Sandro Dan Tatagiba

Leaf Gas Exchange and Chlorophyll a Fluorescence Imaging of Rice Leaves Infected with Monographella albescens

This study was intended to analyze the photosynthetic performance of rice leaf blades infected with Monographella albescens by combining chlorophyll (Chl) a fluorescence images with gas exchange and photosynthetic pigment pools. The net CO2 assimilation rate, stomatal conductance, transpiration rate, total Chl and carotenoid pools, and Chl a/b ratio all decreased but the internal CO2 concentration increased in the inoculated plants compared with their noninoculated counterparts. The first detectable changes in the images of Chl a fluorescence from the leaves of inoculated plants were already evident at 24 h after inoculation (hai) and increased dramatically as the leaf scald lesions expanded. However, these changes were negligible for the photosystem II photochemical efficiency (Fv/Fm) at 24 hai, in contrast to other Chl fluorescence traits such as the photochemical quenching coefficient, yield of photochemistry, and yield for dissipation by downregulation; which, therefore, were much more sensitive than the Fv/Fm ratio in assessing the early stages of fungal infection. It was also demonstrated that M. albescens was able to impair the photosynthetic process in both symptomatic and asymptomatic leaf areas. Overall, it was proven that Chl a fluorescence imaging is an excellent tool to describe the loss of functionality of the photosynthetic apparatus occurring in rice leaves upon infection by M. albescens.

O SILÍCIO POTENCIALIZA O DESEMPENHO FOTOQUÍMICO EM FOLHAS DE ARROZ

Objetivou-se com este trabalho investigar o efeito do silicio (Si) sobre os parâmetros de trocas gasosas da fotossintese [assimilacao liquida de CO 2 ( A ), condutância estomatica ( g s ) e concentracao interna de CO 2 ( C i )], dos parâmetros de fluorescencia da clorofila (Chl) a {fluorescencia minima ( F 0 ), fluorescencia maxima ( F m ), eficiencia quântica maxima da fotoquimica ( F v / F m ), coeficiente de extincao fotoquimica ( q p ), rendimento da fotoquimica [Y(II)], rendimento de dissipacao de energia regulado [Y(NPQ)] e o rendimento das perdas de dissipacao nao reguladas [Y(NO)]}, bem como sobre as concentracoes de pigmentos cloroplastidicos em plantas de arroz cultivadas em solucao nutritiva contendo 0 ou 2 mmol de Si (-Si ou +Si nas plantas, respectivamente). Os resultados do presente estudo indicam que o Si contribuiu para o desempenho fotoquimico em folhas de arroz, o qual, esteve associado a aumentos em F v / F m , q p , Y(II). Nas plantas supridas com Si tambem houve incrementos em A e nos pigmentos fotossinteticos. Dessa forma, podemos concluir que o suprimento de Si pode ser utilizado como uma estrategia de mitigacao para aumentar a produtividade primaria em arroz.

LIMITAÇÕES FOTOSSINTÉTICAS EM FOLHAS DE PLANTAS DE TOMATEIRO SUBMETIDAS A CRESCENTES CONCENTRAÇÕES SALINAS - DOI: 10.13083/1414-3984.v22n02a05

The aim of this study was to evaluate gas exchange, fluorescence parameters of chlorophyll a, photosynthetic pigment concentration, and osmotic potential in tomato plants subjected to increasing salt concentrations. For this purpose tomato plants, cultivar Santa Clara, were grown in 5dm-3 pots containing Hoagland nutrient solution and subjected to treatments of 0, 50, 100 and 150 mM NaCl. The experiment was conducted in a greenhouse of the University Federal de Vicosa in a completely randomized design with four replications. Each experimental unit consisted of one pot containing two plants. The results showed that the osmotic potential in leaves and roots decreased significantly as the NaCl concentration in the nutrient solution increased by detecting the elevation of stress on the plants. The use of energy for the photosynthetic processes and dissipation of excess energy in photosynthetic machinery was compromised by increasing salt concentrations imposed by the treatments, reducing photosynthesis and photochemical efficiency demonstrated by gas exchange and the fluorescence parameters of chlorophyll a, indicating that there was damage to the photosynthetic apparatus in the biochemical phase. The photosynthetic pigments decreased significantly with increasing salt concentration, limiting the absorption of photosynthetically active radiation.