Gametophytes of Jamesoniella colorata (Jungermanniaceae) and Isotachis lyallii (Isotachidaceae) produce red leaves in exposed habitats, but green leaves in shaded environments. To understand the functional significance of this colour polymorphism, the anatomy, pigment composition, optical properties, and kinetics of chlorophyll a fluorescence were compared for red and green gametophytes. Both colour morphs were structurally similar, but the red leaves held unidentified red pigment(s) firmly associated with the cell wall. Green morphs contained more chlorophylls and carotenoids, and had higher ratios of chlorophylls to carotenoids, than did the red morphs. Red leaves absorbed 10% more photosynthetically active radiation, with a maximum at 540 nm, than did the green leaves. Under high irradiance, the red leaves maintained higher apparent quantum efficiencies for photosynthesis, and had larger photochemical and non-photochemical quenching values. The data indicate that red gametophytes have the greater potential to mitigate the damaging effects of high irradiance.
This study tests the hypothesis that red-leaved gametophytes of the liverwort Jamesoniella colorata (Lehm.) Schiffn., which are found in relatively dry habitats, are more desiccation tolerant than their green counterparts, which are found in moister environments, through superior photoprotective systems. The potential role of red foliar pigments in relation to water deficits is investigated by measuring cell water-relations, oxidative damage and photosynthetic responses. The presence of red pigments, or other cellular constituents, did not affect cell water-relations during dehydration and thus appear not to be involved in cell osmotic regulation. During drying, both colour morphs showed a similar non-photochemical quenching activity and did not experience significant oxidative damage, as measured by the amounts of ascorbate, malondialdehyde and photosynthetic pigments. However, the levels of oxidative damage increased directly upon rewetting the gametophytes, especially in low light conditions (25 micromol m(-2) s(-1)). The efficiency of photosystem II only recovered partially after severe water deficits in both phenotypes. However, the red gametophytes recovered faster and more completely from mild water deficits than did the greens. Moreover, they experienced significantly less photobleaching after rehydration in low light. It is suggested that red pigments and/or carotenoids in these gametophytes improve desiccation tolerance by alleviating photooxidative damage.
Candida albicans is an opportunistic fungal pathogen that is a benign member of the microflora of most individuals. A majority of women (Ն75%) experience at least one episode of acute vulvovaginal candidiasis (VVC), and a substantial number (Ն10%) suffer from recurrent chronic vaginal infections, defined as at least 4 episodes per year (1, 2). Prepubescent girls and postmenopausal women with low levels of production of estrogen rarely develop the disease. Consequently, women are susceptible to VVC when their vaginal epithelium is subject to periodic hormonally induced changes with the concomitant infusion of serum and potential intermittent exposure to seminal fluid (SF) (3, 4). Serum and seminal fluid are known to trigger yeastlike-to-hyphal morphogenic transitions in C. albicans, a developmental response linked to virulent growth (5).Filamentous forms of C. albicans are associated with symptomatic VVC (6). True hyphae elaborated by C. albicans are elongated structures with characteristically distinct parallel walls and regularly spaced septae that confine individual nuclei. Hyphae are able to penetrate the mucosal surfaces of the host and cause damage to the epithelium. Importantly, C. albicans strains capable of forming hyphae promote symptomatic experimentally induced VVC in women, whereas mutant strains incapable of hyphal growth show diminished adherence to vaginal epithelial cells and reduced colonization and infection in a murine model of C. albicans vaginitis (7).The vaginal environment is complex. Although the vaginal epithelium together with associated physiological secretions (vaginal fluid [VF]/cervical mucus) and resident commensal bacterial microflora contribute to maintaining an acidic environment that represses filamentation of C. albicans (8, 9), the vaginal epithelium (matrix) represents an inherently conducive environment for morphological switching of fungal cells. Particularly, the physical contact with epithelial surfaces, the constant temperature of 37°C, and elevated levels of CO 2 are established factors that favor filamentous growth (10). Additionally, in sexually mature women, the vaginal epithelium undergoes transient changes that can induce filamentation. The pH of cervical mucus is usually acidic (pH 4 to 4.5) (noninducing); however, during menses, it increases to pH 6.8 (inducing). Similarly, the introduction of seminal fluid, which is alkaline (pH 7 to 8.5), can transiently increase the pH within the vagina (11). Furthermore, serum and seminal fluid contain high concentrations of known morphogenic factors, including amino acids, proteins, and, in the case of seminal fluid, N-acetylglucosamine (GlcNAc).In contrast to many microbial pathogens, C. albicans has a diverse metabolic repertoire, is able to colonize virtually any tissue and organ, and possesses efficient systems to extract nitrogen from diverse host niches (12). Although fungus-specific gene products involved in nitrogen uptake are likely to be essential for C. albicans virulence, only limited information is available re...
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