Activity Of Intercalary Meristem Research Articles

Sugarcane smut: shedding light on the development of the whip-shaped sorus.

Sugarcane smut is caused by the fungus Sporisorium scitamineum (Ustilaginales/Ustilaginomycotina/Basidiomycota), which is responsible for losses in sugarcane production worldwide. Infected plants show a profound metabolic modification resulting in the development of a whip-shaped structure (sorus) composed of a mixture of plant tissues and fungal hyphae. Within this structure, ustilospores develop and disseminate the disease. Despite the importance of this disease, a detailed histopathological analysis of the plant-pathogen interaction is lacking. The whip-shaped sorus was investigated using light microscopy, scanning and transmission electron microscopy, histochemical tests and epifluorescence microscopy coupled with deconvolution. Sorus growth is mediated by intercalary meristem activity at the base of the sorus, where the fungus causes partial host cell wall degradation and formation of intercellular spaces. Sporogenesis in S. scitamineum is thallic, with ustilospore initials in intercalary or terminal positions, and mostly restricted to the base of the sorus. Ustilospore maturation is centrifugal in relation to the ground parenchyma and occurs throughout the sorus median region. At the apex of the sorus, the fungus produces sterile cells and promotes host cell detachment. Hyphae are present throughout the central axis of the sorus (columella). The plant cell produces callose around the intracellular hyphae as well as inside the papillae at the infection site. The ontogeny of the whip-shaped sorus suggests that the fungus can cause the acropetal growth in the intercalary meristem. The sporogenesis of S. scitamineum was described in detail, demonstrating that the spores are formed exclusively at the base of the whip. Light was also shed on the nature of the sterile cells. The presence of the fungus alters the host cell wall composition, promotes its degradation and causes the release of some peripheral cells of the sorus. Finally, callose was observed around fungal hyphae in infected cells, suggesting that deposition of callose by the host may act as a structural response to fungal infection.

Floral Development of Hydrocharis morsus-ranae (Hydrocharitaceae)

In both male and female flowers of H. morsus-ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.

FLORAL DEVELOPMENT OF HYDROCHARIS MORSUS‐RANAE (HYDROCHARITACEAE)

In both male and female flowers of H. morsus‐ranae the primordia of the floral appendages appear in an acropetal succession consisting of alternating trimerous whorls. In the male flower a whorl of sepals is followed by a whorl of petals, three whorls of stamens, and a whorl of filamentous staminodes. The mature androecial arrangement therefore consists of two antisepalous stamen whorls, an antipetalous whorl of stamens, and antipetalous staminodes. Shortly before anthesis, basal meristematic upgrowth between filaments of adjacent whorls produces paired stamens, joining Whorls 1 and 3, and Whorl 2 with the staminodial whorl. A central domelike structure develops between the closely appressed filaments of the inner stamen and staminodial whorl, giving the structure a lobed appearance. After petal inception in the female flower a whorl of antisepalous staminodes develop, each of which may bifurcate to form a pair of staminodes. During staminode development a girdling primordium arises by upgrowth at the periphery of the floral apex. The girdling primordium rapidly forms six gynoecial primordia, which then go on to produce six free styles with bifid stigmas. Intercalary meristem activity, below the point of floral appendage attachment, leads to the production of a syncarpous inferior ovary with six parietal placentae. The styles and carpels remain open along their ventral sutures. During the final stages of female floral development, several hundred ovules develop along the carpel walls, and three nectaries develop dorsally and basally on the three antipetalous styles.

Die Nektarien der Apiaceae

Summary This paper deals with the morphology and anatomy of the nectaries of the Apiaceae , particularly of the Saniculoideae and the Hydrocotyloideae which are thought to be not so highly evolved. The analysed parameters show a surprisingly great variation. Typically the nectary is developed on the foot of the stylodia. There are three phylogenetical tendencies (Fig. 9): 1. A centrifugal shift over the roof of the loculaments to adaxial parts of the peripherical phylloms and/or to the adaxial parts of a gamophyllous pedestal (a); 2. an acrocentrical shift to the tips of the stylodia (b); 3. an also acrocentrical shift in the genus Actinotus but with a completely different gynoeceal structure (c). — The term stylopodium cannot therefore be used for all nectaries of the Apiaceae. — The nectariferous tissue is located both on the phyllomes and on the axes of the epigynous flower. — The nectarothecas have when present a small capacity. There are three types: 1. simple depressions in the nectary itself; 2. cavities resulting from the growth of stylodia, ovary-roof and the nectary halves; 3. Cavities formed by growth of a peripherical torus and the ovary-roof; there are several variations of the latter (e.g. pseudoseptale nectary) depending on the intercalary meristem activity. The vertical anatomical structure is uniform: epiderm with transformed stomata, nectary parenchym, normal parenchym, conductive tissue. On the other hand there is a great variety of the epiderm cells: block-shaped, papillary, hairy. In a few cases the nectary can be multifunctional: 1. attraction of the pollinators by intensive colouring; 2. postfloral function as an elaiosom; 3. it can perhaps also have a protective function and 4. may serve as a second stigmatoid surface. The phylogeny of the nectary is discussed.