Effect of plant growth regulators on water transport and carbon balance in seedling establishment of grape cuttings

Abstract：【Objective】The maintenance of water- and carbon-balance is the basis of plant survival. Current research shows that both hydraulic failure and carbon starvation are important causes of plant death in abiotic stresses such as drought, but at present there is a lack of understanding of the changes in water transport and carbon metabolism during the seedling development of cuttings. This study explored the water- and carbon-metabolism during the seedling establishment from grape (Vitis vinifera L.) cuttings by comparing the dynamic changes in water status and carbon balance among treatments with different auxin concentrations and cutting media used. The effect of auxin concentration on water- and carbon-balance during cutting development was analyzed. Results will provide technical support for nursery production of grapes.【Methods】Grape cuttings were treated with IAA250 mg·kg-1 +IBA250 mg·kg^-1 , or IAA 750 mg · kg^-1 +IBA 750 mg · kg^-1 , or water (CK), then inserted into nutrient cups filled with cutting medium. Root length, seedling height, leaf number and single leaf area of the cuttings were mea-sured in July. Predawn and midday water potentials, stem xylem embolism (percentage loss of conductivity, PLC), maximum hydraulic conductivity, leaf photosynthesis, and concentrations of soluble sugars, starch and nonstructural carbohydrates (NSC) were measured monthly from March to July.【Results】Root length, seeding height and leaf number of grape cuttings under IAA 250 mg · kg-1 + IBA 250 mg·kg-1 treatment were significantly higher than those under IAA 750 mg·kg^-1 + IBA 750 mg·kg^-1 treatment and those in the control. The growth of seedlings in the IAA 250 mg·kg-1 + IBA 250 mg·kg^-1 treatment was better than that treated with IAA 750 mg·kg-1 + IBA 750 mg·kg^-1 and that in the control. During the seedling establishment of grape cuttings, there was no significant change in the predawn water potential in different treatments, being all around -0.2 MPa, while the midday water potential showed a decreasing trend. In July, the midday water potential in the IAA 250 mg · kg^-1 +IBA 250 mg · kg- 1 treatment was significantly lower than that in the IAA 750 mg·kg^-1 + IBA 750 mg·kg^-1 treatment. It was also slightly lower than in the control, but there was no significantly difference among different treatments in June. PLC increased continuously, from about 20% to nearly 50%. The PLC in the IAA 250 mg·kg^-1 + IBA 250 mg·kg^-1 treatment was the highest among the three treatments in July. The maximum hydraulic conductivity decreased continuously except for a small increase at the end of the period, from 3.8×10-4 kg·m^-1 ·s ^-1 ·MPa-1 at the early stage to 1.53×10-4 kg·m^-1 ·s ^-1 ·MPa-1 in June, with a reduction of about 60%, and to 1.89×10- 4 kg ·m^-1 ·s ^-1 · MPa-1 in July. The IAA 250 mg · kg^-1 + IBA 250 mg · kg^{- 1} treatment had a higher photosynthesis rate and stomatal conductance than the IAA 750 mg·kg-1 +IBA 750 mg·kg-1 treatment and the control. The contents of soluble sugars, starch and NSC all declined in the early stage, but remained constant or slightly increased in the late stage. The contents of soluble sugars decreased from 2.28% at the beginning of the experiment to 0.88% in June. The content of starch decreased from 1.21% at the beginning of the experiment to 0.43% in June. And the content of NSC dropped from 3.48% at the beginning of the experiment to 1.31% in June. The descent degree for soluble sugars, starch, NSC was 62%, 65% and 63%, respectively. Meanwhile, treatment A（IAA 250 mg · kg^-1 + IBA 250 mg · kg^-1） had a faster decline in NSC concentration in the early stage, but higher NSC concentration in later period.【Conclusion】Although grape cuttings treated with IAA 250 mg·kg^-1 + IBA 250 mg·kg^-1 had a lower water potential and larger PLC than IAA 750 mg·kg^-1 + IBA 750 mg·kg^-1 treatment and CK, they had a higher photosynthesis rate and a faster growth rate, which showed their water utilization was not affected and thus they were not stressed by hydraulic disfunction. Their NSC concentration declined rapidly by more than 60%, but recovered at the end of seedling establishment, which was consistent with the growth of the cuttings. The results suggest that the cuttings were not affected by water transport but affected by carbon reserves to a certain extent. Appropriate auxin concentration could shorten seedling growth time, reduce stress degree and rapidly achieve carbon balance of the cuttings.