Cyanobacterial Flavodoxin Provides Multiple Stress Tolerance

MATIAS D. ZURBRIGGEN; VANESA B. TOGNETTI; ESTELA M. VALLE; NÉSTOR CARRILLO

Biotechnology: Perspectives and prospects

C. P. Malik, C. Wadhwani, B. Kaur, eds. MD Publications Pvt Ltd

Lugar: Delhi, India; Año: 2008; p. 255 - 260

Plants growing under natural conditions unavoidably face episodic situations ofenvironmental stress in the course of their life times. They have developed numerousstrategies to survive in such adverse conditions. Crops, in contrast, are selected by humansfor their high productivity in agriculture, but this is usually not accompanied by increasingresistance to hostile environments. Diseases, unfavorable climates, or inappropriate soilsare responsible for most agricultural losses. Analysis of major crops with economicallyvaluable reproductive or vegetative structures (corn, soybeans, barley, potatoes, amongothers) shows potential record yields 3- to 7-fold greater than average yields1.One approach to obtain plants adapted to unfavorable environments may be toimprove essential nutrient (nitrogen, phosphorus, or iron) acquisition. Although iron isabundant, plants need to solubilize it from insoluble oxides in alkaline, calcareous soils,which cover approximately one-third of the earth’s surface and represent a major deterrentfor agriculture2. Plants deprived of iron develop interveinal chlorotic symptoms in youngleaves and a general decrease in photosynthetic activity that can lead to death. Chlorosishas been attributed to inhibition of chlorophyll synthesis, which requires the function of Fecontaining enzymes, but chlorophyll-binding proteins and other photosynthetic componentsare down-regulated with relative independence of pigment levels. Chloroplasts are thereforeprimary targets of iron deficiency.On the other hand, plants sustain different types of environmental hardships,such as drought, flood, chilling, salinity, and radiation. Being motionless organisms,a plant’s defense to adverse conditions is limited to physiological and biochemicalresponses, including stomatal closure, osmotic adjustment, ion pumping, etc. Inresponse to regulated changes in gene expression, central and secondary metabolismsare redirected to cope with the undesired effects of the hostile situation. This is achievedby up-regulating the synthesis of proteins and metabolites involved in protection (i.e.,compatible solutes, antioxidant enzymes and compounds, heat-shock proteins, etc.).Whenever these defensive mechanisms are overcome by the intensity of the adversecondition, the plant is under environmental stress.Although different types of nutritional and environmental adversities have their own features and display idiosyncratic responses, they all have in common a significant perturbation of the electron transfer network of the stressed cells, leading to electron derivation to non-productive routes, breakage of redox homeostasis,and eventually to the generation of reactive oxygen species (ROS) such as singletoxygen, the superoxide and hydroxyl radicals, and hydrogen peroxide.