The development of a fungal endophyte in the tissue of Lolium perenne during flowering, seed set, and germination is described. The endophyte progresses intercellularly from the vegatative apex into/t~ inflorescence primordium and floral apices, from where it penetrates the tissues of ovary and ovule. At megagametophyte maturity, hyphae are concentrated outside its wall adjacent to the large lateral antipodal cells and subsequently gain entry to the embryo sac, probably soon after fertilisation. During early embryogenesis, hyphae occur on the surface of the embryo, and penetrate it at the 'notched' stage. At seed maturity, hyphae are widespread within the embryo, including the plumule apex, as well as below the testa, between cells of the aleurone layer, and between scutellum and endosperm. At germination, hyphae outside the embryo appear to play no further part in invasion of the already infected embryo. The endophyte of Festuca arundinacea has a similar relationship with its host and appears to be ultrastructurally indistinguishable from that of Lolium perenne.
The incidence and intensity of infection by a Gliocladium-like symptomless endophyte were monitored in a pasture of Lolium perenne L. by observing fungal hyphae in sections ofpseudostems of ryegrass tillers in the vegetative phase of growth. Incidence and intensity were low during summer, increased to a maximum in winter, and then declined in spring. A second endophyte, Acremonium lolii Latch, Christensen and Samuels was also present in most plants, but its incidence and intensity became greatest as the Gliocladium-like endophyte declined. Hyphae of the Glioc ladium-like endophyte occurred in intercellular spaces of the leaf sheath, and less profusely of the leaf blade, assuming swollen or contorted forms during the period of highest intensity of infection in winter. At this time, sporodochia of the Gliocladium-like endophyte protruded through the stomata of leaf blades whose tissues were beginning to degenerate. Simultaneously, conidia developed in air spaces in the mesophyll, and sporodochia occurred in the air lacunae of leaf sheaths. This is the first report of sporulation of a symptomless endophyte in nature.
SUMMARY\^^%y^\\.^^^x\s x^^on^ ol dd?>t.o^am^ m Dmthonia spicata (L.) Beauv., recent authors have based their work on the incorrect assumption that aerial panicles are entirely chasmogamous and that cleistogamy is confined to axillary spikelets (cleistogenes). Of the fiorets contained in 122 panicles, 48% were chasmogamous and 52% cleistogamous. Only one panicle was entirely chasmogamous, whereas 58 were entirely cleistogamous. Chasmogamy was most prevalent in the lower parts of the spikelets and in the lower spikelets of the panicles. In addition to self-fertilizing cleistogamous fiorets, an unknown but small proportion of non-opening fiorets was sufficiently aberrant in their megasporogenesis to suggest that apomixis occurred. The possibility of the presence of apomixis should be considered within a typical cleistogamous system.
PALSER, B. F., PHILIPSON, W. R. & PHILIPSON, M. N., 1989. Development of ovule, megagametophyte and early endosperm in Rhododendron L. (Ericaceae). Complete development of ovule, megagametophyte and early endosperm is compared for 15 species (almost complete for four additional species) representing all subgenera and most sections of Rhododendron. In all the ovule is anatropous, unitegmic, tenuinucellate with the lateral and micropylar nucellus disintegrating completely. The integument has a tanniniferous epidermis, starch around egg apparatus and micropyle, an endothelium and hypostase. Differences occur in time of closure of the micropyle and its final length, total proportion of ovule occupied by gametophyte and by formation of ovule tails only in section Vireya. Megagametophyte development follows the Polygonum pattern in all species. A single archesporial cell becomes the megaspore mother cell directly, and the chalazal spore of a linear tetrad functions. Between the eight‐nucleate stage and maturity the micropylar end of the gametophyte elongates into the micropyle. Starch is characteristically present in the mature central cell. The pollen tube penetrates porogamously and double fertilization is rapid. Endosperm development starts promptly and is cellular, first forming a linear row of four cells. The zygote elongates slightly but does not divide during the stages followed. Differences may occur in time of enlargement, orientation of some mitoses, some cellular characteristics, amount of starch present and final size of megagametophyte. Rare abnormalities occur.
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