Trehalose is a nonreducing disaccharide of glucose that functions as a compatible solute in the stabilization of biological structures under abiotic stress in bacteria, fungi, and invertebrates. With the notable exception of the desiccation-tolerant ''resurrection plants, '' trehalose is not thought to accumulate to detectable levels in most plants. We report here the regulated overexpression of Escherichia coli trehalose biosynthetic genes (otsA and otsB) as a fusion gene for manipulating abiotic stress tolerance in rice. The fusion gene has the advantages of necessitating only a single transformation event and a higher net catalytic efficiency for trehalose formation. The expression of the transgene was under the control of either tissue-specific or stress-dependent promoters. Compared with nontransgenic rice, several independent transgenic lines exhibited sustained plant growth, less photo-oxidative damage, and more favorable mineral balance under salt, drought, and low-temperature stress conditions. Depending on growth conditions, the transgenic rice plants accumulate trehalose at levels 3-10 times that of the nontransgenic controls. The observation that peak trehalose levels remain well below 1 mg͞g fresh weight indicates that the primary effect of trehalose is not as a compatible solute. Rather, increased trehalose accumulation correlates with higher soluble carbohydrate levels and an elevated capacity for photosynthesis under both stress and nonstress conditions, consistent with a suggested role in modulating sugar sensing and carbohydrate metabolism. These findings demonstrate the feasibility of engineering rice for increased tolerance of abiotic stress and enhanced productivity through tissue-specific or stress-dependent overproduction of trehalose.T he explosive increase in world population, along with the continuing deterioration of arable land, scarcity of fresh water, and increasing environmental stress pose serious threats to global agricultural production and food security. Despite focused efforts to improve major crops for resistance to abiotic stresses (1) such as drought, excessive salinity, and low temperature by traditional breeding, success has been limited. This lack of desirable progress is attributable to the fact that tolerance to abiotic stress is a complex trait that is influenced by coordinated and differential expression of a network of genes. Fortunately, it is now possible to use transgenic approaches to improve abiotic stress tolerance in agriculturally important crops with far fewer target traits than had been anticipated (2).Abiotic stresses can directly or indirectly affect the physiological status of an organism by altering its metabolism, growth, and development. A common response of organisms to drought, salinity, and low-temperature stresses is the accumulation of sugars and other compatible solutes (3). These compounds serve as osmoprotectants and, in some cases, stabilize biomolecules under stress conditions (3,4). One such compound is trehalose, a nonreducing disaccharid...

We adopted previous N : P stoichiometric models for zooplankton relative growth to predict the relative growth rates of the leaves l L of vascular plants assuming that annual leaf growth in dry mass is dictated by how leaf nitrogen N L is allocated to leaf proteins and how leaf phosphorus P L is allocated to rRNA. This model is simplified provided that N L scales as some power function of P L across the leaves of different species. This approach successfully predicted the l L of 131 species of vascular plants based on the observation that, across these species, N L scaled, on average, as the 3/4 power of P L , i.e. N L µ P 3=4 L . When juxtaposed with prior allometric theory and observations, our findings suggest that a transformation in N : P stoichiometry occurs when the plant body undergoes a transition from primary to secondary growth.

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