Photosynthetic characteristics of a tropical population of Nitella cernua (Characeae, Chlorophyta)

Abstract

Photosynthetic characteristics (assessed by chlorophyll fluorescence and O 2 evolution) were analysed monthly during one year in a tropical population of Nitella cernua from southeastern Brazil (20 o 50 32" S, 49 o 26 15" W). Parameters derived from photosynthesis-irradiance (PI) curves by fluorescence (high values of the photosynthetic parameter, I k , and lack or low values of photoinhibition, β) suggested adaptation to high irradiance, whereas those by O 2 evolution showed a different pattern (low values of I k and compensation irradiance, I c , high values of photosynthetic efficiency, α, and photoinhibition). Parameters from PI curves by O 2 evolution suggested light acclimation: I k and maximum photosynthetic rate, P max (as rETR, relative electron transfer rate) increased, whereas α became significantly lower under higher irradiance (winter). This pattern is an adjustment of both number and size of photosynthetic units. Photosynthetic performance assessed by fluorescence revealed two seasonal periods: higher values of P max (rETR), I k and nonphotochemical quenching from October to March (rainy season), and lower values from April to October (dry season). Temperature responses were observed only in summer, but temperature optima were different between methods: peaks of net photosynthesis occurred at 20 o C, whereas rETR increased towards higher temperatures (up to 30 o C). Dark respiration increased with higher temperatures. Current velocity had a stimulatory effect on photosynthetic rates, as suggested by positive correlations with P max (rETR) and α. pH experiments revealed highest net photosynthetic rates under pH 4.0, suggesting higher affinity for CO 2 than HCO 3 -. This broad range of responses of photosynthetic characteristics of this N. cernua population to irradiance, temperature, and pH/inorganic carbon reflects a wide tolerance to variations in these environmental variables, which probably contribute to the wide distribution of this species. Key words: charophytes, irradiance, Nitella, pH, photosynthesis, seasonal dynamics, temperature Características fotossintéticas de uma população tropical de Nitella cernua (Characeae, Chlorophyta): Foram analisadas mensalmente, durante um ano, as características fotossintéticas (por meio de fluorescência da clorofila e evolução de O 2 ) de uma população tropical de Nitella cernua do sudeste do Brasil (20 o 50 32" S, 49 o 26 15" W). Parâmetros derivados das curvas fotossíntese-irradiância (FI) por fluorescência (alto valor do parâmetro de saturação de luz, I k , e ausência ou baixa fotoinibição, β) sugeriram adaptação a alta irradiância, enquanto aqueles por evolução de oxigênio mostraram adaptações à sombra (baixo valores de I k e de irradiância de compensação, I c , altos valores de eficiência fotossintética, α, e β). Parâmetros das curvas FI por oxigênio sugeriram aclimatação à luz: I k e taxa fotossintética máxima, F max (analisada como rETR, taxa relativa de transporte de elétrons) aumentaram e α foi significativamente menor sob irradiância mais alta (i...

Ultraweak luminescence of the Characeae plants under the circumstances of cyclical changes in temperature

“…A process whose intensity in plants depends on the temperature is also respiration (Necchi, 2004, Vieira & Necchi, 2006. Respiration processes lead to electron leakage in the respiratory chain and consequently to peroxidation of mitochondrial membrane lipids accompanied by spontaneous emission of photons (Hideg, Kobayashi & Inaba, 1991).…”