RESUMO
Gevuina avellana (Proteaceae) is a typical tree from the South American temperate rainforest. Although this species mostly regenerates in shaded understories, it exhibits an exceptional ecological breadth, being able to live under a wide range of light conditions. Here we studied the genetic basis that underlies physiological acclimation of the photosynthetic responses of G. avellana under contrasting light conditions. We analyzed carbon assimilation and light energy used for photochemical processes in plants acclimated to contrasting light conditions. Also, we used a transcriptional profile of leaf primordia from G. avellana saplings growing under different light environments in their natural habitat, to identify the gene coexpression network underpinning photosynthetic performance and light-related processes. The photosynthetic parameters revealed optimal performance regardless of light conditions. Strikingly, the mechanism involved in dissipation of excess light energy showed no significant differences between high- and low-light-acclimated plants. The gene coexpression network defined a community structure consistent with the photochemical responses, including genes involved mainly in assembly and functioning of photosystems, photoprotection, and retrograde signaling. This ecophysiological genomics approach improves our understanding of the intraspecific variability that allows G. avellana to have optimal photochemical and photoprotective mechanisms in the diverse light habitats it encounters in nature.
Assuntos
Regulação da Expressão Gênica de Plantas/efeitos da radiação , Redes Reguladoras de Genes , Luz , Aclimatação/fisiologia , Aclimatação/efeitos da radiação , Clorofila/metabolismo , Fluorescência , Redes Reguladoras de Genes/efeitos da radiação , Fotossíntese/efeitos da radiação , Folhas de Planta/fisiologia , Folhas de Planta/efeitos da radiação , Transpiração Vegetal/efeitos da radiação , Análise de Componente PrincipalRESUMO
Net photosynthetic carbon uptake of Panamanian lowland tropical forest species is typically optimal at 30-32 °C. The processes responsible for the decrease in photosynthesis at higher temperatures are not fully understood for tropical trees. We determined temperature responses of maximum rates of RuBP-carboxylation (VCMax ) and RuBP-regeneration (JMax ), stomatal conductance (Gs ), and respiration in the light (RLight ) in situ for 4 lowland tropical tree species in Panama. Gs had the lowest temperature optimum (TOpt ), similar to that of net photosynthesis, and photosynthesis became increasingly limited by stomatal conductance as temperature increased. JMax peaked at 34-37 °C and VCMax ~2 °C above that, except in the late-successional species Calophyllum longifolium, in which both peaked at ~33 °C. RLight significantly increased with increasing temperature, but simulations with a photosynthesis model indicated that this had only a small effect on net photosynthesis. We found no evidence for Rubisco-activase limitation of photosynthesis. TOpt of VCMax and JMax fell within the observed in situ leaf temperature range, but our study nonetheless suggests that net photosynthesis of tropical trees is more strongly influenced by the indirect effects of high temperature-for example, through elevated vapour pressure deficit and resulting decreases in stomatal conductance-than by direct temperature effects on photosynthetic biochemistry and respiration.
Assuntos
Carbono/metabolismo , Fotossíntese/fisiologia , Árvores/fisiologia , Calophyllum/fisiologia , Calophyllum/efeitos da radiação , Ficus/fisiologia , Ficus/efeitos da radiação , Florestas , Garcinia/fisiologia , Garcinia/efeitos da radiação , Lagerstroemia/fisiologia , Lagerstroemia/efeitos da radiação , Luz , Fotossíntese/efeitos da radiação , Folhas de Planta/fisiologia , Folhas de Planta/efeitos da radiação , Estômatos de Plantas/fisiologia , Estômatos de Plantas/efeitos da radiação , Transpiração Vegetal/fisiologia , Transpiração Vegetal/efeitos da radiação , Ribulose-Bifosfato Carboxilase/metabolismo , Temperatura , Árvores/efeitos da radiaçãoRESUMO
The influence of extremely low frequency electromagnetic fields on net photosynthesis, transpiration, photosynthetic pigment concentration, and gene expression of ribulose 1,5-bisphosphate carboxylase/oxygenase small subunit (RBCS1), during in vitro establishment, in vitro multiplication and acclimatization phases of coffee seedlings were investigated. Untreated coffee plants were considered as control, whereas treated plants were exposed to a 60 Hz sinusoidal magnetic field of 2 mT of magnetic induction during 3 min. This magnetic field was generated by an electromagnet, connected to a wave generator. The results revealed that magnetically treated plants showed a significant increase in net photosynthesis (85.4% and 117.9%, in multiplication and acclimatization phases, respectively), and in photosynthetic pigment concentration (66.6% for establishment phase, 79.9% for multiplication phase, and 43.8% for acclimatization phase). They also showed a differential RBCS1 gene expression (approximately twofold) and a decrease of transpiration rates in regard to their control plants. In conclusion, the findings suggest that the application of 60 Hz magnetic field to in vitro coffee plants may improve the seedlings quality by modifying some photosynthetic physiological and molecular processes, increasing their vigor, and ensuring better plant development in later stages.
Assuntos
Coffea/fisiologia , Coffea/efeitos da radiação , Campos Magnéticos , Plântula/fisiologia , Plântula/efeitos da radiação , Aclimatação/fisiologia , Aclimatação/efeitos da radiação , Clorofila/metabolismo , Expressão Gênica/fisiologia , Expressão Gênica/efeitos da radiação , Magnetismo , Microscopia Eletrônica de Varredura , Periodicidade , Fotossíntese/fisiologia , Fotossíntese/efeitos da radiação , Proteínas de Plantas/metabolismo , Transpiração Vegetal/fisiologia , Transpiração Vegetal/efeitos da radiaçãoRESUMO
In open places, plants are exposed to higher fluence rates of photosynthetically active radiation and to higher red to far-red ratios than under the shade of neighbor plants. High fluence rates are known to increase stomata density. Here we show that high, compared to low, red to far-red ratios also increase stomata density in Arabidopsis (Arabidopsis thaliana). High red to far-red ratios increase the proportion of phytochrome B (phyB) in its active form and the phyB mutant exhibited a constitutively low stomata density. phyB increased the stomata index (the ratio between stomata and epidermal cells number) and the level of anphistomy (by increasing stomata density more intensively in the adaxial than in the abaxial face). phyB promoted the expression of FAMA and TOO MANY MOUTHS genes involved in the regulation of stomata development in young leaves. Increased stomata density resulted in increased transpiration per unit leaf area. However, phyB promoted photosynthesis rates only at high fluence rates of photosynthetically active radiation. In accordance to these observations, phyB reduced long-term water-use efficiency estimated by the analysis of isotopic discrimination against (13)CO(2). We propose a model where active phyB promotes stomata differentiation in open places, allowing plants to take advantage of the higher irradiances at the expense of a reduction of water-use efficiency, which is compensated by a reduced leaf area.