Cyanobacterial Flavodoxin provides multiple stress tolerance

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

Information System for Biotechnology (ISB) News Report, Virginia Tech, US Department of Agriculture (USDA)

USDA/CSREES

Año: 2007 p. 1 - 5

Plants growing under natural conditions unavoidably face episodic situations of environmental stress in the course of their life times. They have developed numerous strategies to survive in such adverse conditions. Crops, in contrast, are selected by humans for their high productivity in agriculture, but this is usually not accompanied by increasing resistance to hostile environments. Diseases, unfavorable climates, or inappropriate soils are responsible for most agricultural losses. Analysis of major crops with economically valuable reproductive or vegetative structures (corn, soybeans, barley, potatoes, among others) shows potential record yields 3- to 7-fold greater than average yields1. One approach to obtain plants adapted to unfavorable environments may be to improve essential nutrient (nitrogen, phosphorus, or iron) acquisition. Although iron is abundant, 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 deterrent for agriculture2. Plants deprived of iron develop interveinal chlorotic symptoms in young leaves and a general decrease in photosynthetic activity that can lead to death. Chlorosis has been attributed to inhibition of chlorophyll synthesis, which requires the function of Fe-containing enzymes, but chlorophyll-binding proteins and other photosynthetic components are down-regulated with relative independence of pigment levels. Chloroplasts are therefore primary 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 biochemical responses, including stomatal closure, osmotic adjustment, ion pumping, etc. In response to regulated changes in gene expression, central and secondary metabolisms are redirected to cope with the undesired effects of the hostile situation. This is achieved by 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 adverse condition, 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 singlet oxygen, the superoxide and hydroxyl radicals, and hydrogen peroxide.