Effect of antisense L-Δ1-pyrroline-5-carboxylate reductase transgenic soybean plants subjected to osmotic and drought stress

The potential value of proline accumulation during environmental stress reveals a collection of controversial statements. Some argue that proline accumulation is beneficial to the plant, while others suggest the opposite to be true. It is thus still unknown whether or not a constitutive higher level of proline accumulation enhances plant tolerance to environmental stress. Since proline in plants is synthesised from both glutamic acid and ornithine, we generated antisense soybean plants with an L-Delta(1)-pyrroline-5-carboxylate reductase (P5CR) gene, as it controls the common step of both pathways. The gene expression and consequently proline production was manipulated, with the use of an inducible heat shock promoter (IHSP). The activation of the IHSP resulted in the inactivation of the P5CR gene, which resulted in decreased proline synthesis. The antisense plants have provided us with insight into the correlation between proline accumulation, drought and osmotic stress. A mannitol stress at 32 and 42 degrees C enhanced the accumulation of proline in control plants, in contrast to a significant decrease observed in the transformants. The proline accumulation documented in this paper provides additional evidence that the increase in proline levels during osmotic stress constitute an adaptive response by the plant. It was confirmed that there is an association between P5CR translation and proline accumulation, as the proline accumulation was markedly decreased by the activation of the heat inducible promoter and thus the antisense construct in transformed plants. A woodenbox screening indicated that proline plays a definite role in survival of soybean plants under a drought stress, the transformants failed to survive a 6 day drought stress at 37 degrees C. This was in contrast with the control plants which experienced the treatment only as a mild stress.