Pvlea-18, a member of a new late-embryogenesis-abundant protein family that accumulates during water stress and in the growing regions of well-irrigated bean seedlings

Pvlea-18 is a novel stress gene whose transcript is present in the dry embr yo and the endosperm from bean (Phaseolus vulgaris) seeds. It accumulates i n vegetative tissues in response to water deficit and abscisic acid applica tion (J.M. Colmenero-Flores, F. Campos, A. Garciarrubio, A.A. Covarrubias [ 1997] Plant Mol Biol 35: 393-405). We show that the Pvlea-18 gene encodes a 14-kD protein that accumulates during late embryogenesis. Related proteins have been detected in both monocots and dicots, indicating that PvLEA-18 i s a member of a new family of LEA (Late Embryogenesis Abundant) proteins. W e also show that the PvLEA-18 transcript and protein accumulate not only in different organs of the bean seedlings during water stress but also in wel l-irrigated seedlings. This accumulation occurs in seedling regions with mo re negative values of water and osmotic potentials, such as the growing reg ion of the hypocotyl. This phenomenon has not previously been described for LEA proteins. Immunohistochemical localization showed that the PvLEA-18 pr otein is present in the nucleus and cytoplasm of all cell types, with a hig her accumulation in the epidermis and vascular cylinder tissues, particular ly in protoxylem cells and root meristematic tissues. We found a similar lo calization but a higher abundance in water-stressed seedlings.