Zea diploperennis , Poaceae). The early ontogeny of pistillate inflorescences of %ea diploperennis in plants grown at the latitude of Buenos Aires, Argentina, is investigated using the scanning electron microscope. The pattern of development of the inflorescence is similar to that in staminate and mixed inflorescences, starting with the formation of a pair of spikelets from a common branch primordium initiated in the axil of a bract on the ear axis. This bract arrests its development and aborts early. After initiation of an outer glume on both spikelet primordia, the pedicellate spikelet arrests its growth and aborts resulting in the mature inflorescence having two rows of solitary spikelets arranged distichally. This is significantly different from the pattern observed by other authors in plants grown in different environments (such as in natural populations in Mexico).     

Development of the mixed inflorescence in Zea diploperennis litis, Doebley & Guzman (Poaceae)

Development of the mixed inflorescence in Zea diploperennis Iltis, Doebley & Guzman (Poaceae) Mixed inflorescences of diploperennial teosinte, which terminate the main branches of the plant, arise in the same fashion as tassel spikes. The apical meristem produces bracts in a decussate arrangement. A single axillary bud primordium is initiated in the axil of each bract. Growth of the bract is retarded as the bud enlarges and divides longitudinally into two separate spikelet primordia. The paired spikelets running in two ranks on either side of the inflorescence primordium produce the four-rowed condition typical of teosinte tasselS. In the transition region between male and female portions of the inflorescence, development of the pedicellate spikelet of each spikelet pair is arrested at an early ontogenetic stage. Continued growth of the sessile spikelet and associated rachis flaps destroy the remnants of the arrested spikelet in basal portions of the inflorescence. A similar abortion of the lower floret of the sessile spikelet results in a single pistillate floret per node at anthesis. These results provide further support for the hypothesis that a tassel-like mixed inflorescence of teosinte is ancestral to the maize ear.     

INFLORESCENCE DEVELOPMENT IN TWO ANNUAL TEOSINTES: ZEA MAYS SUBSP. MEXICANA AND Z. MAYS SUBSP. PARVIGLUMIS

The ontogeny of tassels and ears in two annual Mexican teosintes, Zea mays subsp. mexicana and Z. mays subsp. parviglumis, was examined using scanning electron microscopy and light microscopy. Ear development in these annual teosintes follows a pattern previously described as leading to the bisexual mixed inflorescence in Z. diploperennis. Common bud primordia are initiated in the axils of distichously arranged bracts along the ear axis. These common primordia bifurcate to form paired sessile and pedicellate spikelet primordia. Development of pedicellate spikelets is arrested leaving the sessile spikelets, along with the adjoining rachis segment, to form solitary grains enclosed within cupulate fruitcases. Development of the central tassel spike is similar to that previously described in the Z. diploperennis tassel, except that the first formed axillary bud primordia form precocious tassel branches. The origin of these tassel branches suggests a possible mechanism for the transition from a distichous spike, characteristic of teosinte, to a polystichous spike, typical of maize.     

Inflorescence development in a new teosinte: Zea nicaraguensis (Poaceae)

Inflorescence development in a newly discovered teosinte, Zea nicaraguensis (Poaceae), from Nicaragua has been investigated using scanning electron microscopy (SEM). The SEM examination revealed that the pattern of both male and female inflorescence development was similar to previously described inflorescence in other Zea taxa. Branch primordia were initiated acropetally in a distichous pattern along the rachis of male and female inflorescences. Spikelet pair primordia bifurcated into pedicellate and sessile spikelet primordia. Predictably, pedicellate spikelet development was arrested and aborted in the female teosinte inflorescence. Organogenesis of functional spikelets and florets was similar to that previously described in maize and teosintes. The results were consistent with our hypothesis that both femininity and masculinity share a common mechanism of inflorescence development in Zea and Tripsacum and are in accord with a putative common mechanism of sex determination in the Andropogoneae. Interestingly, this population of teosinte, unique in its ability to grow in water-logged soils, showed a stable pattern of early inflorescence development. Our results also revealed the uncharacteristic presence of inflorescence polystichy in this population of Zea nicaraguensis. We propose this novel phenotypic variation raises the possibility that a domestic evolution of polystichy in maize was enabled by an occasional polystichous phenotypic in teosinte.     

Inflorescence development in a perennial teosinte: Zea perennis (Poaceae)

The ontogeny of tassels and ears in a perennial Mexican teosinte, Zea perennis (Hitchc.) Reeves and Mangelsdorf, was examined using scanning electron microscopy and light microscopy. Ear development follows a pattern previously described for two annual teosintes, Z. mays subsp. mexicana and Z. mays subsp. parviglumis var. parviglumis (race Balsas), and for the bisexual mixed inflorescence in a diploperennial teosinte, Z. diploperennis; it differs from that described for the ear of Z. diploperennis plants grown at the latitudes of Iowa and Wisconsin. Common bud primordia of the ear are initiated in the axil of distichously arranged bracts along the ear axis. These common primordia bifurcate to form paired pedicellate and sessile spikelet primordia. Development of the pedicellate spikelets in the ear is arrested leaving the sessile spikelets, along with the adjoining rachis segment, to form solitary grains enclosed within cupulate fruitcases. The organogenesis of the central spike of the tassel is similar to that previously described in other Zea taxa. This developmental study supports the hypothesis that both femaleness and maleness are derived from and expressed on a common background; it is consistent with the view that the maize ear was derived from the central spike of a male inflorescence terminating a primary branch of the main axis of the inflorescence.     

Floral development and the formation of unisexual spikelets in the Andropogoneae (Poaceae)

We investigated spikelet development in four distantly related species of the grass tribe Andropogoneae to determine whether spikelet development and the formation of unisexual florets are uniform throughout the tribe. We studied development in Bothriochloa bladhii, Coelorachis aurita, Heteropogon contortus, and Hyparrhenia hirta, and compared these with Panicum, a member of the sister tribe Paniceae. Many aspects of spikelet development in the species we have studied correlate with what is already known for Tripsacum and maize (both Andropogoneae), despite variation in how unisexual florets are distributed on the plant. The formation of unisexual spikelets is also uniform. All florets initiate both pistil and stamen primordia. In florets destined to be male, cell death occurs in the subepidermal layers of the gynoecium after the formation of a gynoecial ridge. In florets destined to be female, there is no apparent cell death in the stamens, but growth ceases after anther formation. The similarity in spikelet development and the formation of unisexual florets point to a common genetic mechanism for sex determination throughout the Andropogoneae and possibly the entire Panicoideae. Use of a cell death pathway to cause gynoecial abortion may be the basis of one morphological character that defines the subfamily.     

Evidence for distinct roles of the SEPALLATA gene LEAFY HULL STERILE1 in Eleusine indica and Megathyrsus maximus (Poaceae)

LEAFY HULL STERILE1 (LHS1) is an MIKC-type MADS-box gene in the SEPALLATA class. Expression patterns of LHS1 homologs vary among species of grasses, and may be involved in determining palea and lemma morphology, specifying the terminal floret of the spikelet, and sex determination. Here we present LHS1 expression data from Eleusine indica (subfamily Chloridoideae) and Megathyrsus maximus (subfamily Panicoideae) to provide further insights into the hypothesized roles of the gene. E. indica has spikelets with three to eight florets that mature acropetally; E. indica LHS1 (EiLHS1) is expressed in the palea and lemma of all florets. In contrast, M. maximus has spikelets with two florets that mature basipetally; M. maximus LHS1 (MmLHS1) is expressed in the palea and lemma of the distal floret only. These data are consistent with the hypothesis that LHS1 plays a role in determining palea and lemma morphology and specifies the terminal floret of basipetally maturing grass spikelets. However, LHS1 expression does not correlate with floret sex expression; MmLHS1 is restricted to the bisexual distal floret, whereas EiLHS1 is expressed in both sterile and bisexual floret meristems. Phylogenetic analyses reconstruct a complex pattern of LHS1 expression evolution in grasses. LHS1 expression within the gynoecium has apparently been lost twice, once before diversification of a major clade within tribe Paniceae, and once in subfamily Chloridoideae. These data suggest that LHS1 has multiple roles during spikelet development and may have played a role in the diversification of spikelet morphology.     

Early inflorescence and floral development in Zea mays land race Chapalote (Poaceae)

Tassel and ear primordia were collected from greenhouse-grown specimens of the Mexican maize landrace Chapalote and prepared for scanning electron microscopic (SEM) examination. Measurements of inflorescence apices and spikelet pair primordia (spp) were made from SEM micrographs. Correlation of inflorescence apex diameter with number of spikelet ranks showed no significant difference between tassels and ears, except at the two-rank level where the ear apical meristem had a significantly smaller diameter than corresponding two-ranked tassels. Within individual inflorescences, spp in different ranks enlarged at comparable rates, although the rates from one ear to the next along the stem differed. In both tassels and ears, spp divide to form paired sessile and pedicellate spikelet primordia when the spp is 150 μm wide; ear axes are significantly thicker than tassel axes at the time of bifurcation. The similarities in growth between ear and tassel primordia lend further support to the hypothesis that both the maize tassel and ear are derived from a common inflorescence pattern, a pattern shared with teosinte. Inflorescence primordial growth also suggests that a key character difference between teosinte and maize, distichous vs. polystichous arrangement of spikelets, may be related to size of the apical dome and/or rate of primordium production by the apical meristem. There appears to be more than a single morphological event in the shift from vegetative to reproductive growth. The evocation of axillary buds (ears) is independent of, and temporally separated from, the transition to flowering at the primary shoot apex (tassel).     

Studies on Morphological Evolution,Classification and Distribution of the Triticeae in China

_{The classification and the relationships among the genera of Chinese Triticeae were studied based on morphological characters with reference to geographical distribution and habitat conditions. The spike of Triticeae might have been derived from a panicled inflorescence like that in the Bromeae through a racemose inflorescence like the one in the Brachypodieae. There might be three evolutionary lines in the tribe. 1. Pedicels of the panicled inflorescence have become short and bracts decreased in size, which has resulted in a panicled spike with indefinite spikelets or false solitary spikelets at each node of rachis. The middle ribes of both glumes and lemmas and rachilla are not in a single plane. 2. A simple spike with usual solitary spikelets at each node of rachis has been derived from the raceme. The middle ribe of both glumes and lemmas and rachilla are in a single plane. 3. A cymose spike with 3-spikelets at each node of rachis has evolved from the cymose panicle. The glume on the central spikelet is behind the lemma, while those on the lateral spikelets are on lateral sides of the lemmas. From what we have described above Triticeae may be divided into three subtribes: Elyminae, Triticinae and Hordeinae. Then according to the morphological characters of glume, lemma and other organs as well as the habitats and distribution, the native and introduced triticeous plants are classified into 13 genera (Leymus, Elymus, Roegneria, Elytrigia, Aegilops, Triticum, Agropyron, Eremopyrum, Secale, Haynaldia, Psathyrostachys, Hordeum and Hystrix) and their relationships are also discussed meanwhile.}     

对小麦顶生小穗的初步研究

1.顶生小穗的护颖具有特殊的形态,第二护颖常为小花外稃状,腋内有时还保留着雌雄蕊或内稃残余。说明其不稳定和可变的本质。2.顶生小穗具特殊的坐落位置,其小穗轴与主穗轴一致。顶生小穗原始体发生在穗生长锥顶端,其下无苞原始体,长成后也无小穗领。其护颖和小花外稃与侧生小穗下的小穗领呈严格连续互生状态。说明其一次轴的渊源。3.顶生小穗护颖腋内可长出小穗,小花也可代之以小穗,护颖和小花外稃有时以苞片的形式保留于新侧生小穗外侧。新顶生小穗的护颖来自小花外稃。说明顶生小穗护颖腋内的退化花芽、外稃腋内的小花与侧生小穗都是花序一次轴上的二次轴分枝。4.顶生小穗产生小穗的变异严格按自下而上的顺序进行,与原侧生小穗有严格的连续性。5.事实证明,顶生小穗是一次轴花序,它属于穗状花序顶端的可变部分。     

The wandering carpel mutation of Zea mays (Gramineae) causes misorientation and loss of zygomorphy in flowers and two-seeded kernels

We have isolated a new mutation, wandering carpel (wcr), which affects polarity of the maize flower, altering its orientation or converting it from zygomorphy to radial symmetry. These changes result in the development of embryos on locations other than the normal, acropetal side of the kernel. More than two carpels can develop into silks. More rarely, two ovules develop in a single ovary, giving rise to kernels with two seeds. The wcr mutation is a maternal-sporophyte-effect, semidominant mutation whose expression is background dependent. As spikelets with abnormal flowers are almost always paired with a normal spikelet, we hypothesize that WCR+ is required for establishing polarity in spikelet meristems during inflorescence development.     

Development and Floret Survival in Wheat Ears With Supernumerary Spikelets

In the supernumerary spikelet wheat, AUS159I0, the supernumeraryspikelet primordia appeared just after the ear reached the terminalspikelet stage. Appearance of the primordia of the multiplesessile spikelets preceded that of indeterminate rachilla spikelets.Supernumerary spikelets had a lower number of potentially fertileflorets per spikelet than normal (non-supernumerary) spikeletsin the ear and thus a smaller number of grains per spikelet.Mean weight per grain in the supernumerary spikelet wheat waslower than in the cultivar, Meering, without supernumerary spikelets.Total grain number in the supernumerary spikelet ear was greaterthan in the normal ear despite the lower spikelet fertilityin the former. Within the supernumerary spikelet ear the multiplesessile spikelets had a higher number of grains per spikeletand mean weight per grain than the indeterminate rachilla spikelets.It appears possible to improve the productivity of the supernumeraryspikelet ear by breeding for reduced expression of the indeterminaterachilla spikelets. Wheat, ear development, floret survival, supernumerary spikelets, grain number     

Investigation of morphogenesis of inflorescence and determination of the nature of inheritance of “supernumerary spikelets” trait of bread wheat (Triticum aestivum L.) mutant line

Using C-banding and FISH methods, the karyotype of MC1611 induced mutant of bread wheat, which develop additional spikelets at a rachis node (trait “supernumerary spikelets”) was characterized. It was determined that the mutant phenotype is not associated with aneuploidy and major chromosomal rearrangements. The results of genetic analysis showed that supernumerary spikelets of the line are caused by a mutation of the single Bh-D.1 gene, influenced by the genetic background. The mutation causes abnormalities of inflorescence morphogenesis associated with the development of ectopic spikelet meristems in place of floral meristems in the basal part of the spikelets, causing the appearance of additional spikes at a rachis node. The mutant phenotype suggests that the Bh-D gene determines the fate of the lateral meristems in ear, which develops as floral meristem and gives rise to floral organs in wild-type inflorescences. In the bh-D.1 mutant, the floral meristem identity is impaired. The characterized mutant can be used in further studies on molecular genetic basis of development of wheat inflorescence.     

Combinatorial control of meristem identity in maize inflorescences

The architecture of maize inflorescences, the male tassel and the female ear, is defined by a series of reiterative branching events. The inflorescence meristem initiates spikelet pair meristems. These in turn initiate spikelet meristems which finally produce the floret meristems. After initiating one meristem, the spikelet pair and spikelet meristem convert into spikelet and floret meristems, respectively. The phenotype of reversed germ orientation1 (rgo1) mutants is the production of an increased number of floret meristems by each spikelet meristem. The visible phenotypes include increased numbers of flowers in tassel and ear spikelets, disrupted rowing in the ear, fused kernels, and kernels with embryos facing the base of the ear, the opposite orientation observed in wild-type ears. rgo1 behaves as single recessive mutant. indeterminate spikelet1 (ids1) is an unlinked recessive mutant that has a similar phenotype to rgo1. Plants heterozygous for both rgo1 and ids1 exhibit nonallelic noncomplementation; these mutants fail to complement each other. Plants homozygous for both mutations have more severe phenotypes than either of the single mutants; the progression of meristem identities is retarded and sometimes even reversed. In addition, in rgo1; ids1 double mutants extra branching is observed in spikelet pair meristems, a meristem that is not affected by mutants of either gene individually. These data suggest a model for control of meristem identity and determinacy in which the progress through meristem identities is mediated by a dosage-sensitive pathway. This pathway is combinatorially controlled by at least two genes that have overlapping functions.     

A new multiflorous species of Leymus (Poaceae: Triticeae) from western China

A new species of Leymus section Racemosus, L. pluriflorus L.B.Cai & T.L.Zhang, is described and illustrated. It grows in the eastern part of Qinghai Province and the southern part of Gansu Province, China. It most closely resembles L. crassiusculus L.B.Cai, from which it differs in having longer rachis internodes, some pedicellate spikelets, more florets per spikelet, glabrous lemmas, shorter paleas and shorter anthers. It differs from all other Chinese species taxa in Leymus with regard to the large number (8–12) of florets in its spikelets, and from all species of Leymus in adjacent countries in having three to four spikelets per node. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 343–348.     

Suppressor of sessile spikelets1 functions in the ramosa pathway controlling meristem determinacy in maize

The spikelet, which is a short branch bearing the florets, is the fundamental unit of grass inflorescence architecture. In most grasses, spikelets are borne singly on the inflorescence. However, paired spikelets are characteristic of the Andropogoneae, a tribe of 1,000 species including maize (Zea mays). The Suppressor of sessile spikelets1 (Sos1) mutant of maize produces single instead of paired spikelets in the inflorescence. Therefore, the sos1 gene may have been involved in the evolution of paired spikelets. In this article, we show that Sos1 is a semidominant, antimorph mutation. Sos1 mutants have fewer branches and spikelets for two reasons: (1) fewer spikelet pair meristems are produced due to defects in inflorescence meristem size and (2) the spikelet pair meristems that are produced make one instead of two spikelet meristems. The interaction of Sos1 with the ramosa mutants, which produce more branches and spikelets, was investigated. The results show that Sos1 has an epistatic interaction with ramosa1 (ra1), a synergistic interaction with ra2, and an additive interaction with ra3. Moreover, ra1 mRNA levels are reduced in Sos1 mutants, while ra2 and ra3 mRNA levels are unaffected. Based on these genetic and expression studies, we propose that sos1 functions in the ra1 branch of the ramosa pathway controlling meristem determinacy.     

Phyllotaxis in the Oil Palm: Arrangement of Male/Female Florets along the Spikelets

The paper continues an earlier study of the geometry of inflorescencestructures in the oil palm in which geometry is measured interms of Equivalent Phyllotaxis Index (E.P.I.). In this casethe phyllotaxis of male and female florets along their respectivespikelets is considered. Regardless of the spikelet positionon the inflorescence or the palm age the very small male floretshave a higher E.P.I. than the large female structures and acompletely different apparent parastichy arrangement. TheseE.P.I. estimates seem to be independent of the age of palmsfrom which inflorescences and hence spikelets are sampled. However,there is considerable variation in phyllotaxis within bunches,E.P.I. being lower on spikelets sampled toward the base of theinflorescence and increasing in a more or less linear mannerin spikelets sampled at the tip; this pattern is not so definiteon male spikelets. The results are discussed in relation toother more simple measurements of spikelet architecture.