Promotion of proline accumulation in apple leaves by bioregulators

Proline is one kind of organic osmoregulator that can improve the drought resistance of plants. In this experiment, three-year-old apple trees (Malus domestica Borkh cv. Rehd Fuji/Malus hupehensis (Pamp) Rehd.) were used to study the accumulation of proline in leaves after spraying with various bioregulators. The results show that the proline concentration increases by 110.67, 135.12 and 115.96% respectively on the 9th day of spraying abscisic acid (ABA), salicylic acid (SA) and oxalic acid (OA) in soils where the relative water content (SWC) was maintained at 75%. The concentration of proline in leaves still remained at higher levels following ABA and SA applications at the 10th day after stopping the supply of water. The concentration of malondialdehyde (MDA), a product of lipoid peroxidation, decreases after spraying ABA, SA and OA under natural drought. In another experiment, spraying glycinebetaine (GB) increased proline concentration and decreased MDA content significantly under slight and moderate drought-stress (SWC 50̃60%). These results suggest that ABA, SA, GB and OA all can protect apple leaves from drought-stressinduced oxidative damage via increasing proline concentration.