A barley (Hordeum vulgare L.) LEA3 protein, HVA1, is abundant in protein storage vacuoles

Abstract

Abstract. The HVAI protein belongs to the LEA3 group, which is expressed during the late stage of seed maturation. It is also induced by exogenous abscisic acid (ABA) and a variety of environmental stresses in germinating barley (Hordeum vulgare L.). In the present work, the potential role of HVA! was investigated by studying its tissue distribution and subcellular localization in mature and stressed seeds by immuno-microscopic methods. In the mature seed, HVA1 protein was detected in all tissues except the non-living starchy endosperm. During germination the amount of HVA 1 protein decreased but did not totally disappear. Incubation with 100/aM ABA, cold treatment or drought stress dramatically increased HVA1 expression in the germinated seed. In this work, the distribution of a LEA3 group protein was studied in a cereal seed for the first time by immuno-electron microscopy. In the scutellum and aleurone layer, HVA1 was localized both in the cytoplasm and protein storage vacuoles (PSVs). HVA1 protein was found to be threefold more abundant in PSVs than in the cytoplasm of an unstressed seed tissue. The ratio increased with ABA or stress treatments to at least ninefold. The role of HVA1 in PSVs remains unclear: a previously suggested possibility is ion sequestration to prevent precipitation during stress. On the other hand, HVA1 protein could also be degraded in PSVs. HVA1 protein does not have the signal peptide typical of proteins which are glycosylated and targeted into the vacuole via the Golgi complex. Because HVA1 is not glycosylated, it may use an alternative, ER-independent vacuolar pathway, also found in yeast cells.

The Enigmatic LEA Proteins and Other Hydrophilins

“…Group 3 D-7 LEA protein from cotton accumulates to a concentration of about 200 mM in mature cotton embryos (Roberts et al, 1993). Studies of seeds have localized group 3 LEA proteins to the cytoplasm and protein storage vacuoles, as is the case for HVA1 from barley (Hordeum vulgare; Marttila et al, 1996), whereas PsLEAm is distributed within the mitochondrial matrix of pea seeds (Grelet et al, 2005). Group 3 proteins are also detected in vegetative tissues.…”

Heat Stress Response in Pea Involves Interaction of Mitochondrial Nucleoside Diphosphate Kinase with a Novel 86-Kilodalton Protein

“…Semithin sections were prepared from purified pea mitochondria, pea flower buds, young (6 d old), and mature leaves (fully expanded, 11 d old) as in Marttila et al, (1996). To be brief, the material was fixed in 4% (w/v) paraformaldehyde and 0.25% (v/v) glutaraldehyde in phosphatebuffered saline (PBS) (10 mm Na-phosphate buffer, pH 7.4, 150 mm NaCl) for 2 h at room temperature, dehydrated, infiltrated with medium-grade London Resin White (London Resin Company Ltd., Reading, UK; distributed by TAAB, Aldermaston, UK), and polymerized for 24 h at 58°C.…”

Sorting of proteins to vacuoles in plant cells

“…Several plant proteins that are likely to reach the vacuole by a similar process have been identified. Prominent among these is a soybean lipoxygenase that accumulates in paraveinal mesophyll cell vacuoles as a vegetative storage protein [10,113], as well as certain late embryogenesis-abundant proteins [24,63].…”