Alterations in Chloroplast Ultrastructure and Chlorophyll Content in Rust-Infected Pinto Beans at Different Stages of Disease Development

Development of Symptoms of Brown Rust of Barley in Relation to the Distribution of Fungal Mycelium, Starch Accumulation and Localized Changes in the Concentration of Chlorophyll

“…In contrast, D'Oliveira (1938) found in a cytological study of barley leaves infected with brown rust that the loss of green colour in infected areas did not reflect any obvious damage to the chloroplasts. A recent study of rust-infected bean leaves (Sziraki et al, 1984) suggested that there was net synthesis of chlorophyll at infection sites early during disease development, so tbat tbe concentration was higher than in uninfected leaves, and that from the flecking to green island stages chlorophyll concentration remained constant. Thus, green islands formed as a result of chlorophyll retention.…”

“…Leaves infected with many biotrophic pathogens accumulate chloroplastic starch (MacDonald & Strobel, 1970;Whipps & Lewis, 1981) but the pattern and extent of starch accumulation is disputed (Bushnell & Allen, 1962;Sziraki et al, 1984). This information is particularly important in studies of localized changes in the rate of photosynthesis in infected leaves because one of the mechanisms that has been proposed to account for this accumulation [alterations in the concentration of inorganic phosphate (Pi) in the host cytoplasm] also directly affects the rate of photosynthesis.…”

“…It is not clear whether chlorotic flecks represent areas of chlorophyll breakdown or whether the yellow colour is due to other factors, and this is related to the controversy surrounding the formation of green islands. Although green islands were first described 85 years ago by Cornu, and in spite of many studies since (Shaw & Samborski, 1956;Bushnell and Allen, 1962;Sziraki et al, 1984), their mode of formation is not understood. Some investigators propose there is retention of chlorophyll throughout disease development (Allen, 1923 ;D'Oliveira, 1938), while others propose an initial breakdown of chlorophyll followed later by 'regreening' with net synthesis of chlorophyll (Rice, 1927;Sziraki et al, 1984).…”

Microscopic observations of a compatible host/pathogen interaction between a potential biocontrol agent (Uromyces pencanus) and its target weed (Nassella neesiana)

“…1f). The degradation of chloroplasts in cells in the infection zone, as observed by Sziráki et al (1984), would probably account for these differences, because chloroplasts were easily visualized in mesophyll cells at healthy sites. However, necrosis or collapse of mesophyll cells was not observed at infected sites, as it has been in other studies of rust-susceptible host relationships (Bonde et al 1976;McLean 1979).…”

Estimativa do nível de dano de Orthezia praelonga Douglas, 1891 e de Leucoptera coffeella (Guérin-Mèneville, 1842) por varíaveis fisiológicas vegetais.

“…Segundo Baastians (1991) a redução na f otossíntese de uma folha doente em função de alterações produzidas no metabolismo da área verde remanescente, deve-se a diversos mecanismos que poderiam modificar a eficiência fotossintética de pla ntas em condições de estresse, incluindo: mudanças na taxa de absorção de gás carbônico devido a alterações no comportamento de abertura/fechamento dos estômatos (Gordon & Duniway, 1982); diminuição na interceptação da radiação solar como conseqüência de desfolha ou mudanças no formato e/ou orientação das folhas (Madeira & Clark, 1995); incremento da atividade da enzima clorofilase, responsável pela hidrólise de clorofila (Bailiss, 1970); destruição acelerada e contínua de cloroplastos (Abo-Foul et al, 1996); retenção dos níveis de clorofila com a formação de regiões verdes (Sziráki et al, 1984); alteração na atividade ou nos níveis de mRNA que codificam enzimas do ciclo de Calvin, como a ribulose -1,5 bifosfato carboxilase-oxigenase (rubisco), responsável pela fixação de CO 2 na planta (Scholes & Rolfe, 1995) e acúmulo de carboidratos causando retroinibição e regulação da expressão gênica (Scholes et al, 1994).…”