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Proline Accumulation during Drought Rhizogenesis inBrassica napusvar.oleifera

Journal of Plant Physiology
Publication Date
DOI: 10.1016/s0176-1617(11)80799-6
  • Brassica Napus
  • Drought Rhizogenesis
  • Stress Metabolism
  • Proline


Summary Free proline accumulation, in response to gradual drought stress in Brassica napus var. oleifera (cv. Darmor), is detectable from a threshold shoot water potential (Υ) of −0.6 MPa. The earliest response occurs in the shoot apex just before the onset of the adaptive drought-induced rhizogenesis. Short tuberized roots (STRs), induced through water shortage, were found to contain a very high amount of free proline, reaching up to 4.6 % of total dry matter. The tap root bearing the STRs also exhibited a very high free proline level, quite in contrast to normal lateral roots where the values did not exceed 2.5 % of total dry matter. Proline accumulation during drought rhizogenesis was also high in other shoot parts, but especially in the apex where proline accounted for 8 % of the total dry matter. The highest proline levels were thus located in «survival organs» of rapeseed (shoot apex, hardened leaves, STRs and tap root). Furthermore, particularly noticeable was the lack of proline increase in the drought susceptible cotyledons. When stress conditions were relieved, after completion of drought rhizogenesis, proline was rapidly utilized and its rate of mobilization, directly related to the growth recovery of the different tissues, was especially high in the growth resuming drought-induced roots. Accordingly, proline can be considered as a storage compound supplying reductants, reduced N and carbon skeletons for post-stress growth recovery. Thus, B. napus' drought adaptive behaviour enabled the detection of a differential proline response within the plant, according to the level of drought tolerance or drought susceptibility of the different tissues. In addition, comparative experiments were performed in order to investigate the temporal relationship between drought rhizogenesis of rapeseed and proline accumulation under various water stress regimes. It is shown that rapid changes in Υ shoot of gell-watered plants subjected to water stress were associated with high net rates of proline accumulation, but induced only limited STRs production. In contrast, slower changes in Υ shoot caused less proline accumulation but higher rhizogenetic activity.

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