Distribution and morphology of extrafloral nectaries in some Cucurbitaceae

A study of extrafloral nectaries has been made in the Cucurbitaceae to ascertain their structure and assess their taxonomic potential. Nineteen species representing nine Old World genera and one New World genus were examined. These included Telfairia occidentalis, Telfairia pedata, Momordica charantia, Lagenaria siceraria, Citrullus lanatus, Luffa aegyptiaca, Cucurbita moschata and Trichosanthes cucumerina , which are of economic importance and cultivated in Nigeria for their leaves and/or fruits.
Observation of the regularity of ant and insect-visitors, along with tests for glucose and β-glucosidase enzymes, revealed the presence of extrafloral nectaries in nine species. Considerable variation exists in the distribution and morphology of nectaries between genera, especially in the tribe Benincaseae. The nutritional and ecological significance of the occurrence of extrafloral nectaries in Telfairia occidentalis is discussed.     

Floral ontogeny inMazus pumilus (Scrophulariaceae)

InMazus pumilus, all the floral appendages are initiated in acropetal sequence in the second cell layer (except stamens) of the floral primordium by periclinal divisions. The actinomorphic calyx tube is formed due to zonal growth. The zygomorphy in corolla is evident from the inception of petal primordia which arise sequentially as independent units in order of one anterior, a pair of anterio-lateral followed by a pair of posterio-lateral. Later these primordia exhibit differential growth because of which zygomorphy becomes more pronounced. The upper corolla tube is formed by interprimordial growth and lower corolla tube by zonal growth. Stamens are initiated in the third layer of the floral apex. Unlike sepals and petals, in the development of stamens (4) underlying cells of corpus also contribute. Posterior stamen is absent. The stamens become epipetalous because of interprimordial and zonal growth in the common region below the bases of petals as well as stamens. The two carpel primordia arise as crescent shaped structures which become continuous due to interprimordial growth. The ovary is formed by a ring of zonal meristem. The style develops later between stigma and ovary because of intercalary growth. The residual apex grows vertically along with the ovary and forms the septum of the ovary. All the floral appendages exhibit similar pattern of histogenesis and early growth suggesting thereby the appendicular nature of these appendages.     

Changes in density of chromatin in the meristematic cells ofSinapis alba during transition to flowering

Summary Changes in the density of nuclear chromatin in the shoot apical meristem ofSinapis alba L. during floral transition (floral evocation) are described using Feulgen-stained 2 m thick semi-thin sections and scanning cytophotometric techniques. In both G1 and G2 nuclei the chromatin becomes less heterogeneous and less dense in evoked meristems compared to vegetative meristems. When chromatin is resolved into two fractions the dispersed fraction increases relative to the condensed fraction at evocation. This decondensation process occurs earlier in G1 than in G 2 nuclei. These chromatin changes are presumably closely related to the dramatic stimulation of biosynthetic activity and cell division during floral transition.     

Differences in the diversity and composition of the pollinator assemblage of two co-flowering congeneric alpine wallflowers, Erysimum nevadense and E. baeticum

Many alpine plants display a generalist pollination system where almost any available flower visitor could act as a legitimate pollinator. Co-flowering related plant species displaying a generalized pollination system can decrease their fitness due to interspecific mating. In this study, we determine the difference in diversity and composition of the pollination systems of two co-occurring species endemic to the alpine region of the Sierra Nevada (SE Spain), Erysimum nevadense Reut. and Erysimum baeticum baeticum (Heywood) Polatschek (Brassicaceae), and check for the potential role of floral and plant traits in explaining the observed differences. For this, we labeled 30 plants in two populations of each plant species located in the same area. We determined flower visitor assemblage by sampling all insects approaching the flowers and contacting the sexual organs during 60-min surveys. We found that the diversity of the pollinator assemblage was similar between the two studied wallflower species, both species showing a much generalized pollination system. However, the composition of the pollinator assemblage was different, since the flowers of E. nevadense were visited mostly by beetles and in a lesser extent by hover-flies, whereas the flowers of E. baeticum baeticum were visited mostly by ants and bees. Interestingly, flower traits varied between species, with E. nevadense displaying yellow, smaller and shallower flowers and E. baeticum baeticum displaying purple, large and deeper flowers. These findings suggest that differences in floral traits can explain the observed differences in the composition of the pollinator assemblage between both wallflower species.     

Comparison of floral scent between and within Buddleja fallowiana and Buddleja officinalis (Scrophulariaceae)

Floral scents are important olfactory signals for communication between plants and pollinators. Several studies have focused on inter-specific variation of floral scents, but little is known about the intra-specific variation, especially in some polychromic species. In this study, we investigated the floral scent compositions of Buddleja fallowiana and Buddleja officinalis in situ by dynamic headspace collection and coupled GC–MS. Variations of scent compositions within and between populations as well as among species were compared. In spite of substantial intra- and inter-population variability, B. fallowiana and B. officinalis were clearly differentiated in their scent profiles. In B. fallowiana, obvious differentiation was found between studied populations, while all investigated populations in B. officinalis are part of a metapopulation. These high intra-specific variations are discussed in relation to the introgression through hybridization and founder effects from different populations.     

High-frequency in vitro flowering of Murraya paniculata (L.) Jack

Shoots of orange jessamine (Murraya paniculata) a member of the Rutaceae family flowered in vitro on half-strength MT basal medium containing 5% sucrose. The highest percentage (95%) of flowering was obtained on medium supplemented with 0.1 mg l^–1 N⁶-benzyladenine and pH 5.7. A “floral gradient” was detected among the stem internodes and root segments derived from seedlings, with shoot and flower formation significantly influenced by position on the shoot internodes and root segments. Flower buds originating from shoots derived from seeds but not other tissues developed into normal flowers and produced zygotic embryos. Received: 10 December 1997 / Revision received: 5 November 1998 / Accepted: 2 December 1998     

Solid-phase microextraction of volatile compounds from flowers of two Brunfelsia species

Two plant species belonging to the genus Brunfelsia, commonly known as “Yesterday-Today-and-Tomorrow”, are closely related, however, differ by their flower fragrance. Flowers of Brunfelsia australis present a pleasant fragrance, whereas flowers of Brunfelsia pauciflora are scentless. SPME/GC/MS analysis on flower samples of both species of Brunfelsia indicated that flowers of B. australis emitted a fresh flowery fragrance, essentially comprising two monoterpenic compounds (linalool and (E)-ocimene). B. pauciflora, on the other hand, produced only a few sesquiterpenoids. These results are considered in an ecological and evolutionary context.     

多胺对离体黄瓜子叶花芽构建的影响

研究了外源多胺对离体黄瓜(CucumissativusL.)子叶内在多胺含量和花芽构建的影响。在MS培养基中添加5×10-2mmol·L-1亚精胺(Spd)、精胺(Spm)能明显提高子叶内Spd含量和SpdPut值,子叶成花率也明显高于对照组,而添加5×10-2mmol·L-1Put、5mmol·L-1环己胺硫酸盐(CHAS)培养的结果则相反。表明子叶内Spd含量和SpdPut与成花率呈正相关关系。在添加5mmol·L-1D精氨酸(DArg)处理后,子叶内SpdPut高于Spd处理,但子叶成花率低于对照组,表明Put、Spd含量也影响离体子叶花芽的构建。在实验中添加CHAS处理后子叶内Spm含量高出对照组10倍,子叶成花率却为0,其它各处理与对照组的内源Spm变化基本一致,成花率却差别明显,表明子叶内Spm含量与黄瓜子叶花芽构建之间无明显相关性。