Plant Haemoglobins, Nitric Oxide and Hypoxic Stress

Abstract

It is now known that there are several classes of haemoglobins in plants. A specialized class of haemoglobins, symbiotic haemoglobins, were discovered 62 years ago and are found only in nodules of plants capable of symbiotic nitrogen fixation. Plant haemoglobins, with properties distinct from symbiotic haemoglobins were discovered 18 years ago and are now believed to exist throughout the plant kingdom. They are expressed in different organs and tissues of both dicot and monocot plants. They are induced by hypoxic stress and by oversupply of certain nutrients. Most recently, truncated haemoglobins have been shown to also exist in plants. While hypoxic stress-induced haemoglobins are widespread in the plant kingdom, their function has not been elucidated. This review discusses the recent findings regarding the function of these haemoglobins in relation to adaptation to hypoxia in plants. We propose that nitric oxide is an important metabolite in hypoxic plant cells and that at least one of the functions of hypoxic stress-induced haemoglobins is to modulate nitric oxide levels in the cell.

Mitochondrial Reactive Oxygen Species. Contribution to Oxidative Stress and Interorganellar Signaling

“…The NO 2 -dependent pathway is stimulated under oxygen deprivation (Gupta et al, 2005), leading to NO accumulation (e.g. Dordas et al, 2003). NO inhibits COX, facilitating an increase in mtROS production even under mild hypoxia (Cooper and Davies, 2000).…”

Emission and Function of Volatile Organic Compounds in Response to Abiotic Stress

“…NO lowers O 2 consumption by repressing cytochrome C oxigenase (COX), and shifts the metabolism toward fermentation, as a mechanism for hypoxic stress avoidance (Borisjuk et al, 2007). A class of plant stress-induced hemoglobins might help the de-repression of COX, or prevent PCD in the short term, allowing the development of adventitious root primordia (Dordas et al, 2003). The reaction to the metal ions excess also involves NO.…”

Respostas fisiológicas de plantas amazônicas de regiões alagadas às mudanças climáticas globais

“…Esses autores observaram que os níveis de mRNA de hemoglobina em tecido de aleurona de cevada eram mais altos em baixo oxigênio e além disso, que o controle da expressão parece não estar relacionado diretamente ao oxigênio, mas aos níveis de ATP (o principal composto de armazenamento de energia no metabolismo) no tecido. Mais recentemente, Hunt et al (2002) e Dordas et al (2003) observaram que hemoglobinas aparecem em tecidos em crescimento rápido. É possível que as taxas respiratórias relativamente baixas em tecidos vegetais ocorram em condições em que o transporte de oxigênio não seja necessário, mas acima de certo limiar, por exemplo, sob condições de hipóxia geradas por alagamento, as hemoglobinas seriam responsáveis pelo transporte desse gás.…”