PSI photoinhibition is more related to electron transfer from PSII to PSI rather than PSI redox state in Psychotria rubra.

Although it has been believed that wild-type plants are capable of protecting photosystem I (PSI) under high light, our previous study indicates that PSI is sensitive to high light in the shade-established tree species Psychotria rubra. However, the underlying physiological mechanisms are unclear. In this study, we examined the roles of electron transfer from PSII to PSI and PSI redox state in PSI photoinhibition in P. rubra by treatments with lincomycin (Lin), diuron (DCMU), and methyl viologen (MV). After exposure to 2000 µmol photons m(-2) s(-1) for 2 h, PSI activity decreased by 35, 29, 3, and 49 % in samples treated with H2O, Lin, DCMU, and MV, respectively. Meanwhile, the MV-treated samples showed higher P700 oxidation ratio than the H2O-treated samples, suggesting the PSI photoinhibition under high light was accompanied by high levels of P700 oxidation ratio. PSI photoinhibition was alleviated in the DCMU-treated samples but was accelerated in the MV-treated samples, suggesting that PSI photoinhibition in P. rubra was mainly controlled by electron transfer from PSII to PSI. Taking together, PSI photoinhibition is more related to electron transfer from PSII to PSI rather than PSI redox state in P. rubra, which is different from the mechanisms of PSI photoinhibition in Arabidopsis thaliana and cucumber.

Early changes in gene expression induced by acute UV exposure in leaves of Psychotria brachyceras, a bioactive alkaloid accumulating plant.

UV-B radiation can damage biomolecules, such as DNA, RNA, and proteins, halting essential cellular processes; this damage is partly due to ROS generation. Plant secondary metabolites may protect against UV-B. Psychotria brachyceras Müll. Arg. (Rubiaceae), a subtropical shrub, produces brachycerine, a monoterpene indole alkaloid mainly accumulated in leaf tissues, which displays antioxidant and antimutagenic activities. Exposure of P. brachyceras cuttings to UV-B radiation significantly increases leaf brachycerine concentration. It has been suggested that this alkaloid might contribute to protection against UV-B damage both through its quenching activity on ROS and as UV shield. To identify differentially expressed genes of P. brachyceras in response to UV-B and investigate a possible influence of this stimulus on putative brachycerine-related genes, suppressive subtractive hybridization was applied. Complementary DNA from UV-B-treated leaves for 24 h was used as tester, and cDNA from untreated leaves, as driver. After BLASTX alignments, 134 sequences matched plant genes. Using quantitative RT-PCR, selected genes potentially related to brachycerine showed significant increases in transcription after UV-B exposure: tryptophan decarboxylase, ACC oxidase, UDP-glucose glucosyltransferase, lipase, and serine/threonine kinase. Results suggest a possible involvement of brachycerine in acute UV-B responses and show that alkaloid accumulation seems at least partly regulated at transcriptional level.

Photochemical efficiency of adult and young leaves of the neotropical understory shrub Psychotria limonensis (Rubiaceae)in response to changes in the light environment

We explored the short-term adjustment in photochemical efficiency (Fv /Fm )in adult and young leaves of the understory neotropical shrub Psychotria limonensis Krause (Rubiaceae)in response to rapid changes in the light environment.Leaves were collected from 20 individual plants growing under sun and shade conditions on Gigante Peninsula,Barro Colorado Natural Monument (Republic of Panama),during the wet season of 1996. Leaves were distributed in four sequences of light treatments (AB leaves were expanded under sun and were transferred to shade,BA leaves experienced the opposite transfer,and the controls AA and BB leaves that were expanded and maintained under sun or shade conditions).Adult and young leaves did not differ in overall photochemical efficiency.Instead,differences were found among light environments,for which leaves transferred from shade to sun showed the lowest F v /F m ratios.There was no relationship between photochemical efficiency and leaf temperature.In P.limonensis,understory plants are susceptible of photoinhibition independently of the leaf ontogenetic stage.The approach utilized in this experiment allowed the rapid exploration of this capacity, and could be applied to poorly studied understory species

Se exploró el ajuste a corto plazo en la eficiencia fotosintética (Fv /Fm )en hojas jovenes y adultas del arbusto del sotobosque neotropical Psychotria limonensis Krause (Rubiaceae)en respuesta a cambios rápidos de luz ambiental. Las hojas fueron recolectadas de 20 plantas individuales bajo condiciones de sol y sombra en Peninsula Gigante, Monumento Natural Barro Colorado (Panamá),durante la estación lluviosa de 1996.Las hojas fueron distribuidas en una secuencia cuatro tratamientos de luz (AB las hojas fueron expandidas bajo el sol y fueron transferidas a la sombra,BA las hojas experimentaron la transferencia contraria,y las hojas controles AA y BB que fueron expandidas y mantenidas bajo condiciones de sol o de sombra).Las hojas adultas o jóvenes no difieren en la eficiencia fotoquímica general.Por el contrario,se encontró diferencias entre los ambientes de luz (iluminados), para los cuales las hojas transferidas de la sombra al sol mostraron las menores tasas Fv /Fm .No hubo relación entre la eficiencia fotoquímica y la temperatura de las hojas. En P.limonensis ,las plantas son suceptibles a la foto -inhibición independientemente del estado ontogenético de la hoja. El enfoque utilizado en este experimento permitió la rápida exploración de esta capacidad y demostró que puede ser utilizado en otras especies poco estudiadas del sotobosque

N,beta-D-Glucopyranosyl vincosamide, a light regulated indole alkaloid from the shoots of Psychotria leiocarpa.

From leaves of Psychotria leiocarpa, an indole alkaloid was isolated to which the structure N,beta-D-glucopyranosyl vincosamide (1) was assigned. This represents the first report of an N-glycosylated monoterpenoid indole alkaloid. In field-grown plants highest amounts of 1 were found in the leaves (2.5% of dry wt) and fruit pulp (1.5% dry wt). Lower amounts were found in the stems (0.2% dry wt) and the seeds (0.1% of dry wt), whereas the alkaloid was not detected in the roots. The accumulation of 1 in aseptic seedlings was also restricted to the shoots and increased with plant age and light exposure, independent of the supply of sucrose in the culture medium.

Photochemical efficiency of adult and young leaves of the neotropical understory shrub Psychotria limonensis (Rubiaceae) in response to changes in the light environment.

We explored the short-term adjustment in photochemical efficiency (Fv/Fm) in adult and young leaves of the understory neotropical shrub Psychotria limonensis Krause (Rubiaceae) in response to rapid changes in the light environment. Leaves were collected from 20 individual plants growing under sun and shade conditions on Gigante Peninsula, Barro Colorado Natural Monument (Republic of Panama), during the wet season of 1996. Leaves were distributed in four sequences of light treatments (AB leaves were expanded under sun and were transferred to shade, BA leaves experienced the opposite transfer, and the controls AA and BB leaves that were expanded and maintained under sun or shade conditions). Adult and young leaves did not differ in overall photochemical efficiency. Instead, differences were found among light environments, for which leaves transferred from shade to sun showed the lowest Fv/Fm ratios. There was no relationship between photochemical efficiency and leaf temperature. In P. limonensis, understory plants are susceptible of photoinhibition independently of the leaf ontogenetic stage. The approach utilized in this experiment allowed the rapid exploration of this capacity, and could be applied to poorly studied understory species.

The alkaloid brachycerine is induced by ultraviolet radiation and is a singlet oxygen quencher.

The effects of ultraviolet (UV) radiation on chlorophyll content and accumulation of the anti-inflammatory monoterpene-indole alkaloid brachycerine in plants and calli of Psychotria brachyceras (Rubiaceae) were investigated. In this study, we also investigated a protective role for brachycerine against stress conditions. Calli and tip cuttings incubated in nutrient media were daily supplemented with 4 or 16 h of UV. High-performance liquid chromatography analyses of methanolic extracts showed only traces of brachycerine in irradiated aseptic cultures, with no alkaloid being observed in control calli. In cuttings, a 10-fold increase in brachycerine content was seen after exposure for 16 h to UV-C, whereas a 4 h daily supplementation doubled the amount of the alkaloid in leaves. Exposure to a UV-B source also doubled the alkaloid yield. In vitro brachycerine was able to quench singlet oxygen. The data indicate a potential protective role for brachycerine against UV radiation, acting as a UV filter (absorption peaks are within the UV range) and a reactive oxygen species scavenger. In addition, UV radiation may be used to increase yields of this compound of pharmaceutical interest.