Proline metabolism and transport in maize seedlings at low water potential.
The growing zone of maize seedling primary roots accumulates proline at low water potential. Endosperm removal and excision of root tips rapidly decreased the proline pool and greatly reduced proline accumulation in root tips at low water potential. Proline accumulation was not restored by exogenous amino acids. Labelling root lips with [14C]glutamate and [14C]proline showed that the rate of proline utilization (oxidation and protein synthesis) exceeded the rate of biosynthesis by five-fold at high and low water potentials. This explains the reduction in the proline pool following root and endosperm excision and the inability to accumulate proline at low water potential. The endosperm is therefore the source of the proline that accumulates in the root tips of intact seedlings. Proline constituted 10% of the amino acids released from the endosperm. [14C]Proline was transported from the scutellum to other parts of the seedling and reached the highest concentration in the root tip. Less [14C]proline was transported at low water potential but because of the lower rate of protein synthesis and oxidation, more accumulated as proline in the root tip. Despite the low biosynthesis capacity of the roots, the extent of proline accumulation in relation to water potential is precisely controlled by transport and utilization rate.
Raymond
Marjorie J
MJ
School of Biological Sciences, University of Exeter, Washington Singer Laboratories, UK.
Smirnoff
Nicholas
N
D000064:Acclimatization / Q000502:physiology; D001692:Biological Transport / Q000187:drug effects; D002250:Carbon Radioisotopes; D018698:Glutamic Acid / Q000378:metabolism / Q000494:pharmacology; D018519:Meristem / Q000187:drug effects / Q000378:metabolism; D009997:Osmotic Pressure / Q000187:drug effects; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism; D010940:Plant Proteins / Q000096:biosynthesis; D018517:Plant Roots / Q000187:drug effects / Q000378:metabolism*; D011392:Proline / Q000378:metabolism* / Q000494:pharmacology; D012639:Seeds / Q000187:drug effects / Q000378:metabolism; D014867:Water / Q000494:pharmacology / Q000502:physiology*; D003313:Zea mays / Q000187:drug effects / Q000378:metabolism*
D002250:Carbon Radioisotopes; D010940:Plant Proteins; D014867:Water; D018698:Glutamic Acid; D011392:Proline; D010100:Oxygen