Flavonol aglycones are required for pollen germination in petunia (Petunia hybrida 1.). Mutant plants lacking chalcone synthase (CHS), which catalyzes the first committed step in flavonoid synthesis, do not accumulate flavonols and are self-sterile. l h e mutant pollen can be induced to germinate by supplementing it with kaempferol, a flavonol aglycone, either at the time of pollination or by addition to an in vitro germination system. Biochemical complementation occurs naturally when the mutant, flavonol-deficient pollen is crossed to wild-type, flavonoid-producing stigmas. We found that successful pollination depends on stigma maturity, indicating that flavonol aglycone accumulation may be developmentally regulated. Quantitative immunoblotting, in vitro and in vivo pollen germination, and high-performance liquid chromatographic analyses of stigma and anther extracts were used to determine the relationship between CHS levels and flavonol aglycone accumulation in developing petunia flowers. Although substantial levels of CHS were measured, we detected no flavonol aglycones in wild-type stigma or anther extracts. Instead, the occurrence of a conjugated form (flavonol glycoside) suggests that a mechanism may operate to convert glycosides to the active aglycone form.

Epulopiscium fishelsoni n. g., n. sp., is described from the gut of Acanthurus nigrofuscus, an herbivorous surgeonfish (Acanthuridae: Teleostei) from the Red Sea, Israel. The symbiont is placed in the kingdom Protoctista (or Protista) but more specific taxonomic assignment is impossible at this time. The organism is of an elongate oval shape, round in cross‐section, and highly mobile, with the ability to reverse direction rapidly. It lacks a mouth or other external structures, with the exception of fine surface filaments of an undetermined nature. Internally, there is a complex of folded membranes or tubules and a nucleus. No other organelles are evident. Reproduction is characterized by doubling of nuclei within the parental cell and emergence of daughter cells from a perforation in the parental cortex. Symbionts appear to exhibit circadian cycles of growth, reproductive activity, and movement within the gut. Although the organism greatly reduces local gut pH when present in large numbers, we know nothing of interactions between host and symbiont.

Flavonols are essential for pollen germination and tube growth in petunia and can be supplled by either the pollen or stigma at pollinatlon. HPLC analysis and a sensitive bloassay demonstrated that both pollinatlon and wounding induce flavonol accumulation, especlally kaempferol, in the outer cell layers and exudate of the stigma. Pollination and wounding induced nearly identical flavonol kinetics and patterns of accumulation in the same target tissue, suggesting that they sham elements of a common signal transductlon pathway. The wound response was systemlc, because kaempferol accumulated in the stlgma when dista1 tissues, such as the corolla, stamens, or sepals, were wounded. We have exploited the germination requirement for flavonols and the high leve1 of kaempferol that accumulates after wounding to enhance plant fecundity. Seed set was slgnificantly increased by mechanically wounding the corolla and stamens prior to the application of pollen to the stigma. A reproductive role for a plant secondary metabolite and the specific function of stigmatic kaempferol are discussed from an evolutionary perspective. INTRODUCTIONIn angiosperms, the stigma is the pollen-receptive surface of the female gametophyte-bearing pistil. In many species, the stigmatic surface is covered with a chemically complex exudate that provides the hospitable conditions and factors required for pollen adhesion, hydration, germination, and pollen tube penetration (Konar and Linskens, 1966;Knox, 1984; HeslopHarrison, 1987). In addition, discriminatory events, such as the rejection of self-pollen in sporophytic incompatible reactions, occur at the stigmatic surface (Nasrallah et al., 1991).The stigma also appears to offer a hostile environment to bacteria and fungi because growth of these organisms on the stigma is rare (Jung, 1956).Transcripts homologous to genes induced by wounding and stress have been detected in flowers from nonwounded plants (Gasser, 1991), and in some cases, defenserelated compounds have been found to accumulate specifically in the stigma. For example, high levels of proteinase inhibitor (PI) proteins (Atkinson et al., 1993) and chitinase (Leung, 1992) have been measured in stigmas of solanaceous plants, and the promoters of an hydroxyproline-rich glycoprotein gene and a phenylpropanoid biosynthetic gene, phenylalanine ammonia-lyase, direct transcription of a reporter gene in transgenic tobacco stigmas (Liang et al., 1989; Wycoff et al., 1990). Although thedefensive Current address: lnstitut für Pflanzenbiochemie, Halle, Germany. To whom correspondence should be addressed.role of these compounds in wounded tissue is well known, a reproductive function has not been established.Phenolic compounds function as stress indicators because they accumulate to high levels in many plant tissues in response to a wide range of biotic and abiotic signals, including wounding (Lawton and Lamb, 1987). Biosynthesis and accumulation of phenolics also occur as part of normal developmental programs in most higher plants (Wiermann, 1981). Ch...

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Epulopiscium fishelsoni, gut symbiont of the brown surgeonfish (Acanthurus nigrofuscus) in the Red Sea, attains a larger size than any other eubacterium, varies 10- to 20-fold in length (and >2,000-fold in volume), and undergoes a complex daily life cycle. In early morning, nucleoids contain highly condensed DNA in elongate, chromosome-like structures which are physically separated from the general cytoplasm. Cell division involves production of two (rarely three) nucleoids within a cell, deposition of cell walls around expanded nucleoids, and emergence of daughter cells from the parent cell. Fluorescence measurements of DNA, RNA, and other cell components indicate the following. DNA quantity is proportional to cell volume over cell lengths of ∼30 μm to >500 μm. For cells of a given size, nucleoids of cells with two nucleoids (binucleoid) contain approximately equal amounts of DNA. And each nucleoid of a binucleoid cell contains one-half the DNA of the single nucleoid in a uninucleoid cell of the same size. The life cycle involves approximately equal subdivision of DNA among daughter cells, formation of apical caps of condensed DNA from previously decondensed and diffusely distributed DNA, and “pinching” of DNA near the middle of the cell in the absence of new wall formation. Mechanisms underlying these patterns remain unclear, but formation of daughter nucleoids and cells occurs both during diurnal periods of host feeding and bacterial cell growth and during nocturnal periods of host inactivity when mean bacterial cell size declines.