Xerophytophysiological Regulations And Xeric Gene Expressions In Response To Partial Root-Zone Alternate Irrigation In Potato Crops

Partial root-zone alternate irrigation belongs to deficit irrigation. It is proposed on the principle of water-saving irrigation and applications of signal transduction and xerophytophysiology. In partial root-zone alternate irrigation, half the roots are allowed to dehydrate and meanwhile the irrigated roots on the other side continue to provide sufficient amounts of water. The theory of xerophytophysiology proposes that giving a false drought stimulus, the plant grows healthier with higher physiological activities through activating drought responsive genes. There is no decrease in yield, but increase in water use efficiency. Partial root-zone alternate irrigation, as one application of xerophytophysiology, is considered as an important technique for improving crop quality, increasing water use efficiency and solving the shortage of agricultural water resource for sustainable agriculture.In the present research, pot experiment was designed using potato plant as material with three irrigation treatments at early growth stage. The three treatments were as follows,1) control-full irrigation,2) PRD-partial root-zone alternate irrigation and 3) drought. Some physiological responses such as plant growth, leaf photosynthesis, osmotic adjustment and antioxidant activity were analyzed to elucidate the physiological mechanisms for growth and yield improvement by partial root-zone alternate irrigation. The expression of some activated genes was also analyzed to investigate the molecular biological reaction caused by xeric signal stimulus perception and transduction. Conclusions were as follows.(1) Partial root-zone alternate irrigation improved potato plant growth.No significance was found in plant growth rate and leaf area under partial root-zone alternate irrigation compared with full irrigation control and drought treatment. After release from partial root-zone alternate irrigation, plant growth was improved by the high physiological activities. Plant height and leaf area were higher in partial root-zone alternate irrigation than those in full irrigation and drought. Plant dry biomass accumulation and accumulation rate from 50 to 70 days after germination were higher in partial root-zone alternate irrigation than those in full irrigation and drought. The whole plant growth was partial root-zone alternate irrigation> full irrigation> drought.(2) Leaf photosynthetic ability was improved by partial root-zone alternate irrigation.Leaf photosynthetic light-response curve showed that the net photosynthetic rate under the same light density was high in partial root-zone alternate irrigation followed by full irrigation and that in drought treatment was the lowest. Leaf photosynthetic capacity in partial root-zone alternate irrigation was significantly higher than those in full irrigation and drought. Dark respiration was lower in partial root-zone alternate irrigation and drought than in full irrigation. Partial root-zone alternate irrigation increased photosynthetic capacity and quantum use efficiency. The increase in ability of using weak light and decrease in dark respiration contributed to the accumulation of photosynthetic products leading to improved growth.(3) Partial root-zone alternate irrigation increased leaf water retention ability.P-V curve showed that osmotic potential at full turgid status (pFT) in partial root-zone alternate irrigation was lower than those in full irrigation and drought, which indicated that the leaf ability to maintain turgor under partial root-zone alternate irrigation was higher than the other treatments. Cell water was recompartmented by partial root-zone alternate irrigation with higher symplastic water fraction and lower apoplastic water fraction due to the active increase in cell solutes and decrease on osmotic potential. The high symplastic water fraction contributed to cell biochemical and physiological metabolisms.Leaf water retention ability was analyzed using excised leaf transpiration declining curve. It was found that the time used to dry the excised leaf to a relative water content of 0.10 was longer in partial root-zone alternate irrigation than in full irrigation and drought. Water lose in excised leaf was decreased by partial root-zone alternate irrigation. This result showed that the short period treatment by partial root-zone alternate irrigation stimulated to active physiological responses with thicken cell epicuticular layer or more wax depositing onto the leaf surface, which indicated high drought resistance.(4) High antioxidant activities were induced by partial root-zone alternate irrigation.SOD, POD and CAT activities were higher in partial root-zone alternate irrigation than those in full irrigation and drought treatments. MDA produced high during the treatment period of partial root-zone alternate irrigation, but showed lower level than in the other two irrigation treatments after rewatering, indicating the low cell membrane injury. The same result was found in the production of super anion radicals (O2). All these results indicated that partial root-zone alternate irrigation did not induce a real stress but a transient drought stimulation to potato plant.(5) Partial root-zone alternate irrigation increased the accumulation of osmoregulation substances.As the soil water decrease during the treatments of both partial root-zone alternate irrigation and drought, some osmoregulation substances like poline, soluble sugars and soluble proteins in leaves accumulated actively and showed high concentration in partial root-zone alternate irrigation compared with full irrigation and drought. Therefore, the active accumulation of osmotic solutes would increase leaf water retention ability to avoid the damage caused by water stress.(6) Partial root-zone alternate irrigation increased water use efficiency and the final potato tuber yield. The decrease of leaf excessive water transpiration could stimulate the compensation effects of plant growth and water absorption, which increased yield by 4.06% and water use efficiency increased by 31.6%. Therefore, partial root-zone alternate irrigation has the potential in attain water saving and yield increasing.(7) Partial root-zone alternate irrigation induced the high level of RD28 gene expression.The high expression level of RD28 gene in partial root-zone alternate irrigation showed that some drought resistant genes were activated, and the plant might have high resistance to water stress.In conclusion, partial root-zone alternate irrigation increased plant resistance to drought and improved plant growth and tuber quality. It could provide the effective guarantee to realize the aim of saving water and increasing yield production and could be applied to the field production.