Biological functions of proline in morphogenesis and osmotolerance revealed in antisense transgenic Arabidopsis thaliana

Abstract

SummaryMany organisms, including higher plants, accumulate free proline (Pro) in response to osmotic stress. Although various studies have focused on the ability of Pro as a compatible osmolyte involved in osmotolerance, its specific role throughout plant growth is still unclear. It has been reported that Pro is synthesized from Glu catalyzed by a key enzyme, ∆ 1 -pyrroline-5-carboxylate synthetase (P5CS), in plants. To elucidate essential roles of Pro, we generated antisense transgenic Arabidopsis plants with a P5CS cDNA. Several transgenics accumulated Pro at a significantly lower level than wild-type plants, providing direct evidence for a key role of P5CS in Pro production in Arabidopsis. These antisense transgenics showed morphological alterations in leaves and a defect in elongation of inflorescences. Furthermore, transgenic leaves were hypersensitive to osmotic stress. Microscopic analysis of transgenic leaves, in which the mutated phenotype clearly occurred, showed morphological abnormalities of

Proline, Sugars, and Antioxidant Enzymes Respond to Drought Stress in the Leaves of Strawberry Plants

“…The intracellular proline can be used as osmotic substance with high compatibility with enzymes and other cellular macromolecules, thus to protect them from damage induced by drought stress (Hare et al, 1998). Osmotic adjustment produced by proline causes a drop of the osmotic potential in plant tissues (Nanjo et al, 1999). A very important role of proline in response to osmotic stress may promote the biosynthesis of cell wall matrix proteins, such as extensin, which has an important role in maintaining cell morphology and provides a mechanical support of plant cells subjected to stress conditions (Nanjo et al, 1999).…”

“…Osmotic adjustment produced by proline causes a drop of the osmotic potential in plant tissues (Nanjo et al, 1999). A very important role of proline in response to osmotic stress may promote the biosynthesis of cell wall matrix proteins, such as extensin, which has an important role in maintaining cell morphology and provides a mechanical support of plant cells subjected to stress conditions (Nanjo et al, 1999). The current study observed higher levels of proline accumulation in strawberry leaves under drought stress from two to ten days, and the proline levels increased as the severity and duration of drought stress increased.…”

The AtProT Family. Compatible Solute Transporters with Similar Substrate Specificity But Differential Expression Patterns

“…AtProT2 might be important for transport of GABA to neighboring cells or for the delivery of Pro to the sites of wounding, where it could serve as a source for nitrogen and reduction equivalents. Pro might also be used as a precursor for the synthesis of (hydroxy) Pro-rich proteins that are abundant in the cell walls and thus would be crucial for increased demand during cell wall reinforcement (Showalter, 1993;Nanjo et al, 1999). Pathogen attack, which also results in mechanical damage, has been shown to induce the Arabidopsis monosaccharide transporter AtSTP4.…”

“…Pro accumulation in developing grapevine berries and maturing pollen occurs independently of changes of the key enzyme(s) of Pro biosynthesis, arguing for a different level of regulation or for import of Pro (Fujita et al, 1998;Stines et al, 1999). Additional indications for Pro transport throughout the plant come from transgenic Arabidopsis (Arabidopsis thaliana) lines with reduced Pro biosynthesis (Nanjo et al, 1999), as the morphological alterations in these lines could be rescued by exogenous Pro application.…”

Removal of Feedback Inhibition of Δ1-Pyrroline-5-Carboxylate Synthetase Results in Increased Proline Accumulation and Protection of Plants from Osmotic Stress

“…In tomato, it has been reported that there are two Pro loci in the nuclear genome: one specifies a bifunctional P5CS (tomPro2) and the other one (tomPro1) apparently encodes a polycistronic mRNA that directs the synthesis of ␥-GK and GSA dehydrogenase as two separate peptides (GarciaRios et al, 1997). Two P5CS genes have also been shown to be present in both Arabidopsis and alfalfa (Strizhov et al, 1997;Ginzberg et al, 1998;Yoshiba et al, 1999). The Arabidopsis P5CS1 gene is expressed in most organs and is induced rapidly by stress (Strizhov et al, 1997;Zhang et al, 1997;Yoshiba et al, 1999).…”