Protein changes induced by salinity stress were investigated in the roots of the salt-sensitive rice cultivar Taichung native 1. We found eight proteins to be induced and obtained partia1 sequences of one with a molecular mass of 15 kilodaltons and an isoelectric point of 5.5. Using an oligonucleotide probe based on this information, a cDNA clone, sa/T, was selected and found to contain an open reading frame coding for a protein of 145 amino acid residues. sa/T mRNA accumulates very rapidly in sheaths and roots from mature plants and seedlings upon treatment with Murashige and Skoog salts (1%0), air drying, abscisic acid (20 pM), polyethylene glycol (5%), sodium chloride (l%), and potassium chloride (1%). Generally, no induction was seen in the leaf lamina even when the stress should affect all parts of the plant uniformly. The organ-specific response of sa/T is correlatable with the pattern of Na+ accumulation during salt stress.

Regulated gene expression of chimeric genes has been studied extensively in electroporated protoplasts. The applicability of these assays is limited, however, because protoplasts are not always physiologically identical to the cells from which they are derived. We have developed a procedure to electroporate DNA into intact and organized leaf structures of rice. Optimization of the new gene delivery system mainly involved eliminating explant-released nucleases, prolonging the DNA/explant incubation time, and expanding the pulse time. Using a [beta]-glucuronidase gene under the control of constitutive promoters, we demonstrated that all cell types within a leaf base were susceptible to electroporation-mediated DNA uptake. Although the technique was initially developed for leaf bases of young etiolated rice seedlings, we proved that it was equally applicable both to other monocotyledons, including wheat, maize, and barley, and to other explants, such as etiolated and green sheath and lamina tissues from rice. Transient gene expression assays with electroporated leaf bases showed that the promoter from a pea light-harvesting chlorophyll a/b-binding protein gene displayed both light- and chloroplast-dependent expression in rice, and that the promoter from the Arabidopsis S-adenosylmethionine synthetase gene was, as in transgenic Arabidopsis and tobacco, preferentially expressed in cells surrounding the vascular bundles.